A full range passive injection system

Abstract

The present invention relates to a full-range passive safety injection system, including a core water supply tank, a safety injection tank, and an internal refueling water tank connected to the primary circuit of the reactor, wherein the positions of the core water supply tank and the internal refueling water tank are higher than the primary circuit pipeline elevation; a waterproof layer is arranged in the room where the main equipment is arranged, and a flooding pool is formed after an accident, and the reactor coolant and safety injection water sprayed from the primary circuit rupture are collected in the flooding pool, becoming a recirculating water source for providing long-term core cooling. The present invention proposes a universal full-range passive safety injection system design scheme for existing large pressurized water reactors, realizing emergency core cooling, water supply and boronization functions after accidents. The system can provide high, medium, low pressure and long-term passive safety injection after an accident in a nuclear power plant, so as to maintain the primary circuit water loading, export the core residual heat and long-term passive recirculation injection.

Description

Technical Field

[0001] The invention belongs to nuclear power plant design technology, and in particular relates to a full-range passive injection system. Background Art

[0002] Traditional nuclear power plants usually use more powerful and more controllable active equipment (such as pumps, valves, fans, etc.) to achieve the required fluid transmission functions. Passive technology has regained attention in advanced nuclear power technology and once represented a more advanced technological development trend. The main advantage of passive systems over active systems is simplification. Active equipment is eliminated and generally does not require complex (redundant and diverse) control systems or external power sources, which can greatly simplify the construction, operation and maintenance of the system. Passive systems also contribute to safety, such as reducing dependence on operator intervention, providing more ample response time, and reducing the harm of human error to power plants; passive systems can eliminate accident scenarios related to active equipment failures and power source loss. Therefore, passive systems provide a solution to further improve safety without increasing costs too much.

[0003] Among the passive safety systems, the design and development of the passive residual heat removal system and the passive containment heat removal system are relatively mature, while the passive injection system has many constraints on its realization and has always been the focus of research and development design. Currently, among the large commercial pressurized water reactors, only the AP1000 unit of Westinghouse in the United States has achieved full-range passive injection. However, the passive injection system of AP1000 has the defects of limited application objects and scenarios and poor engineering feasibility. First of all, the passive injection of AP1000 can only be achieved under the compact layout scheme of two loops and shielded main pumps in the first loop. In this layout, the first loop occupies a small area and can be arranged with a large volume of low-pressure injection water source (internal displacement water tank). At the same time, the area to be flooded is relatively small, which can form a higher flooding water level. At the same time, the realization of long-term passive recirculation of AP1000 also relies on its steel containment, which can be used as a heat exchanger, making steam condensation and reflux more efficient. AP1000 uses IVR (inside melt pressure vessel retention) to cool the core melt, without the need to keep the reactor cavity dry. At present, in addition to the AP1000 configuration, my country's pressurized water reactor nuclear power units still have a large number of reactor types that use three-loop or four-loop configurations, shaft-sealed main pumps, and concrete containment designs. In addition to IVR, the core melt solution also uses EVR (outside melt pressure vessel retention) solutions. This type of pressurized water reactor has a more common number of loops, main pumps and containment forms. However, due to the large number of loops, the main pump and steam generator have their own supports, and there are connecting pipes between the main pump and the steam generator, so the first loop occupies a large area, and the amount of flooding water required for the full range of passive is relatively large; at the same time, the steam condensation reflux rate of the concrete containment is limited; and the core catcher is used to cool the core melt, and the reactor cavity must be kept basically dry while flooding the first loop. Therefore, the design of the passive injection system of AP1000 cannot be promoted and applied to reactor types other than AP1000, and the application scenarios are subject to many restrictions and limitations. In addition, during the engineering implementation of AP1000, its poor engineering feasibility was also exposed. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and to provide a universal full-range passive safety injection system design that can provide high, medium, low pressure and long-term passive safety injections after an accident in a nuclear power plant, so as to maintain the primary water charge, remove the core residual heat and provide long-term passive recirculation injection.

