In-reactor fuel irradiation test loop based on working condition of pressurized water reactor

Abstract

The invention discloses an in-reactor fuel irradiation test loop based on the working condition of a pressurized water reactor. The in-reactor fuel irradiation test loop comprises a main circulation system, a purification system, a fission substance release monitoring system, a water supplementing system, an emergency cooling system, a cooling water system, an in-reactor device pressure failure online monitoring system, a reactor shutdown protection system, a thermal parameter measurement system, a power supply system and an air ventilation and exhaust system. According to the loop, a pressurized water reactor working condition environment is realized, and various technical indexes such as temperature, pressure, flow velocity and water quality required by fuel test are ensured to be reached; the safety level of each system is reasonably configured, so that the requirements of laws and regulations are met, and the safety performance of the loop is improved; by reasonably arranging a multi-stage cooling water system, an air exhaust system and the like, the radioactive activity of an exhaust flow is reduced, the environmental safety is ensured, the release of radioactive aerosol in a process is eliminated, the exposure dose of workers is reduced, the safety of the workers is ensured, the safety risk of devices in the reactor to the reactor under the working condition of a fracture accident is eliminated, and the reliability of the system is improved.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear fuel assembly irradiation testing, in particular to an in-pile fuel irradiation testing loop based on a pressurized water reactor working condition. Background Art

[0002] According to the nuclear safety guideline HAF003, newly developed fuel assemblies must be irradiated in the reactor to simulate their actual operating conditions, and only after verifying the design feasibility, structural stability, and reliability of manufacturing and assembly processes of the fuel assemblies can they be used in engineering. Therefore, new pressurized water reactor fuel assemblies must be irradiated in the reactor circuit that can simulate the operating conditions of the pressurized water reactor.

[0003] The only 2000kW high-temperature and high-pressure test loop in service in China was built in the 1990s. It has conducted irradiation tests on various fuel assemblies and made positive contributions to the development of nuclear power. However, with the improvement of the nuclear safety supervision system in recent years, the safety requirements for nuclear facilities such as test loops have become increasingly stringent. The existing irradiation test related systems have certain limitations and only have unilateral functions. Therefore, there is an urgent need for a comprehensive system design scheme for the irradiation test loop, which needs to optimize the system design scheme of the in-pile fuel irradiation test loop and improve the comprehensive performance of the in-pile fuel irradiation test loop. Summary of the invention

[0004] The present invention provides an in-pile fuel irradiation test loop based on a pressurized water reactor operating condition, which optimizes system configuration and improves loop performance to meet current nuclear safety regulatory requirements.

[0005] The present invention provides a fuel irradiation test loop in a pile based on a pressurized water reactor working condition, the loop comprising: a main circulation system, a purification system, a fissile material release monitoring system, a water replenishment system, an emergency cooling system, a cooling water system, an online monitoring system for pressure failure of a device in the pile, a shutdown protection system, a thermal parameter measurement system, a power supply system and a ventilation and exhaust system; the main circulation system operates under a pressurized water reactor working condition to provide an environmental condition consistent with that of a prototype pile for the fuel irradiation test; the purification system, the fissile material release detection system, the water replenishment system, the emergency cooling system and the cooling water system are respectively connected to the main circulation system;

[0006] The purification system is used to adjust the water quality so that the water chemical parameters during the test meet the requirements of the prototype reactor; the fission material release monitoring system is used to monitor whether the fuel assembly under test in the reactor has fission product release; the water replenishment system is used to fill the system with water when the loop is started, during normal operation, and when the system is pressurized; the emergency cooling system is used to inject water into the system when the loop loses water to ensure that the temperature of the fuel assembly does not exceed the specified limit; the cooling water system is used to provide cooling water to each heat exchanger and heating equipment as the final heat sink of the loop;

[0007] The on-line monitoring system for pressure failure of the in-pile device is connected to the air cavity of the in-pile device and is used to monitor whether the pressure boundary between the in-pile device and the reactor has rupture failure; the shutdown protection system is interlocked with the reactor control system and can directly shut down the reactor in an emergency; the thermal parameter measurement system is used to monitor the operating parameters of each system in the loop in real time; the operating parameters include at least one of temperature, pressure, flow, and liquid level; one end of the power supply system is connected to the municipal power supply, and the other end is connected to the controlled equipment; one end of the exhaust system is connected to the equipment in the loop that requires local ventilation, and the other end is connected to the exhaust vent of the plant.

[0008] Optionally, the main circulation system includes at least two main circulation pumps, at least one in-pile device, at least two heat exchangers, a pressure stabilizer, at least two safety valves, a main pump bypass flow regulating valve and its pipeline, a heat exchanger bypass flow regulating valve and its pipeline, and at least two check valves;

[0009] The pipeline of the main circulation system starts from the outlet of the main circulation pump and is connected to the check valve, the inlet of the in-pile device, the outlet of the in-pile device, the inlet of the heat exchanger, the outlet of the heat exchanger in sequence, and finally returns to the inlet of the main circulation pump to form a closed independent cycle; the main circulation pump provides the power required for the circulation of the coolant in the main circulation system.

[0010] Optionally, the at least two main circulation pumps are arranged in parallel, and a micro-flow reflux bypass pipeline is provided between the outlets of any two main circulation pumps; the outlets of the main circulation pumps are connected to the inlet of the in-pile device through a main route after being gathered, and a branch route is separated and connected to the inlet of the main circulation pump;

[0011] The at least two heat exchangers are connected in parallel or in series.

[0012] Optionally, pipeline electric heaters are provided on the pipelines entering and exiting the in-pile device of the main circulation system, and the electric heaters on each section of the pipeline are divided into at least two groups, at least one group adopts on-off control and the other group adopts proportional control.

[0013] Optionally, the purification system includes a reheater, a sampling glove box, a liquid addition container, a gas addition container, a first filter, a second filter, at least one cation exchange column, and at least one mixed ion exchange column;

[0014] The purification system draws out a branch flow of a certain flow rate from the outlet of the main circulation pump, enters the hot end inlet of the reheater, and after being cooled by the reheater, is connected to the first filter, the first sampling port of the glove box, the cation exchange column, the mixed ion exchange column, the second sampling port of the glove box, the second filter, the liquid addition container, and the gas addition container in sequence from the cold end outlet of the reheater, returns to the cold end outlet of the reheater, and after being heated by the reheater, finally returns to the inlet of the main circulation pump from the hot end outlet of the reheater.

