Modular nuclear small reactor efficient cogeneration heating system

Abstract

The application relates to the technical field of nuclear power, and discloses a modular nuclear energy small reactor efficient heat and power cogeneration heating system, which comprises the following steps: a modular nuclear energy small reactor supplies steam to a high-pressure cylinder of a steam turbine through a once-through steam generator, and exhaust steam enters a reheater after passing through a steam-water separator. Three parallel branches are formed at the outlet of the reheater, a first branch is a heating steam extraction pipeline, a second branch is a low-pressure cylinder cooling steam pipeline, and a third branch is a low-pressure cylinder steam inlet pipeline. A heat network heater is isolated from a two-stage network water-water heat exchanger in medium, generated drain water is sent back to a deaerator through a heat network drain pump and is incorporated into a heat recovery system. A control device adjusts the opening degree of a heating steam extraction regulating valve and the rotating speed of a primary network heat network circulating water pump, and limits the upper limit of the opening degree of the heating steam extraction regulating valve and the lower limit of the opening degree of a low-pressure cylinder cooling steam regulating valve. The application realizes high-proportion steam extraction of reheated steam, stabilizes user-side water supply temperature and two-network pressure difference, reduces cold source loss, and enhances the anti-disturbance capacity of heat supply operation.

Description

Technical Field

[0001] This invention relates to the field of nuclear power technology, and more specifically, to a modular small nuclear reactor high-efficiency cogeneration heating system. Background Technology

[0002] With the advancement of nuclear power heating projects and the application of modular small modular reactors (SMRs), utilizing secondary loop steam to provide a heat source for urban district heating has become an important direction. Traditional nuclear power extraction heating typically extracts steam from the high-pressure or intermediate-pressure cylinder section, transferring the heat to the primary heating network via the plant's heating network heaters. Then, through water-to-water heat exchange, it achieves medium isolation with the secondary heating network to meet user-side safety and temperature zone requirements. In the SMR scenario, to improve the overall utilization rate of nuclear energy and reduce cold source losses at the condenser end, it is necessary to achieve both "high-proportion extraction heating" and "safe cooling of the low-pressure cylinder" while ensuring safety boundaries, while simultaneously ensuring a stable pressure difference between the primary and secondary heating networks and closed-loop linkage for radioactive safety monitoring.

[0003] While existing nuclear power heating solutions disclose a general architecture for extraction steam heating and multi-stage heat exchange isolation, some shortcomings remain. For example, CN113864750B discloses a nuclear power plant heating system, emphasizing that high-pressure cylinder exhaust steam is separated and reheated before being used for heating, but it does not consider the long-term zero-output and only basic cooling conditions of the low-pressure cylinder as a normal strategy; CN217640671U proposes a nuclear power plant heating control system, providing an overall approach to extraction steam valves and primary station control, but it does not establish a complete link for the switchable structure of the reheat end branching to low-pressure cylinder cooling and exiting zero output; CN210485839U involves a regenerative closed loop for condensate return to the deaerator, but it does not provide parameterized constraints for the linkage with the high-proportion extraction steam scenario of small modular reactors; in the thermal power sector, CN110566296A discloses a decoupling approach for low-pressure cylinder zero output, but it does not establish a priority cut-off and restoration sequence for extraction steam for media isolation and radioactivity monitoring in nuclear heating. Therefore, existing technologies lack structured organization and application boundaries for the three branches of the reheater outlet, lack constraints with zero output of the low-pressure cylinder as the normal heating condition, and lack control details that are mainly controlled by the supply and return water temperatures and the pressure difference between the two networks, and interlocked with the final stage metal temperature, exhaust steam humidity, and radioactivity monitoring. This makes it difficult to achieve the optimal synergy of high-proportion steam extraction, safe cooling of the low-pressure cylinder, and safe isolation between the two networks in small reactor scenarios.

[0004] Therefore, it is necessary to design a modular nuclear small reactor high-efficiency cogeneration heating system to solve the problems existing in the current technology. Summary of the Invention

[0005] In view of this, the present invention proposes a modular nuclear small reactor high-efficiency cogeneration heating system, which aims to solve the problem that existing technologies, under the premise of ensuring the safe zero output of the turbine low-pressure cylinder and the medium isolation between the primary and secondary networks, are unable to achieve high proportion of steam extraction at the reheat end, stable user-side water supply temperature and coordinated control of the pressure difference between the two networks.

[0006] This invention proposes a modular small nuclear reactor high-efficiency cogeneration heating system, comprising: The modular nuclear small reactor supplies steam to the high-pressure cylinder of the steam turbine through a direct current steam generator, and the exhaust steam from the high-pressure cylinder enters the reheater after passing through a steam-water separator. The reheater outlet forms three parallel branches. The first branch is the heating extraction steam pipeline, which leads to the heating network heater via the heating extraction steam regulating valve to heat the primary heating network. The second branch is the low-pressure cylinder cooling steam pipeline, which leads to the turbine low-pressure cylinder via the low-pressure cylinder cooling steam regulating valve to maintain the turbine low-pressure cylinder at zero output under normal heating conditions. The third branch is the low-pressure cylinder inlet steam pipeline, which leads to the turbine low-pressure cylinder via the low-pressure cylinder inlet steam regulating valve. The low-pressure cylinder is connected to the generator to exit the zero-output or power-only operation mode. The heating network heater is isolated from the secondary network water-to-water heat exchanger by a medium. The secondary network heating network circulating water pump is used to maintain the secondary network circulation. The condensate generated by the heating network heater is returned to the deaerator by the heating network condensate pump and incorporated into the regenerative system. The control device is configured to maintain the low-pressure cylinder at zero output as the normal heating state, keep the low-pressure cylinder cooling steam regulating valve at the cooling minimum opening, adjust the opening of the heating extraction steam regulating valve and the speed of the primary heating network circulating water pump according to the supply and return water temperature of the primary heating network and the pressure difference between the two networks, and limit the upper limit of the opening of the heating extraction steam regulating valve and the lower limit of the opening of the low-pressure cylinder cooling steam regulating valve according to the metal temperature of the last stage of the low-pressure cylinder, the exhaust steam humidity and the radioactivity monitoring value. When unit protection, main steam pressure abnormality, two-network pressure difference abnormality, or radioactivity monitoring exceeding the limit occurs, the control device sequentially closes the heating extraction steam regulating valve and the main steam emergency isolation valve, while maintaining the low-pressure cylinder cooling steam regulating valve at the cooling minimum opening, and resumes heating after the abnormality is resolved.

[0007] Furthermore, multiple DC steam generators are arranged in parallel, with the steam outlets of each DC steam generator flowing into the main steam pipeline. Safety valves, main steam isolation valves, and main steam emergency isolation valves are installed sequentially on the main steam pipeline. The main steam pipeline is connected to the steam inlet of the high-pressure cylinder of the steam turbine. The exhaust port of the high-pressure cylinder of the steam turbine is connected in series with the steam-water separator and the reheater.

[0008] Furthermore, the outlet of the reheater forms a parallel heating extraction steam pipeline and a low-pressure cylinder cooling steam pipeline. The heating extraction steam pipeline is connected to the steam inlet of the heating network heater, and the low-pressure cylinder cooling steam pipeline is connected to the steam inlet of the low-pressure cylinder. The two pipelines are not connected to each other.

[0009] Furthermore, the heating network heater and the primary heating network circulating water pump form a closed loop and exchange heat with the secondary network water-to-water heat exchanger through medium isolation. The primary heating network circulating water pump is also connected to the makeup water pump. The condensate generated by the heating network heater is sent to the deaerator via the heating network condensate pump and then into the feedwater side of the regenerative system. The outlet side of the low-pressure cylinder is connected in sequence to the condenser, condensate pump, low-pressure heater, deaerator, and feedwater pump, and supplies feedwater to the DC steam generator.

[0010] Furthermore, the control device uses the set value of the primary network water supply temperature as the main control target and the lower and upper limits of the pressure difference between the two networks as constraints. It first adjusts the speed of the primary network circulating water pump and then adjusts the opening of the heating steam extraction regulating valve in the following sequence: when the primary network water supply temperature is lower than the set value and the pressure difference between the two networks is not lower than the lower limit, the speed of the primary network circulating water pump is increased; when the increased speed still does not reach the set value, the opening of the heating steam extraction regulating valve is increased; when the primary network water supply temperature is higher than the set value, the opening of the heating steam extraction regulating valve and the speed of the primary network circulating water pump are decreased in reverse order, while maintaining the pressure difference between the two networks not exceeding the upper limit and not lower than the lower limit.

[0011] Furthermore, the control device sets the single adjustment step size, the maximum change per unit time, and the minimum holding time between two adjustments for the heating steam extraction regulating valve and the primary network circulating water pump, respectively. When the final stage metal temperature of the low-pressure cylinder is lower than the temperature warning threshold or the exhaust humidity of the low-pressure cylinder is higher than the humidity warning threshold, the single adjustment step size and the maximum change amount per unit time of the heating extraction steam regulating valve are reduced to the preset small step size and the preset small change amount, and the minimum holding time of the two adjustments is increased to the preset holding time. At the same time, the speed change of the primary network heating network circulating water pump is limited to not exceeding the preset small speed change amount.

[0012] Furthermore, the control device sets three levels of limiting based on the final stage metal temperature of the low-pressure cylinder and the exhaust humidity of the low-pressure cylinder: At the warning level, the allowable opening degree of the heating steam extraction regulating valve is limited to not exceeding the steam extraction opening limit value, and the opening degree of the cooling steam regulating valve of the low-pressure cylinder is not lower than the cooling opening limit value. At the restriction level, the allowable opening degree of the heating steam extraction regulating valve is limited to no higher than the steam extraction opening limit value two, and the opening degree of the low-pressure cylinder cooling steam regulating valve is limited to no lower than the cooling opening limit value two. At the cut-off level, the heating steam extraction regulating valve is closed and the low-pressure cylinder cooling steam regulating valve is kept at the cooling minimum opening; when the monitored quantity continuously reaches the preset time of the release condition, the limit is released step by step in reverse order of cut-off level, restriction level, and warning level.

