Pressurized water reactor chemical shutdown system and method using cadmium nitrate as shutdown solution

Abstract

The invention discloses a pressurized water reactor chemical shut-down system and method using cadmium nitrate as a shut-down solution. The system comprises a chemical shut-down system and a main loop, the chemical shutdown system adopts an active or passive mode and mainly comprises a concentrated cadmium nitrate storage tank, a high-pressure injection pump and an injection pipeline; when a poison emergency injection signal or a cold shutdown maintaining signal is received, an inlet valve and an outlet valve of the injection pipeline are opened, and the concentrated cadmium nitrate solution is driven in an active or passive mode, is injected into a nuclear reactor cold end main pipeline from a concentrated cadmium nitrate storage tank through the injection pipeline, and is discharged out of the nuclear reactor cold end main pipeline. And the flow is further distributed everywhere in the pressure vessel after being stirred in the lower chamber of the pressure vessel. At the same temperature, compared with the traditional neutron poison boric acid, cadmium nitrate has higher solubility and neutron absorption cross section, and the method enhances the reliability of chemical shutdown of the reactor under the accident condition, improves the shutdown safety of the nuclear reactor, and reduces the arrangement and maintenance cost at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power plant reactor safety design, and in particular relates to a pressurized water reactor chemical shutdown system and method using cadmium nitrate as a shutdown solution. Background Art

[0002] Nuclear power plants often use control rods as a shutdown method. However, under the accident condition of "anticipated transients without emergency shutdown (ATWS)", the control rods are not inserted deep enough and cannot meet the negative reactivity requirements of shutdown. Therefore, the "HAF102-2016 Nuclear Power Plant Design Safety Regulations" contain requirements such as "different depth defense levels should be kept independent as much as possible" and "there must be at least one system that can independently keep the reactor in a subcritical state with sufficient depth and high reliability". Therefore, the chemical shutdown system is necessary for nuclear power plants.

[0003] Currently, boric acid is commonly used as a chemical shutdown solution for nuclear power plants. However, boric acid has a low solubility at room temperature and cannot meet the concentrated boron storage needs of nuclear power plants. Additional heaters are required to maintain the high concentration of boric acid solution required for the shutdown solution.

[0004] Patent CN102881340 discloses an emergency shutdown system and method combining active and passive, the system includes a control rod emergency shutdown subsystem and an emergency boron injection subsystem, the emergency shutdown is provided with negative reactivity by the control rod, and the emergency boron injection subsystem injects concentrated boric acid to provide negative reactivity when the emergency shutdown fails or the core neutron flux is too high. However, from the full life operation experience of existing nuclear power plants, the method of using control rods to shut down accounts for the vast majority, and the probability of the emergency boron injection subsystem playing a role is extremely small. The emergency boron injection subsystem as a backup shutdown system requires a high cost to maintain. First, the temperature of the emergency boron injection subsystem needs to be maintained above the crystallization temperature limit of 9000ppm boric acid solution, and the high reliability of the electric heater needs to be ensured; second, the emergency boron injection subsystem is a total of two concentrated boron storage tanks in two series, and the negative reactivity provided by each concentrated boron storage tank must be able to ensure the shutdown requirements of the entire reactor. At the same time, considering that the concentrated boron storage tank needs to be as close to the nuclear reactor as possible to provide a faster injection speed, the larger volume of the concentrated boron storage tank and the close arrangement provide requirements for the layout of the nuclear reactor plant. Summary of the invention