[0015] Optionally, the fission material release monitoring system includes a reheater, at least one delayed neutron monitor, at least one gamma dose monitor, and a fission product spectrum analyzer;

[0016] The fission material release monitoring system draws out a branch flow of a certain flow rate from the outlet of the in-core device, enters the hot end inlet of the reheater, is connected to the delayed neutron monitor, the gamma dose monitor, and the fission product energy spectrum analyzer from the cold end outlet of the reheater after being cooled down by the reheater, returns to the cold end inlet of the reheater, and finally returns to the inlet of the main circulation pump from the hot end outlet of the reheater after being heated up by the reheater.

[0017] Optionally, the water replenishment system includes a water replenishment tank, a nitrogen bottle, at least one water replenishment pump and its outlet check valve, and an electric heating rod;

[0018] The top branch pipe of the water supply tank is connected to the nitrogen bottle, and the bottom pipe mouth of the water supply tank is connected to the water supply pump. The outlet of the water supply pump is connected to the cold end inlet of the reheater of the purification system after passing through a check valve. At least three plug-in electric heating rods are arranged inside the water supply tank.

[0019] Optionally, the emergency cooling system includes a passive safety injection system and a low-pressure safety injection system; the passive safety injection system includes a high-pressure gas cylinder, a high-pressure safety injection box, and a check valve, which are divided into two independent routes for respectively injecting into the device inlet main pipeline and the device outlet main pipeline; the low-pressure safety injection system includes a low-pressure safety injection box, a low-pressure safety injection pump, and a check valve, which are divided into two independent routes for respectively injecting into the device inlet main pipeline and the device outlet main pipeline.

[0020] Optionally, the cooling water system adopts primary or secondary cooling, and each cooling system includes a cooling water tank, a cooling water pump, and a cooler; when secondary cooling is adopted, an intermediate cooling water system is set between the primary water and the cooling water system discharged to the environment.

[0021] Optionally, the in-pile device pressure failure online monitoring system comprises a nitrogen cylinder, a buffer tank, a gas circulation pump, a safety valve and an isolation valve; a pipeline of the in-pile device pressure failure online monitoring system is inserted into the bottom of the in-pile device air cavity, passes through the upper part of the in-pile device and is connected to the first inlet of the buffer tank, and is connected to the inlet of the gas circulation pump through the buffer tank, and finally is connected to the top of the air cavity of the in-pile device through the outlet of the gas circulation pump; monitoring instruments for temperature, pressure and humidity are provided between the in-pile device and the buffer tank; the high-pressure nitrogen in the nitrogen cylinder is sent to the second inlet of the buffer tank through a pressure reducing valve.

[0022] The in-pile fuel irradiation test loop for a pressurized water reactor working condition provided by the present invention can realize the pressurized water reactor working condition environment and ensure various technical indicators such as temperature, pressure, flow rate, water quality, etc. required for realizing the fuel test; the safety level of the shutdown protection system, the emergency cooling system, and the radioactive material containment system is reasonably set, thereby improving the loop safety performance; a multi-stage cooling water system is reasonably set, thereby reducing the radioactive activity of the discharge flow and ensuring environmental safety; a local exhaust system is reasonably set, thereby eliminating the release of radioactive aerosols between processes, reducing the exposure dose of workers and ensuring the safety of workers; an overpressure discharge device is set, thereby eliminating the safety risk of the in-pile device to the reactor under the condition of a rupture accident; and key equipment is reasonably set redundantly to improve the reliability of the system.

[0023] The present invention proposes a new type of in-pile fuel irradiation test circuit scheme for pressurized water reactor conditions, which optimizes the system configuration and improves the circuit performance to meet the current nuclear safety supervision requirements. The details are as follows:

[0024] 1. The main circulation system is used to realize the pressurized water reactor working environment, ensuring the temperature, pressure, flow rate, water quality and other technical indicators required for fuel testing; the pipeline heater can heat the cooling water temperature to the required value, the stabilizer can control the system pressure fluctuation, the regulating valve can control the cooling water flow rate, and the purification system can adjust the cooling water quality.

[0025] 2. The safety level of the shutdown protection system is 1E, the emergency cooling system is nuclear safety level 3, and the main circulation system is nuclear safety level 2, which improves the safety performance of the circuit;

[0026] 3. A two-stage cooling water system is set up, and an intermediate cooling water system is set up between the high-radioactive dose primary water and the cooling water system discharged to the environment, which effectively reduces the radioactive activity of the discharge flow and ensures environmental safety.

[0027] 4. Local exhaust systems are installed at all exposed pipe openings that may generate radioactive aerosols to eliminate radioactive aerosols in the process room, reduce the radiation dose of workers, and ensure the safety of workers;

[0028] 5. Safety valves are installed on the inlet and outlet pipelines of the online monitoring system for pressure failure of the in-core device to eliminate the safety risk of the in-core device to the reactor in the event of a rupture accident;

[0029] 6. Some key equipment in the system has been designed with redundancy to improve the reliability of the system:

[0030] (1) At least two main circulation pumps are set up, one of which is a standby during operation. Failure of any pump will not cause flow loss.

[0031] (2) Two heat exchangers are installed in the main circulation system, one for operation and one for standby.

[0032] (3) In addition to two safety valves, a pressure relief valve is also provided for overpressure discharge of the pressurizer.

[0033] (4) Two safety valves are installed in the online monitoring system for pressure failure of the in-pile device.

[0034] (5) The fission material release monitoring system is equipped with a variety of monitoring methods such as delayed neutrons, gamma dose, and nuclide energy spectrum.

[0035] (6) The online monitoring system for pressure failure of in-pile devices is equipped with multiple monitoring methods such as temperature, pressure, and humidity.