[0013] Furthermore, the control device uses the radioactivity monitoring values ​​of the outlet and return water inlet of the secondary network water-to-water heat exchanger and the pressure difference between the two networks as interlocking criteria. When the radioactivity monitoring value exceeds the radioactivity threshold or the pressure difference between the two networks is lower than the lower limit of the pressure difference, the heating steam extraction regulating valve is closed, so that the primary network heating network circulating water pump maintains the primary network in a closed loop, and the low-pressure cylinder cooling steam regulating valve is kept at the cooling minimum opening. Once the radioactivity monitoring value and the pressure difference between the two networks continuously meet the recovery threshold and the lower limit of the pressure difference for a preset time, the heat exchange cycle between the primary network and the secondary network is restored first, and then the heating steam extraction regulating valve is opened in a step-by-step manner until the heating is restored to normal.

[0014] Furthermore, when unit protection, main steam pressure abnormality, pressure difference between the two networks abnormality, or radioactivity monitoring exceeding the limit occurs, the control device closes the heating extraction steam regulating valve within the first action time limit, and closes the main steam emergency isolation valve within the second action time limit after the first action time limit expires; the low-pressure cylinder cooling steam regulating valve is kept at the cooling minimum opening throughout the process, the primary network heating network circulating water pump is controlled to switch to internal circulation mode to maintain the primary network closed circulation, and the reopening of the heating extraction steam regulating valve is prohibited until all triggering conditions are eliminated.

[0015] Furthermore, when the control device resumes heating after the abnormality is resolved, it includes: Keep the cooling steam regulating valve of the low-pressure cylinder at a constant cooling bottom opening, and control the primary network heat network circulating water pump to establish a heat exchange cycle between the primary network and the secondary network at a set speed; The heating steam extraction regulating valve is opened in stages with an opening increment no greater than the recovery step size and at intervals of recovery holding time. The primary network supply water temperature and the pressure difference between the two networks are checked at each stage. When any monitored quantity deviates from the set range, the opening of the heating steam extraction regulating valve is stopped, the opening of the heating steam extraction regulating valve is returned to the previous stage, and the primary network heating network circulating water pump returns to the internal circulation mode.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: By setting three parallel branches at the reheater outlet—a heating extraction steam pipeline, a low-pressure cylinder cooling steam pipeline, and a low-pressure cylinder inlet steam pipeline—and using zero output of the low-pressure cylinder as the normal heating condition, retaining only the cooling steam required for the final stage under the minimum cooling opening, while directly sending the heating extraction steam into the heating network heater and achieving medium isolation and condensate return to the deaerator via a secondary network water-to-water heat exchanger, the regenerative closed loop is improved, the proportion of usable extraction steam at the reheat end is increased, the cold source loss at the condenser end is reduced, the overall utilization rate of nuclear energy and the heat-to-power ratio are improved, and a stable supply water temperature is achieved at the user side. Temperature and pressure difference between the two networks; by using the supply and return water temperature of the primary heating network and the pressure difference between the two networks as the main control, combined with the final stage metal temperature of the low-pressure cylinder, exhaust steam humidity and radioactivity monitoring values ​​to set the upper limit of extraction steam and the lower limit of cooling, and prioritizing the cutting off of heating extraction steam and then closing the main steam accident isolation valve when the unit is protected, the main steam pressure is abnormal or radioactivity exceeds the limit, this achieves boundary protection for low-pressure cylinder condensation and blade safety, radioactivity isolation between the primary and secondary networks and rapid accident handling, thereby simultaneously achieving high proportion of heating, unit safety margin, heat exchange link compliance and vibration resistance and recoverability of operation adjustment in the small reactor scenario. Attached Figure Description

[0017] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic diagram of the structure of a modular nuclear small reactor high-efficiency cogeneration heating system provided in an embodiment of the present invention.

[0018] The components include: 1. Modular small modular reactor; 2. High-pressure cylinder; 3. Reheater; 4. Low-pressure cylinder cooling steam regulating valve; 5. Heating steam extraction regulating valve; 6. Low-pressure cylinder inlet steam regulating valve; 7. Low-pressure cylinder; 8. Generator; 9. Heater network heater; 10. Primary heater network circulating water pump; 11. Secondary heater network water-to-water heat exchanger; 12. Feed water pump; 13. Deaerator; 14. Low-pressure heater; 15. Condensate pump; 16. Condenser; 17. Heater network drain pump; 18. Makeup water pump; 19. Secondary heater network circulating water pump. Detailed Implementation

[0019] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] In traditional modular small modular reactor (SMR) heating applications, existing technologies struggle to achieve coordinated optimization of high-proportion extraction heating, low-pressure cylinder safety cooling, and thermal network isolation safety. Specifically, the reheater outlet lacks a structured three-branch design, making it impossible to simultaneously meet both the high-proportion extraction demand and the minimum cooling requirements under normal heating conditions. Furthermore, the control strategy fails to interlock and limit the supply and return water temperatures of the primary heating network, the pressure difference between the two networks, the final stage metal temperature of the low-pressure cylinder, exhaust humidity, and radioactivity monitoring values. This results in abnormal increases in the final stage metal temperature of the low-pressure cylinder, excessive exhaust humidity, and fluctuations in radioactivity monitoring signals during the process of increasing the extraction ratio, thus affecting heating continuity, equipment safety margins, and the reliability of media isolation.

[0021] For example, in a nuclear-powered district heating project in a frigid region, when encountering prolonged periods of low temperatures, the demand for heat load increases, and the system attempts to increase the proportion of reheater outlet steam allocated to the heating extraction steam pipeline. At this time, because the reheater outlet has only a single extraction steam path, the cooling steam flow to the low-pressure cylinder is insufficient, causing the final stage metal temperature of the low-pressure cylinder to rise continuously and approach the safety threshold. Simultaneously, the widening temperature difference between the primary heating network's supply and return water leads to an imbalance in the pressure difference between the two networks, resulting in unstable operation of the secondary heating network's circulating water pumps, and abnormal signals detected by the radioactivity monitoring device. In this scenario, the system is forced to reduce the extraction steam ratio to restore low-pressure cylinder cooling, but this leads to a decrease in heating capacity and fluctuations in user-side temperature, requiring frequent intervention from operators to maintain basic operation.

[0022] If the above problems are not resolved, under long-term high-proportion steam extraction conditions, the low-pressure cylinder may suffer thermal stress damage or material fatigue due to insufficient cooling, increasing the risk of unplanned equipment shutdowns; runaway pressure differential in the heating network will weaken the physical isolation barrier effect of the water-to-water heat exchanger, increasing the potential migration of radioactive materials; in addition, the lack of an abnormal operating condition response mechanism will gradually narrow the safety boundary, expand the scope of system failure, and ultimately threaten the overall reliability and public safety boundary of the nuclear heating system.

[0023] For this, please refer to Figure 1 As shown, this application proposes a modular nuclear small reactor high-efficiency cogeneration heating system, comprising: The modular nuclear small reactor 1 supplies steam to the high-pressure cylinder 2 of the steam turbine through a DC steam generator. The exhaust steam from the high-pressure cylinder 2 enters the reheater 3 after passing through a steam-water separator.

[0024] The reheater 3 outlet forms three parallel branches. The first branch is the heating extraction steam pipeline, which leads to the heating network heater 9 via the heating extraction steam regulating valve 5 to heat the primary heating network. The second branch is the low-pressure cylinder cooling steam pipeline, which leads to the turbine low-pressure cylinder 7 via the low-pressure cylinder cooling steam regulating valve 4 to maintain the turbine low-pressure cylinder 7 at zero output under normal heating conditions. The third branch is the low-pressure cylinder inlet steam pipeline, which leads to the turbine low-pressure cylinder 7 via the low-pressure cylinder inlet steam regulating valve 6. The low-pressure cylinder 7 is connected to the generator 8 to exit the zero-output or power-only operation mode.

[0025] The heating network heater 9 is isolated from the secondary network water-to-water heat exchanger 11 by a medium. The secondary network heating network circulating water pump 19 is used to maintain the secondary network circulation. The condensate generated by the heating network heater 9 is returned to the deaerator 13 via the heating network condensate pump 17 and incorporated into the regenerative system.

[0026] The control device is configured to maintain the low-pressure cylinder 7 at zero output as the normal heating state, keep the low-pressure cylinder cooling steam regulating valve 4 at the cooling minimum opening, adjust the opening of the heating extraction steam regulating valve 5 and the speed of the primary heating network circulating water pump 10 according to the primary heating network supply and return water temperature and the pressure difference between the two networks, and limit the upper limit of the opening of the heating extraction steam regulating valve 5 and the lower limit of the opening of the low-pressure cylinder cooling steam regulating valve 4 according to the final stage metal temperature of the low-pressure cylinder 7, the exhaust steam humidity and the radioactivity monitoring value.

[0027] When unit protection, main steam pressure abnormality, two-network pressure difference abnormality, or radioactivity monitoring exceeding the limit occurs, the control device sequentially closes the heating extraction steam regulating valve 5 and the main steam accident isolation valve, while maintaining the low-pressure cylinder cooling steam regulating valve 4 at the cooling minimum opening, and resumes heating after the abnormality is resolved.

