Passive residual heat removal system of fuel salt discharge tank

Abstract

The invention relates to a passive residual heat removal system of a fuel salt discharge tank, a heat transfer working medium is in a solid state at room temperature and is in a liquid state after being heated, the passive residual heat removal system comprises the fuel salt discharge tank, a salt discharge pipe, a natural circulation loop, an air cooler and a circulation keeping heat exchange device, the fuel salt discharge tank is communicated with the reactor core of the nuclear reactor through a salt discharge pipe, and the fuel salt discharge tank is respectively communicated with the air cooler and the circulation keeping heat exchange device through a natural circulation loop; wherein the circulation keeping heat exchange device is in thermal contact with a molten salt reactor main loop pipeline, so that heat loss of the passive residual heat removal system is compensated through heat energy of a normal working loop. According to the passive residual heat removal system, a heat transfer working medium is non-water and is in a standby state when a reactor normally works, the natural circulation fluid is kept in a molten liquid state and slowly and naturally circulates, once an accident occurs, reactor core fuel salt is discharged into the discharge tank, and the natural circulation fluid in the molten liquid state can rapidly establish natural circulation to discharge decay heat.

Description

Technical Field

[0001] The present invention relates to thermal management of a molten salt reactor, and more particularly to a passive residual heat removal system of a fuel salt discharge tank. Background Art

[0002] As a fourth-generation nuclear reactor, the molten salt reactor is the only liquid fuel nuclear reactor. Compared with other reactor types, the molten salt reactor has good inherent safety, nuclear non-proliferation and economic characteristics.

[0003] After an accident occurs in a reactor, even if the reactor is shut down urgently, decay heat will continue to be generated. This residual heat is still considerable for a considerable period of time and needs to be removed to the final heat sink through a specially designed residual heat removal system. Otherwise, the accumulated heat in the reactor will cause the temperature to rise, which may lead to the failure of the reactor safety barrier, causing radioactive release and causing serious nuclear safety accidents.

[0004] The residual heat removal system is divided into active residual heat removal system and passive residual heat removal system. The difference between the two is that the active residual heat removal system must rely on external power or external action, while the passive residual heat removal system does not require external action and is completely driven by natural phenomena. It can be seen that the passive residual heat removal system can fundamentally solve the safety of nuclear reactors under accidents.

[0005] As early as the 1960s, Oak Ridge National Laboratory (ORNL) in the United States adopted a passive heat exchange method in the design of the MSRE salt discharge tank for the molten salt reactor. For details, see RC Robertson and SE Beall's MSRE design and operation report published by the US Atomic Energy Commission in 1965. The working principle of MSRE is: the cooling water at the bottom of the steam drum flows into the water inlet pipe through the water inlet of the shell and tube heat exchange element and flows downward. At the bottom of the shell, it turns upward and enters the annular cavity and is heated to boiling. The steam enters the upper part of the steam drum along the annular cavity and flows to the condenser along the steam pipeline. The condensed water returns to the steam drum under the action of gravity and enters the water inlet pipe, forming a closed natural cycle. Existing passive residual heat removal technologies, such as the passive residual heat removal systems, experimental devices and heat exchange devices for molten salt reactors disclosed in CN201310286718.7, CN201610899803.4, CN201710566887.4 and CN202011538069.1, all use the above-known MSRE scheme for passive heat exchange principles, and water is used as the heat transfer medium. In the absence of water, the above-mentioned existing technical solutions cannot solve the problem of residual heat removal. Summary of the invention

[0006] In order to solve the problem caused by the use of water as a heat transfer medium in the above-mentioned prior art, the present invention provides a passive waste heat removal system for a fuel salt discharge tank.

[0007] According to the passive waste heat removal system of the fuel salt discharge tank of the present invention, its heat transfer medium is solid at room temperature and liquid after heating. The passive waste heat removal system includes a fuel salt discharge tank, a salt discharge pipe, a natural circulation loop, an air cooler and a circulation maintaining heat exchange device. The fuel salt discharge tank is connected to the nuclear reactor core through the salt discharge pipe, and the fuel salt discharge tank is connected to the air cooler and the circulation maintaining heat exchange device through the natural circulation loop. The circulation maintaining heat exchange device is in thermal contact with the main loop pipeline of the molten salt reactor to compensate for the heat loss of the passive waste heat removal system through the heat energy of the normal working loop.