[0036] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0038] Figure 1 This is a schematic diagram of the overall structure of an in-pile fuel irradiation test circuit based on a pressurized water reactor working condition according to an embodiment of the present invention;

[0039] Figure 2 It is a detailed schematic diagram of a fuel irradiation test circuit in a pile based on a pressurized water reactor working condition according to an embodiment of the present invention;

[0040] Among them, 1001-first main pump; 1002-second main pump; 1003-third main pump; 1004-first check valve; 1005-second check valve; 1006-third check valve; 1007-main pump bypass regulating valve; 1008-main pump bypass flowmeter; 1009-A-first section of inlet pipeline electric heater; 1009-B-second section of inlet pipeline electric heater; 1010-in-pile device; 1011-A-first section of outlet pipeline electric heater; 1011-B-second section of outlet pipeline electric heater; 1012-first manual stop valve; 1013-first electric stop valve; 1014-A-first main heat exchanger; 1014-B-second main heat exchanger; 1015-second manual stop valve; 1016-first main heat exchanger flowmeter; 1017-second electric stop valve; 1018-second manual stop valve; 1019- The second main heat exchanger flow meter; 1020-the third electric stop valve; 1021-the heat exchanger bypass flow regulating valve; 1022-the main heat bypass flow meter; 1023-the stabilizer; 1024-the electric stop valve; 1025-A-the first safety valve; 1025-B-the second safety valve; 1026-the spray electric stop valve; 1027-the first return pipeline; 1028 the second return pipeline; 1029-the third return pipeline; 1030-the first isolation valve of the stabilizer; 1031-the second isolation valve of the stabilizer; 1101-the inlet flow signal of the device; 1102-the outlet temperature signal of the device; 1103-the outlet pressure signal of the device; 1104-the liquid level signal of the stabilizer; 1105-the pressure signal of the stabilizer; 1106-the outlet pressure signal of the pressure relief electric valve; 1107-the outlet pressure signal of the second safety valve; 1108-the outlet pressure signal of the first safety valve;

[0041] 2001-the first electric stop valve of the purification system; 2002-the reheater of the purification system; 2002-1-the hot end outlet of the reheater of the purification system; 2002-2-the cold end outlet of the reheater of the purification system; 2002-3-the cold end inlet of the reheater of the purification system; 2002-4-the hot end inlet of the reheater of the purification system; 2003-the solenoid valve of the purification system; 2004-the first filter of the purification system; 2005-the glove box; 2005-1-the first sampling port of the glove box; 2005-2-the second sampling port of the glove box; 2006-the cation exchange column; 2007-A-the first mixed ion column; 2007-B-the second mixed ion column; 2008-the second filter; 2009-the liquid addition container; 2010-the gas addition container; 2011-the second electric stop valve of the purification system; 2101-the flow signal of the purification system; 2102-the temperature signal of the purification system;

[0042] 3001-the first electric stop valve of the fissile material release monitoring system; 3002-the reheater of the fissile material release monitoring system; 3002-1-the hot end inlet of the reheater of the fissile material release monitoring system; 3002-2-the cold end outlet of the reheater of the fissile material release monitoring system; 3002-3-the cold end inlet of the reheater of the fissile material release monitoring system; 3002-4-the hot end outlet of the reheater of the fissile material release monitoring system; 3003-the first solenoid valve of the fissile material release monitoring system; 3004-the total gamma detector; 3005-the delayed neutron monitor; 3006-the fission product energy spectrum analyzer; 3007-the second electric stop valve of the fissile material release monitoring system; 3101-the flow signal of the fissile material release monitoring system; 3102-the temperature signal of the fissile material release monitoring system;

[0043] 4001-water supply tank; 4002-electric heating rod; 4003-water supply pump; 4004-export check valve; 4005-water supply nitrogen bottle; 4006-water supply first stop valve; 4007-water supply second stop valve;

[0044] 5001-A-first nitrogen cylinder; 5001-B-second nitrogen cylinder; 5002-A-first high-pressure injection tank; 5002-B-second high-pressure injection tank; 5003-A-first high-pressure injection check valve; 5003-B-second high-pressure injection check valve; 5004-A-first solenoid valve; 5004-B-second solenoid valve; 5101-A-first high-pressure injection tank pressure signal; 5102-A-first high-pressure injection tank liquid level signal; 5101-B-first Second high-pressure injection tank pressure signal; 5102-B-second high-pressure injection tank liquid level signal; 5005-A-first low-pressure injection tank; 5005-B-second low-pressure injection tank; 5006-A-first low-pressure injection pump; 5006-B-second low-pressure injection pump; 5007-A-first low-pressure injection check valve; 5007-B-second low-pressure injection check valve; 5103-A-first low-pressure injection tank liquid level signal; 5103-B-second low-pressure injection tank liquid level signal;

[0045] 6001-nitrogen cylinder; 6002-pressure reducing valve; 6003-solenoid valve of the on-line monitoring system for pressure failure of the in-pile device; 6004-buffer tank; 6005-gas circulation pump; 6006-first gas safety valve; 6007-second gas safety valve; 6101-gas temperature signal; 6102-gas pressure signal; 6103-gas humidity signal; 6104-gas flow signal;

[0046] 7001-first cooling water tank; 7002-first cooling water pump; 7003-first cooling water pump outlet check valve; 7004-first cooling water pump reflux electric valve; 7005-first electric valve of cooling water system; 7006-second electric valve of cooling water system; 7007-cooler; 7008-second cooling water tank; 7009-second cooling water pump; 7010-second cooling water pump outlet check valve; 7011-second cooling water pump reflux electric valve; 7101-first cooling water tank liquid level signal; 7102-second cooling water tank liquid level signal. DETAILED DESCRIPTION