[0005] The technical solution of the present invention is as follows: a full-range passive safety injection system, including a core water makeup tank, a safety injection tank, and an internal refueling water tank connected to the primary circuit of the reactor, the core water makeup tank and the internal refueling water tank are located higher than the primary circuit pipeline elevation; a waterproof layer is set in the room where the main equipment is arranged, and a flooding pool is formed after an accident, and the reactor coolant and safety injection water sprayed from the rupture of the primary circuit are collected in the flooding pool to become a recirculating water source for providing long-term cooling of the core.

[0006] Further, in the full-range passive injection system as described above, the submerged water pool is connected to the pressure vessel direct injection (DVI) pipeline via a redundant recirculation pipeline, and the submerged water level of the submerged water pool is higher than the pressure vessel direct injection (DVI) pipeline.

[0007] Furthermore, a normally open electric valve and a check valve are arranged on the recirculation pipeline, and a filter is arranged at the suction port.

[0008] Furthermore, in the full-range passive injection system as described above, a water-isolating device is provided between the submerged water pool and the outer wall of the reactor pressure vessel to prevent water from leaking into the reactor cavity and lower places.

[0009] Furthermore, in the full-range passive injection system as described above, a guide groove with an inclination is provided in a compartment higher than the main equipment layer, so that high-level condensate water of the heat exchanger of the passive containment heat removal system continuously converges toward the center during the downward flow.

[0010] Furthermore, in the full-range passive injection system as described above, the elevation of the reactor pressure vessel and the primary circuit main pipeline is lowered by one floor relative to a conventional pressurized water reactor nuclear power unit, so that the flooding pool is located at a lower position within the large containment space.

[0011] Furthermore, in the full-range passive injection system as described above, there are two core water supply tanks, each of which is connected to a primary circuit via an inlet pressure balance pipeline and an outlet injection pipeline.

[0012] Furthermore, the outlet injection pipeline of the core water makeup tank is connected to the pressure vessel direct injection (DVI) pipeline through two parallel normally closed pneumatic isolation valves and two series check valves.

[0013] Furthermore, in the full-range passive safe injection system as described above, there are two safe injection boxes, and the outlet pipeline of each safe injection box is connected to the pressure vessel direct injection (DVI) pipeline through a normally open electric isolation valve and two check valves in series.

[0014] Furthermore, in the full range passive injection system as described above, the injection line of the internal refueling water tank is connected to the pressure vessel direct injection (DVI) line through two parallel isolation valves and two series check valves.

[0015] The beneficial effects of the present invention are as follows:

[0016] (1) The present invention proposes a universal full-range passive injection system design for existing large pressurized water reactors, which can realize emergency core cooling, water replenishment and boronization functions after an accident;

[0017] (2) The present invention breaks through the limitations of existing passive injection systems in terms of application scenarios and objects by providing flooding pools, diversion grooves, and water isolation devices. It can be designed for various types of pressurized water reactors and can arrange sufficient low-pressure injection water sources in the shell to achieve long-term passive recirculation injection.

[0018] (3) The present invention improves the economic efficiency of the unit by eliminating active equipment, complex (redundant and diverse) control systems or external power sources, and simplifies the construction, operation and maintenance of the system, while ensuring the safety and automation level of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the full range passive injection system of the present invention;

[0020] Figure 2 It is a schematic diagram of the passive long-term recirculation injection scheme of the full-range passive injection system of the present invention.

