Method for establishing natural circulation of pool type research reactor

Abstract

The invention discloses a method for establishing natural circulation of a pool type research reactor and belongs to the field of nuclear power. The method comprises the following steps: under an accident condition, when a pump set of the pool type research reactor stops working, injecting pressure fluid driven in a passive form into a reactor bottom chamber of the pool type research reactor, driving a coolant in a reactor core to flow from the bottom to the top, and establishing natural circulation of the coolant. According to the method, the flowing direction of the coolant in the reactor core can be quickly reversed, coolant stagnation is avoided, the overheating risk of the reactor core is reduced, and the safety of the pool type research reactor is improved.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear power, and particularly relates to a method for establishing natural circulation in a pool-type research reactor. Background Art

[0002] A pool-type research reactor is a research reactor in which the reactor core is immersed at the bottom of a cooling pool. During the normal operation of the reactor, the cooling water is forced to flow downward through the reactor core by a pump group, and then the residual heat of the reactor core is removed by the circulating flow of the cooling water in the cooling pool. When an accident occurs in the pool-type research reactor and the pump group stops working, the cooling water in the reactor core will maintain the downward flow direction due to inertia for a certain period of time, and then the flow direction will reverse and become a natural circulation from bottom to top. The time required for the kinetic energy provided by the pump group to be exhausted and the natural circulation to be established spontaneously is long, and flow stagnation may occur during the process of the reversal of the cooling water flow direction, resulting in the inability to quickly remove the residual heat of the reactor core and increasing the risk of excessive fuel temperature or even melting. Therefore, it is of positive significance to provide a method for quickly establishing natural circulation in a pool-type research reactor. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for establishing natural circulation in a pool-type research reactor to improve the safety of the pool-type research reactor under accident conditions.

[0004] According to an embodiment of the present invention, a method for establishing natural circulation in a pool-type research reactor is provided, wherein the pool-type research reactor includes a cooling pool and a reactor core, the cooling pool contains a coolant, the reactor core is immersed in the coolant, a bottom cavity is provided below the reactor core, the bottom cavity is connected to the flow channel in the reactor core, and the method for establishing natural circulation in the pool-type research reactor includes the following steps:

[0005] Under accident conditions, when the pump group of the pool-type research reactor stops working, a pressurized fluid is injected into the bottom cavity to drive the coolant in the reactor core to flow from bottom to top to establish natural circulation of the coolant, wherein the pressurized fluid is driven in a passive form.

[0006] Further, in some embodiments, the passive injection device includes a connected injection tank and a nozzle, the injection tank stores the pressurized fluid, and the nozzle is arranged towards the bottom flow channel of the reactor core.

[0007] Further, in some embodiments, the pool-type research reactor further includes a passive injection device, and the pressurized fluid is injected into the bottom cavity through the passive injection device.

[0008] Further, in some embodiments, the passive injection device includes a connected injection tank and a spray head. The injection tank stores the pressurized fluid, and the spray head is arranged facing the bottom flow channel of the reactor core.

[0009] Further, in some embodiments, the pressurized fluid is configured as water or a boric acid solution pressurized by compressed gas.

[0010] Further, in some embodiments, the compressed gas includes compressed nitrogen or compressed air.

[0011] Further, in some embodiments, the pressure of the pressurized fluid is provided by compressed gas and / or gravity.

[0012] Further, in some embodiments, a valve communicating with the cooling pool is provided on the bottom cavity of the reactor. When the coolant in the reactor core flows from the bottom to the top, the coolant in the cooling pool flows into the bottom cavity of the reactor through the valve to achieve natural circulation.

[0013] Further, in some embodiments, the valve is configured as a one-way valve leading from the cooling pool into the bottom cavity of the reactor. Description of the Drawings

[0014] Figure 1 Schematic diagram of the structure of a pool-type research reactor in one embodiment;

[0015] Figure 2 Schematic diagram of the structure of a pool-type research reactor in another embodiment;

[0016] Figure 3 Schematic diagram of the structure of a spray head in one embodiment;

[0017] Figure 4 Schematic diagram of the structure of a pool-type research reactor in yet another embodiment;

[0018] Figure 5 Schematic diagram of the structure of a pool-type research reactor in still another embodiment.

[0019] Meanings of the reference numerals: 1 - cooling pool; 2 - cooling water; 3 - reactor core; 4 - bottom cavity of the reactor; 41 - side wall body; 5 - natural circulation valve; 6 - reactor core support structure; 7 - steel cladding; 8 - passive injection device; 81 - spray head; 811 - water outlet; 82 - check valve; 83 - control valve; 84 - injection tank; 841 - compressed gas; 842 - boric acid solution; 85 - injection pipe; 86 - open injection tank; 9 - siphon break valve; 10 - hot section.