[0047] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0048] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0049] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0051] like Figure 1As shown, this embodiment provides an in-pile fuel irradiation test loop based on the working condition of a pressurized water reactor, including a main circulation system with a closed circulation under the working condition of a pressurized water reactor, a purification system, a fissile material release monitoring system, a water replenishment system, an emergency cooling system, a cooling water system, an online monitoring system for pressure boundary failure, a shutdown protection system, a thermal parameter measurement system, a power supply system, and a ventilation system. The purification system, the fissile material release monitoring system, the water replenishment system, and the emergency cooling system are respectively connected to the main circulation system, the cooling water system is connected to the secondary side of the heat exchanger in the main circulation system, the in-pile device pressure failure online monitoring system is connected to the air cavity of the in-pile device, the shutdown protection system is interlocked with the reactor control system, and the thermal parameter measurement system collects parameters such as temperature, pressure, flow, and liquid level from each subsystem of the loop. One end of the power supply system is connected to the municipal power supply, and the other end is connected to the controlled equipment (such as pumps, valves, heaters and other electrical equipment). One end of the ventilation system is connected to the equipment that needs local ventilation in the loop (such as fans, iodine removal filters, etc.), and one end is connected to the exhaust outlet of the plant area. Among them, the secondary side of the heat exchanger refers to the cooling end. The primary side is the high temperature end, and the function of the heat exchanger is to reduce the temperature of the primary side through the cooling end of the secondary side, thereby realizing heat exchange. The reactor control system is the control system of the reactor. The shutdown protection signal of the loop is connected to the control system of the reactor, so that the interlocking control of the reactor can be realized.

[0052] An embodiment of the present invention provides an in-pile fuel irradiation test loop based on a pressurized water reactor operating condition, wherein the nuclear safety level of the main circulation system is safety level 2 or safety level 1, the nuclear safety level of the emergency cooling system is safety level 3 or safety level 2, and the shutdown protection system is level 1E.

[0053] Furthermore, the main circulation system operates under the conditions of a pressurized water reactor, providing environmental conditions consistent with those of the prototype reactor for the fuel irradiation test, with a temperature not higher than 350°C, a pressure not lower than 15.5MPa, and a flow rate not lower than 1m / s. Figure 2As shown, the main circulation system is composed of at least two main circulation pumps, at least one in-pile device (1010), at least two heat exchangers (first main heat exchanger 1014-A, second main heat exchanger 1014-B), one pressure regulator (1023), at least two safety valves (first safety valve 1025-A, second safety valve 1025-B), one main pump bypass flow regulating valve (1007) and its pipeline, one heat exchanger bypass flow regulating valve (1021) and its pipeline, at least two check valves (first check valve 1004, second check valve 1005), several isolation valves, several temperature measuring points, pressure measuring points, and flow measuring points. The main circulation pumps of this embodiment include a first main pump (1001), a second main pump (1002) and a third main pump (1003), which are respectively connected to the first check valve (1004), the second check valve (1005), and the third check valve (1006). The main pump bypass flow regulating valve (1007) may also be connected to a main pump bypass flow meter (1008).

[0054] The main circulation system, whose pipeline starts from the outlet of the main circulation pump (the first main pump 1001, the second main pump 1002, the third main pump 1003), is connected to the check valve (the first check valve 1004, the second check valve 1005, the third check valve 1006), the inlet of the in-pile device (1010), the outlet of the in-pile device (1010), the inlet of the heat exchanger (the first main heat exchanger 1014-A, the second main heat exchanger 1014-B), the outlet of the heat exchanger (the first main heat exchanger 1014-A, the second main heat exchanger 1014-B), and finally returns to the inlet of the main circulation pump (the first main pump 1001, the second main pump 1002, the third main pump 1003), forming a closed independent circulation. Among them, the in-pile device 1010 is a device for placing test samples in the reactor.

[0055] The main circulation pump (including the first main pump 1001, the second main pump 1002, and the third main pump 1003) provides the power required for the circulation of the coolant in the main circulation system. At least two main circulation pumps (the first main pump 1001, the second main pump 1002, and the third main pump 1003) are arranged in parallel. A micro-flow reflux bypass small pipeline (the first reflux pipeline 1027, the second reflux pipeline 1028, and the third reflux pipeline 1029, respectively) is arranged between the outlets of any two main circulation pumps (the first main pump 1001, the second main pump 1002, and the third main pump 1003). The flow cross-section of the small pipeline is not greater than 10 mm; the outlets of the main circulation pumps (the first main pump 1001, the second main pump 1002, and the third main pump 1003) are connected to the inlet of the in-pile device (1010) by a main road after being gathered, and a branch road is separated to connect to the main circulation pump (the first main pump 1001, the second main pump 1002, and the third main pump 1003). The at least two heat exchangers (the first main heat exchanger 1014-A and the second main heat exchanger 1014-B) are connected in parallel or in series, and each heat exchanger, i.e., the first main heat exchanger 1014-A, the second main heat exchanger 1014-B and their bypass branches, are provided with regulating valves, i.e., one end of the first main heat exchanger 1014-A is provided with a first electric stop valve (1013), and one end of the second main heat exchanger (1014-B) is provided with a second electric stop valve (1017), the first electric stop valve (1013) and the second electric stop valve (1017) are connected in sequence to the heat exchanger bypass flow regulating valve (1021) and the main heat bypass flow meter (1022), and the regulating valve is adjustable within the range of 0 to 100%. A first manual stop valve (1012) may also be provided on the branch pipe of the first electric stop valve 1013. A second manual stop valve (1015) and a first main heat exchanger flow meter (1016) may also be provided at the other end of the first main heat exchanger 1014-A. A second manual stop valve (1018) and a second main heat exchanger flow meter (1019) are provided at the other end of the second main heat exchanger (1014-B). A third electric stop valve (1020) is provided between the first manual stop valve (1012) and the second manual stop valve (1015).

[0056] The main circulation system has pipeline electric heaters (inlet pipeline electric heaters and outlet pipeline electric heaters) on the pipelines entering and exiting the in-pile device. The inlet pipeline electric heaters are divided into at least two groups, which are divided into the first section (1009-A) of the inlet pipeline electric heaters and the second section (1009-B) of the inlet pipeline electric heaters in this embodiment; at least one group adopts on-off control and one group adopts proportional control, and the power of proportional control is not less than 20% of the total power; the outlet pipeline electric heaters are divided into at least two groups, which are divided into the first section (1011-A) of the outlet pipeline electric heaters and the second section (1011-B) of the outlet pipeline electric heaters in this embodiment; at least one group adopts on-off control and one group adopts proportional control, and the power of proportional control is not less than 20% of the total power. The control of the electric heater is interlocked with the inlet temperature measurement point signal of at least one in-pile device (1010), and the inlet temperature of the in-pile device (1010) is tracked and controlled by setting PID control logic.