[0028] Specifically, with the advancement of nuclear heating projects and the application of modular small modular reactors (SMRs), utilizing secondary loop steam to provide a heat source for urban centralized heating has become an important direction. Traditional nuclear power extraction heating schemes extract steam from the high-pressure cylinder 2 or the intermediate-pressure cylinder section, but do not take the long-term zero-output and only basic cooling conditions of the low-pressure cylinder 7 as a normal strategy, nor have they formed a complete link from the reheat end to the cooling of the low-pressure cylinder 7 and the exit from zero output. This makes it difficult to achieve the optimal synergy of high-proportion steam extraction, safe cooling of the low-pressure cylinder 7, and safe isolation between the two networks in the SMR scenario. Among them, the parallel three-branch reheater 3 outlet refers to the structural design in which the steam at the reheater 3 outlet is distributed to three independent pipelines. This can be achieved using a three-way valve or a fixed flow distribution structure. For example, the steam flow can be dynamically distributed by an electric three-way valve according to the control signal, or a fixed proportion distribution can be achieved by using a flow distribution plate with a preset orifice. The main purpose is to achieve physical isolation of heating, cooling, and power generation functions and avoid functional conflicts. Furthermore, maintaining zero output from the low-pressure cylinder 7 as the normal heating condition refers to the state where the turbine's low-pressure cylinder 7 has no net power output under normal heating conditions. This can be achieved by adjusting the cooling steam flow rate to only meet the rotor's coasting requirements. For example, the low-pressure cylinder 7 rotor can be kept rotating but with torque balance by controlling the cooling steam flow rate, or power output can be suppressed by combining an auxiliary braking device. The main purpose is to ensure the safe cooling of the low-pressure cylinder 7 during high-proportion extraction steam heating. Specifically, the minimum opening value for cooling refers to the minimum opening setting value of the low-pressure cylinder cooling steam regulating valve 4. This value can be calculated and determined based on the thermal expansion characteristics of the low-pressure cylinder 7, for example, set to 5% to 10% of the valve's full stroke, or dynamically adjusted according to the ambient temperature to maintain the threshold for thermal stress safety of metal components. The main purpose is to continuously provide a basic cooling steam flow under normal heating conditions. Therefore, based on the adjustment mechanism of the supply and return water temperature of the primary heating network and the pressure difference between the two networks, a proportional-integral-derivative control algorithm or a lookup table method can be used. For example, adjustment commands can be generated based on the combined signals of temperature deviation and pressure difference deviation, or the adjustment amount of the opening of the heating extraction steam regulating valve 5 and the speed of the primary heating network circulating water pump 10 can be determined through a preset mapping relationship. This is mainly to achieve coordinated control of the primary heating network temperature stability and the circulating pressure difference. In addition, limiting the upper and lower limits of the opening based on the metal temperature of the last stage of the low-pressure cylinder 7, the exhaust steam humidity, and the radioactivity monitoring values ​​refers to dynamically constraining the operating range of the regulating valve using safety parameters. This can be achieved by using multi-level threshold triggering or continuous function calculation. For example, when the monitoring value exceeds the preset threshold, the upper limit of the opening of the heating extraction steam regulating valve 5 can be linearly reduced, or the lower limit of the opening of the low-pressure cylinder cooling steam regulating valve 4 can be dynamically adjusted based on the humidity value. This is mainly to achieve the safety goal of preventing mechanical damage caused by overheating of the last stage of the low-pressure cylinder 7 or excessive humidity.As a preferred embodiment, the media isolation between the heat network heater 9 and the secondary network water-to-water heat exchanger 11 can be achieved using a plate heat exchanger or a shell-and-tube heat exchanger. For example, a stainless steel plate heat exchanger can be used to complete the heat exchange process, or a shell-and-tube heat exchanger with a double tube sheet structure can be used to block direct media contact. This is mainly to achieve radioactive risk isolation between the primary and secondary heat networks. This application solves the problem of coordinating high-proportion extraction steam heating, maintaining the safe cooling of the low-pressure cylinder 7, and ensuring the safety of heat network isolation in the modular nuclear small reactor 1 heating system by combining the structured organization of the three branches at the reheater 3 outlet with a control strategy that uses zero output of the low-pressure cylinder 7 as the normal heating condition, and a multi-parameter interlocking safety constraint mechanism. This achieves physical isolation of functional allocation and dynamic protection of safety boundaries under heating conditions.

[0029] Specifically, during system implementation, the modular small modular reactor 1 supplies steam to the high-pressure cylinder 2 of the turbine via a direct-current steam generator. The exhaust steam from the high-pressure cylinder 2 is processed by a steam-water separator before entering the reheater 3. The reheater 3 outlet forms a parallel three-branch structure. The first branch is the heating extraction steam pipeline, which connects to the heating network heater 9 via the heating extraction steam regulating valve 5 to heat the primary heating network. The second branch is the low-pressure cylinder cooling steam pipeline, which connects to the low-pressure cylinder 7 of the turbine via the low-pressure cylinder cooling steam regulating valve 4, maintaining the low-pressure cylinder 7 in a zero-output state under normal heating conditions. The third branch is the low-pressure cylinder inlet steam pipeline, which connects to the low-pressure cylinder 7 of the turbine via the low-pressure cylinder inlet steam regulating valve 6. The low-pressure cylinder 7 is connected to the generator 8 to exit the zero-output or power-only operation mode. The heating network heater 9 is media-isolated from the secondary network water-to-water heat exchanger 11. The secondary network circulating water pump 19 is used to maintain the secondary network circulation. The condensate generated by the heating network heater 9 is returned to the deaerator 13 via the heating network condensate pump 17 and incorporated into the regenerative system. The control device is configured to maintain the low-pressure cylinder 7 at zero output as the normal heating state, keep the low-pressure cylinder cooling steam regulating valve 4 at the minimum cooling opening, adjust the opening of the heating extraction steam regulating valve 5 and the speed of the primary network circulating water pump 10 according to the primary network supply and return water temperatures and the pressure difference between the two networks, and limit the upper limit of the opening of the heating extraction steam regulating valve 5 and the lower limit of the opening of the low-pressure cylinder cooling steam regulating valve 4 according to the final stage metal temperature of the low-pressure cylinder 7, the exhaust steam humidity and the radioactivity monitoring value. When unit protection, main steam pressure abnormality, two-network pressure difference abnormality, or radioactivity monitoring exceeding the limit occurs, the control device sequentially closes the heating extraction steam regulating valve 5 and the main steam accident isolation valve, while maintaining the low-pressure cylinder cooling steam regulating valve 4 at the cooling minimum opening, and resumes heating after the abnormality is resolved.

[0030] Specifically, the system operates based on a dynamic distribution mechanism of the reheater 3 outlet steam parameters. The heating extraction steam regulating valve 5 can be an electric butterfly valve for precise flow control, while the low-pressure cylinder cooling steam regulating valve 4 can be a pneumatic regulating valve for rapid response. The control device is a programmable logic controller (PLC) based system, integrating temperature sensors, differential pressure sensors, and a radiation monitor to collect real-time data on the primary heating network supply and return water temperatures, the pressure difference between the two networks, the final stage metal temperature of the low-pressure cylinder, and exhaust steam humidity, and to execute preset control logic. For example, under normal heating conditions, the control device maintains the low-pressure cylinder cooling steam regulating valve 4 at a minimum cooling opening, ensuring a continuous minimum cooling steam flow through the low-pressure cylinder 7 to prevent overheating of the final stage blades. Simultaneously, based on the deviation between the primary heating network supply water temperature and the set value, the speed of the primary heating network circulating water pump 10 is preferentially adjusted to stabilize the pressure difference between the two networks. The opening of the heating extraction steam regulating valve 5 is adjusted only when the pressure difference meets the constraints, thereby maximizing the extraction ratio while ensuring the safety of the heating network isolation. When the radioactivity monitoring value exceeds the threshold, the control device immediately closes the heating extraction steam regulating valve 5, cutting off the heat exchange path between the primary heating network and the secondary network, but keeps the low-pressure cylinder cooling steam regulating valve 4 at the cooling minimum opening to ensure continuous cooling of the turbine low-pressure cylinder 7.

[0031] Thus, through the structured organization of the three branches at the reheater 3 outlet, the system achieves physical isolation between high-proportion extraction steam heating and safe cooling of the low-pressure cylinder 7. The first branch is dedicated to heating without affecting the operation of the low-pressure cylinder 7; the second branch provides a baseline cooling flow to maintain zero output; and the third branch retains flexibility in switching operating conditions. The condensate return mechanism sends the condensate generated by the heating network heater 9 to the deaerator 13 via the heating network condensate pump 17, effectively recovering heat energy and reducing cold source losses. The control strategy is based on multi-parameter interlocking and limiting, dynamically restricting the opening boundary of the regulating valve to prevent mechanical damage caused by excessively low final-stage metal temperature or excessively high exhaust steam humidity in the low-pressure cylinder 7. Simultaneously, the anomaly handling mechanism prioritizes the safety of core equipment to avoid the spread of radioactive risks. Furthermore, the system adopts a phased start-up strategy during the recovery process after anomalies are resolved. By checking the primary network supply water temperature and the pressure difference between the two networks, the opening of the heating extraction steam regulating valve 5 is gradually adjusted to ensure the stability and reliability of heating recovery.

[0032] Specifically, in some of the embodiments described above in this application, multiple DC steam generators are arranged in parallel to improve the reliability and steam supply capacity of the heating system. However, in the process of implementation, the failure of a single DC steam generator will cause the entire heating system to shut down, which cannot meet the continuity requirements of modular small stack high-proportion extraction steam heating. At the same time, the steam output capacity of a single generator is limited, making it difficult to support the stable and large-flow steam supply required by the low-pressure cylinder 7 under the normal heating condition.

[0033] In response, this application further proposes that multiple DC steam generators be arranged in parallel, with the steam outlets of each DC steam generator converging into the main steam pipeline. A safety valve, a main steam isolation valve, and a main steam emergency isolation valve are sequentially installed on the main steam pipeline. The main steam pipeline is connected to the steam inlet of the high-pressure cylinder 2 of the turbine. The exhaust port of the high-pressure cylinder 2 of the turbine is sequentially connected in series with the steam-water separator and the reheater 3.