[0008] In a preferred embodiment, the fuel salt discharge tank has a natural circulation inlet and a natural circulation outlet, the natural circulation loop has a first natural circulation loop hot section, a second natural circulation loop hot section and a natural circulation loop cold section, and the air cooler has an air cooler primary side inlet and an air cooler primary side outlet, wherein the two ends of the first natural circulation loop hot section are respectively connected to the natural circulation outlet and the circulation maintaining heat exchange device, the two ends of the second natural circulation loop hot section are respectively connected to the circulation maintaining heat exchange device and the primary side inlet of the air cooler, and the two ends of the natural circulation loop cold section are respectively connected to the primary side outlet of the air cooler and the natural circulation inlet, forming a natural circulation loop.

[0009] In a preferred embodiment, in the natural circulation loop, the power source of the natural circulation fluid flow is the height difference H1 between the center of the fuel salt discharge tank and the center of the air cooler and the height difference H2 between the center of the circulation maintaining heat exchange device and the center of the air cooler.

[0010] In a preferred embodiment, the fuel salt discharge tank includes a plurality of fuel salt discharge tank heat exchange elements, an upper tube sheet, a lower tube sheet, a side wall, an upper head, a lower head, a lower chamber and an upper chamber, wherein the upper tube sheet and the lower tube sheet are spaced apart from each other to accommodate the core fuel salt therebetween, the fuel salt discharge tank heat exchange elements are installed in the side wall through the upper tube sheet and the lower tube sheet, the lower head is connected to the side wall to define a lower chamber below the lower tube sheet, the upper head is connected to the side wall to define an upper chamber above the upper tube sheet, the lower chamber and the upper chamber are connected through the fuel salt discharge tank heat exchange elements to accommodate a natural circulation fluid therein, and the core fuel salt and the natural circulation fluid perform heat exchange in the fuel salt discharge tank through the fuel salt discharge tank heat exchange elements.

[0011] In a preferred embodiment, the fuel salt discharge tank further has an exhaust port connected to the fuel salt inlet, the exhaust port is located on the side wall close to the upper tube sheet, and the liquid level of the core fuel salt filled between the upper tube sheet and the lower tube sheet does not submerge the exhaust port.

[0012] In a preferred embodiment, the circulation maintaining heat exchange device includes a plurality of circulation maintaining heat exchange device heat exchange elements, which are tightly fixed around the main loop pipeline of the molten salt reactor to achieve thermal contact.

[0013] According to the passive residual heat removal system of the fuel salt discharge tank of the present invention, the heat transfer medium is non-water. When the reactor is operating normally, the main circuit operates normally, and the heat energy transmitted by the main circuit compensates the heat loss of the passive residual heat removal system through the circulation and heat exchange device to maintain its standby state. At this time, the natural circulation fluid is in a molten liquid state and circulates slowly naturally to avoid heating by an additional heating device. The heat energy of the nuclear reactor is used to compensate the heat loss of the passive residual heat removal system when it is on standby, and the natural circulation fluid is prevented from being blocked by over-freezing. The power source of the natural circulation is H2. Once an accident occurs, after the core fuel salt is discharged into the fuel salt discharge tank, the molten liquid natural circulation fluid can quickly establish a natural circulation to discharge decay heat, and the passive heat removal function can be immediately put into operation. The power source of the natural circulation is H1. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the overall structure of a molten salt reactor cooling system with a fuel salt discharge tank according to a preferred embodiment of the present invention.

[0015] Figure 2 yes Figure 1 Schematic diagram of the structure of the fuel salt discharge tank.

[0016] Figure 3 yes Figure 1 Schematic diagram of the structure of the circulation maintaining heat exchange device.

[0017] Figure 4 It is a structural schematic diagram of a fuel salt discharge tank of a molten salt reactor cooling system according to another preferred embodiment of the present invention. DETAILED DESCRIPTION

[0018] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.