[0005] The object of the present invention is to provide a pressurized water reactor chemical shutdown system and method using cadmium nitrate as a shutdown solution in view of the defects of the existing boric acid as a pressurized water reactor shutdown solution.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution is driven in an active manner and comprises a chemical shutdown system 1 and a main loop 2; the chemical shutdown system 1 comprises a concentrated cadmium nitrate storage tank 4, an electric heater 5 arranged inside the concentrated cadmium nitrate storage tank 4 to ensure that the cadmium nitrate does not crystallize, a high-pressure gas cylinder 3 connected to the top of the concentrated cadmium nitrate storage tank 4, an injection pipeline 14 connected to the bottom of the concentrated cadmium nitrate storage tank 4, a high-pressure injection pump 10 arranged on the injection pipeline 14, and an inlet valve 8 and an outlet valve 13 respectively arranged at the inlet and outlet of the injection pipeline 14; when a poison emergency injection signal or a cold shutdown maintenance signal is received, the inlet valve 8 and the outlet valve 13 of the injection pipeline 14 are opened, and the concentrated cadmium nitrate solution is provided with a driving pressure head by the high-pressure injection pump 10 and / or the high-pressure gas cylinder 3, and is injected from the concentrated cadmium nitrate storage tank 4 through the injection pipeline 14 into the cold end main pipeline 12 of the main loop 2, and further passes through the lower chamber 11 of the pressure vessel to be turbid and the flow is redistributed and distributed in various places in the pressure vessel 9. At the same temperature, cadmium nitrate has greater solubility and neutron absorption cross section than traditional neutron poison boric acid. The present invention enhances the reliability of reactor chemical shutdown under accident conditions, improves the shutdown safety of nuclear reactors, and reduces layout and maintenance costs.

[0008] Preferably, the electric heater 5, the inlet valve 8, the high-pressure injection pump 10 and the outlet valve 13 are all connected to the nuclear reactor shutdown protection system, and are remotely started and shut down by the nuclear reactor shutdown protection system, or manually started and shut down.

[0009] Preferably, the high-pressure injection pump 10 is a multi-stage centrifugal pump with multiple impellers connected in series, which can gradually increase the pressure to meet the 15.5 MPa environmental high-pressure injection condition in the main loop 2 when the reactor is shut down urgently.

[0010] Preferably, the high-pressure gas cylinder 3 can be a nitrogen cylinder, a helium cylinder or other high-pressure gas.

[0011] The shutdown method of a pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution is as follows: when a poison emergency injection signal or a cold shutdown maintenance signal is received, the nuclear reactor shutdown protection system automatically or manually opens the inlet valve 8 and the outlet valve 13 of the injection pipeline 14; the concentrated cadmium nitrate solution is provided with a driving pressure head by a high-pressure injection pump 10 and / or a high-pressure gas cylinder 3; it is injected from the concentrated cadmium nitrate storage tank 4 into the cold end main pipeline 12 of the main loop through the injection pipeline 14; it is further stirred in the lower chamber 11 of the pressure vessel and the flow rate is redistributed to various places in the pressure vessel 9; the concentrated cadmium nitrate solution is uniformly mixed with the coolant, and finally converges in the upper chamber 6 of the pressure vessel, and flows out of the pressure vessel 9 through the hot end main pipeline 7; the coolant circulates in the entire pressurized water reactor main loop through the hot end main pipeline 7, and then returns to the cold end main pipeline 12 to enter the pressure vessel 9; finally, the coolant with cadmium nitrate flows in the entire pressurized water reactor main loop.

[0012] A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution is driven in a passive manner and comprises a chemical shutdown system 1 and a main loop 2; the chemical shutdown system 1 comprises a concentrated cadmium nitrate storage tank 4, an electric heater 5 arranged inside the concentrated cadmium nitrate storage tank 4 to ensure that the cadmium nitrate does not crystallize, an injection pipeline 14 connected to the bottom of the concentrated cadmium nitrate storage tank 4, an inlet valve 8 arranged on the injection pipeline 14, a pressure equalizing pipeline 16 connected to the top of the concentrated cadmium nitrate storage tank 4, and a pressure equalizing valve 17 arranged on the pressure equalizing pipeline 16; a pressure vessel 9 having a vertical height greater than that of the main loop 2; when receiving a poison emergency injection signal or a cold shutdown maintenance signal, the pressure equalizing valve 17 is opened, and after the concentrated cadmium nitrate storage tank 4 and the main loop are pressure-equalized, the inlet valve 8 of the injection pipeline 14 is opened, and the concentrated cadmium nitrate solution is injected from the concentrated cadmium nitrate storage tank 4 through the injection pipeline 14 into a cold end main pipeline 12 of the main loop under the action of gravity.