[0034] The parallel arrangement of multiple DC steam generators refers to a structure in which multiple independent steam generating units are connected in parallel. This can be achieved through a physically distributed arrangement or a centralized modular array, with the aim of ensuring continuous system operation in the event of a single unit failure through equipment redundancy. The safety valve, main steam isolation valve, and main steam emergency isolation valve sequentially installed on the main steam pipeline constitute a three-stage valve system configured according to the steam flow direction. The safety valve can use a spring-loaded or pilot-operated pressure relief structure to achieve automatic overpressure protection. The main steam isolation valve can be an electric or pneumatic shut-off valve for planned maintenance isolation. The main steam emergency isolation valve can be a quick-closing gate valve or butterfly valve structure to achieve steam flow cutoff in emergency conditions, with the aim of establishing a tiered safety protection mechanism. The sequential connection of the exhaust port of the high-pressure cylinder 2 of the steam turbine with the steam-water separator and reheater 3 refers to the process path where the exhaust medium flows sequentially through the steam-water separation and reheat treatment. This can be achieved using a combination of a horizontal cyclone separator and a shell-and-tube reheater 3, with the aim of removing steam moisture and improving steam dryness.

[0035] Specifically, this application's solution utilizes multiple DC steam generators operating in parallel, ensuring that even if one generator fails, the others can continue supplying steam to the main steam pipeline, preventing a complete interruption of the heating system. The steam outlets of each generator converge into the main steam pipeline, achieving flow integration and providing a stable, high-flow-rate steam source for high-proportion extraction. Safety valves, main steam isolation valves, and main steam emergency isolation valves are sequentially installed to form layered protection. Safety valves automatically release pressure to prevent equipment damage in case of overpressure, main steam isolation valves are used for localized isolation during routine maintenance, and main steam emergency isolation valves quickly cut off the steam flow in case of severe anomalies, ensuring a tiered approach to fault handling. After the exhaust steam from the high-pressure cylinder 2 of the steam turbine passes through a steam-water separator to remove liquid moisture, the reheater 3 further heats the dried steam, ensuring that the steam entering subsequent distribution stages has high dryness and suitable thermodynamic parameters, providing reliable medium conditions for heating extraction and cooling of the low-pressure cylinder 7.

[0036] In one specific implementation, this application employs three direct-current steam generators arranged in a ring around the reactor pressure vessel. The steam outlets of each generator converge into the main steam pipeline via a tapered steam collecting pipe. A spring-loaded safety valve, an electrically operated shut-off valve, and a pneumatically operated quick-closing butterfly valve are sequentially installed on the main steam pipeline as main steam emergency isolation valves. The exhaust pipe of the turbine high-pressure cylinder 2 is first connected to a horizontal cyclone steam-water separator, and then to a shell-and-tube reheater 3. The steam dryness fraction at the outlet of reheater 3 is maintained above 0.95.

[0037] Through the above solutions, this application can maintain the continuity of heating even when a single DC steam generator fails. The steam output of multiple generators is superimposed to meet the large flow demand of the low-pressure cylinder 7 under zero-output conditions. The layered valve configuration prevents minor faults from escalating into system shutdowns. Steam-water separation and reheat treatment ensure steam quality and prevent wet steam from corroding subsequent equipment.

[0038] Specifically, in some embodiments of this application, a reheater 3 outlet pipe structure is proposed to achieve independent distribution of heating steam extraction and low-pressure cylinder 7 cooling steam. However, in its implementation, the existing reheat end branch design lacks a clear physical isolation mechanism, which leads to mutual interference between heating steam extraction regulation and low-pressure cylinder 7 cooling steam supply. It is difficult to stably maintain the low-pressure cylinder 7 at zero output under normal heating conditions. At the same time, there is a safety risk that cooling steam may accidentally enter the heating system or that the low-pressure cylinder 7 may overheat due to steam extraction fluctuations.

[0039] In this regard, this application further proposes that the outlet of the reheater 3 forms a parallel heating extraction steam pipeline and a low-pressure cylinder cooling steam pipeline. The heating extraction steam pipeline is connected to the steam inlet of the heating network heater 9, and the low-pressure cylinder cooling steam pipeline is connected to the steam inlet of the low-pressure cylinder 7. The two pipelines are not connected to each other.

[0040] The heating extraction steam pipeline refers to a piping system specifically designed to directionally transport reheat steam to the heating network heater 9. It can be implemented using independently laid carbon steel or alloy steel pipelines to ensure stable flow of heating steam and efficient heat transfer. The low-pressure cylinder cooling steam pipeline can be understood as a pipeline specifically designed to continuously supply cooling medium to the turbine's low-pressure cylinder 7. It can be implemented using an isolated pipeline structure arranged parallel to the heating extraction steam pipeline to maintain the safe temperature of the metal components of the low-pressure cylinder 7 under zero-output conditions. Specifically, the two pipelines being unconnected means that the heating extraction steam pipeline and the low-pressure cylinder cooling steam pipeline are completely separated in physical structure and have no connection points. This can be achieved by setting an independent branch at the reheater 3 outlet and using a sealed isolation design to completely prevent mutual interference between the two steam lines, ensuring the independence and safety of system operation.

[0041] Specifically, the solution in this application separates the reheat steam at the source by setting parallel and physically isolated heating extraction steam pipelines and low-pressure cylinder cooling steam pipelines at the outlet of reheater 3. The heating extraction steam pipeline precisely delivers steam to the heating network heater 9 to meet the heat energy requirements of the primary heating network. The low-pressure cylinder cooling steam pipeline continuously supplies cooling medium to the low-pressure cylinder 7 to prevent metal components from overheating due to insufficient heat dissipation. Since the two pipelines are not connected to each other, adjusting the heating extraction steam flow rate will not affect the stable supply of cooling steam to the low-pressure cylinder 7, thereby reliably maintaining the low-pressure cylinder 7 at zero output under normal heating conditions, while avoiding the risk of radioactivity caused by accidental mixing of cooling steam into the heating system or the potential for insufficient cooling of the low-pressure cylinder 7 due to fluctuations in heating extraction steam.

[0042] As a preferred embodiment, the solution of this application is implemented as follows: Two independent pipelines branch off from the outlet of reheater 3 via a bifurcation joint. The heating extraction steam pipeline is connected to the steam inlet side of the heating network heater 9 via a flange. The low-pressure cylinder cooling steam pipeline is directly connected to the steam inlet flange of the low-pressure cylinder 7. The piping system is made of 304 stainless steel to withstand the high-temperature steam environment, and the installation layout ensures that the two pipelines are completely spatially isolated, with no crossing points or shared valves.

[0043] Through the above scheme, this application achieves physical isolation between heating steam extraction regulation and cooling steam supply to low-pressure cylinder 7, eliminates mutual interference, ensures that low-pressure cylinder 7 can stably maintain zero output under normal heating conditions, and prevents the risk of overheating of low-pressure cylinder 7 caused by cooling steam accidentally entering the heating system or by steam extraction fluctuations, thereby improving the safety and reliability of system operation.

[0044] Specifically, in some embodiments of this application, a scheme is proposed in which the heat network heater 9 and the primary heat network circulating water pump 10 form a closed loop and perform medium isolation heat exchange with the secondary network water-to-water heat exchanger 11. However, in the process of its implementation, if the condensate generated by the heat network heater 9 is not effectively returned to the regenerating system, it will lead to heat energy waste and working fluid loss. Moreover, the circulation between the primary network and the secondary network lacks a closed loop and a water replenishment mechanism, which may cause system pressure fluctuations, radioactive isolation failure, or decreased operational stability.

[0045] To address this, this application further proposes that the heating network heater 9 forms a closed loop with the primary heating network circulating water pump 10 and performs medium-isolated heat exchange with the secondary network water-to-water heat exchanger 11. The primary heating network circulating water pump 10 is also connected to the makeup water pump 18. The condensate generated by the heating network heater 9 is sent to the deaerator 13 via the heating network condensate pump 17 and then fed into the feedwater side of the regenerative system. The outlet side of the low-pressure cylinder 7 is sequentially connected to the condenser 16, condensate pump 15, low-pressure heater 14, deaerator 13, and feedwater pump 12, and supplies feedwater to the DC steam generator.

[0046] The closed-loop system formed by the heating network heater 9 and the primary heating network circulating water pump 10 refers to the circulation of primary heating network water in a completely sealed loop. This can be achieved using a fully welded piping system or a flange connection with sealing gaskets, aiming to prevent heating network water leakage to the external environment and ensure the isolation of radioactive materials. The media isolation heat exchange between the heating network heater 9 and the secondary network water-to-water heat exchanger 11 can be understood as a heat exchange process achieved through a physical barrier. Specifically, it can employ a double-walled tube heat exchanger or a plate heat exchanger combined with an isolation chamber structure. Its purpose is to prevent direct contact between the working fluid on the nuclear side and the user side while transferring heat, thus avoiding the migration of radioactive materials. The connection between the primary heating network circulating water pump 10 and the makeup water pump 18 refers to the dynamic connection established between the makeup water pump 18 and the primary network circulation loop through pipelines. This can be achieved using an automatic makeup water valve controlled by a pressure sensor, aiming to replenish the working fluid in real time according to system pressure changes and maintain the stable operation of the primary network circulation. The condensate generated by the heating network heater 9 is sent to the deaerator 13 via the heating network condensate pump 17, which means that the condensate is recycled to the water supply system. This can be done by using a centrifugal pump or a volumetric pump in conjunction with a condensate collector. The purpose is to recover the heat energy and working fluid of the condensate and reduce heat energy waste.

