A cooling water system for a research reactor irradiation test loop and its design and use method

Abstract

The present invention provides a cooling water system for a research reactor irradiation test loop and its design and use method, which relates to the technical field of nuclear fuel and material in-pile irradiation, and solves the technical problem that the complete interruption of the external water source in the existing cooling water system will bring about safety hazards. In the present invention, the volume corresponding to the first liquid level alarm point and the second liquid level alarm point is the operating buffer volume V1, the volume between the second liquid level alarm point and the first water intake point is the minimum cooling water volume V2 in the early stage of shutdown, and the volume between the first water intake point and the second water intake point is the minimum cooling water volume V3 in the late stage of shutdown; the sum of V1, V2 and V3 is the optimal volume V of the cooling water pool. The present invention simplifies the complexity of the system, reduces the space occupied by the equipment, and reduces the construction cost. At the same time, it ensures the reliability of the equipment and system through the nuclear safety level; ensures the safety of the fuel elements, optimizes the size design of the cooling water pool, and further reasonably utilizes the space between the research reactor process rooms.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear fuel and material in-pile irradiation, and in particular to a cooling water system for a research reactor irradiation test loop and a design and use method thereof. Background Art

[0002] The irradiation test circuit simulates the actual operating environment of fuel elements, providing specific temperature, flow, and water chemistry parameters to verify the physical, thermal, and manufacturing process performance of the fuel elements. The circuit cooling water system typically serves as the final heat sink of the circuit, extracting heat from the fuel elements within the circuit and ensuring that the temperatures of the fuel elements and the primary coolant system remain within a specified range. Therefore, the cooling water system is directly related to the safety of the primary coolant system and fuel elements.

[0003] For example, the patent with publication number CN116847623A proposes a modular water cooling system for irradiation test temperature control, which uses a dual-circuit method to cool the irradiation device and adopts modular design and layout. It introduces water cooling technology into the nuclear fuel and material irradiation temperature control technology, improves the temperature regulation capability and control accuracy of the irradiation device, and further ensures that the irradiation test temperature meets the requirements.

[0004] First, in traditional system solutions, the cooling water system is divided into a safety-grade cooling water system and a non-safety-grade cooling water system. The safety-grade cooling water system is used to supply water to equipment with safety functions, such as the main pump, while the non-safety-grade cooling water system is used to supply water to non-safety-grade equipment, such as heat exchangers. This results in a complex system design and high construction costs. Second, traditional designs do not calculate the optimal capacity of the cooling water tank, often using the most conservative capacity for envelope analysis. This results in a large tank volume and excessive floor space, which wastes the efficiency of the research reactor process room. There is no automatic tracking and adjustment mechanism for the cooling water flow of the cooling water tank, resulting in the cooling water flow not being adjusted in time according to equipment temperature fluctuations. Furthermore, in the event of an accident, the cooling water in the cooling water tank is easily misallocated, resulting in the ineffective cooling of high-priority overheating equipment, posing certain safety risks. Summary of the Invention

[0005] The present invention provides a cooling water system for a research reactor irradiation test loop and a design and use method thereof, so as to solve the technical problem that a complete interruption of external water source in existing cooling water systems may cause potential safety hazards.

[0006] The embodiments of the present invention are achieved through the following technical solutions:

[0007] A cooling water system for a research reactor irradiation test loop includes a cooling water pool, a loop main pump, and a loop heat exchanger. The cooling water pool is provided with a second liquid level alarm point for controlling the minimum water level, a first water intake point, and a second water intake point for supplying cooling water to the loop main pump and the loop heat exchanger, respectively. The second liquid level alarm point, the first water intake point, and the second water intake point are located in descending order.

[0008] The initial shutdown period is when the residual heat power of the nuclear fuel is equal to the natural heat dissipation power of the system from shutdown, which is recorded as t1. The volume between the second liquid level alarm point and the first water intake point is the minimum cooling water volume V2 in the initial shutdown period.