[0013] Preferably, the electric heater 5, the inlet valve 8 and the equalizing valve 17 are all connected to the nuclear reactor shutdown protection system, and are remotely started and shut down by the nuclear reactor shutdown protection system, or manually started and shut down.

[0014] The shutdown method of a pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution is as follows: when a poison emergency injection signal or a cold shutdown maintenance signal is received, the nuclear reactor shutdown protection system automatically or manually opens the equalizing valve 17, and after the concentrated cadmium nitrate storage tank 4 and the main circuit are equalized in pressure, the inlet valve 8 of the injection pipeline 14 is opened, and the concentrated cadmium nitrate solution is injected from the concentrated cadmium nitrate storage tank 4 and the injection pipeline 14 into the cold end main pipeline 12 of the main circuit under the action of gravity, and further passes through the lower chamber 11 of the pressure vessel to be turbid and the flow rate is redistributed to various places in the pressure vessel 9, and the concentrated cadmium nitrate solution is uniformly mixed with the coolant, and finally converges in the upper chamber 6 of the pressure vessel, and flows out of the pressure vessel 9 through the hot end main pipeline 7; the coolant circulates in the entire pressurized water reactor main circuit through the hot end main pipeline 7, and then returns to the cold end main pipeline 12 to enter the pressure vessel 9, and finally the coolant with cadmium nitrate flows in the entire pressurized water reactor main circuit.

[0015] Preferably, in actual nuclear power plant layout, two or more independent chemical shutdown systems 1 are included, and each chemical shutdown system 1 can independently meet the shutdown capacity requirement and ensure the safety redundancy requirement.

[0016] Preferably, the main circuit 2 includes a pressure vessel 9, an upper pressure vessel chamber 6 located above the pressure vessel 9, a lower pressure vessel chamber 11 located below the pressure vessel 9, a hot end main pipeline 7 connected to the upper pressure vessel chamber 6, and a cold end main pipeline 12 connected to the lower pressure vessel chamber 11.

[0017] Preferably, the concentrated cadmium nitrate storage tank 4 can be externally connected to a circulation pipeline, a pressure gauge and a temperature gauge, and the concentrated cadmium nitrate storage tank 4 can be regularly checked to see if it meets the shutdown requirements, and the solution can be replaced regularly.

[0018] Preferably, if an actively driven chemical shutdown system 1 is used, the chemical shutdown system 1 can be arranged inside or outside the containment vessel; if a passively driven chemical shutdown system 1 is used, the chemical shutdown system 1 can be arranged inside the containment vessel.

[0019] Compared with the prior art, the present invention has at least the following advantages:

[0020] (1) The present invention uses cadmium nitrate as a chemical shutdown solution instead of traditional boric acid as a chemical shutdown solution, thereby enriching the types of chemical shutdown solutions for nuclear power plants.

[0021] (2) The high solubility of cadmium nitrate solution can effectively save the volume of storage tanks, which is beneficial to the layout of nuclear power plant buildings, especially pressurized water reactors on marine nuclear buoyancy platforms.

[0022] (3) The high solubility of cadmium nitrate solution avoids the strong demand for electric heaters and reduces the electricity cost of maintaining electric heaters.

[0023] (4) The high neutron absorption capacity of cadmium nitrate solution can quickly absorb excess neutrons in the reactor, thereby quickly shutting down the reactor, increasing the speed of the chemical shutdown system and improving reliability.

[0024] (5) The high solubility and high neutron absorption capacity of cadmium nitrate solution reduce the volume of shutdown poison solution that needs to be injected into the reactor at high pressure, reduce the reliability test of the high-pressure injection pump, and shorten the high-pressure injection time.

[0025] (6) The present invention is not only applicable to the design of nuclear power plants, but also beneficial to the transformation of chemical shutdown of existing nuclear power plants. The transformation requires few changes while improving the shutdown capacity redundancy.

[0026] (7) The present invention provides two driving modes, active and passive, for the shutdown system during the nuclear reactor design stage, providing options for adapting to different nuclear reactor plant layouts. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic diagram of a chemical shutdown system for a pressurized water reactor which adopts an active mode and uses cadmium nitrate as a shutdown solution.