[0020] The purpose of the above-mentioned drawings is to make a detailed description of the present invention in combination with the drawings, so that those skilled in the art can understand the technical concept of the present invention, rather than aiming to limit the present invention. For the sake of concise expression, the above-mentioned drawings only schematically show the features related to the structure of the present invention, and do not strictly draw the complete structure and all details according to the actual proportion. Detailed Embodiments

[0021] The present invention will be further described in detail below with reference to specific embodiments in conjunction with the drawings.

[0022] As used herein, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein can be combined with other embodiments without structural conflict.

[0023] In the description herein, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "coupling" should be understood in a broad sense. For example, it can be a movable connection, a fixed connection, or integrated. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0024] In the description herein, terms indicating orientation or positional relationships such as "upper", "lower", "left", "right", "horizontal", "vertical", "height", "length", "width", etc. are intended to accurately describe the embodiments and simplify the description, rather than limiting the parts or structures involved to having a specific orientation, being installed or operated in a specific orientation, and should not be construed as a limitation to the embodiments herein.

[0025] In the description herein, terms such as "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order, or primary-secondary relationship of the described technical features. In the description herein, the meaning of "a plurality of" is at least two.

[0026] The pool-type research reactor is a "swimming pool" reactor for research. The core is immersed in the bottom of the reactor cooling pool, and the residual heat of the core is removed through the coolant in the cooling pool. Under normal conditions, the reactor pump group provides a forced flow driving force, and the coolant in the core flows from top to bottom to remove the heat from the core. Under accident conditions, when the pump group stops operating, due to the existence of inertia, the flow direction in the core is still maintained for a period of time, but the flow rate will gradually decrease until it is close to static. There is a certain static pressure difference between the water with lower temperature in the cooling pool beside the reactor core and the water with higher temperature on the core side. When the inertia of the downward flow is not enough to overcome the static pressure difference, the flow pattern in the core changes to natural circulation: the water in the cooling pool beside the reactor core enters the bottom of the core and mixes with the water with higher temperature on the core side. The flow in the core begins to reverse and the direction changes from bottom to top. And this direction is consistent with the convection direction of the coolant in the core after heating. Therefore, the circulation can be established and sustainable without relying on external energy supply.

[0027] The driving force for establishing the above-mentioned natural circulation is small and the establishment time is long, during which flow stagnation (flow rate is zero) may occur. Under accident conditions, the residual heat of the core cannot be quickly discharged, which may easily cause the fuel temperature to be too high or even melted.

[0028] In order to solve the above problems, an embodiment of the present invention provides a method for establishing natural circulation in a pool-type research reactor. A direct injection port of a passive injection system is set in the reactor bottom chamber. The injection box can provide a large-flow pressure fluid injection to forcibly reverse the flow direction of the coolant in the core, accelerate the establishment of natural circulation, prevent flow stagnation, quickly remove the core waste heat, and improve the safety of the research reactor.

[0029] According to one embodiment of the present invention, a method for establishing natural circulation of a pool-type research reactor is provided.

[0030] Among them, the structure of the pool-type research reactor involved is as follows: Figure 1 As shown, it includes a cooling pool 1 and a core 3, the cooling pool 1 contains cooling water 2 as a coolant, and the core 3 is completely immersed in the cooling water 2. In different embodiments, the cooling water 2 can be pure light water, heavy water, or a solution with light water or heavy water as a solvent. The cooling pool 1 has a bottom wall and a side wall. In one embodiment, the bottom wall and the side wall of the cooling pool 1 are covered with steel 7. The core 3 includes a core wall, and the semi-enclosed space formed by the core wall accommodates the fuel assembly. The core wall is formed with a coolant flow channel that runs from top to bottom, so that the cooling water 2 can flow through the fuel assembly to take away the heat generated by the fuel assembly.

[0031] Under normal operating conditions, a pump group (not shown) of the pool-type reactor drives the cooling water to flow downward through the reactor core 3, taking out the heat generated by the reactor core 3. A reactor bottom chamber 4 is provided at the bottom of the reactor core 3. The reactor bottom chamber 4 is jointly surrounded by the bottom surface of the reactor core 3, the steel cladding 7 forming the bottom wall of the cooling pool 1, and the circumferentially surrounding side wall body 41. The bottom flow channel of the reactor core 3 is only connected to the reactor bottom chamber 4.

[0032] In a preferred embodiment, the reactor core support structure 6 that supports the reactor core 3 is an integral structure with the side wall body 41. In other embodiments, an independent structure can also be used to support the reactor core 3, such as support columns independent of the side wall body 41. A valve is provided on the side wall body 41 of the reactor bottom chamber 4, and through this valve, the reactor bottom chamber 4 is connected to the cooling pool 1.