[0009] The period from when the delayed residual heat power of the nuclear fuel is equal to the natural heat dissipation power of the system to when the temperature of the fuel assembly reaches the safety temperature limit of 60°C is the late shutdown period, denoted as t2. The volume between the first water intake point and the second water intake point is the minimum cooling water volume V3 in the late shutdown period.

[0010] The sum of the minimum cooling water volume V2 at the initial shutdown stage, the minimum cooling water volume V3 at the later shutdown stage, and the operating buffer volume V1 is the optimal volume V of the cooling water pool.

[0011] Preferably, the cooling water pool is further provided with a first liquid level alarm point for controlling the maximum water level, and the volume corresponding to the first liquid level alarm point and the second liquid level alarm point is the operation buffer volume V1.

[0012] Preferably, it also includes a first cooling water pump and a second cooling water pump for respectively delivering cooling water to the loop main pump and the loop heat exchange equipment. The inlet pipe and outlet pipe of the first cooling water pump are nuclear safety grade pipes, and the inlet pipe and outlet pipe of the second cooling water pump are non-nuclear safety grade pipes.

[0013] Preferably, the inlet pipe and outlet pipe of the first cooling water pump and the second cooling water pump are respectively provided with a shut-off valve for controlling the inflow of cooling water and a check valve for preventing the backflow of cooling water; there are also a reflux branch for returning the cooling water to the cooling water pool and a reflux regulating valve for controlling the reflux amount of cooling water.

[0014] Preferably, the loop main pump and the loop heat exchange device are provided with a flow meter for detecting the cooling water flow rate, a temperature detector for detecting the outlet cooling water temperature, and a flow regulating valve for regulating the inlet cooling water flow rate.

[0015] Preferably, the loop main pump and the loop heat exchange device are also provided with a discharge valve for controlling the discharge of cooling water.

[0016] A design method for a research reactor irradiation test loop cooling water system includes the following steps:

[0017] S1: Determine the minimum cooling water volume V2 at the initial shutdown stage: The amount of cooling water required when the residual heat released by the nuclear fuel exceeds the heat Q1 naturally dissipated by the system at the initial shutdown stage t1 is the minimum cooling water volume V2 at the initial shutdown stage;

[0018] S2: Determine the minimum cooling water volume V3 in the late shutdown period: The amount of cooling water required corresponding to the heat Q2 dissipated by the fuel assembly in the late shutdown period t2 is the minimum cooling water volume V3 in the late shutdown period;

[0019] S3: Determine the operating buffer volume V1: V1 is the total flow of the cooling water system for 5-15 minutes under normal operating conditions;

[0020] S4: Determine the optimal volume V of the cooling water pool:

[0021] V=V1+V2+V3. (1)

[0022] Preferably, in steps S1 and S2, the delayed residual heat power W of the loop after the nuclear fuel reactor is shut down is:

[0023] W=N(t)+N S1 (t)+N S2 (t) (2)

[0024] Wherein, N(t) is the residual fission power, N(t)=N(0)0.15exp(-0.1t);

[0025] N s1 (t) is the decay power of fission products, N s1 (t) = N(0)A / 200[t -a -(t+t o ) -a ];

[0026] N s2 (t) is the decay power of neutron capture products, N s2 (t) = N(0) × 2.28 × 10 -3 c(1+α)exp(-4.91×10 -4 t)+2.19×10 -3 c(1+α)exp(-3.14×10 -6 t);

[0027] Where, N(0) is the initial shutdown power;

[0028] t is the time variable from the shutdown moment;

[0029] t o is the initial reaction time of the fuel element, here t o =20d=1.7×106 ;

[0030] A=26.02;

[0031] a = 0.2834c is the conversion ratio, α is the ratio of radiation capture to fission number of U-235, c = 0.6, α = 0.2.