[0028] Figure 2 The schematic diagram of a chemical shutdown system for a pressurized water reactor using cadmium nitrate as a shutdown solution is shown in the figure.

[0029] In the figure, 1 is a chemical shutdown system, 2 is a main loop, 3 is a high-pressure gas cylinder, 4 is a concentrated cadmium nitrate storage tank, 5 is an electric heater, 6 is an upper chamber of a pressure vessel, 7 is a hot end main pipeline, 8 is an inlet valve, 9 is a pressure vessel, 10 is a high-pressure injection pump, 11 is a lower chamber of a pressure vessel, 12 is a cold end main pipeline, 13 is an outlet valve, 14 is an injection pipeline, 15 is a containment, 16 is a pressure equalizing pipeline, and 17 is a pressure equalizing valve. DETAILED DESCRIPTION

[0030] Combined with the accompanying drawings of the examples of the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0031] Example 1

[0032] This embodiment provides a pressurized water reactor chemical shutdown system and method using cadmium nitrate as a shutdown solution. Figure 1 The schematic diagram of a pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution in an active manner is shown in the present invention. The system of this embodiment includes a chemical shutdown system 1 and a main loop 2; the chemical shutdown system 1 includes a high-pressure gas cylinder 3, a concentrated cadmium nitrate storage tank 4, an electric heater 5, an inlet valve 8, a high-pressure injection pump 10, an outlet valve 13 and an injection pipeline 14; the electric heater 5 is arranged inside the concentrated cadmium nitrate storage tank 4 to ensure that the cadmium nitrate does not crystallize, the high-pressure gas cylinder 3 is connected to the top of the concentrated cadmium nitrate storage tank 4, the injection pipeline 14 is connected to the bottom of the concentrated cadmium nitrate storage tank 4, the high-pressure injection pump 10 is arranged on the injection pipeline 14, and the inlet valve 8 and the outlet valve 13 are respectively arranged at the inlet and outlet of the injection pipeline 14. The main loop 2 includes a pressure vessel 9, an upper chamber 6 of the pressure vessel located at the upper part of the pressure vessel 9, a lower chamber 11 of the pressure vessel located at the lower part of the pressure vessel 9, a hot end main pipeline 7 connected to the upper chamber 6 of the pressure vessel, and a cold end main pipeline 12 connected to the lower chamber 11 of the pressure vessel.

[0033] When receiving the poison emergency injection signal or the cold shutdown signal, the inlet valve 8 and the outlet valve 13 of the injection pipeline 14 are opened, and the concentrated cadmium nitrate solution is provided with a driving pressure head by the high-pressure injection pump 10 and / or the high-pressure gas cylinder 3, and is injected from the concentrated cadmium nitrate storage tank 4, through the injection pipeline 14, into the cold end main pipeline 12 of the main loop 2, and further through the lower chamber 11 of the pressure vessel, the flow is redistributed and distributed in various places in the pressure vessel 9 after being stirred. Under the same temperature, cadmium nitrate has a greater solubility and neutron absorption cross section than the traditional neutron poison boric acid. The present invention enhances the reliability of the chemical shutdown of the reactor under accident conditions, improves the shutdown safety of the nuclear reactor, and reduces the layout and maintenance costs.

[0034] Pressurized water reactors are usually thermal neutron reactors. The equivalent absorption cross section of thermal neutrons of natural boron B is 764 barns, and the equivalent absorption cross section of thermal neutrons of natural cadmium Cd is 2529 barns. Theoretically, if the molar ratio of boron and cadmium is the same, the neutron absorption capacity of cadmium is 3.3 times that of boron. The chemical shutdown method of the existing power plant is modified, that is, the boric acid solution is replaced with a cadmium nitrate solution, that is, the concentrated boron storage tank is replaced with a concentrated cadmium nitrate storage tank. The volume of the storage tank remains unchanged, and the neutron absorption capacity is doubled, which can increase the negative reactivity provided by the chemical shutdown and reduce the shutdown time.