[0047] Specifically, the solution in this application utilizes a closed-loop structure formed by the heating network heater 9 and the primary heating network circulating water pump 10 to ensure that the primary heating network water operates in a completely isolated loop, avoiding contact with the external environment. Simultaneously, this closed loop achieves medium-isolated heat exchange with the secondary network water-to-water heat exchanger 11, realizing physical isolation between the nuclear-side heat source and the user-side heating network. The interconnected design of the primary heating network circulating water pump 10 and the makeup water pump 18 allows the system to automatically replenish the working fluid according to pressure changes, maintaining circulation stability. The condensate generated by the heating network heater 9 is sent to the deaerator 13 via the heating network condensate pump 17 and then incorporated into the feedwater side of the regenerative system. This path recovers the waste heat and working fluid from the condensate, avoiding heat energy waste. The outlet side of the low-pressure cylinder 7 is connected in sequence to the condenser 16, condensate pump 15, low-pressure heater 14, deaerator 13 and feedwater pump 12, and supplies feedwater to the DC steam generator. This regenerative cycle structure is based on the thermodynamic characteristics of the exhaust steam of the low-pressure cylinder 7, gradually increasing the feedwater temperature, reducing cold source loss, and supporting the modular nuclear small reactor 1 to maintain efficient cogeneration under high proportion steam extraction conditions.

[0048] In one specific implementation, the heat network heater 9 can be a plate heat exchanger, with its steam side and condensate side physically isolated by stainless steel plates. The primary heat network circulating water pump 10 and the makeup water pump 18 are connected via a three-way valve. The makeup water pump 18 is equipped with a pressure sensor, which automatically starts makeup water when the system pressure falls below a set threshold. The heat network condensate pump 17 is a centrifugal pump that delivers the condensate to the deaerator 13. In the regenerative system, the low-pressure heaters 14 are surface heaters, and the condensate pump 15 sequentially sends condensate to each low-pressure heater 14 for preheating before entering the deaerator 13.

[0049] The above scheme recovers the hydrophobic heat energy and working fluid generated by the heating network heater 9, avoiding heat energy waste and working fluid loss. The closed-loop system and water replenishment mechanism of the primary network circulation ensure stable system pressure, prevent radioactive isolation failure, and improve operational reliability.

[0050] Specifically, in some of the embodiments described above in this application, a control device is proposed with the set value of the primary network water supply temperature as the main control target and the lower limit and upper limit of the pressure difference between the two networks as constraints. However, in its implementation, if the order of adjusting the water pump speed first and then adjusting the steam extraction valve is not followed, the pressure difference between the two networks may fluctuate beyond the safety limit, thereby triggering the protection mechanism or reducing the reliability of heating.

[0051] In response, this application further proposes the following adjustment steps for the control device: Using the set value of the primary network supply water temperature as the main control objective and the lower and upper limits of the pressure difference between the two networks as constraints, the adjustment is performed sequentially: first, the speed of the primary network circulating water pump 10 is adjusted, followed by the opening of the heating steam extraction regulating valve 5. When the primary network supply water temperature is lower than the set value and the pressure difference between the two networks is not lower than the lower limit, the speed of the primary network circulating water pump 10 is increased. When increasing the speed still fails to reach the set value, the opening of the heating steam extraction regulating valve 5 is increased. When the primary network supply water temperature is higher than the set value, the opening of the heating steam extraction regulating valve 5 and the speed of the primary network circulating water pump 10 are decreased sequentially in the reverse order, while maintaining the pressure difference between the two networks not exceeding the upper limit and not lower than the lower limit.

[0052] The setpoint for the primary network water supply temperature refers to the target control value for the primary heating network water supply temperature in the heating system. This value can be dynamically set based on meteorological parameters, user heat load demands, and other factors, aiming to ensure that the heating quality meets the user's temperature control requirements. The lower and upper limits of the pressure difference between the two networks can be understood as the safe operating boundaries of the pressure difference between the primary and secondary heating networks. These limits can be determined through analysis of the network's hydraulic characteristics, aiming to prevent circulation interruption due to excessively small pressure differences or leakage risks due to excessively large pressure differences. The sequence of adjusting the speed of the primary network circulating water pump 10 before adjusting the opening of the heating extraction steam regulating valve 5 can be implemented using a priority control strategy, such as event-triggered sequential logic. This strategy leverages the direct impact of pump speed adjustment on circulation flow and its relatively small impact on pressure difference, reducing the frequency of steam extraction valve operation and thus mitigating the risk of pressure difference fluctuations.

[0053] Specifically, the proposed solution establishes a coordinated control mechanism for temperature and pressure difference by using the setpoint of the primary network water supply temperature as the main control target and the upper and lower limits of the pressure difference between the two networks as hard constraints. During temperature regulation, the control device prioritizes adjusting the speed of the primary network circulating water pump 10, as changes in pump speed primarily affect the circulation flow rate and have a rapid response, resulting in minimal pressure difference disturbance. Only when speed adjustment is insufficient to achieve the temperature target is the opening of the heating steam extraction regulating valve 5 adjusted to avoid a sudden drop in pressure difference caused by abrupt changes in steam flow. During cooling, the opening of the heating steam extraction regulating valve 5 is first reduced to decrease heat source input, followed by a reduction in the speed of the primary network circulating water pump 10 to prevent a sudden decrease in flow rate that could cause a surge in pressure difference. Throughout the entire regulation process, the pressure difference between the two networks is maintained within a safe range, ensuring both the accuracy of temperature control and preventing abnormal triggering of protection actions due to pressure difference.

[0054] As a specific implementation method, the solution of this application is implemented as follows: When the temperature of the primary heating network supply water is detected to be lower than the set value and the pressure difference between the two networks is within a safe range, the control device first increases the speed of the primary heating network circulating water pump 10 to increase the heating network flow. If the temperature still does not reach the set value, the heating steam extraction regulating valve 5 is gradually opened to increase the steam supply. When the temperature of the primary heating network supply water is higher than the set value, the control device first closes the heating steam extraction regulating valve 5, then reduces the speed of the primary heating network circulating water pump 10, while simultaneously monitoring the pressure difference between the two networks in real time to ensure that it is between the lower limit and the upper limit of the pressure difference.

[0055] Through the above solution, this application avoids the pressure difference fluctuation between the two networks exceeding the safety limit due to improper adjustment sequence, prevents false triggering of the protection mechanism, and improves the reliability and stability of the heating system.

[0056] Specifically, in some of the embodiments described above in this application, an adjustment strategy is proposed with the primary network water supply temperature as the main control target and the pressure difference between the two networks as the constraint condition. However, in its implementation, the control method with fixed adjustment parameters cannot adapt to changes in the equipment safety boundary when the final stage metal temperature of the low-pressure cylinder 7 is too low or the exhaust steam humidity is too high. This may lead to excessive adjustment action, which may aggravate the thermal stress of the final stage blades or the risk of water erosion, and cause potential equipment damage.

[0057] In this regard, this application further proposes that the control device set the single adjustment step size, the maximum change per unit time, and the minimum holding time between two adjustments for the heating extraction steam regulating valve 5 and the primary network circulating water pump 10, respectively.

[0058] When the final stage metal temperature of the low-pressure cylinder 7 is lower than the temperature warning threshold or the exhaust humidity of the low-pressure cylinder 7 is higher than the humidity warning threshold, the single adjustment step size and the maximum change per unit time of the heating extraction steam regulating valve 5 are reduced to the preset small step size and the preset small change, and the minimum holding time of the two adjustments is increased to the preset holding time. At the same time, the speed change of the primary network heating network circulating water pump 10 is limited to not exceeding the preset small speed change.

[0059] Among them, the single adjustment step size refers to the maximum change in valve opening or pump speed allowed by the control device in each adjustment operation. It can be expressed as a percentage or an absolute value, aiming to control the precision of the adjustment action and avoid system oscillation caused by excessively large step sizes. The maximum change per unit time refers to the upper limit of the cumulative change of the adjustment parameter within a specific time window. It can be implemented through a rate limiter or a time integration module, aiming to prevent system instability caused by excessively rapid adjustment rates. The minimum hold time between two adjustments refers to the minimum time interval between two consecutive adjustment operations. It can be implemented based on a timer or state hold logic, aiming to give the system sufficient response time and avoid the accumulation of mechanical stress from frequent adjustments. The preset small step size, preset small change, and preset hold time refer to more conservative adjustment parameters used under abnormal operating conditions. They can be dynamically calculated based on the equipment safety boundary or preset safety values, aiming to converge the control strategy and protect critical components when the equipment faces safety risks.

[0060] Specifically, the solution proposed in this application regulates the adjustment behavior under normal operating conditions by setting adjustment parameters in advance through the control device. When the physical quantity that directly reflects the thermal stress state of the material or the water erosion risk associated with the exhaust steam humidity exceeds the safety boundary, the strictness of the adjustment parameters is dynamically adjusted to compress the adjustment range and rate of the heating steam extraction regulating valve 5 to a safe range. At the same time, the adjustment interval is extended and the speed change rate of the heating network circulating water pump is limited. Thus, while maintaining the stability of the primary network water supply temperature, the solution ensures that the final stage blades of the low-pressure cylinder 7 are protected from thermal shock or water erosion damage, thereby achieving a synergistic guarantee of heating stability and equipment safety.

[0061] As a preferred embodiment, the solution of this application is specifically implemented as follows: The control device adopts a distributed control system. When the final stage metal temperature sensor of the low-pressure cylinder 7 detects that the temperature is lower than the warning threshold, it automatically switches to the fine adjustment mode, reduces the opening adjustment range of the heating steam extraction regulating valve 5 and extends the adjustment interval, and at the same time limits the speed change rate of the primary network heating network circulating water pump 10, so that the system smoothly transitions to a stable state within the safety boundary.