[0019] like Figure 1 As shown, the passive residual heat removal system of the fuel salt discharge tank according to a preferred embodiment of the present invention comprises a fuel salt discharge tank 1, a natural circulation loop 2, an air cooler 3, a circulation holding heat exchange device 4 and a salt discharge pipe 6, wherein the fuel salt discharge tank 1 is connected to the nuclear reactor core (not shown) through the salt discharge pipe 6, the fuel salt discharge tank 1 is respectively connected to the air cooler 3 and the circulation holding heat exchange device 4 through the natural circulation loop 2, and the circulation holding heat exchange device 4 is in thermal contact with the main loop pipeline 7 of the molten salt reactor. It should be understood that each pipeline and equipment of the molten salt reactor cooling system can be coated with a heating and insulation device.

[0020] Among them, the primary side of the air cooler 3 refers to the heat source side, and the secondary side refers to the heat load side (i.e., the cold side). The primary side fluid transfers heat to the secondary side fluid through the partition heat exchange in the air cooler 3. For example, in a shell and tube heat exchanger, if the heat source fluid runs inside the tube, the inside of the tube is the primary side and the outside of the tube is the secondary side. It can also be exchanged. If the heat source fluid runs outside the tube, the outside of the tube is the primary side and the inside of the tube is the secondary side. The difference depends on which side the heat source is on. Specifically, the natural circulation fluid in the natural circulation loop 2 exchanges heat with the air in the air cooler 3. The natural circulation fluid can be a molten salt, or it can be a liquid metal, heat transfer oil, or other fluid that is liquid at high temperature. The air cooler 3 is placed in the air cooling tower 5, and the secondary side of the air cooler 3 discharges heat to the atmosphere through natural convection heat exchange of air. It should be understood that the structural type of the air cooler 3 can be diverse, such as U-tube type, spiral tube type, plate type, etc.

[0021] like Figure 1 As shown, the fuel salt discharge tank 1 includes a fuel salt inlet 1 - 1 , and both ends of the salt discharge pipe 6 are respectively connected to the nuclear reactor core (not shown) and the fuel salt inlet 1 - 1 , so that the fuel salt in the nuclear reactor core is discharged into the fuel salt discharge tank 1 .

[0022] like Figure 2 As shown, the fuel salt discharge tank 1 includes a plurality of fuel salt discharge tank heat exchange elements 1-4, an upper tube sheet 1-8, a lower tube sheet 1-9 and a side wall 1-12, wherein the fuel salt discharge tank heat exchange element 1-4 is fixedly installed in the side wall 1-12 through the upper tube sheet 1-8 and the lower tube sheet 1-9 spaced apart from each other. The fuel salt discharge tank 1 also has an exhaust port 1-5 connected to the fuel salt inlet 1-1, which is connected to the gas path system (not shown, which is filled with sinus gas) and is located on the side wall 1-12 near the upper tube sheet 1-8. When the core fuel salt is emptied from the core of the nuclear reactor, the space between the upper tube sheet 1-8 and the lower tube sheet 1-9 is filled with the core fuel salt, and the liquid level reaches the fuel salt liquid level 8, and the exhaust port 1-5 is not submerged. It should be understood that the fuel salt discharge tank heat exchange element 1-4 can be a straight tube, a longitudinal fin tube, a twisted tube, a serpentine tube (or a spiral tube), etc.

[0023] like Figure 2As shown, the fuel salt discharge tank 1 includes a lower chamber 1-2, an upper chamber 1-3, an upper head 1-10 and a lower head 1-11, wherein the lower head 1-11 is connected to the side wall 1-12 to define the lower chamber 1-2 below the lower tube sheet 1-9, and the upper head 1-10 is connected to the side wall 1-12 to define the upper chamber 1-3 above the upper tube sheet 1-8, and the lower chamber 1-2 and the upper chamber 1-3 are connected through the fuel salt discharge tank heat exchange element 1-4, so that the core fuel salt and the natural circulation fluid are heat exchanged in the fuel salt discharge tank 1 through the fuel salt discharge tank heat exchange element 1-4. It should be understood that the shapes of the upper head 1-10 and the lower head 1-11 are not limited, and can be elliptical heads, flat heads or other shapes.