[0035] When designing a pressurized water reactor nuclear power plant, the volume of the storage tank is kept unchanged, and cadmium nitrate is used as the chemical shutdown solution. The higher chemical shutdown neutron absorption capacity can match the neutron flux density under higher nuclear fuel enrichment. High-enriched nuclear fuel can provide high economy, high refueling cycle, high heat source output, etc.

[0036] When designing a pressurized water reactor nuclear power plant, the neutron absorption capacity provided by the poison is ensured to remain unchanged, and the volume of the concentrated cadmium nitrate storage tank is less than half of the volume of the concentrated boron storage tank, which is beneficial to the relevant layout of the nuclear reactor building.

[0037] The existing concentrated boric acid storage tank stores 8000ppm concentrated boric acid. With the same thermal neutron absorption capacity, the concentrated cadmium nitrate storage tank 4 stores 2400ppm. The concentrated boric acid storage tank needs to be maintained above 25°C to ensure the solubility of boric acid. The corresponding solubility of cadmium nitrate at 25°C is 650000ppm, which fully meets the existing pressurized water reactor chemical shutdown requirements. Optionally, an electric heater 5 is used to ensure that the internal temperature of the concentrated cadmium nitrate storage tank 4 is higher than the crystallization temperature of 2400ppm cadmium nitrate, further increase the internal temperature of the concentrated cadmium nitrate storage tank 4, increase the concentration of the cadmium nitrate solution to the corresponding saturated solubility, and ensure the same chemical shutdown capacity. The volume of the concentrated cadmium nitrate storage tank 4 can be further reduced.

[0038] Preferably, the electric heater 5, inlet valve 8, high-pressure injection pump 10 and outlet valve 13 described in this embodiment are all connected to the nuclear reactor shutdown protection system, and are remotely started and shut down by the nuclear reactor shutdown protection system, or manually started and shut down.

[0039] Preferably, when this embodiment is deployed in an actual nuclear power plant, it includes three independent chemical shutdown systems 1 corresponding to three loops of the 100-kilowatt pressurized water reactor units. Each chemical shutdown system 1 can independently meet the shutdown capacity requirement and ensure the safety redundancy requirement.

[0040] Preferably, the high-pressure injection pump 10 of this embodiment is a multi-stage centrifugal pump with multiple impellers connected in series, which can gradually increase the pressure to meet the 15.5MPa environmental high-pressure injection condition in the main loop 2 when the reactor is shut down urgently.

[0041] Preferably, the high-pressure gas cylinder 3 of this embodiment can be a nitrogen cylinder, a helium cylinder or other high-pressure gas.

[0042] Preferably, the concentrated cadmium nitrate storage tank 4 of this embodiment can be connected to an external circulation pipeline, a pressure gauge and a temperature gauge, and the concentrated cadmium nitrate storage tank 4 is regularly checked to see if it meets the shutdown requirements, and the solution is regularly replaced. In this embodiment, the concentrated cadmium nitrate storage tank 4 and the injection pipeline 14 are made of 316L austenitic stainless steel, which can effectively prevent the corrosion of the concentrated cadmium nitrate solution.

[0043] Preferably, this embodiment adopts an actively driven chemical shutdown system 1, and the chemical shutdown system 1 can be arranged inside or outside the containment vessel.

[0044] In the shutdown method of a pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution described in the present embodiment, upon receiving a poison emergency injection signal or a cold shutdown maintenance signal, the nuclear reactor shutdown protection system automatically or manually opens the inlet valve 8 and the outlet valve 13 of the injection pipeline 14, and the concentrated cadmium nitrate solution is injected from the concentrated cadmium nitrate storage tank 4 and the injection pipeline 14 into the cold end main pipeline 12 of the main loop by providing a driving pressure head with the high-pressure injection pump 10 and / or the high-pressure gas cylinder 3, and further passes through the lower chamber 11 of the pressure vessel to be turbid and then the flow rate is redistributed and distributed in various places in the pressure vessel 9, and the concentrated cadmium nitrate solution is uniformly mixed with the coolant, and finally converges in the upper chamber 6 of the pressure vessel, and flows out of the pressure vessel 9 through the hot end main pipeline 7; the coolant circulates in the entire pressurized water reactor main loop through the hot end main pipeline 7, and then returns to the cold end main pipeline 12 to enter the pressure vessel 9, and finally the coolant with cadmium nitrate flows in the entire pressurized water reactor main loop.