[0062] Through the above solution, this application avoids the risk of increased thermal stress or water erosion of the last stage blades caused by excessive adjustment under the safety risk conditions of the low-pressure cylinder 7, and ensures the safe and stable operation of the heating system under abnormal conditions.

[0063] Specifically, in some of the embodiments described above in this application, a method for adjusting the regulating valve parameters is proposed when the final stage metal temperature of the low-pressure cylinder 7 is lower than the temperature warning threshold or the exhaust humidity is higher than the humidity warning threshold. However, in its implementation, when the abnormal situation continues to worsen, simply reducing the single adjustment step size, the amount of change, and extending the holding time cannot effectively cope with the safety risks that increase in severity. This may cause the low-pressure cylinder 7 to suffer brittle damage due to excessively low metal temperature or water erosion due to excessively high exhaust humidity. Therefore, a limiting strategy based on dynamic classification of monitoring values ​​is urgently needed to achieve accurate matching and progressive protection of the degree of abnormality.

[0064] In response, this application further proposes a control device that sets three levels of limiting based on the final stage metal temperature of the low-pressure cylinder 7 and the exhaust humidity of the low-pressure cylinder 7: At the warning level, the allowable opening degree of the heating extraction steam regulating valve 5 is limited to not exceeding the extraction steam opening limit value, and the opening degree of the cooling steam regulating valve of the low-pressure cylinder 7 is not lower than the cooling opening limit value.

[0065] At the restricted level, the allowable opening degree of the heating extraction steam regulating valve 5 is limited to no higher than the extraction steam opening limit value two, and the opening degree of the low-pressure cylinder cooling steam regulating valve 4 is limited to no lower than the cooling opening limit value two.

[0066] At the cut-off level, the heating extraction steam regulating valve 5 is closed and the low-pressure cylinder cooling steam regulating valve 4 is kept at the cooling minimum opening. After the monitored quantity continuously reaches the preset time for the release condition, the limit is released level by level in reverse order of cut-off level, restriction level, and warning level.

[0067] Among them, the three-level limiting refers to a protection mechanism that dynamically divides protection based on the severity of monitoring parameters. It can be implemented using multi-level threshold intervals or fuzzy logic algorithms. Its purpose is to match the corresponding protection strength according to the level of abnormal risk, so as to avoid the protection measures being out of touch with actual safety requirements. The allowable opening limit of the heating steam extraction regulating valve 5 refers to the upper limit constraint on the valve opening. It can be understood as being implemented through controller software limiting or mechanical limit devices. Its purpose is to prevent excessive steam extraction from weakening the cooling effect of the low-pressure cylinder 7 and to ensure a basic balance between heat load and cooling capacity. The lower limit of the opening of the low-pressure cylinder cooling steam regulating valve 4 refers to the set boundary for maintaining the minimum cooling flow rate. It can be implemented by setting the minimum opening using a valve positioner or a flow controller. Its purpose is to ensure that the low-pressure cylinder 7 receives continuous basic cooling under heating conditions and to avoid a sudden drop in metal temperature or excessive humidity. The reverse-sequential step-by-step release of the limiting refers to a release strategy that gradually restores protection starting from the most stringent protection level. It can be implemented based on time delay confirmation or continuous monitoring verification mechanisms. Its purpose is to ensure that the system smoothly transitions to normal operating conditions after the anomaly is eliminated and to prevent repeated actions caused by short-term fluctuations.

[0068] Specifically, the control device collects real-time data on the final stage metal temperature and exhaust humidity of the low-pressure cylinder 7, dynamically compares the monitored values ​​with preset thresholds, and triggers corresponding limiting actions. At the warning level, the system slightly limits the upper limit of the opening of the heating extraction steam regulating valve 5 while ensuring the lower limit of the opening of the cooling steam regulating valve, suppressing initial heat load fluctuations. When the monitored values ​​further deteriorate and enter the limiting level, the system tightens the extraction steam opening limit and increases the cooling opening requirement, achieving a step-by-step reduction in heat load and simultaneous enhancement of cooling capacity. If the anomaly reaches a critical state triggering the cut-off level, the heating extraction steam regulating valve 5 is immediately closed to eliminate heat source impact, maintaining only the minimum cooling opening to ensure uninterrupted basic cooling. After the monitored values ​​remain continuously stable within the safe range for a preset duration, the system strictly follows the reverse order of the cut-off level, limiting level, and warning level to gradually release the limiting, allowing the protection state to orderly revert from the most stringent level, ensuring the reliability and stability of the recovery process.

[0069] As a specific embodiment, the solution of this application is implemented as follows: The control device is configured to automatically enter the warning stage when the final stage metal temperature of the low-pressure cylinder 7 is slightly lower than the warning threshold or the exhaust steam humidity is slightly higher than the warning threshold. At this time, the opening of the heating extraction steam regulating valve 5 is limited to the extraction steam opening limit value range, and the opening of the low-pressure cylinder cooling steam regulating valve 4 is maintained above the cooling opening limit value one. If the monitored value continues to deteriorate, the system is upgraded to the restriction stage, and the extraction steam opening limit value two is set to a threshold that is more stringent than the limit value one. The cooling opening limit value two is correspondingly increased to a level higher than the limit value one. When the monitored value reaches the cut-off threshold, the heating extraction steam regulating valve 5 is immediately closed, and only the cooling minimum opening is maintained. In the recovery stage, after the monitored value has been continuously normal for more than a preset time, the system first releases the cut-off stage protection, then the restriction stage, and finally the warning stage, gradually restoring the heating normal.

[0070] Through the above scheme, this application realizes dynamic and refined control of the safety boundary of the low-pressure cylinder 7, provides progressive protection during the process of increasing abnormality, avoids the risk of brittle damage caused by excessively low metal temperature and water erosion corrosion caused by excessively high exhaust humidity, and ensures the long-term safe and stable operation of the modular nuclear small reactor 1 under high proportion extraction steam heating conditions.

[0071] In practical applications, some embodiments of this application propose a three-stage limiting control based on the final stage metal temperature and exhaust humidity of the low-pressure cylinder 7 to ensure the safe operation of the low-pressure cylinder 7. However, in its implementation, the system lacks a real-time interlocking response mechanism for radioactive monitoring values ​​and the pressure difference between the two networks. When the water-to-water heat exchanger 11 of the secondary network fails to isolate, potentially causing radioactive materials to leak to the user side, or when the abnormal pressure difference between the two networks indicates a pipe rupture, it cannot automatically and quickly cut off the heat source and maintain the safe state of the system. Relying on manual intervention can easily cause response delays, increase the risk of radioactive spread, and make the system operation unstable.

[0072] In response, this application further proposes that the control device uses the radioactivity monitoring values ​​at the outlet and return water inlet of the secondary network water-to-water heat exchanger 11, as well as the pressure difference between the two networks, as interlocking criteria. When the radioactivity monitoring value exceeds the radioactivity threshold or the pressure difference between the two networks falls below the lower limit of the pressure difference, the heating steam extraction regulating valve 5 is closed, allowing the primary network circulating water pump 10 to maintain the primary network in a closed loop, and keeping the low-pressure cylinder cooling steam regulating valve 4 at the cooling minimum opening. When the radioactivity monitoring value and the pressure difference between the two networks continuously meet the recovery threshold and the lower limit of the pressure difference for a preset time, the heat exchange cycle between the primary and secondary networks is restored first, and then the heating steam extraction regulating valve 5 is opened in a step-by-step manner until the heating normal is restored.

[0073] The interlocking criterion refers to the set of conditions used to trigger automatic response in the safety protection mechanism. It can be implemented using a logical OR relationship between radioactive monitoring values ​​and the pressure difference between the two networks. The purpose is to identify in real-time the risk of media isolation failure or hydraulic instability, avoiding protection failure due to misjudgment of a single parameter. The cooling minimum opening can be understood as the valve opening state corresponding to the minimum steam flow required to maintain the safe operation of the low-pressure cylinder 7. Specifically, it can be achieved through mechanical limits of the valve actuator or lower limits of control signals. Its purpose is to ensure that the low-pressure cylinder 7 continuously receives basic cooling under zero-output conditions, preventing overheating of the final-stage metal or excessive exhaust humidity. The step-by-step approach specifically refers to a phased, gradual adjustment strategy. It can be implemented using fixed-time intervals of opening increments or adaptive step sizes based on temperature feedback. The purpose is to avoid system parameter oscillations caused by sudden changes in heating load and to ensure the smoothness of the recovery process.

[0074] Specifically, the proposed solution uses the radioactivity monitoring values ​​at the outlet and return water inlet of the secondary network water-to-water heat exchanger 11, along with the pressure difference between the two networks, as interlocking criteria. When any monitored value exceeds a safety threshold, the control device immediately closes the heating extraction steam regulating valve 5 to block the heat transfer path from the heat source to the primary network. Simultaneously, it instructs the primary network circulating water pump 10 to switch to a closed-loop circulation mode to maintain system thermal balance and keeps the low-pressure cylinder cooling steam regulating valve 4 at a minimum cooling opening to ensure final-stage cooling of the turbine. After the anomaly is resolved, the control device prioritizes restoring the heat exchange cycle between the primary and secondary networks to verify the integrity of the media isolation. Then, it gradually opens the heating extraction steam regulating valve 5 through phased step-by-step adjustments. At each stage, the primary network supply water temperature and the pressure difference between the two networks are checked to ensure that the system remains within the safety boundary during the recovery process, thus forming a closed-loop control logic from risk identification and rapid protection to safe recovery.

[0075] As a specific implementation method, the scheme of this application is implemented as follows: Radioactivity monitoring values ​​are obtained through gamma-ray detectors installed at the outlet and return water inlet of the secondary network water-to-water heat exchanger 11. The control device uses an industrial-grade programmable logic controller to implement interlocking logic operations. When an abnormal increase in radioactivity is detected, the controller outputs a signal to drive the pneumatic actuator to close the heating steam extraction regulating valve 5 and switch the primary network circulating water pump 10 to internal circulation mode. After the monitoring data stabilizes continuously, the controller first starts the secondary network circulating pump to rebuild the heat exchange path, and then increases the opening of the heating steam extraction regulating valve 5 in stages at preset time intervals, continuously monitoring system parameters at each stage until the heating supply is fully restored to normal.