[0057] The pressure of the main circulation system is controlled by a two-phase pressurizer vapor-liquid system. The lower liquid space of the pressurizer (1023) is connected to the hot end (the outlet of the in-pile device (1010)) or the cold end (the outlet of the first main heat exchanger (1014-A) and the second main heat exchanger (1014-B)) of the main pipeline through a branch line, and at least two isolation valves (the first isolation valve 1030 of the pressurizer and the second isolation valve 1031 of the pressurizer) are arranged on the branch line. The upper gas space of the pressurizer (1023) is connected to the outlet of the main circulation pump (the first main pump 1001, the second main pump 1002, and the third main pump 1003) through a branch line, and at least one regulating valve, such as a spray electric stop valve 1026, is arranged on the branch line.

[0058] At least two automatic safety discharge branches and one pressure relief branch are also arranged in the gas space above the pressurizer (1023). The automatic safety discharge branch is composed of a spring-type or pilot safety valve (first safety valve 1025-A, second safety valve 1025-B) and a pipeline, and the pressure relief branch is composed of an electric stop valve (1024) and a pipeline. The valve low-pressure sides of the above-mentioned at least three branches are all provided with pressure alarm signals, including the pressure relief electric valve outlet pressure signal (1106), the second safety valve outlet pressure signal (1107), and the first safety valve outlet pressure signal (1108). When the pressure exceeds 0.1MPa, an alarm is triggered. In addition, the main circulation system can also be provided with a device inlet flow signal (1101), a device outlet temperature signal (1102), a device outlet pressure signal (1103), a pressurizer liquid level signal (1104), and a pressurizer pressure signal (1105) to realize the monitoring of various signals.

[0059] Furthermore, the purification system can adjust the water quality of the main circulation system to ensure that the water chemical parameters during the test meet the requirements of the prototype reactor, and the control parameters at least include pH value, conductivity, suspended solids concentration, dissolved oxygen concentration, dissolved hydrogen concentration, copper ion concentration, sulfate ion concentration, sodium ion concentration, calcium ion concentration, boron ion concentration, fluoride ion concentration, etc. The purification system consists of a reheater (2002), a sampling glove box (2005), a liquid addition container (2009), a gas addition container (2010), two filters (a first filter 2004, a second filter 2008), at least one cation exchange column (2006), and at least one mixed ion exchange column. The mixed ion exchange column can include a first mixed ion column 2007-A and a second mixed ion column 2007-B.

[0060] The purification system has a first electric stop valve (2001) connected to the first main pump (1001), the second main pump (1002), and the third main pump (100). The purification system draws out a branch flow of no more than 1% of the main flow from the outlet of the main circulation pump (the first main pump 1001, the second main pump 1002, and the third main pump 1003), enters the hot end inlet (2002-4) of the recuperator, and after cooling down in the recuperator (2002), is connected to the first filter (2004), the first sampling port (2005-1) of the glove box, the cation exchange column (2006), the mixed ion exchange column (the first mixed ion column) from the cold end outlet (2002-2) of the recuperator in sequence. 2007-A, the second mixed ion column 2007-B), the second sampling port of the glove box (2005-2), the second filter (2008), the liquid addition container (2009), the gas addition container (2010), return to the cold end outlet (2002-2) of the recuperator, and after being heated by the recuperator (2002), finally return to the inlet of the main circulation pump (the first main pump 1001, the second main pump 1002, and the third main pump 1003) through the hot end outlet (2002-1) of the recuperator. The recuperator (2002) can also be connected to the first check valve (1004) of the first main pump (100) through the second electric stop valve (2011).

[0061] The first filter (2004) has a filtration accuracy better than 1um and is used to remove suspended solids in the coolant; the first sampling port (2005-1) of the glove box can sample the cooling water before purification; the cation exchange column (2006) and the mixed ion exchange column (the first mixed ion column 2007-A, the second mixed ion column 2007-B) can adsorb and remove the impurity ions in the coolant, first adsorbed by the cation exchange column (2006), and then directly returned to the cold end inlet (2002-3) of the heat exchanger or sent to the mixed ion exchange column (the first mixed ion column 2007-A, the second mixed ion column 2007-B) for further purification, and the mixed ion exchange column (2006) can be used to remove the impurity ions in the coolant. Ion exchange columns (first mixed ion column 2007-A, second mixed ion column 2007-B) can be arranged in parallel in multiple units; the second filter (2008) has a filtration accuracy better than 200 meshes and is mainly used to filter resin residues; to ensure the purification effect of the system, the temperature of the cold end outlet (2002-2) of the reheater needs to be reduced to below 40°C. When the temperature exceeds 40°C, the flow is cut off by the solenoid valve (2003); to ensure that the return water of the purification system does not cause excessive thermal stress shock to the main line, the temperature of the hot end outlet (2002-1) of the reheater needs to be increased to above 100°C. When the temperature is below 100°C, it is adjusted by reducing the cooling water flow rate on the secondary side of the reheater. The purification system can also have a purification system flow signal (210-) and a purification system temperature signal (2102) for signal monitoring.

[0062] Furthermore, the fissile material release monitoring system can monitor whether the tested fuel assembly (a test sample placed in the reactor, specifically a tested fuel assembly) has fission product release, and the monitoring parameters at least include delayed neutrons, gamma dose, fission product spectrum, etc. The fissile material release monitoring system is composed of a reheater (3002), at least one delayed neutron monitor (3005), at least one gamma dose monitor (3004), and a fission product spectrum analyzer (3006).

[0063] The fission material release monitoring system draws a branch flow of a certain flow rate from the outlet of the in-core device (1010), enters the hot end inlet (3002-1) of the reheater, and after cooling down in the reheater, is connected to the delayed neutron monitor (3005), the gamma dose monitor (3004), and the fission product energy spectrum analyzer (3006) from the cold end outlet (3002-2) of the reheater, returns to the cold end inlet (3002-3) of the reheater, and after heating up in the reheater, finally returns to the inlet of the main circulation pump (the first main pump 1001, the second main pump 1002, and the third main pump 1003) from the hot end outlet (3002-4) of the reheater. The hot end inlet (3002-1) of the recuperator is connected to a first electric stop valve (3001), and the hot end outlet (3002-4) of the recuperator is connected to a second electric stop valve (3007). A flow signal (3101) of a fissile material release monitoring system is provided at the second electric stop valve (3007) to monitor the flow signal. A temperature signal (3102) of a fissile material release monitoring system is provided at the first solenoid valve (3003) to monitor the temperature signal of the fissile material release monitoring system.