[0045] In this embodiment, when an expected transient (ATWS) fails to cause an emergency shutdown, the control rod insertion fails or the insertion degree is insufficient, the control system provides an emergency injection signal, and the chemical shutdown system 1 acts quickly to reduce the reactivity of the nuclear reactor and ensure the safety of the nuclear reactor.

[0046] Example 2

[0047] like Figure 2As shown, in this embodiment, a pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution is used. The system is driven in a passive manner. The system in this embodiment includes a chemical shutdown system 1 and a main loop 2; the chemical shutdown system 1 includes a concentrated cadmium nitrate storage tank 4, an electric heater 5, an inlet valve 8, an injection pipeline 14, a pressure equalizing pipeline 16 and a pressure equalizing valve 17; the electric heater 5 is arranged inside the concentrated cadmium nitrate storage tank 4 to ensure that the cadmium nitrate does not crystallize, the injection pipeline 14 is connected to the bottom of the concentrated cadmium nitrate storage tank 4, the inlet valve 8 is arranged at the inlet of the injection pipeline 14, the pressure equalizing pipeline 16 is connected to the top of the concentrated cadmium nitrate storage tank 4, and the pressure equalizing valve 17 is arranged on the pressure equalizing pipeline 16. The main loop 2 includes a pressure vessel 9, an upper chamber 6 of the pressure vessel located at the upper part of the pressure vessel 9, a lower chamber 11 of the pressure vessel located at the lower part of the pressure vessel 9, a hot end main pipeline 7 connected to the upper chamber 6 of the pressure vessel, and a cold end main pipeline 12 connected to the lower chamber 11 of the pressure vessel.

[0048] Preferably, the electric heater 5, the inlet valve 8 and the equalizing valve 17 in this embodiment are all connected to the nuclear reactor shutdown protection system, and are remotely started and shut down by the nuclear reactor shutdown protection system, or manually started and shut down.

[0049] Preferably, when this embodiment is deployed in an actual nuclear power plant, it includes three independent chemical shutdown systems 1 corresponding to three loops of the 100-kilowatt pressurized water reactor units. Each chemical shutdown system 1 can independently meet the shutdown capacity requirement and ensure the safety redundancy requirement.

[0050] Preferably, the concentrated cadmium nitrate storage tank 4 of this embodiment can be connected to an external circulation pipeline, a pressure gauge and a temperature gauge, and the concentrated cadmium nitrate storage tank 4 is regularly checked to see if it meets the shutdown requirements, and the solution is regularly replaced. In this embodiment, the concentrated cadmium nitrate storage tank 4 and the injection pipeline (14) are made of 316L austenitic stainless steel, which can effectively prevent the corrosion of the concentrated cadmium nitrate solution.

[0051] Preferably, this embodiment adopts a chemical shutdown system 1 driven in a passive manner, and the chemical shutdown system 1 can be arranged inside the containment vessel.

[0052] In this embodiment, the vertical height of the concentrated cadmium nitrate storage tank 4 is greater than that of the pressure vessel 9 .

[0053] Preferably, in this example, the pressure equalizing valve 17 is a cut-off valve.

[0054] In the shutdown method of a pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution described in the present embodiment, when a poison emergency injection signal or a cold shutdown maintenance signal is received, the nuclear reactor shutdown protection system automatically or manually opens the equalizing valve 17, and after the concentrated cadmium nitrate storage tank 4 and the main circuit are equalized in pressure, the inlet valve 8 of the injection pipeline 14 is opened, and the concentrated cadmium nitrate solution is injected from the concentrated cadmium nitrate storage tank 4 and the injection pipeline 14 into the cold end main pipeline 12 of the main circuit under the action of gravity, and further passes through the lower chamber 11 of the pressure vessel to be turbid and the flow rate is redistributed and distributed in various places in the pressure vessel 9, and the concentrated cadmium nitrate solution is evenly mixed with the coolant, and finally converges in the upper chamber 6 of the pressure vessel, and flows out of the pressure vessel 9 through the hot end main pipeline 7; the coolant circulates in the entire pressurized water reactor main circuit through the hot end main pipeline 7, and then returns to the cold end main pipeline 12 to enter the pressure vessel 9, and finally the coolant with cadmium nitrate flows in the entire pressurized water reactor main circuit.