[0076] The above technical solutions enable automatic and rapid response to potential radioactive leaks and system hydraulic instability, block abnormal heat transfer paths from the heat source to the user side, avoid response delays caused by manual intervention, ensure that the primary network maintains a controllable thermal balance during protection, and ensure a smooth transition of the heating system from abnormal conditions to normal operation through a phased recovery mechanism, thereby improving the media isolation safety and system operation stability in nuclear heating scenarios.

[0077] In practical applications, some of the embodiments described above in this application propose interlocking control based on radioactivity monitoring and the pressure difference between the two networks to ensure safe isolation under normal heating conditions. However, in the process of implementation, when more extensive and serious abnormal situations such as unit protection or abnormal main steam pressure occur, there is a lack of phased response mechanisms and continuous cooling guarantees. This may lead to overheating of the low-pressure cylinder 7 due to cooling interruption, sudden system shutdown causing the heating network to freeze or radioactive risk to spread, affecting the fault adaptability and safety boundary maintenance of the nuclear small reactor heating system.

[0078] In response, this application further proposes that when unit protection, main steam pressure abnormality, differential pressure between the two networks abnormality, or radioactivity monitoring exceeding limits occur, the control device shall close the heating extraction steam regulating valve 5 within the first action time limit, and close the main steam emergency isolation valve within the second action time limit after the first action time limit expires. Throughout the process, the low-pressure cylinder cooling steam regulating valve 4 shall be kept at the minimum cooling opening, the primary network circulating water pump 10 shall be switched to internal circulation mode to maintain the primary network closed circulation, and the reopening of the heating extraction steam regulating valve 5 shall be prohibited until all triggering conditions are eliminated.

[0079] The first action time limit refers to the initial time window for the control device to respond to an anomaly. This can be achieved using preset fixed time parameters or dynamically adjusted timing logic based on the anomaly type. Its purpose is to quickly block heat source input to prevent the spread of radioactive risks or pressure runaway. The second action time limit refers to the period after the first action time limit ends during which main steam isolation is delayed. This can be achieved using a programmable delay circuit or software timing module. Its purpose is to provide a buffer period for the system to avoid mechanical shock to the turbine caused by sudden steam interruption. The cooling minimum opening refers to the minimum opening threshold maintained by the low-pressure cylinder cooling steam regulating valve 4. This can be achieved using a mechanical limit device or an electronically set minimum opening value. Its purpose is to ensure that the low-pressure cylinder 7 continuously receives a minimum amount of cooling steam during an anomaly to suppress metal temperature rise. The internal circulation mode refers to the operating state of the primary network circulating water pump 10 after secondary network isolation. This can be achieved by switching the valve to a closed loop or automatically adjusting the pump speed. Its purpose is to maintain the flow of the primary network medium to prevent pipe freezing caused by a sudden drop in local temperature. Re-opening prohibition refers to the locking mechanism for the operation authority of heating steam extraction regulating valve 5. It can be implemented by software interlock logic or hardware relay circuit. The purpose is to force the system to maintain a safe state before the hidden dangers are completely eliminated.

[0080] Specifically, the proposed solution employs a phased response mechanism triggered by anomaly monitoring: when the control device detects unit protection, abnormal main steam pressure, abnormal pressure difference between the two networks, or radioactivity exceeding limits, it immediately initiates the first action time limit. Within this time limit, the heating extraction steam regulating valve 5 is preferentially closed to cut off the heat input to the primary heating network, thereby preventing the abnormal energy from spreading to the user side. After the first action time limit expires, the second action time limit is entered, and the main steam emergency isolation valve is closed. This delayed operation ensures a stable transition on the main steam side after the heat source is cut off, preventing turbine vacuum damage. Simultaneously, the low-pressure cylinder cooling steam regulating valve 4 is maintained at a minimum cooling opening throughout the process, providing continuous cooling for the low-pressure cylinder 7 to suppress the rise in the metal temperature of the last-stage blades and abnormal exhaust humidity. The primary network circulating water pump 10 is controlled to switch to internal circulation mode, allowing the primary network to circulate within a closed loop to maintain thermal stability. The reopening of the heating extraction steam regulating valve 5 is prohibited until all triggering conditions are completely eliminated, thus forming a complete closed-loop logic of anomaly detection, phased cutoff, continuous cooling maintenance, and safe recovery.

[0081] As a specific implementation method, the solution of this application is implemented as follows: When the main steam pressure is abnormally triggered, the control device uses a programmable logic controller to perform phased operations. First, within the preset first action time limit, the heating extraction steam regulating valve 5 is quickly closed, and then within the second action time limit, the main steam emergency isolation valve is gradually closed. The low-pressure cylinder cooling steam regulating valve 4 is maintained at a preset cooling minimum opening degree by a spring loading mechanism to ensure continuous flow of cooling steam. The primary network circulating water pump 10 automatically switches to internal circulation mode, and the primary network medium is restricted to circulate within a closed loop through a bypass valve. The opening permission of the heating extraction steam regulating valve 5 is locked by a software interlock module, and the lock is released only after all abnormal monitoring values ​​continuously meet the recovery threshold.

[0082] Through the above scheme, this application achieves rapid isolation of heat sources and dynamic maintenance of system safety boundaries under severe abnormal operating conditions, prevents the risk of metal overheating caused by cooling interruption in low-pressure cylinder 7, avoids freezing problems caused by sudden shutdown of the heating network system, and ensures the control of radioactive risks, thereby improving the adaptability and operational reliability of the nuclear small reactor heating system in extreme failure scenarios.

[0083] Specifically, in some of the embodiments described above in this application, a control strategy for restoring heating after the anomaly is resolved is proposed to ensure the safety and stability of the system. However, if the heating extraction steam regulating valve 5 is directly fully depleted during this process, it may cause a sudden increase in the primary network water supply temperature or a sudden change in the pressure difference between the two networks, resulting in the low-pressure cylinder 7 metal temperature exceeding the limit, abnormal exhaust steam humidity, or radioactivity monitoring exceeding the limit, thereby triggering a protection action to interrupt the heating restoration process.

[0084] In this regard, this application further proposes that when the control device resumes heating after the abnormality is resolved, it includes: Keep the low-pressure cylinder cooling steam regulating valve 4 at the cooling bottom opening unchanged, and control the primary network heat network circulating water pump 10 to establish the heat exchange cycle between the primary network and the secondary network at the set speed.

[0085] The heating steam extraction regulating valve 5 is opened in stages, with an opening increment no greater than the recovery step size and at intervals according to the recovery holding time. The primary network supply water temperature and the pressure difference between the two networks are checked at each stage. When any monitored quantity deviates from the set range, the opening of the heating steam extraction regulating valve 5 is stopped, the opening of the heating steam extraction regulating valve 5 is returned to the previous stage, and the primary network heating network circulating water pump 10 returns to the internal circulation mode.

[0086] Maintaining the low-pressure cylinder cooling steam regulating valve 4 at a constant cooling minimum opening means keeping the valve opening at a preset safe minimum cooling threshold. This can be achieved by setting a fixed opening or by feedback closed-loop control based on the final stage metal temperature of the low-pressure cylinder 7. The purpose is to continuously provide cooling steam to ensure that the metal temperature and exhaust humidity of the low-pressure cylinder 7 are within safe limits. Controlling the primary network circulating water pump 10 to establish a heat exchange cycle between the primary and secondary networks at a set speed means driving the heating network medium to form a stable flow in the absence of heat source input. This can be achieved by using a variable frequency speed control motor to drive the pump or a constant speed pump in conjunction with a flow regulating valve. The purpose is to first achieve hydraulic stability to avoid the impact of thermal shock on the heat exchange equipment. Opening the heating extraction steam regulating valve 5 in stages with an opening increment no greater than the recovery step and according to the interval of the recovery holding time means decomposing the valve opening adjustment into multiple small steps and setting a stable waiting period. This can be achieved by using a step-by-step opening increment strategy or an exponential decay adjustment strategy. The purpose is to limit the amount of single steam flow change to prevent the primary network water supply temperature from going out of control. Verifying the primary network supply water temperature and the pressure difference between the two networks at each stage involves real-time monitoring and range determination of key operating parameters. This can be achieved using temperature sensors and pressure differential transmitters in conjunction with a logic judgment unit, with the aim of dynamically assessing whether the system status meets safety constraints. When any monitored quantity deviates from the set range, stopping the addition of heating steam extraction regulating valve 5, returning the opening to the previous stage, and causing the primary network heating network circulating water pump 10 to return to the internal circulation mode triggers a safety back-off mechanism. This can be achieved by the automatic control system executing a preset reverse adjustment program, with the aim of quickly eliminating abnormal trends and restoring the heat source isolation state.

[0087] Specifically, the proposed solution first maintains the low-pressure cylinder cooling steam regulating valve 4 at a constant cooling minimum opening after the anomaly is resolved. This ensures that the low-pressure cylinder 7 continuously receives cooling steam to maintain the metal temperature and exhaust humidity within safe thresholds, providing thermal boundary protection for the recovery process. Simultaneously, the primary network circulating water pump 10 is controlled to establish a heat exchange cycle between the primary and secondary networks at a set speed, allowing the heating network medium to achieve hydraulic stability without steam extraction, avoiding the risk of thermal shock caused by directly introducing a heat source. Subsequently, the heating extraction steam regulating valve 5 is opened in stages with small increments and intervals. Each opening increment is strictly limited within the recovery step range, and the system's thermal inertia response is awaited during the recovery holding interval to ensure sufficient stabilization of temperature and pressure differential parameters. At each stage, the primary network supply water temperature and the pressure differential between the two networks are checked, using real-time monitoring data as a basis for dynamic decision-making. When any monitored quantity deviates from the set range, the valve opening is immediately stopped, the opening is returned to the previous stable stage, and the primary network circulating water pump 10 is switched to internal circulation mode to cut off heat source transfer, forming a closed-loop safety protection. The entire process, through a collaborative design of small-step adjustments, interval waiting, and dynamic verification, achieves a smooth transition from abnormal conditions to normal heating, avoiding the risk of secondary anomalies caused by parameter mutations.