[0032] Preferably, in step S1, the amount of cooling water is calculated as follows:

[0033]

[0034] Wherein, T1 is the temperature of the cooling water in the cooling water pool (1);

[0035] T2 is the temperature of the cooling water of the discharge valve (17);

[0036] C is the specific heat capacity of water, C = 4.2KJ / (kg·℃);

[0037] ρ is the density of water, ρ = 10 -3 kg / m 3 ;

[0038] In step S2, the amount of cooling water is calculated as follows:

[0039]

[0040] Wherein, T3 is the temperature of the cooling water in the cooling water pool (1);

[0041] T4 is the temperature of the cooling water of the discharge valve (17).

[0042] A method for using a cooling water system for a research reactor irradiation test loop comprises the following steps:

[0043] R1: Water injection operation: Control water injection to keep the liquid level between the first level alarm point and the second level alarm point;

[0044] R2: Operation under accident conditions;

[0045] R2.1: Initial shutdown phase: The first and second cooling water pumps continue to deliver cooling water to the loop main pump and loop heat exchange equipment, respectively, until the cooling water pool level falls below the first water intake point.

[0046] R2.2: Late shutdown period: The second cooling water pump stops running, and the first cooling water pump continues to deliver cooling water to the main pump of the circuit.

[0047] This technical solution optimizes the distribution of cooling water flow at different time stages after fuel element shutdown, resulting in the optimal capacity of the cooling water pool and the optimal cooling water distribution plan. This results in a highly secure cooling water system, eliminates potential safety hazards caused by a complete interruption of external water flow, and improves the safety characteristics of the test circuit.

[0048] By designing a shared cooling water pool, the system complexity is simplified, the space occupied by the equipment is reduced, and the construction cost is lowered, while the reliability of the equipment and system is guaranteed by the nuclear safety level;

[0049] By establishing a comprehensive model of temperature, cooling water, and time at different stages, the cooling water flow requirements for each stage were calculated, thereby determining the optimal volume of the cooling water tank. This not only ensures the safety of the fuel elements, but also optimizes the size design of the cooling water pool and further rationally utilizes the space in the research reactor process room.

[0050] By installing temperature detectors at the cooling water outlets of each device and flow control valves at the inlets, and automatically matching the optimal cooling flow by setting the outlet temperature limit, cooling water resources are saved and the environment is protected.

[0051] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0052] 1. The present invention simplifies the complexity of the system, reduces the space occupied by the equipment, and reduces the construction cost, while ensuring the reliability of the equipment and system through nuclear safety levels;

[0053] 2. This invention ensures the safety of fuel elements, optimizes the size design of the cooling water pool, and further rationally utilizes the space in the research reactor process room;

[0054] 3. The present invention automatically matches the optimal cooling flow, saving cooling water resources and protecting the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0056] Figure 1 This is a schematic structural diagram of a cooling water system for a research reactor irradiation test loop provided in Example 1 of the present invention.

[0057] Icons: 1. Cooling water tank; 11. Shut-off valve; 12. Check valve; 13. Flow meter; 14. Quantity regulating valve; 15. Temperature detector; 16. Reflux regulating valve; 17. Discharge outlet valve; 2. First cooling water pump; 21. First water intake point; 22. Second water intake point; 23. First liquid level alarm point; 24. Second liquid level alarm point; 3. Second cooling water pump; 4. Loop main pump; 5. Loop heat exchange equipment. DETAILED DESCRIPTION

[0058] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0059] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0060] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not require further definition or explanation in subsequent drawings.

[0061] In the description of the present invention, it should be noted that if the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the application is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0062] It should also be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific contexts.

[0063] Example 1

[0064] A cooling water system for a research reactor irradiation test loop includes a cooling water pool 1 for storing cooling water and a first cooling water pump 2 and a second cooling water pump 3 for respectively delivering cooling water to a loop main pump 4 and a loop heat exchange device 5.