[0055] In this embodiment, when an expected transient (ATWS) fails to cause an emergency shutdown, the control rod insertion fails or the insertion degree is insufficient, the control system provides an emergency injection signal, and the chemical shutdown system 1 acts quickly to reduce the reactivity of the nuclear reactor and ensure the safety of the nuclear reactor.

[0056] The present invention maintains the cold shutdown signal after the nuclear reactor successfully shuts down the nuclear reactor using control rods. Considering that the nuclear reactor may return to criticality due to consumption of iodine pits and xenon poisons, the chemical and volume control systems of commercial nuclear power plants may not have sufficient boric acid reserve concentrations, and the marine nuclear power reactor may not use neutron poisons to adjust reactivity in normal operation, the chemical shutdown system 1 can be used to inject poisons to keep the nuclear reactor in a long-term shutdown state.

[0057] The above contents are only used to illustrate the present invention, and the specific implementation modes of the present invention cannot be considered to be limited thereto. Any changes made on the basis of the technical solution shall fall within the protection scope of the claims of the present invention.

Claims

1. A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution, characterized in that: The system is driven in an active manner and comprises a chemical shutdown system (1) and a main loop (2); the chemical shutdown system (1) comprises a concentrated cadmium nitrate storage tank (4), an electric heater (5) arranged inside the concentrated cadmium nitrate storage tank (4) to ensure that the cadmium nitrate does not crystallize, a high-pressure gas cylinder (3) connected to the top of the concentrated cadmium nitrate storage tank (4), an injection pipeline (14) connected to the bottom of the concentrated cadmium nitrate storage tank (4), a high-pressure injection pump (10) arranged on the injection pipeline (14), and inlet and outlet ports respectively arranged at the inlet and outlet of the injection pipeline (14). valve (8) and an outlet valve (13); when receiving a poison emergency injection signal or a cold shutdown signal, the inlet valve (8) and the outlet valve (13) of the injection pipeline (14) are opened, and the concentrated cadmium nitrate solution is injected from the concentrated cadmium nitrate storage tank (4) and the injection pipeline (14) into the cold end main pipeline (12) of the main circuit (2) by providing a driving pressure head with a high-pressure injection pump (10) and / or a high-pressure gas cylinder (3), and further passes through the lower chamber (11) of the pressure vessel for turbidity and then the flow is redistributed and distributed to various places in the pressure vessel (9).

2. A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution as claimed in claim 1, characterized in that: When an actual nuclear power plant is arranged, it includes two or more independent chemical shutdown systems (1), each of which can independently meet the shutdown capacity requirements and ensure safety redundancy requirements.

3. A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution as claimed in claim 1, characterized in that: The main circuit (2) comprises a pressure vessel (9), an upper chamber (6) of the pressure vessel located above the pressure vessel (9), a lower chamber (11) of the pressure vessel located below the pressure vessel (9), a hot end main pipeline (7) connected to the upper chamber (6) of the pressure vessel, and a cold end main pipeline (12) connected to the lower chamber (11) of the pressure vessel.

4. A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution as claimed in claim 1, characterized in that: The electric heater (5), inlet valve (8), high-pressure injection pump (10) and outlet valve (13) are all connected to a nuclear reactor shutdown protection system and are remotely started and shut down by the nuclear reactor shutdown protection system, or manually started and shut down.