[0021] In the figure, 1. Pressure vessel 2. Reactor core 3. Pressurizer 4. Steam generator 5. Cold section 6. Hot section 7. Inner shell 8. Reactor core water tank 9. Injection tank 10. High-level internal refueling water tank 11. Quick pressure relief valve 12. Internal refueling water tank filter 13. Recirculation filter 14. Pressure vessel direct injection (DVI) pipeline 15. Flooding pool 16. Long-term flooding water level 17. Diversion groove 18. Water isolation device DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] The full-range passive injection system provided by the present invention has the same functions as the traditional safety system, both of which need to realize emergency core cooling under LOCA accidents and emergency boronization and water replenishment functions under non-LOCA accidents. It generally includes several subsystems to realize injection capabilities under different primary back pressures. Among them, long-term low-pressure recirculation injection is the difficulty of realizing the passive injection system and is also the innovation point of the present invention.

[0024] In order to achieve the above functions, the passive injection system includes the following water sources, which automatically provide emergency water injection and boronization to the reactor in stages after an accident:

[0025] (1) Two core water supply tanks provide high-pressure injection flow for a long time and with a large flow rate;

[0026] (2) Two injection tanks provide a very large flow of medium-pressure injection flow within minutes;

[0027] (3) A high-level internal displacement water tank provides a long-term small low-pressure injection flow;

[0028] (4) After the injection of the above three water sources, the reactor coolant and injection water sprayed from the primary loop rupture are collected in the flooding pool and become the recirculating water source for long-term cooling of the core.

[0029] In order to cooperate with passive injection under different back pressures, an automatic pressure relief system with graded pressure relief needs to be set up.

[0030] In principle, after the high-level internal refueling water tank is filled, the reactor coolant and injection water ejected from the primary loop breach are collected at the bottom of the containment, and the submerged water level is raised by design, and the natural circulation flow formed by the potential difference and temperature difference between the submerged water level and the core provides long-term recirculation cooling for the core. Compared with the reference passive high-pressure injection, the mature passive medium-pressure injection, and the relatively simple passive low-pressure injection, the specific implementation of passive long-term recirculation injection is the main innovation of the present invention.

[0031] The present invention proposes a universal design scheme for existing large pressurized water reactors, comprehensively considering the characteristics of the application objects and application scenarios, and comprehensively considering the technical characteristics and design requirements of the large amount of flooding water, low steam condensation reflux efficiency, and the need to keep the reactor cavity basically dry while flooding the primary circuit during the passive long-term recirculation injection stage. In order to achieve long-term passive recirculation injection under the above technical characteristics and technical requirements, the present invention adopts the following measures:

[0032] Lower the elevation of the pressure vessel and main pipeline by one floor, raise the internal material replacement water tank and increase the height of the water tank. The internal material replacement water tank is used as a low-pressure injection water source;

[0033] Design a waterproof layer in the room where the main equipment is arranged to form a flooding pool after an accident;

[0034] Set up redundant recirculation lines connecting the flooding pool to the DVI injection lines;

[0035] In the compartment higher than the main equipment layer, a diversion groove with an inclination is provided;

[0036] A water barrier is provided between the submerged water tank and the outer wall of the pressure vessel.

[0037] Example

[0038] like Figure 1 As shown, two core water supply tanks 8 (only one is shown in the figure) are arranged higher than the elevation of the primary main pipeline. Each core water supply tank 8 is filled with boron-containing water and is connected to the primary circuit through an inlet pressure balance line and an outlet injection line. The outlet injection line is connected to the pressure vessel direct injection (DVI) pipeline 14 through two parallel normally closed pneumatic isolation valves and two series check valves. The pressure balance line is connected to the nozzle at the top of the cold section 5 of the main pipeline and is provided with a normally open electric valve to maintain the pressure of the core water supply tank 8 consistent with the operating pressure of the primary circuit to avoid water hammer when the injection is triggered. The insulation and direction of the pressure balance line ensure that the normal water temperature of the inlet pipe is higher than that of the outlet pipe, which is conducive to the formation of an additional driving pressure head.

[0039] The injection tank 9 is filled with boron-containing water, which is quickly injected by compressed nitrogen above the liquid level. A normally open electric isolation valve and two series-connected check valves are provided on the outlet pipeline of the injection tank 9. The outlet pipelines of two injection tanks 9 (only one is shown in the figure) are directly connected to two DVI pipelines 14 respectively.