[0065] The cooling water pool 1 is provided with a first water intake point 21 and a second water intake point 22 connected to the first cooling water pump 2 and the second cooling water pump 3, respectively, and is further provided with a first liquid level alarm point 23 and a second liquid level alarm point 24 for controlling the opening and closing of an external water source, respectively. The first liquid level alarm point 23, the second liquid level alarm point 24, the first water intake point 21 and the second water intake point 22 are lowered in height in sequence;

[0066] The volume between the first liquid level alarm point 23 and the second liquid level alarm point 24 is the operating buffer volume V1, the volume between the second liquid level alarm point 24 and the first water intake point 21 is the minimum cooling water volume V2 in the initial shutdown phase, and the volume between the first water intake point 21 and the second water intake point 22 is the minimum cooling water volume V3 in the later shutdown phase.

[0067] The sum of the operating buffer volume V1, the minimum cooling water volume V2 at the initial shutdown stage, and the minimum cooling water volume V3 at the later shutdown stage is the optimal volume V of the cooling water pool 1.

[0068] In this embodiment, the inlet pipe and the outlet pipe of the first cooling water pump 2 are nuclear safety grade pipes, and the inlet pipe and the outlet pipe of the second cooling water pump 3 are non-nuclear safety grade pipes.

[0069] In this embodiment, the inlet pipe and the outlet pipe of the first cooling water pump 2 and the second cooling water pump 3 are respectively provided with a stop valve 11 for controlling the flow of cooling water and a check valve 12 for preventing the backflow of cooling water.

[0070] In this embodiment, the loop main pump 4 and the loop heat exchange device 5 are provided with a flow meter 13 for detecting the cooling water flow, a temperature detector 15 for detecting the outlet cooling water temperature, and a flow regulating valve 14 for regulating the inlet cooling water flow.

[0071] In this embodiment, the first cooling water pump 2 and the second cooling water pump 3 are provided with a reflux branch for returning the cooling water to the cooling water pool 1 and a reflux regulating valve 16 for controlling the reflux amount of the cooling water.

[0072] In this embodiment, the loop main pump 4 and the loop heat exchange device 5 are further provided with a discharge port valve 17 for controlling the discharge of cooling water.

[0073] This technical solution optimizes the distribution of cooling water flow at different time stages after fuel element shutdown, resulting in the optimal capacity of cooling water pool 1 and the optimal cooling water distribution plan. This results in a highly secure cooling water system, eliminates potential safety hazards caused by a complete interruption of external water flow, and improves the safety characteristics of the test circuit.

[0074] By designing a shared cooling water pool 1, the system complexity is simplified, the space occupied by the equipment is reduced, and the construction cost is lowered, while the reliability of the equipment and system is guaranteed by the nuclear safety level;

[0075] By establishing a comprehensive model of temperature, cooling water, and time at different stages, the cooling water flow requirements for each stage were calculated, thereby determining the optimal volume of the cooling water tank. This not only ensures the safety of the fuel elements, but also optimizes the size design of cooling water pool 1 and further rationalizes the space in the research reactor process room.

[0076] By arranging temperature detectors 15 at the cooling water outlets of each device and flow regulating valves 14 at the inlets, the optimal cooling flow rate can be automatically matched by setting the outlet temperature limit, thereby saving cooling water resources and protecting the environment.

[0077] Example 2

[0078] A design method for a research reactor irradiation test loop cooling water system includes the following steps:

[0079] S1: Determine the minimum cooling water volume V2 at the initial shutdown stage: The initial shutdown stage is when the delayed residual heat of the nuclear fuel equals the natural heat dissipation power of the system, which is recorded as t1. The amount of cooling water required to correspond to the amount of heat Q1 dissipated by the delayed residual heat of the nuclear fuel exceeding the natural heat dissipation power of the system during this time is the minimum cooling water volume V2 at the initial shutdown stage;

[0080] S2: Determine the minimum cooling water volume V3 in the late shutdown phase: The late shutdown phase is defined as the time from when the delayed residual heat power of the nuclear fuel equals the natural heat dissipation power of the system to when the fuel assembly temperature reaches the safe temperature limit of 60°C, denoted as t2. The amount of cooling water required corresponding to the heat Q2 dissipated by the fuel assembly during this time is the minimum cooling water volume V3 in the late shutdown phase.