[0064] The location of the instrument should ensure that the time between the coolant from the core to the instrument is about 80s. To ensure the detection effect of the system, the temperature of the cold end outlet (3002-2) of the recuperator needs to be reduced to below 40°C. When the temperature exceeds 40°C, the flow is cut off by the first electric stop valve (3001); to ensure that the return water of the purification system does not cause excessive thermal stress shock to the main pipeline, the temperature of the hot end outlet (3002-4) of the recuperator needs to be increased to above 100°C. When the temperature is below 100°C, it is adjusted by reducing the cooling water flow on the secondary side of the recuperator.

[0065] Furthermore, the water replenishment system can fill the system with water when the loop is started, when it is operating normally, and when the system is pressurized. The water replenishment system consists of a water replenishment tank (4001), a nitrogen bottle (4005), at least one water replenishment pump (4003) and its outlet check valve (4004), an electric heating rod (4002), and a plurality of isolation valves (a first water replenishment stop valve 4006 and a second water replenishment stop valve 4007). The top branch of the water replenishment tank (4001) is connected to the nitrogen bottle (4005), and the bottom pipe mouth is connected to the water replenishment pump (4003). The outlet of the water replenishment pump (4003) is connected to the cold end inlet (2002-3) of the purification system reheater after passing through the outlet check valve (4004). At least three plug-in electric heating rods (4002) are arranged inside the water replenishment tank (4001). The outlet pressure of the water supply pump (4003) should be at least 22MPa, and the flow rate of the water supply pump (4003) should not be too large or too small, and 4 times the system volume / hour is the best. The top branch of the water supply tank (4001) is connected to the nitrogen bottle (4005), and the bottom pipe is connected to the water supply pump (4003). The outlet of the water supply pump (4003) is connected to the cold end inlet (2002-3) of the purification system reheater after passing through a check valve. At least 3 plug-in electric heating rods (4002) are set inside the water supply tank (4001). The power of the electric heating rods must ensure that the water temperature of the water supply tank can be raised to 80°C in a short time.

[0066] Furthermore, the emergency cooling system can inject water into the system when the loop loses water to ensure that the temperature of the fuel assembly does not exceed the specified limit. The emergency cooling system consists of a passive safety injection system and a low-pressure safety injection system. The passive safety injection system consists of high-pressure gas cylinders (the first nitrogen cylinder 5001-A, the second nitrogen cylinder 5001-B), high-pressure safety injection boxes (the first high-pressure safety injection box 5002-A, the second high-pressure safety injection box 5002-B), and check valves (the first high-pressure safety injection check valve 5003-A, the second high-pressure safety injection check valve 5003-B). It is divided into two independent routes to inject into the inlet main pipeline of the in-pile device and the outlet main pipeline of the in-pile device respectively. The trigger pressure is not less than 10MPa, which can quickly provide cooling water to the fuel assembly in the early stage of a loss of water accident.

[0067] The low-pressure safety injection system is pump-driven and consists of a low-pressure safety injection tank (the first low-pressure safety injection tank 5005-A, the second low-pressure safety injection tank 5005-B), a low-pressure safety injection pump (the first low-pressure safety injection pump 5006-A, the second low-pressure safety injection pump 5006-B), and a check valve (the first high-pressure safety injection check valve 5003-A, the second high-pressure safety injection check valve 5003-B). It is divided into two independent routes and injected into the device inlet main pipeline and the device outlet main pipeline respectively. The trigger pressure is not less than 0.5MPa, which can ensure that cooling water is continuously supplied to the fuel assemblies in the later stage of a loss of coolant accident. The cooling water capacity of the low-pressure safety injection tank (the first low-pressure safety injection tank 5005-A, the second low-pressure safety injection tank 5005-B) is at least greater than the flow rate required to supply water to the system for 1 hour. In this embodiment, the first high-pressure safety injection box pressure signal (5101-A) and the first high-pressure safety injection box liquid level signal (5102-A), the second high-pressure safety injection box pressure signal (5101-B), and the second high-pressure safety injection box liquid level signal (5102-B) are respectively set at the first high-pressure safety injection box (5002-A) and the second high-pressure safety injection box (5002-B) to realize the monitoring of the pressure and liquid level of the first high-pressure safety injection box and the second high-pressure installation box.

[0068] Furthermore, the in-pile device pressure failure online monitoring system monitors whether the pressure boundary between the in-pile device and the reactor has rupture failure through signals such as temperature, pressure, and humidity. The in-pile device pressure failure online monitoring system consists of a nitrogen bottle (6001), a buffer tank (6004), a gas circulation pump (6005), a safety valve (a first gas safety valve 6006, a second gas safety valve 6007), and a plurality of isolation valves. The system pipeline is inserted into the bottom of the in-pile device gas cavity, passes through the upper part of the in-pile device (1010) and is connected to the first inlet of the buffer tank (6004), and is connected to the inlet of the gas circulation pump through the buffer tank (6004), and finally connected to the top of the gas cavity of the in-pile device (1010) through the outlet of the gas circulation pump; monitoring instruments such as temperature, pressure, and humidity are provided between the in-pile device (1010) and the buffer tank (6004) to respectively sense the gas temperature signal (6101), the gas pressure signal (6102), and the gas humidity signal (6103).