[0024] like Figure 3 As shown, the circulating heat exchange device 4 includes a plurality of circulating heat exchange device heat exchange elements 4-1, which are tightly fixed around the main loop pipe 7 to achieve thermal contact, and achieve heat exchange through heat conduction, heat radiation and contact heat conduction. It should be understood that the circulating heat exchange device 4 can be of various types, such as tube-in-tube type, spiral plate type, spiral tube type, microchannel plate type, etc. The circulating heat exchange device 4 and the main loop pipe section 7 where it is located can be structurally integrated to form a heat exchanger, such as a shell-and-tube heat exchanger.

[0025] like Figure 1 and Figure 2 As shown, the fuel salt discharge tank 1 has a natural circulation inlet 1-6 and a natural circulation outlet 1-7, the natural circulation loop 2 has a first natural circulation loop hot section 2-1-1, a second natural circulation loop hot section 2-1-2 and a natural circulation loop cold section 2-2, and the air cooler 3 has an air cooler primary side inlet 3-1 and an air cooler primary side outlet 3-2, wherein the two ends of the first natural circulation loop hot section 2-1-1 are respectively connected to the natural circulation outlet 1-7 and the circulation holding heat exchange device 4, the two ends of the second natural circulation loop hot section 2-1-2 are respectively connected to the circulation holding heat exchange device 4 and the air cooler primary side inlet 3-1, and the two ends of the natural circulation loop cold section 2-2 are respectively connected to the air cooler primary side outlet 3-2 and the natural circulation inlet 1-6, forming a natural circulation loop. In the natural circulation loop, the power source of the natural circulation fluid flow is the height difference H1 between the center of the fuel salt discharge tank 1 and the center of the air cooler 3 and the height difference H2 between the center of the circulation holding heat exchange device 4 and the center of the air cooler 3, as shown in FIG. Figure 1 shown.

[0026] In this embodiment, the natural circulation inlet 1-6 is arranged on the lower head 1-11, and the cold section 2-2 of the natural circulation loop directly enters the lower chamber 1-2 through the natural circulation inlet 1-6. Figure 2In another embodiment, the natural circulation inlet 1-6 is arranged on the upper head 1-10, and the natural circulation loop cold section 2-2 passes through the natural circulation inlet 1-6, and then passes through the upper tube sheet 1-8 and the lower tube sheet 1-9 in sequence and enters the lower chamber 1-2. Figure 4 shown.

[0027] Under normal operation of the nuclear reactor, the main loop works normally to carry out nuclear heat. At the same time, after the natural circulation fluid passes through the circulation and heat exchange device 4, the temperature rises, the density is low, and it flows upward, and flows through the second natural circulation loop hot section 2-1-2 and the air cooler primary side inlet 3-1 in sequence. After the heat exchange on the primary side of the air cooler 3, the temperature drops, the density is high, and it flows downward, and flows through the air cooler primary side outlet 3-2, the natural circulation loop cold section 2-2, the lower chamber 1-2, the fuel salt discharge tank heat exchange element 1-4, the upper chamber 1-3 and the first natural circulation loop hot section 2-1-1 in sequence, and finally returns to the circulation and heat exchange device 4 to form a cycle.

[0028] In the case of nuclear reactor accident shutdown and fuel salt discharge from the core, the fuel salt in the core of the nuclear reactor flows through the salt discharge pipe 6 and enters the fuel salt discharge tank 1 through the fuel salt inlet 1-1. At this time, the decay heat of the core fuel salt increases the temperature of the natural circulation fluid in the heat exchange element 1-4 of the fuel salt discharge tank through the partition heat exchange, and the density is small, and it flows upward and enters the upper chamber 1-3, and flows through the first natural circulation loop hot section 2-1-1, the circulation holding heat exchange device 4, the second natural circulation loop hot section 2-1-2 and the air cooler primary side inlet 3-1 in sequence through the natural circulation outlet 1-7. After the heat exchange on the primary side of the air cooler 3, the temperature is reduced, the density is large, and it flows downward, and flows through the air cooler primary side outlet 3-2 and the natural circulation loop cold section 2-2 in sequence, and enters the lower chamber 1-2 through the natural circulation inlet 1-6, and finally returns to the fuel salt discharge tank heat exchange element 1-4, forming a natural cycle.