[0081] In this embodiment, in steps S1 and S2, the delayed residual heat power W of the loop after the nuclear fuel reactor is shut down is:

[0082] W=N(t)+N S1 (t)+N S2 (t) (2)

[0083] Wherein, N(t) is the residual fission power, N(t)=N(0)0.15exp(-0.1t);

[0084] N s1 (t) is the decay power of fission products, N s1 (t) = N(0)A / 200[t -a -(t+t o ) -a ];

[0085] N s2 (t) is the decay power of neutron capture products, N s2 (t) = N(0) × 2.28 × 10 -3 c(1+α)exp

[0086] (-4.91×10 -4 t)+2.19×10 -3 c(1+α)exp(-3.14×10 -6 t);

[0087] Where, N(0) is the initial shutdown power;

[0088] t is the time variable from the shutdown moment;

[0089] t o is the initial reaction time of the fuel element, here t o =20d=1.7×10 6 ;

[0090] A=26.02;

[0091] a = 0.2834c is the conversion ratio, α is the ratio of radiation capture to fission number of U-235, c = 0.6, α = 0.2.

[0092] In this embodiment, in step S1, the amount of cooling water is calculated as follows:

[0093]

[0094] Wherein, T1 is the temperature of the cooling water in the cooling water pool (1);

[0095] T2 is the temperature of the cooling water of the discharge valve (17);

[0096] C is the specific heat capacity of water, C = 4.2KJ / (kg·℃);

[0097] ρ is the density of water, ρ = 10 -3 kg / m 3 ;

[0098] In step S2, the amount of cooling water is calculated as follows:

[0099]

[0100] Wherein, T3 is the temperature of the cooling water in the cooling water pool (1);

[0101] T4 is the temperature of the cooling water of the discharge valve (17).

[0102] In this embodiment, for ease of calculation, the natural cooling capacity K of the circuit design can be directly measured. Based on the balance between the delayed waste heat power and the natural heat dissipation capacity, we have:

[0103] W=K (5)

[0104] Through (2) and (5), the initial shutdown time t1 can be obtained as 550s.

[0105] Calculate the minimum cooling water volume V2 at the initial shutdown stage:

[0106] V2=L·t1 (6)

[0107] Wherein, L is the total cooling flow of the first cooling water pump 2 and the second cooling water pump 3, L = 51m 3 / h; V2 is 7.8m 3 .

[0108] In this embodiment, the minimum cooling water volume V3 at the end of shutdown is calculated as follows:

[0109] First, we need to calculate the temperature at the beginning and end of the shutdown. The temperature change is caused by the change of the total heat of the circuit. The calculation process of the change of the total heat of the circuit is as follows:

[0110] The circuit generates heat by slowly releasing residual heat in the initial stage of shutdown:

[0111]

[0112] The heat removed by cooling water during the initial shutdown period of the circuit:

[0113] Q1=V2·(T2-T1)C·ρ (8)

[0114] Then, the change in total heat of the circuit is:

[0115] ΔQ=Q1-Q3 (9)

[0116] Then, the temperature change of the circuit at the initial shutdown stage is:

[0117] ΔT1=ΔQ / (Cp·m) (10)

[0118] Wherein, m is the initial amount of coolant in the loop system, which is 1200 kg;

[0119] Cp is the specific heat capacity of the circuit;

[0120] During the initial shutdown period t1, the average loop temperature dropped from 290°C to 152°C. At the end of the shutdown period, the average loop temperature was reduced from 152°C to 60°C through natural cooling and the first cooling water pump 2. The enthalpies corresponding to the starting and ending temperatures are H1 and H2, respectively. Since all heat in this stage is dissipated by natural heat dissipation, we have:

[0121]

[0122] V3=L'·t2 (12)

[0123] Wherein, L' is the cooling flow rate of the first cooling water pump 2, which is 3m 3 / h; t2 is 4.9h, V3 is 14.7m 3 .