[0069] The nitrogen cylinder (6001) is connected to the buffer tank (6004) via the pressure reducing valve (6002) and the solenoid valve (6003). The high-pressure nitrogen in the nitrogen cylinder (6001) is sent to the second inlet of the buffer tank (6004) after passing through the pressure reducing valve (6002). The operating pressure of the pressure boundary failure online monitoring system under normal conditions is between 10kPa and 100kPa, the temperature is between 20 and 40°C, and the humidity is less than 10%RH. If the above three parameters are all beyond the normal operating range, it is determined that the pressure boundary has ruptured and failed. At the same time, in order to quickly remove high-temperature and high-pressure steam under the pressure boundary failure condition, safety valves (first gas safety valve 6006, second gas safety valve 6007) are respectively installed on the pipelines entering and exiting the in-pile device of this system. The displacement of the safety valve meets the requirement that the pressure boundary failure online monitoring system does not overpressure under accident conditions. The buffer tank (6004) is also connected to a gas circulation pump (6005) and a first gas safety valve (6006), and a gas flow signal (6104) is also provided between the gas circulation pump (6005) and the first gas safety valve (6006) to monitor the flow signal.

[0070] Furthermore, the cooling water system provides cooling water to each heat exchanger and heating device as the final heat sink of the loop. The cooling water system can adopt primary or secondary cooling, and each cooling system includes a cooling water tank (first cooling water tank 7001, second cooling water tank 7008), a cooling water pump (first cooling water pump 7002, second cooling water pump 7009), a cooler (7007), and several valves. When using secondary cooling, an intermediate cooling water system is set between the primary water and the cooling water system discharged to the environment, which effectively reduces the radioactive activity of the discharge flow and ensures environmental safety.

[0071] Among them, the first cooling water tank (7001) is connected to the first cooling water pump (7002) and one end of the first cooling water pump outlet check valve (7003), and the other end of the first cooling water pump outlet check valve (7003) is connected to the first cooling water tank (7001) through the first cooling water pump return electric valve (7004) and is connected to the first electric valve (7005) and the second electric valve (7006) of the cooling water system; the first electric valve (7005) and the second electric valve (7006) are respectively connected to the first main heat exchanger (1014A) and the second main heat exchanger (1014B) of the main circulation system.

[0072] The second cooling water tank (7008) is connected to the second cooling water pump (7009) and one end of the second cooling water pump outlet check valve (7010), and the other end of the second cooling water pump outlet check valve (7010) is connected to the second cooling water tank (7008) through the second cooling water pump return electric valve (7011) and is also connected to the cooler (7007). The cooler (7007) is also connected to the first cooling water tank (7001).

[0073] The first cooling water tank (7001) and the second cooling water tank (7008) are respectively provided with a first cooling water tank liquid level signal (7101) and a second cooling water tank liquid level signal (7102) to monitor the liquid levels of the corresponding cooling water tanks.

[0074] Furthermore, the shutdown protection system of this embodiment can directly shut down the reactor in an emergency to ensure safety. For example, the reactor is shut down when parameters such as flow, temperature, and pressure exceed the limit values ​​specified in the operation. The shutdown protection system includes at least a flow signal of the inlet of the in-core device, a temperature signal of the outlet of the in-core device, and a pressure signal of the outlet of the in-core device. At least three measuring points are set for each protection signal. The above protection systems all use 1E-level instruments. The signal delay is not more than 25ms.

[0075] Furthermore, the thermal parameter measurement system monitors the temperature, pressure, flow, liquid level and other signals at several locations of the entire loop in real time. The monitored data can be used to monitor the operating status of the monitoring system, and if there is a deviation, it needs to be adjusted in time; or some parameters can be used for calculation and analysis to obtain the power of the test sample (the fuel assembly being tested) in the pile.

[0076] In some optional embodiments, the thermal parameter measurement system may monitor the parameters of the main circulation system at least, including: the main circulation pump outlet pressure, the main circulation pump bypass flow, the inlet temperature of the in-pile device, the inlet pressure of the in-pile device, the outlet temperature of the in-pile device, the outlet pressure of the in-pile device, the inlet temperature of the in-pile device, the outlet pressure of the in-pile device, the inlet temperature of the heat exchanger, the inlet flow of the heat exchanger, the inlet pressure of the heat exchanger, the bypass flow of the heat exchanger, the temperature of the pressurizer, the pressure of the pressurizer, the liquid level of the pressurizer, the outlet pressure of the safety valve, etc.

[0077] The parameter monitoring of the fission material release monitoring system and the purification system by the thermal parameter measurement system may at least include: the reheater hot end inlet flow, the reheater hot end inlet temperature, the reheater cold end outlet temperature, the reheater cold end outlet pressure, the reheater cold end inlet pressure, the reheater hot end outlet pressure, and the reheater hot end outlet temperature.

[0078] The parameters monitored by the thermal parameter measurement system for the water supply system may at least include: water supply tank pressure, water supply tank liquid level, water supply tank temperature, and water supply pump outlet pressure.

[0079] The thermal parameter measurement system monitors the parameters of the emergency cooling system, including at least: injection tank liquid level, injection tank pressure, and injection pump outlet pressure.

[0080] Furthermore, the ventilation and exhaust system is equipped with local exhaust for all exposed pipe openings that may produce radioactive aerosols, and is composed of a fan and an iodine removal filter. The exposed pipe openings are made into a closed unit, connected to the ventilation duct, and sequentially passed through the iodine removal filter and the fan to the exhaust port of the factory. This system can eliminate the release of radioactive aerosols between processes, reduce the radiation dose of workers, and ensure the safety of workers.

[0081] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A fuel irradiation test circuit in a pressurized water reactor, characterized in that: The circuit includes: a main circulation system, a purification system, a fissile material release monitoring system, a water replenishment system, an emergency cooling system, a cooling water system, an online monitoring system for pressure failure of the in-pile device, a shutdown protection system, a thermal parameter measurement system, a power supply system and a ventilation system; the main circulation system operates under the conditions of a pressurized water reactor to provide environmental conditions consistent with those of the prototype reactor for the fuel irradiation test; the purification system, the fissile material release detection system, the water replenishment system, the emergency cooling system and the cooling water system are respectively connected to the main circulation system; The purification system is used to adjust the water quality so that the water chemical parameters during the test meet the requirements of the prototype reactor; the fission material release monitoring system is used to monitor whether the fuel assembly under test in the reactor has fission product release; the water replenishment system is used to fill the system with water when the loop is started, during normal operation, and when the system is pressurized; the emergency cooling system is used to inject water into the system when the loop loses water to ensure that the temperature of the fuel assembly does not exceed the specified limit; the cooling water system is used to provide cooling water to each heat exchanger and heating equipment as the final heat sink of the loop; The on-line monitoring system for pressure failure of the in-pile device is connected to the air cavity of the in-pile device and is used to monitor whether the pressure boundary between the in-pile device and the reactor has rupture failure; the shutdown protection system is interlocked with the reactor control system and can directly shut down the reactor in an emergency; the thermal parameter measurement system is used to monitor the operating parameters of each system in the loop in real time; the operating parameters include at least one of temperature, pressure, flow, and liquid level; one end of the power supply system is connected to the municipal power supply, and the other end is connected to the controlled equipment; one end of the exhaust system is connected to the equipment in the loop that requires local ventilation, and the other end is connected to the exhaust vent of the plant.