[0040] Low-pressure injection is achieved by the gravity head generated by the position difference between the high-level internal replacement water tank 10 and the primary circuit. The high-level internal replacement water tank 10 is located higher than the primary circuit elevation and stores low-temperature boron-containing water. The two injection pipelines of the high-level internal replacement water tank 10 are connected to two DVI pipelines respectively. Two check valves in series and two isolation valves in parallel are provided on each injection pipeline. A filter screen 12 is provided at the outlet of the high-level internal replacement water tank 10.

[0041] For long-term passive recirculation injection, see Figure 1 , Figure 2 , this embodiment adopts the following design scheme in the containment:

[0042] The pressure vessel 1 and the main pipeline are lowered by one floor (e.g. -5.3m), the internal refueling water tank 10 is raised to ±0.00m and the water tank height is increased. The internal refueling water tank is used as a low-pressure injection water source. The flooding pool 15 formed by collecting the return water is located at the same elevation as the internal refueling water tank 10 to provide long-term recirculation injection.

[0043] A waterproof layer is designed in the room where the main equipment is arranged at the ±0.00m layer so that it can accommodate upper condensation water, injection water from the high-level internal material replacement water tank and primary circuit breach water, forming a long-term flooding water level 16 after an accident, which is higher than the flooding pool 15 of the DVI injection pipeline.

[0044] A redundant recirculation pipeline is provided to connect the flooding pool 15 and the DVI injection pipeline 14. A normally open electric valve and a check valve are provided on the pipeline. A filter screen 13 is provided at the suction port to prevent debris from entering the reactor and blocking the core cooling flow channel.

[0045] In the compartment above the ±0.00m layer, a diversion groove 17 with an inclination is provided so that the high-level condensed water of the heat exchanger of the passive containment heat removal system can be continuously gathered toward the center during the downward flow.

[0046] A water barrier 18 is provided between the submerged water pool 15 and the outer wall of the pressure vessel 1 to prevent water from leaking into the reactor cavity and lower elevations.

[0047] In the long term after the accident, the only passive energy that can be continuously utilized is the decay waste heat of the core. Water is converted into water vapor through evaporation, and then the water vapor is condensed at a high position, regaining gravitational potential energy to achieve reflux cooling. Therefore, the key factors for achieving the passive long-term recycling function are: the low-pressure injection water source must have sufficient capacity to flood the primary circuit; the efficiency of collecting and refluxing the condensed water is sufficient to form a recycling for a long time. The feasibility of realizing passive long-term recycling by the present invention will be demonstrated below.

[0048] The total amount of water required for the long-term recycling phase after a LOCA accident includes the following three parts: 1) the amount of water required to remove the core decay heat; 2) the amount of water required to flood the primary circuit; 3) the amount of water leaked. According to calculations, in order to achieve the goal of 72h passive recycling, the amount of water required to remove the core decay heat is about Q H =5600m 3 , the amount of water required to flood a circuit Q M =700m 3 , ignoring the amount of leaked water, the total amount of water required within 72 hours after the LOCA accident is Q T For: Q T =Q H +Q M =5600+700=6300m 3 .

[0049] According to the passive injection system design of the present invention, the required water volume is provided by the following parts: 1) high, medium and low pressure injection water; 2) reactor coolant leaked from the primary loop breach; 3) recovered condensed water. Conservatively assuming that the total amount of high and medium pressure injection water is 100m 3, the amount of water entering the containment through the primary circuit breach after LOCA is 200m 3 The remaining water is provided by the low-pressure injection water source (high-level internal displacement water tank) and the recovered condensed water, where the amount of condensed water is determined by the amount of evaporated water and the recovery efficiency. Assuming that the condensed water recovery rate is P (0<P<1), the capacity of the low-pressure injection water source is Q L , combining the water balance relationship at the beginning of the recirculation cooling process and the total water balance relationship within 72 hours, we get:

[0050] Q L =(1-P)Q H / (2-P)+Q M -300

[0051] Substitute into Q H and Q M The value of low-pressure injection water source capacity Q is obtained L The relationship with the condensate recovery efficiency P is:

[0052] Q L =(1-P)×5600 / (2-P)+400.