[0088] As a preferred embodiment, the solution of this application is implemented as follows: The control device is specifically implemented using a programmable logic controller (PLC). After the anomaly is cleared, it first maintains the opening of the low-pressure cylinder cooling steam regulating valve 4 at a preset cooling minimum opening, and simultaneously starts the primary network circulating water pump 10 at an appropriate speed to establish a heat exchange cycle between the primary and secondary networks. Subsequently, the heating extraction steam regulating valve 5 is opened in stages with small opening increments at reasonable time intervals. After each adjustment, the primary network supply water temperature and the pressure difference between the two networks are monitored to ensure they are within a safe range. If, at a certain stage, the supply water temperature exceeds the set upper limit or the pressure difference between the two networks falls below the lower limit, the valve opening is stopped, the opening of the heating extraction steam regulating valve 5 is returned to the previous stage value, and the primary network circulating water pump 10 is controlled to switch to internal circulation mode. After the parameters stabilize, the restoration is attempted again.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A modular small nuclear reactor high-efficiency cogeneration heating system, characterized in that, include: The modular nuclear small reactor supplies steam to the high-pressure cylinder of the steam turbine through a direct current steam generator, and the exhaust steam from the high-pressure cylinder enters the reheater after passing through a steam-water separator. The reheater outlet forms three parallel branches. The first branch is the heating extraction steam pipeline, which leads to the heating network heater via the heating extraction steam regulating valve to heat the primary heating network. The second branch is the low-pressure cylinder cooling steam pipeline, which leads to the turbine low-pressure cylinder via the low-pressure cylinder cooling steam regulating valve to maintain the turbine low-pressure cylinder at zero output under normal heating conditions. The third branch is the low-pressure cylinder inlet steam pipeline, which leads to the turbine low-pressure cylinder via the low-pressure cylinder inlet steam regulating valve. The low-pressure cylinder is connected to the generator to exit the zero-output or power-only operation mode. The heating network heater is isolated from the secondary network water-to-water heat exchanger by a medium. The secondary network heating network circulating water pump is used to maintain the secondary network circulation. The condensate generated by the heating network heater is returned to the deaerator by the heating network condensate pump and incorporated into the regenerative system. The control device is configured to maintain the low-pressure cylinder at zero output as the normal heating state, keep the low-pressure cylinder cooling steam regulating valve at the cooling minimum opening, adjust the opening of the heating extraction steam regulating valve and the speed of the primary heating network circulating water pump according to the supply and return water temperature of the primary heating network and the pressure difference between the two networks, and limit the upper limit of the opening of the heating extraction steam regulating valve and the lower limit of the opening of the low-pressure cylinder cooling steam regulating valve according to the metal temperature of the last stage of the low-pressure cylinder, the exhaust steam humidity and the radioactivity monitoring value. When unit protection, main steam pressure abnormality, two-network pressure difference abnormality or radioactivity monitoring exceeds the limit occurs, the control device sequentially closes the heating extraction steam regulating valve and the main steam accident isolation valve, while maintaining the low-pressure cylinder cooling steam regulating valve at the cooling minimum opening, and resumes heating after the abnormality is resolved. The DC steam generators are arranged in parallel, and the steam outlets of each DC steam generator are connected to the main steam pipeline. The main steam pipeline is equipped with a safety valve, a main steam isolation valve and a main steam emergency isolation valve in sequence. The main steam pipeline is connected to the steam inlet of the high-pressure cylinder of the steam turbine. The exhaust port of the high-pressure cylinder of the steam turbine is connected in series with the steam-water separator and the reheater in sequence. The outlet of the reheater forms a parallel heating extraction steam pipeline and a low-pressure cylinder cooling steam pipeline. The heating extraction steam pipeline is connected to the steam inlet of the heating network heater, and the low-pressure cylinder cooling steam pipeline is connected to the steam inlet of the low-pressure cylinder. The two pipelines are not connected to each other. The heating network heater and the primary heating network circulating water pump form a closed loop and exchange heat with the secondary network water-to-water heat exchanger through medium isolation. The primary heating network circulating water pump is also connected to the makeup water pump. The condensate generated by the heating network heater is sent to the deaerator by the heating network condensate pump and then into the feed water side of the regenerative system. The outlet side of the low-pressure cylinder is connected in sequence to the condenser, condensate pump, low-pressure heater, deaerator and feed water pump and supplies feed water to the DC steam generator. The control device uses the set value of the primary network water supply temperature as the main control target and the lower and upper limits of the pressure difference between the two networks as constraints. It first adjusts the speed of the primary network circulating water pump, then adjusts the opening of the heating steam extraction regulating valve in the following sequence: when the primary network water supply temperature is lower than the set value and the pressure difference between the two networks is not lower than the lower limit, the speed of the primary network circulating water pump is increased; when the increased speed still does not reach the set value, the opening of the heating steam extraction regulating valve is increased; when the primary network water supply temperature is higher than the set value, the opening of the heating steam extraction regulating valve and the speed of the primary network circulating water pump are decreased in reverse order, while maintaining the pressure difference between the two networks not exceeding the upper limit and not lower than the lower limit.

2. The modular nuclear small reactor high-efficiency cogeneration heating system according to claim 1, characterized in that, The control device sets the single adjustment step size, the maximum change per unit time, and the minimum holding time between two adjustments for the heating steam extraction regulating valve and the primary network circulating water pump, respectively. When the final stage metal temperature of the low-pressure cylinder is lower than the temperature warning threshold or the exhaust humidity of the low-pressure cylinder is higher than the humidity warning threshold, the single adjustment step size and the maximum change amount per unit time of the heating extraction steam regulating valve are reduced to the preset small step size and the preset small change amount, and the minimum holding time of the two adjustments is increased to the preset holding time. At the same time, the speed change of the primary network heating network circulating water pump is limited to not exceeding the preset small speed change amount.

3. The modular nuclear small reactor high-efficiency cogeneration heating system according to claim 2, characterized in that, The control device sets three levels of limiting based on the final stage metal temperature of the low-pressure cylinder and the exhaust humidity of the low-pressure cylinder: At the warning level, the allowable opening degree of the heating steam extraction regulating valve is limited to not exceeding the steam extraction opening limit value, and the opening degree of the cooling steam regulating valve of the low-pressure cylinder is not lower than the cooling opening limit value. At the restriction level, the allowable opening degree of the heating steam extraction regulating valve is limited to no higher than the steam extraction opening limit value two, and the opening degree of the low-pressure cylinder cooling steam regulating valve is limited to no lower than the cooling opening limit value two. At the cut-off level, the heating steam extraction regulating valve is closed and the low-pressure cylinder cooling steam regulating valve is kept at the cooling minimum opening; when the monitored quantity continuously reaches the preset time of the release condition, the limit is released step by step in reverse order of cut-off level, restriction level, and warning level.

4. The modular nuclear small reactor high-efficiency cogeneration heating system according to claim 3, characterized in that, The control device uses the radioactivity monitoring values ​​of the outlet and return water inlet of the secondary network water-to-water heat exchanger and the pressure difference between the two networks as interlocking criteria. When the radioactivity monitoring value exceeds the radioactivity threshold or the pressure difference between the two networks is lower than the lower limit of the pressure difference, the heating steam extraction regulating valve is closed, so that the primary network heating network circulating water pump maintains the primary network in a closed loop and keeps the low-pressure cylinder cooling steam regulating valve at the cooling bottom opening. Once the radioactivity monitoring value and the pressure difference between the two networks continuously meet the recovery threshold and the lower limit of the pressure difference for a preset time, the heat exchange cycle between the primary network and the secondary network is restored first, and then the heating steam extraction regulating valve is opened in a step-by-step manner until the heating is restored to normal.

5. The modular nuclear small reactor high-efficiency cogeneration heating system according to claim 4, characterized in that, When unit protection, main steam pressure abnormality, pressure difference between the two networks abnormality, or radioactivity monitoring exceeding the limit occurs, the control device closes the heating extraction steam regulating valve within the first action time limit, and closes the main steam emergency isolation valve within the second action time limit after the first action time limit expires; the low-pressure cylinder cooling steam regulating valve is kept at the cooling minimum opening throughout the process, the primary network heating network circulating water pump is controlled to switch to internal circulation mode to maintain the primary network closed circulation, and the reopening of the heating extraction steam regulating valve is prohibited until all triggering conditions are eliminated.

6. The modular nuclear small reactor high-efficiency cogeneration heating system according to claim 5, characterized in that, When the control device resumes heating after the abnormality is resolved, it includes: Keep the cooling steam regulating valve of the low-pressure cylinder at a constant cooling bottom opening, and control the primary network heat network circulating water pump to establish a heat exchange cycle between the primary network and the secondary network at a set speed; The heating steam extraction regulating valve is opened in stages with an opening increment no greater than the recovery step size and at intervals of recovery holding time. The primary network supply water temperature and the pressure difference between the two networks are checked at each stage. When any monitored quantity deviates from the set range, the opening of the heating steam extraction regulating valve is stopped, the opening of the heating steam extraction regulating valve is returned to the previous stage, and the primary network heating network circulating water pump returns to the internal circulation mode.

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