5. A shutdown method for a pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution according to any one of claims 1 to 4, characterized in that: When receiving a poison emergency injection signal or a cold shutdown signal, the nuclear reactor shutdown protection system automatically or manually opens the inlet valve (8) and the outlet valve (13) of the injection pipeline (14), and the concentrated cadmium nitrate solution is injected into the cold end main pipeline (12) of the main loop from the concentrated cadmium nitrate storage tank (4) through the injection pipeline (14) by providing a driving pressure head with a high-pressure injection pump (10) and / or a high-pressure gas cylinder (3). The concentrated cadmium nitrate solution is further stirred in the lower chamber (11) of the pressure vessel and then redistributed to various places in the pressure vessel (9). The concentrated cadmium nitrate solution is uniformly mixed with the coolant and finally merged in the upper chamber (6) of the pressure vessel and flows out of the pressure vessel (9) through the hot end main pipeline (7); the coolant circulates in the entire pressurized water reactor main loop through the hot end main pipeline (7), and then returns to the cold end main pipeline (12) to enter the pressure vessel (9), and finally the coolant carrying cadmium nitrate flows in the entire pressurized water reactor main loop.

6. A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution, characterized in that: The system is driven in a passive manner and comprises a chemical shutdown system (1) and a main loop (2); the chemical shutdown system (1) comprises a concentrated cadmium nitrate storage tank (4), an electric heater (5) arranged inside the concentrated cadmium nitrate storage tank (4) to ensure that the cadmium nitrate does not crystallize, an injection pipeline (14) connected to the bottom of the concentrated cadmium nitrate storage tank (4), an inlet valve (8) arranged on the injection pipeline (14), a pressure equalizing pipeline (16) connected to the top of the concentrated cadmium nitrate storage tank (4), and a valve (9) arranged on the pressure equalizing pipeline (16). (16); the vertical height of the concentrated cadmium nitrate storage tank (4) is greater than the pressure vessel (9) of the main circuit (2); when receiving a poison emergency injection signal or a cold shutdown signal, the pressure equalizing valve (17) is opened, and after the concentrated cadmium nitrate storage tank (4) and the main circuit are pressure-equalized, the inlet valve (8) of the injection pipeline (14) is opened, and the concentrated cadmium nitrate solution is injected into the cold end main pipeline (12) of the main circuit from the concentrated cadmium nitrate storage tank (4) through the injection pipeline (14) under the action of gravity.

7. A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution as claimed in claim 6, characterized in that: When an actual nuclear power plant is arranged, it includes two or more independent chemical shutdown systems (1), each of which can independently meet the shutdown capacity requirements and ensure safety redundancy requirements.

8. A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution as claimed in claim 6, characterized in that: The main circuit (2) comprises a pressure vessel (9), an upper chamber (6) of the pressure vessel located above the pressure vessel (9), a lower chamber (11) of the pressure vessel located below the pressure vessel (9), a hot end main pipeline (7) connected to the upper chamber (6) of the pressure vessel, and a cold end main pipeline (12) connected to the lower chamber (11) of the pressure vessel.

9. A pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution as claimed in claim 6, characterized in that: The electric heater (5), the inlet valve (8) and the equalizing valve (17) are all connected to the nuclear reactor shutdown protection system and are remotely started and shut down by the nuclear reactor shutdown protection system, or manually started and shut down.

10. A shutdown method for a pressurized water reactor chemical shutdown system using cadmium nitrate as a shutdown solution according to any one of claims 6 to 9, characterized in that: When receiving a poison emergency injection signal or a cold shutdown signal, the nuclear reactor shutdown protection system automatically or manually opens the equalizing valve (17). After the concentrated cadmium nitrate storage tank (4) and the main circuit are equalized in pressure, the inlet valve (8) of the injection pipeline (14) is opened. The concentrated cadmium nitrate solution is injected into the cold end main pipeline (12) of the main circuit from the concentrated cadmium nitrate storage tank (4) through the injection pipeline (14) under the action of gravity. After being further stirred in the lower chamber (11) of the pressure vessel, the flow rate is redistributed to various places in the pressure vessel (9). The concentrated cadmium nitrate solution is uniformly mixed with the coolant and finally merged in the upper chamber (6) of the pressure vessel and flows out of the pressure vessel (9) through the hot end main pipeline (7). The coolant circulates in the entire pressurized water reactor main circuit through the hot end main pipeline (7), and then returns to the cold end main pipeline (12) to enter the pressure vessel (9). Finally, the coolant carrying cadmium nitrate flows in the entire pressurized water reactor main circuit.

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