[0124] S3: Determine the operating buffer volume V1: V1 is the total flow of the cooling water system in 10 minutes under normal operating conditions;

[0125] V3=L·(1 / 6)h (13)

[0126] The V3 is 8.5m 3 .

[0127] S4: Determine the optimal volume V of the cooling water pool 1:

[0128] V=V1+V2+V3 (1)

[0129] The optimal volume of the cooling water pool 1 is 31m 3 .

[0130] Example 3

[0131] A method for using a cooling water system for a research reactor irradiation test loop comprises the following steps:

[0132] R1: Water injection operation: Control water injection to keep the liquid level in cooling water tank 1 above 31m 3 ;

[0133] R2: Operation under accident conditions;

[0134] R2.1: Initial shutdown: The first cooling water pump 2 and the second cooling water pump 3 continue to deliver cooling water to the loop main pump 4 and the loop heat exchange equipment 5 respectively until the volume level of the cooling water pool 1 is lower than 14.7m 3 ;

[0135] R2.2: Late shutdown period: the second cooling water pump 3 stops running, and the first cooling water pump 2 continues to deliver cooling water to the loop main pump 4.

[0136] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A cooling water system for a research reactor irradiation test loop, comprising a cooling water pool (1), a loop main pump (4) and a loop heat exchange device (5), characterized in that: The cooling water pool (1) is provided with a second liquid level alarm point (24) for controlling the lowest water level, a first water intake point (21) and a second water intake point (22) for supplying cooling water to the circuit main pump (4) and the circuit heat exchange device (5), respectively, and the heights of the second liquid level alarm point (24), the first water intake point (21) and the second water intake point (22) are successively lowered; The initial shutdown period is when the residual heat power of the nuclear fuel is equal to the natural heat dissipation power of the system from shutdown, which is recorded as t1. The volume between the second liquid level alarm point (24) and the first water intake point (21) is the minimum cooling water volume V2 at the initial shutdown period. The period from when the residual heat power of the nuclear fuel is equal to the natural heat dissipation power of the system to when the temperature of the fuel assembly reaches the safety temperature limit of 60°C is the late shutdown period, which is recorded as t2. The volume between the first water intake point (21) and the second water intake point (22) is the minimum cooling water volume V3 in the late shutdown period. The sum of the minimum cooling water volume V2 at the initial shutdown stage, the minimum cooling water volume V3 at the later shutdown stage, and the operating buffer volume V1 is the optimal volume V of the cooling water pool (1).

2. The cooling water system for a research reactor irradiation test circuit according to claim 1, characterized in that: The cooling water pool (1) is further provided with a first liquid level alarm point (23) for controlling the maximum water level, and the volume corresponding to the first liquid level alarm point (23) and the second liquid level alarm point (24) is the operating buffer volume V1.

3. The cooling water system for a research reactor irradiation test circuit according to claim 2, characterized in that: The invention also includes a first cooling water pump (2) and a second cooling water pump (3) for respectively delivering cooling water to the loop main pump (4) and the loop heat exchange device (5), wherein the inlet pipe and the outlet pipe of the first cooling water pump (2) are nuclear safety grade pipes, and the inlet pipe and the outlet pipe of the second cooling water pump (3) are non-nuclear safety grade pipes.

4. The cooling water system for a research reactor irradiation test circuit according to claim 3, characterized in that: The inlet pipe and outlet pipe of the first cooling water pump (2) and the second cooling water pump (3) are respectively provided with a stop valve (11) for controlling the inflow of cooling water and a check valve (12) for preventing the backflow of cooling water; a reflux branch for returning the cooling water to the cooling water pool (1) and a reflux regulating valve (16) for controlling the amount of reflux of cooling water are also provided.