[0033] In a preferred embodiment, the valve is configured as a natural circulation valve 5. The natural circulation valve 5 is a one-way valve, and in the open state, it allows the cooling water in the cooling pool 1 to flow from the cooling pool 1 to the inside of the reactor bottom chamber 4 through the natural circulation valve 5.

[0034] Under normal operating conditions, the natural circulation valve 5 is closed, and the cooling water 2 flows downward through the reactor core 3 into the reactor bottom chamber 4 and is pumped out through the hot section 10 in the reactor circulation loop, and finally flows back to the cooling pool 1 through the cold section loop (not shown) in the circulation pipeline and mixes with the remaining cooling water 2.

[0035] In one embodiment, a siphon break valve 9 communicating with the cooling pool is provided on the hot section 10, and the position of the siphon break valve 9 is higher than the top of the reactor core 3.

[0036] The reactor bottom chamber 4 is connected to the passive injection device 8. The passive injection device 8 can inject a pressurized fluid into the reactor bottom chamber 4. The pressurized fluid includes light water, heavy water or boric acid solution (specifically including solutions containing boric acid, boron-containing salts, etc.) having a certain pressure (the pressure is greater than the coolant pressure in the reactor bottom chamber 4 under normal operating conditions). The pressure of the pressurized fluid can come from high-pressure gas, or from gravity, or a mixture of high-pressure gas and gravity.

[0037] In the embodiment as Figure 1 shown, the passive injection device 8 is provided with a closed injection tank 84. The injection tank 84 stores compressed gas 841 and boric acid solution 842. The injection tank 84 is connected to the reactor bottom chamber 4 through an injection pipe 85. A check valve 82 and a control valve 83 are provided on the injection pipe 85. The injection pipe 85 is directly connected to the side wall body 41 of the reactor bottom chamber 4, and the pressurized boric acid solution 842 is directly injected into the reactor bottom chamber 4, further pushing the reversal of the flow direction of the cooling water 2.

[0038] Based on this pool-type research reactor, under accident conditions, the method for quickly establishing natural circulation is as follows: When the pump group of the pool-type reactor stops rotating, open the control valve 83 (in the preferred embodiment, the control valve 83 automatically opens after the pump group stops working; in some embodiments, it can also be opened according to a manual command). The boric acid solution 842 is injected into the bottom chamber 4 in a passive form driven by the compressed gas 841. Since the natural circulation valve 5 is a one-way valve, the boric acid solution 842 cannot enter the cooling pool through the natural circulation valve 5. The fluid pressure in the bottom chamber increases and forces the cooling water 2 flowing downward through the core 3 to reverse (flow from bottom to top). After the pressure in the injection tank 84 is exhausted, the cooling water 2 in the cooling pool 1 replenishes the bottom chamber 4 through the natural circulation valve 5, thus quickly establishing and maintaining the natural circulation between the core 3 and the cooling pool 1.

[0039] Reference Figure 2 and Figure 3 As shown, in another embodiment, a nozzle 81 is provided at the end of the injection pipe 85. The nozzle 81 is integrally arranged in a disk shape, and a plurality of water outlets 811 are arranged on its upper surface. The upper surface of the nozzle 81 faces the bottom flow channel of the core 3. During passive injection, the nozzle 81 can directly spray the boric acid solution 842 onto the bottom flow channel of the core 3 to force the reverse flow of the cooling water in the core. At the same time, the boron element in the boric acid solution 842 has good neutron absorption performance, which can effectively absorb the neutrons generated by the core 3, reduce the heat generation power of the core 3, and further reduce the risk of fuel melting in the core 3. In the preferred embodiment, the water outlets 811 are arranged on a plurality of concentric circles on the upper surface of the nozzle 81 and are evenly arranged. The dispersed water outlets help to provide a relatively uniform driving force to reverse the overall flow direction of the coolant in the core 3.

[0040] In yet another embodiment, as Figure 4 shown, the injection pipe 85 may not be connected to the bottom chamber 4, but may be connected to the hot section 10 of the pool-type reactor. The interface position is set below the siphon break valve 9, and the pressurized boric acid solution 842 is injected into the bottom chamber 4 through the inherent pipeline of the hot section 10 to simplify the structure of the bottom chamber 4.

[0041] In different embodiments, when using a closed injection tank 84, the compressed gas can be nitrogen or air; in some embodiments, the boric acid solution 842 can also be replaced with water.