[0053] Since the present invention is provided with a waterproof layer, a diversion groove and a water-isolating device, and after lowering the primary circuit elevation, the submerged water pool is at almost the lowest position in the large space of the containment, the condensate recovery efficiency can be effectively improved. Referring to the condensate recovery efficiency of the third-generation pressurized water reactor in China, the conservative value is about 80%, so the low-pressure injection water source water volume required by the present invention is 1400m 3 For large pressurized water reactors with two-circuit, three-circuit or four-circuit designs, shielded or shaft-sealed main pumps, concrete or steel containment, IVR or EVR core melt cooling schemes, it is possible to arrange sufficient low-pressure injection water sources inside the containment, which has wide applicability and feasibility.

[0054] It will be apparent to those skilled in the art that the structure of the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0055] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A full range passive injection system, characterized in that: The invention comprises a core water supply tank (8), an injection tank (9), and an internal refueling water tank (10) connected to the primary loop of the reactor. The positions of the core water supply tank (8) and the internal refueling water tank (10) are higher than the elevation of the primary loop pipeline. The elevation of the pressure vessel and the main pipeline is lowered by one floor, lower than the room where the main equipment is arranged. A waterproof layer is arranged in the room where the main equipment is arranged. After an accident, a flooding pool (15) is formed. The reactor coolant and injection water sprayed from the primary loop rupture are collected in the flooding pool (15). The flooding pool (15) is connected to the pressure vessel direct injection pipeline (14) through a redundant recirculation pipeline. The flooding water level of the flooding pool (15) is higher than the pressure vessel direct injection pipeline. The natural circulation flow formed by the potential difference and temperature difference between the flooding water level and the core provides long-term recirculation cooling for the core. A water barrier (18) is arranged between the flooding pool (15) and the outer wall of the reactor pressure vessel to prevent water from leaking into the reactor cavity and lower places.

2. The full range passive injection system according to claim 1, characterized in that: A normally open electric valve and a check valve are provided on the recirculation pipeline, and a filter screen (13) is provided at the suction port.

3. The full range passive injection system according to claim 1, characterized in that: A diversion groove (17) with an inclination is provided in a compartment higher than the main equipment layer, so that high-level condensed water of the heat exchanger of the passive containment heat removal system continuously converges toward the center during the process of flowing downward.

4. The full range passive injection system according to claim 1, characterized in that: The elevation of the reactor pressure vessel and the primary circuit main pipeline is lowered by one floor compared with the traditional pressurized water reactor nuclear power unit, so that the submerged water pool is located at a lower position in the large space of the containment.

5. The full range passive injection system according to claim 1, characterized in that: There are two core water supply tanks (8), and each core water supply tank (8) is connected to a primary circuit via an inlet pressure balance pipeline and an outlet injection pipeline.

6. The full range passive injection system as claimed in claim 5, characterized in that: The outlet injection pipeline of the core water supply tank (8) is connected to the pressure vessel direct injection pipeline (14) via two parallel normally closed pneumatic isolation valves and two series check valves.

7. The full range passive injection system as claimed in claim 1, characterized in that: There are two safety injection boxes (9), and the outlet pipeline of each safety injection box is connected to the pressure vessel direct injection pipeline (14) through a normally open electric isolation valve and two check valves connected in series.

8. The full range passive injection system as claimed in claim 1, characterized in that: The injection pipeline of the internal displacement water tank (10) is connected to the direct injection pipeline (14) of the pressure vessel via two parallel isolation valves and two series check valves.

Images