[0029] In the present invention, the main loop fluid and the natural circulation fluid can be the same or different. The entire system does not use water and is widely applicable to waterless areas. The passive residual heat removal system is in standby mode during the normal operation of the nuclear reactor and does not require heating by an additional heating device. The thermal energy of the nuclear reactor is used to compensate for the heat loss of the passive residual heat removal system, preventing the heat transfer medium from being overfrozen and clogging, simplifying the system, and improving inherent safety and economy. In the event of an accidental shutdown of the nuclear reactor and the discharge of fuel salt from the core, the fuel salt discharge tank is cooled without water and completely relies on passive effects to discharge the decay heat.

[0030] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiment of the present invention can also be modified in various ways. That is, all simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. A passive waste heat removal system for a fuel salt discharge tank, characterized in that: The heat transfer medium of the passive waste heat removal system is solid at room temperature and liquid after heating. The passive waste heat removal system includes a fuel salt discharge tank, a salt discharge pipe, a natural circulation loop, an air cooler and a circulation maintenance heat exchange device. The fuel salt discharge tank is connected to the nuclear reactor core through the salt discharge pipe, and the fuel salt discharge tank is connected to the air cooler and the circulation maintenance heat exchange device through the natural circulation loop. The circulation maintenance heat exchange device is in thermal contact with the main loop pipeline of the molten salt reactor to compensate for the heat loss of the passive waste heat removal system through the heat energy of the normal working loop.

2. The molten salt reactor cooling system according to claim 1, characterized in that: The fuel salt discharge tank has a natural circulation inlet and a natural circulation outlet, the natural circulation loop has a first natural circulation loop hot section, a second natural circulation loop hot section and a natural circulation loop cold section, and the air cooler has an air cooler primary side inlet and an air cooler primary side outlet, wherein the two ends of the first natural circulation loop hot section are respectively connected to the natural circulation outlet and the circulation maintaining heat exchange device, the two ends of the second natural circulation loop hot section are respectively connected to the circulation maintaining heat exchange device and the primary side inlet of the air cooler, and the two ends of the natural circulation loop cold section are respectively connected to the air cooler primary side outlet and the natural circulation inlet, forming a natural circulation loop.

3. The molten salt reactor cooling system according to claim 2, characterized in that: In the natural circulation loop, the power source of the natural circulation fluid flow is the height difference H1 between the center of the fuel salt discharge tank and the center of the air cooler and the height difference H2 between the center of the circulation maintaining heat exchange device and the center of the air cooler.

4. The molten salt reactor cooling system according to claim 1, characterized in that: The fuel salt discharge tank comprises a plurality of fuel salt discharge tank heat exchange elements, an upper tube sheet, a lower tube sheet, a side wall, an upper head, a lower head, a lower chamber and an upper chamber, wherein the upper tube sheet and the lower tube sheet are spaced apart from each other to accommodate the core fuel salt therebetween, the fuel salt discharge tank heat exchange elements are installed in the side wall through the upper tube sheet and the lower tube sheet, the lower head is connected to the side wall to define a lower chamber below the lower tube sheet, the upper head is connected to the side wall to define an upper chamber above the upper tube sheet, the lower chamber and the upper chamber are connected through the fuel salt discharge tank heat exchange elements to accommodate a natural circulation fluid therein, and the core fuel salt and the natural circulation fluid perform heat exchange in the fuel salt discharge tank through the fuel salt discharge tank heat exchange elements.

5. The molten salt reactor cooling system according to claim 4, characterized in that: The fuel salt discharge tank also has an exhaust port connected to the fuel salt inlet. The exhaust port is located on the side wall close to the upper tube plate, and the liquid level of the core fuel salt filled between the upper tube plate and the lower tube plate does not submerge the exhaust port.

6. The molten salt reactor cooling system according to claim 1, characterized in that: The circulation-maintaining heat exchange device comprises a plurality of circulation-maintaining heat exchange device heat exchange elements, which are tightly fixed around the main loop pipeline of the molten salt reactor to achieve thermal contact.

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