[0042] In still another embodiment, as Figure 5 shown, the closed injection tank 84 can also be replaced with an open injection tank 86. The installation position of the open injection tank 86 is higher than the liquid level of the cooling water 2 in the cooling pool 1, and the gravity is used to provide the injection pressure of the boric acid solution 842 to inject the boric acid solution 842 into the bottom chamber 4.

[0043] In the above embodiments, during the process of injecting the boric acid solution 842 into the bottom chamber 4 of the reactor, since the natural circulation valve 5 is a one-way valve group, the boric acid solution 842 will not directly enter the cooling pool 1 through the natural circulation valve 5. Instead, it will cause the pressure in the bottom chamber 4 of the reactor to rise rapidly, accelerating the reverse process of the flow direction of the cooling water 2. After the flow direction of the cooling water 2 starts to reverse, as the boric acid solution 842 is depleted, the cooling water 2 outside the bottom chamber 4 joins the circulation through the natural circulation valve 5, and finally the establishment of natural circulation is achieved quickly and stably.

[0044] In some other embodiments, the natural circulation valve 5 can be replaced by an ordinary valve from a one-way valve. In these embodiments, it is necessary to control the opening of the valve in real time. During the operation of the passive injection device 8, the valve needs to be kept closed to prevent the fluid in the bottom chamber 4 of the reactor from leaking through the valve into the cooling pool 1 and hindering the establishment of natural circulation. After the passive injection device 8 stops injecting, the valve needs to be opened in time so that the coolant in the cooling pool 1 can be replenished into the bottom chamber 4 of the reactor in time to maintain the continuous natural circulation. Specifically, the valve can be controlled by a time-delay switch and automatically opened a certain time after the passive injection device 8 is started. Alternatively, a pressure or liquid level sensor can be set in the passive injection device 8 and signal-connected to the controller of the valve, and the valve is controlled to open when the pressure or liquid level drops to a given threshold.

[0045] The method for quickly establishing natural circulation of a pool-type research reactor provided in the above embodiments can effectively shorten the time for establishing natural circulation of the core cooling water after the shutdown of the pool-type research reactor pump group under accident conditions, accelerate the removal of the core residual heat, avoid the long-term stagnation of the cooling water, reduce the risk of core overheating and melting, and improve the safety and reliability of the pool-type research reactor.

[0046] The purpose of the above embodiments is to further elaborate on the present invention in conjunction with the drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope disclosed by the present invention, optimizing or equivalently replacing the component structures or method steps involved, and combining the implementation manners in different embodiments without conflict in structure and principle all fall within the protection scope of the present invention.

Claims

1. A method for establishing natural circulation of a pool-type research reactor, for use in a pool-type research reactor, wherein the pool-type research reactor comprises a cooling pool and a core, the cooling pool contains a coolant, the core is immersed in the coolant, a bottom chamber is provided below the core, the bottom chamber is connected to a flow channel in the core, and is characterized in that: The method for establishing natural circulation of a pool-type research reactor comprises the following steps: Under accident conditions, when the pump group of the pool-type research reactor stops working, pressurized fluid is injected into the bottom chamber of the reactor to drive the coolant in the core to flow from the bottom to the top to establish a natural circulation of the coolant, wherein the pressurized fluid is driven in a passive form.

2. The method for establishing natural circulation of a pool-type research reactor according to claim 1, characterized in that: The pool-type research reactor further comprises a passive injection device, through which the pressure fluid is injected into the reactor bottom chamber.

3. The method for establishing natural circulation of a pool-type research reactor according to claim 2, characterized in that: The passive injection device comprises an injection box and a nozzle which are connected to each other. The injection box stores the pressure fluid, and the nozzle is arranged toward the bottom flow channel of the core.

4. The method for establishing natural circulation of a pool-type research reactor according to claim 1, 2 or 3, characterized in that: The pressure fluid is configured as water or a boron-containing solution pressurized by compressed gas.

5. The method for establishing natural circulation of a pool-type research reactor according to claim 4, characterized in that: The compressed gas includes compressed nitrogen or compressed air.

6. The method for establishing natural circulation of a pool-type research reactor according to claim 1, 2 or 3, characterized in that: The pressure of the pressure fluid is provided by compressed gas and / or gravity.

7. The method for establishing natural circulation of a pool-type research reactor according to claim 1, 2 or 3, characterized in that: The stack bottom chamber is provided with a valve connected to the cooling pool. When the coolant in the core flows from the bottom to the top, the coolant in the cooling pool flows into the stack bottom chamber through the valve to achieve natural circulation.

8. The method for establishing natural circulation of a pool-type research reactor according to claim 7, characterized in that: The valve is configured as a one-way valve from the cooling pool to the stack bottom chamber.

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