2. The in-pile fuel irradiation test circuit based on the pressurized water reactor working condition according to claim 1 is characterized in that: The main circulation system includes at least two main circulation pumps, at least one in-pile device, at least two heat exchangers, a pressure stabilizer, at least two safety valves, a main pump bypass flow regulating valve and its pipeline, a heat exchanger bypass flow regulating valve and its pipeline, and at least two check valves; The pipeline of the main circulation system starts from the outlet of the main circulation pump and is connected to the check valve, the inlet of the in-pile device, the outlet of the in-pile device, the inlet of the heat exchanger, the outlet of the heat exchanger in sequence, and finally returns to the inlet of the main circulation pump to form a closed independent cycle; the main circulation pump provides the power required for the circulation of the coolant in the main circulation system.

3. The in-pile fuel irradiation test circuit based on the pressurized water reactor working condition according to claim 2 is characterized in that: The at least two main circulation pumps are arranged in parallel, and a micro-flow reflux bypass pipeline is provided between the outlets of any two main circulation pumps; the outlets of the main circulation pumps are connected to the inlet of the in-pile device through a main route after being gathered, and a branch route is separated and connected to the inlet of the main circulation pump; The at least two heat exchangers are connected in parallel or in series.

4. The in-pile fuel irradiation test circuit based on the pressurized water reactor working condition according to claim 2 is characterized in that: The pipelines entering and exiting the in-pile device of the main circulation system are all provided with pipeline electric heaters. The electric heaters on each section of the pipeline are divided into at least two groups, at least one group adopts on-off control and the other group adopts proportional control.

5. The in-pile fuel irradiation test circuit based on the pressurized water reactor working condition according to claim 2 is characterized in that: The purification system comprises a reheater, a sampling glove box, a liquid addition container, a gas addition container, a first filter, a second filter, at least one cation exchange column, and at least one mixed ion exchange column; The purification system draws out a branch flow of a certain flow rate from the outlet of the main circulation pump, enters the hot end inlet of the reheater, and after being cooled by the reheater, is connected to the first filter, the first sampling port of the glove box, the cation exchange column, the mixed ion exchange column, the second sampling port of the glove box, the second filter, the liquid addition container, and the gas addition container in sequence from the cold end outlet of the reheater, returns to the cold end outlet of the reheater, and after being heated by the reheater, finally returns to the inlet of the main circulation pump from the hot end outlet of the reheater.

6. The in-pile fuel irradiation test circuit based on the pressurized water reactor working condition according to claim 2 is characterized in that: The fission material release monitoring system includes a reheater, at least one delayed neutron monitor, at least one gamma dose monitor, and a fission product spectrum analyzer; The fission material release monitoring system draws out a branch flow of a certain flow rate from the outlet of the in-core device, enters the hot end inlet of the reheater, is connected to the delayed neutron monitor, the gamma dose monitor, and the fission product energy spectrum analyzer from the cold end outlet of the reheater after being cooled down by the reheater, returns to the cold end inlet of the reheater, and finally returns to the inlet of the main circulation pump from the hot end outlet of the reheater after being heated up by the reheater.

7. The in-pile fuel irradiation test circuit based on the pressurized water reactor working condition according to claim 1 is characterized in that: The water replenishment system includes a water replenishment tank, a nitrogen bottle, at least one water replenishment pump and its outlet check valve, and an electric heating rod; The top branch pipe of the water supply tank is connected to the nitrogen bottle, and the bottom pipe mouth of the water supply tank is connected to the water supply pump. The outlet of the water supply pump is connected to the cold end inlet of the reheater of the purification system after passing through a check valve. At least three plug-in electric heating rods are arranged inside the water supply tank.

8. The in-pile fuel irradiation test circuit based on the pressurized water reactor working condition according to claim 1 is characterized in that: The emergency cooling system includes a passive safety injection system and a low-pressure safety injection system; the passive safety injection system includes a high-pressure gas cylinder, a high-pressure safety injection box, and a check valve, which are divided into two independent routes for respectively injecting into the device inlet main pipeline and the device outlet main pipeline; the low-pressure safety injection system includes a low-pressure safety injection box, a low-pressure safety injection pump, and a check valve, which are divided into two independent routes for respectively injecting into the device inlet main pipeline and the device outlet main pipeline.

9. The in-pile fuel irradiation test circuit based on the pressurized water reactor working condition according to claim 1, characterized in that: The cooling water system adopts primary or secondary cooling, and each cooling system includes a cooling water tank, a cooling water pump, and a cooler; when secondary cooling is adopted, an intermediate cooling water system is arranged between the primary water and the cooling water system discharged to the environment.

10. The in-pile fuel irradiation test circuit based on the pressurized water reactor working condition according to claim 1, characterized in that: The in-pile device pressure failure online monitoring system comprises a nitrogen cylinder, a buffer tank, a gas circulation pump, a safety valve and an isolation valve; a pipeline of the in-pile device pressure failure online monitoring system is inserted into the bottom of the in-pile device air cavity, passes through the upper part of the in-pile device and is connected to the first inlet of the buffer tank, and is connected to the inlet of the gas circulation pump through the buffer tank, and finally is connected to the top of the air cavity of the in-pile device through the outlet of the gas circulation pump; monitoring instruments for temperature, pressure and humidity are provided between the in-pile device and the buffer tank; the high-pressure nitrogen in the nitrogen cylinder is sent to the second inlet of the buffer tank after passing through the pressure reducing valve.

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