5. A cooling water system for a research reactor irradiation test circuit according to any one of claims 1 to 4, characterized in that: The loop main pump (4) and the loop heat exchange device (5) are provided with a flow meter (13) for detecting the cooling water flow rate, a temperature detector (15) for detecting the outlet cooling water temperature, and a flow regulating valve (14) for regulating the inlet cooling water flow rate.

6. A cooling water system for a research reactor irradiation test circuit according to any one of claims 1 to 4, characterized in that: The loop main pump (4) and the loop heat exchange device (5) are also provided with a discharge port valve (17) for controlling the discharge of cooling water.

7. A design method for a research reactor irradiation test loop cooling water system according to any one of claims 1 to 6, characterized in that: The steps include: S1: Determine the minimum cooling water volume V2 at the initial shutdown stage: The amount of cooling water required when the residual heat released by the nuclear fuel exceeds the heat Q1 naturally dissipated by the system at the initial shutdown stage t1 is the minimum cooling water volume V2 at the initial shutdown stage; S2: Determine the minimum cooling water volume V3 in the late shutdown period: The amount of cooling water required corresponding to the heat Q2 dissipated by the fuel assembly in the late shutdown period t2 is the minimum cooling water volume V3 in the late shutdown period; S3: Determine the operating buffer volume V1: V1 is the total flow of the cooling water system within 5 minutes to 15 minutes under normal operating conditions; S4: Determine the optimal volume V of the cooling water pool (1): （1）。 8. The method for designing a cooling water system for a research reactor irradiation test circuit according to claim 7, characterized in that: In the steps S1 and S2, the delayed residual heat power W of the loop after the nuclear fuel reactor is shut down is: （2） Where N(t) is the residual fission power, N(t) = N(0) 0.15exp(-0.1t); N s1 (t) is the decay power of fission products, N s1 (t)= N(0) A / 200[t -a -(t+t o ) -a ]; N s2 (t) is the decay power of neutron capture products, N s2 (t)=N(0) ×2.28×10 -3 c(1+α)exp (-4.91×10 -4 t) +2.19×10 -3 c(1+α) exp(-3.14×10 -6 t); Where, N(0) is the initial shutdown power; t is the time variable from the shutdown moment; t o is the initial reaction time of the fuel element, here t o =20d=1.7×10 6 ; A=26.02； a=0.2834c is the conversion ratio, α is the ratio of radiation capture to fission number of U-235, c=0.6, α=0.

2.

9. A method for designing a cooling water system for a research reactor irradiation test circuit according to claim 7 or 8, characterized in that: In step S1, the amount of cooling water is calculated as follows: ；（3） Wherein, T1 is the temperature of the cooling water in the cooling water pool (1); T2 is the temperature of the cooling water at the discharge valve (17); C is the specific heat capacity of water, C=4.2KJ / (kg·℃); ρ is the density of water, ρ=10 -3 kg / m 3 ; In step S2, the amount of cooling water is calculated as follows: ；（4） Wherein, T3 is the temperature of the cooling water in the cooling water pool (1); T4 is the temperature of the cooling water of the discharge valve (17).

10. A method for using the research reactor irradiation test loop cooling water system according to any one of claims 1 to 6, characterized in that: The steps include: R1: Water injection operation: Control water injection to keep the liquid level between the first liquid level alarm point (23) and the second liquid level alarm point (24); R2: Operation under accident conditions; R2.1: Initial shutdown period: The first cooling water pump (2) and the second cooling water pump (3) continue to deliver cooling water to the loop main pump (4) and the loop heat exchange equipment (5) respectively until the liquid level of the cooling water pool (1) is lower than the first water intake point (21); R2.2: Late shutdown period: The second cooling water pump (3) stops running, and the first cooling water pump (2) continues to deliver cooling water to the loop main pump (4).

Images