Cooling water system for research reactor irradiation test loop and design and use method thereof

Abstract

The invention provides a cooling water system for a research reactor irradiation test loop and a design and use method thereof, relates to the technical field of irradiation in nuclear fuel and material reactors, and solves the technical problem of potential safety hazards caused by complete cutoff of an external water source of an existing cooling water system. A corresponding volume between a first liquid level alarm point and a second liquid level alarm point is an operation buffer volume V1, a volume between the second liquid level alarm point and a first water taking point is a minimum cooling water volume V2 at the initial stage of reactor shutdown, and a volume between the first water taking point and a second water taking point is a minimum cooling water volume V3 at the later stage of reactor shutdown; the sum of V1, V2 and V3 is the optimal volume V of the cooling water tank. According to the invention, the complexity of the system is simplified, the space occupied by equipment is reduced, the construction cost is reduced, and the reliability of the equipment and the system is ensured through the nuclear security level; the safety of the fuel element is ensured, the size design of the cooling water tank is optimized, and the space between research reactor processes is further reasonably utilized.

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 loop is used to simulate the real working environment of the fuel element, provide specific temperature, flow, and water chemical parameters, and verify the physical, thermal, and manufacturing process performance of the fuel element. The loop cooling water system usually serves as the final heat sink of the loop, deriving the heat of the fuel element in the loop and ensuring that the temperature of the fuel element and the main coolant system is maintained within a specific range. Therefore, the cooling water system is directly related to the safety of the main coolant system and the fuel element.

[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 the traditional system solution, the cooling water system is divided into a safety-level cooling water system and a non-safety-level cooling water system. The safety-level cooling water system is used to supply water to equipment with safety functions such as the main pump, while the non-safety-level cooling water system is used to supply water to non-safety-level equipment such as the heat exchanger. The system design is relatively complex and the construction cost is high. Secondly, the traditional design scheme does not calculate the optimal capacity of the cooling water tank volume, and often uses the most conservative capacity for envelope analysis, resulting in a large volume of the water tank, occupying too much area, and wasting 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 cannot be adjusted in time according to the temperature fluctuations of the equipment. And when an accident occurs, it is easy to fail to reasonably distribute the cooling water in the cooling water tank, resulting in the failure of effective cooling of high-priority overheating equipment, causing certain safety hazards. 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 the complete interruption of external water source in the existing cooling water system may bring potential safety hazards.

[0006] The embodiments of the present invention are implemented by the following technical solutions:

[0007] A cooling water system for a research reactor irradiation test loop, comprising a cooling water pool, a loop main pump and a loop heat exchange device, wherein 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 exchange device respectively, and the heights of the second liquid level alarm point, the first water intake point and the second water intake point are successively reduced;

[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 to 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 at the initial shutdown period.

[0009] The late shutdown period is 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 safe temperature limit of 60°C, which is recorded 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 inlet 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 port valve for controlling the discharge of cooling water.

[0016] A design method for a cooling water system of an irradiation test loop of a research reactor comprises 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 later stage of shutdown: the amount of cooling water required corresponding to the heat Q2 dissipated by the fuel assembly in the later stage of shutdown t2 is the minimum cooling water volume V3 in the later stage of shutdown;

[0019] S3: Determine the operation buffer volume V1: V1 is the total flow of the cooling water system for 5min-15min 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 the 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 the 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, in this case t o =20d=1.7×106 ;

[0030] A=26.02;

[0031] a=0.2834c is the conversion ratio, α is the ratio of the radiation capture and 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 port 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 port 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 liquid level alarm point and the second liquid level alarm point;

[0044] R2: Operation under accident conditions;

[0045] R2.1: Initial shutdown period: The first cooling water pump and the second cooling water pump continue to deliver cooling water to the loop main pump and the loop heat exchange equipment respectively until the liquid level of the cooling water pool is lower than the first water intake point;

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

[0047] By adopting this technical solution, the optimal capacity of the cooling water pool and the optimal cooling water distribution plan are obtained by optimizing the cooling water flow at different time stages after the fuel element is shut down, thereby designing a cooling water system with higher safety, eliminating the safety hazards caused by the complete interruption of the external water source, and improving the safety characteristics of the test circuit;

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

[0049] By establishing a comprehensive model of temperature, cooling water and time at different stages, the cooling water flow requirements at each stage were calculated, thereby determining the optimal volume of the cooling water tank, which 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 process room of the research reactor;

[0050] By installing temperature detectors at the cooling water outlets of each device and flow regulating valves at the inlets, the optimal cooling flow rate can be automatically matched by setting the outlet temperature limit, thus saving cooling water resources and protecting the environment.

[0051] The technical solution of the embodiment of the present invention has 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, reduces the construction cost, and at the same time ensures the reliability of the equipment and system through the nuclear safety level;

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

[0054] 3. The present invention automatically matches the optimal cooling flow rate, saves cooling water resources and protects 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 drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0056] Figure 1 This is a schematic diagram of the structure 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 port 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] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 here 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 claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are 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, further definition and explanation thereof is not required 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 used. 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] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" 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 indirectly connected 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.

[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 respectively connected to the first cooling water pump 2 and the second cooling water pump 3, and is also provided with a first liquid level alarm point 23 and a second liquid level alarm point 24 respectively used to control the opening and closing of an external water source, and 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 operation 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 at the initial shutdown stage, and the volume between the first water intake point 21 and the second water intake point 22 is the minimum cooling water volume V3 at the later shutdown stage;

[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 inflow 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 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.

[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] By adopting this technical solution, the optimal capacity of the cooling water pool 1 and the optimal cooling water distribution scheme are obtained by optimizing the cooling water flow at different time stages after the fuel element is shut down, thereby designing a cooling water system with higher safety, eliminating the safety hazards caused by the complete interruption of the external water source, and improving the safety characteristics of the test circuit;

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

[0075] By establishing a comprehensive model of temperature, cooling water and time at different stages, the cooling water flow requirements at each stage were calculated, thereby determining the optimal volume of the cooling water tank, which not only ensured the safety of the fuel elements, but also optimized the size design of the cooling water pool 1, further making rational use of the space in the process room of the research reactor;

[0076] By providing a temperature detector 15 at the cooling water outlet of each device and a flow regulating valve 14 at the inlet, the outlet temperature limit is set to automatically match the optimal cooling flow, thereby saving cooling water resources and protecting the environment.

[0077] Example 2

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

[0079] S1: Determine the minimum cooling water volume V2 at the initial shutdown stage: The initial shutdown stage is when the power of the nuclear fuel delayed residual heat is equal to the power of the system's natural heat dissipation, which is recorded as t1. During this time, the amount of cooling water required for the amount of heat Q1 that the nuclear fuel delayed residual heat exceeds the system's natural heat dissipation is the minimum cooling water volume V2 at the initial shutdown stage;

[0080] S2: Determine the minimum cooling water volume V3 in the later stage of shutdown: From the time when the residual heat power of nuclear fuel is equal to the natural heat dissipation power of the system to the time when the temperature of the fuel assembly reaches the safe temperature limit of 60°C, it is the later stage of shutdown, recorded 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 later stage of shutdown;

[0081] In this embodiment, in the 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 the 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, in this case t o =20d=1.7×10 6 ;

[0090] A=26.02;

[0091] a=0.2834c is the conversion ratio, α is the ratio of the radiation capture and 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 port 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 port valve (17).

[0102] In this embodiment, for the convenience of calculation, the natural cooling capacity K of the circuit design can be directly measured. According to 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), we can calculate that the initial shutdown time t1 is 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:

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

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

[0111]

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

[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 loop 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] In the initial shutdown period t1, the average temperature of the loop dropped from 290℃ to 152℃. At the end of the shutdown period, the average temperature of the loop was reduced from 152℃ to 60℃ through natural cooling and the first cooling water pump 2. The enthalpy corresponding to the starting point and the end point of the temperature are H1 and H2 respectively. According to the fact that the heat in this stage is all discharged 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 operation 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 higher than 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: 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 only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope 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 loop main pump (4) and the loop 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, recorded as t2, 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 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. A cooling water system for a research reactor irradiation test loop according to claim 1, characterized in that: The cooling water pool (1) is also 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 operation buffer volume V1.

3. A cooling water system for a research reactor irradiation test loop according to claim 2, characterized in that: It also includes a first cooling water pump (2) and a second cooling water pump (3) for conveying cooling water to the loop main pump (4) and the loop heat exchange device (5) respectively. 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. A cooling water system for a research reactor irradiation test loop 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 loop 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 loop 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 later stage of shutdown: the amount of cooling water required corresponding to the heat Q2 dissipated by the fuel assembly in the later stage of shutdown t2 is the minimum cooling water volume V3 in the later stage of shutdown; S3: Determine the operation buffer volume V1: V1 is the total flow of the cooling water system within 5min-15min under normal operating conditions; S4: Determine the optimal volume V of the cooling water pool (1): V=V1+V2+V3. (1).

8. A method for designing a cooling water system for a research reactor irradiation test loop according to claim 7, characterized in that: In the steps S1 and S2, the slow-release residual heat power W of the loop after the nuclear fuel reactor is shut down is: W =N(t)+N S1 (t)+N S2 (t) (2) Wherein, N(t) is the residual fission power, N(t)=N(0)0.15exp(-0.1t); N s1 (t) is the decay power of the 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, in this case t o =20d=1.7×10 6 ; A＝26.02； a=0.2834c is the conversion ratio, α is the ratio of the radiation capture and 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 loop according to claim 7 or 8, characterized in that: In step S1, the amount of cooling water is calculated as follows: Wherein, T1 is the temperature of the cooling water in the cooling water pool (1); T2 is the temperature of the cooling water of the discharge port 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: 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 port valve (17).

10. A method for using a cooling water system for a research reactor irradiation test loop 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).

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