A lead-bismuth pool secondary cooling type passive residual heat removal system

Abstract

This invention belongs to the field of pool-type lead-bismuth reactor technology, specifically relating to a passive residual heat removal system for secondary cooling of lead-bismuth reactors. In this invention, the reactor core is immersed in pool-type lead-bismuth reactor coolant, with a cold pool below the core and a hot pool above it. The steam generator is also immersed in pool-type lead-bismuth reactor coolant. The reactor secondary loop feedwater system sends feedwater to the steam generator, generating steam which is then sent to the turbine. Coolant exchange occurs between the hot and cold pools via a main pump. The condenser is submerged in a cooling water tank and connected to an isolation valve via a condensate pipe. The isolation valve is connected to a residual heat exchanger via a condensate pipe, and the residual heat exchanger is connected to a tee via a steam pipe. The tee is connected to a pressure relief valve and the condenser, respectively. This invention ensures effective removal of residual heat from the reactor core under lead-bismuth reactor accident conditions, guaranteeing effective removal of residual heat after accident shutdown of the pool-type lead-bismuth reactor, achieving the goal of long-term non-intervention by personnel.

Description

Technical Field

[0001] This invention belongs to the field of pool-type lead-bismuth stack technology, specifically relating to a passive waste heat removal system for secondary cooling of lead-bismuth stacks. Background Technology

[0002] As a fourth-generation nuclear reactor, the lead-bismuth reactor uses liquid lead-bismuth alloy as its coolant. Its stable physicochemical properties, good thermal conductivity, and high boiling point give it inherently high safety. Therefore, its safety after an accident primarily depends on the effective removal of residual heat from the reactor core under accident conditions. Accident conditions are influenced by various factors, including the possibility of loss of external power and reliable power supply. Therefore, the design and optimization of the passive residual heat removal system is a crucial way to protect reactor safety and prevent core meltdown. Summary of the Invention

[0003] The technical problem solved by this invention is to provide a passive residual heat removal system for secondary cooling of lead-bismuth reactors, which can ensure the effective removal of residual heat from the reactor core under accident conditions, and ensure that the residual heat from the reactor core of the pool-type lead-bismuth reactor can be effectively removed after the accident shutdown, so as to achieve the goal of long-term non-intervention by personnel.

[0004] The technical solution adopted in this invention is as follows:

[0005] A passive residual heat removal system for a lead-bismuth reactor with secondary cooling includes a cooling water tank, a condenser, an isolation valve, a residual heat exchanger, a pressure relief valve, and a reactor coolant system. The reactor coolant system includes a reactor core, a hot pool, a steam generator, a main pump, and a cold pool. The reactor core is immersed in a pool-type lead-bismuth reactor coolant system. The cold pool is located below the reactor core, and the hot pool is located above the reactor core. The steam generator is immersed in the pool-type lead-bismuth reactor coolant system. The reactor secondary loop feedwater system sends feedwater to the steam generator, which generates steam, which is then sent to the turbine. The hot pool and cold pool exchange coolant via the main pump. The condenser is submerged in the cooling water tank and is connected to the isolation valve via a condensate pipe. The isolation valve is connected to the residual heat exchanger via a condensate pipe. The residual heat exchanger is connected to a tee via a steam pipe. The tee is connected to the pressure relief valve and the condenser, respectively.

[0006] The residual heat exchanger is immersed in the pool-type lead-bismuth reactor coolant system. In the pool-type lead-bismuth reactor coolant system, the coolant is heated by the reactor core and its temperature rises. It then enters the hot pool and flows sequentially through the upper part of the residual heat exchanger, the steam generator, and the lower part of the residual heat exchanger. After being driven by the main pump, it enters the cold pool and re-enters the reactor core, completing the coolant circulation process.

[0007] The cooling water tank is positioned above the coolant system, and the height between the cooling water tank and the coolant system needs to be determined based on the passive exhaust cooling capacity and flow rate.

[0008] The condenser uses a wall-mounted heat exchanger to transfer the core waste heat to the cooling water tank, including tube bundle type, shell and tube type, spiral tube type, and C-tube type.

[0009] The residual heat exchanger is a partitioned heat exchanger.

[0010] The residual heat exchanger employs a secondary cooling method and is fixed to the tube sheet of the lead-bismuth stack coolant system. Its upper half is located in the hot pool, and its lower half in the cold pool, allowing the coolant in the hot pool to exchange heat with water vapor, and the coolant in the cold pool to exchange heat with cooling water and a two-phase flow of steam and water.

[0011] The reactor shutdown signal triggers an emergency shutdown, which in turn opens the isolation valves and activates the passive residual heat removal system. When the passive residual heat removal system is activated, the condenser and condensate pipes contain cooling water, while the steam pipes of the passive residual heat removal system contain steam. Under gravity, a gravity-driven passive circulation is established. The cooling water in the condenser and condensate pipes flows downwards into the residual heat removal heat exchanger. After descending from the central tube of the heat exchanger to the bottom and exchanging heat with the primary coolant, the cooling water vaporizes within the vapor space of the heat exchanger. The steam turns into water vapor and enters the steam pipe, where it flows to the condenser. The outer wall of the waste heat exchanger contacts the primary coolant for heat exchange. The upper half of the waste heat exchanger has high-temperature steam and a high-temperature hot pool on its inner and outer sides, while the lower half has low-temperature cooling water and a low-temperature cold pool on its inner and outer sides, achieving equivalent counter-current heat exchange. The condenser exchanges heat fully with the cooling water tank, condensing the water vapor into cooling water, which flows to the waste heat exchanger, completing the cooling water circulation of the closed passive waste heat discharge system.

[0012] The beneficial effects of this invention are:

[0013] (1) The passive waste heat removal system for secondary cooling of lead-bismuth pile provided by the present invention can reduce the violent boiling or flashing phenomenon caused by large temperature difference heat exchange when the cooling water of the passive waste heat removal system enters the heat exchanger, and alleviate the pressure shock of cooling water vaporization. It has a simple structure and high safety and reliability.

[0014] (2) The passive residual heat removal system for secondary cooling of lead-bismuth reactor provided by the present invention adopts gravity-driven passive circulation flow. Under the premise that the coolant in the reactor coolant system can circulate, the residual heat in the reactor core can be safely and reliably removed, thus ensuring reactor safety.

[0015] (3) The present invention provides a passive residual heat removal system for lead-bismuth stacks with secondary cooling, which adopts a secondary cooling layout scheme to achieve equivalent countercurrent heat exchange, improve heat exchange efficiency, alleviate violent boiling and flashing phenomena, and alleviate pressure shock and pressure fluctuation of closed residual heat removal system.

[0016] (4) The present invention provides a passive waste heat removal system for secondary cooling of lead-bismuth piles, which uses a bayonet tube heat exchanger to alleviate pressure fluctuations in the passive waste heat removal system. Attached Figure Description

[0017] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in describing the embodiments of the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments recorded in the present invention. Those skilled in the art can derive other drawings from the following drawings without any creative effort.

[0018] Figure 1 This invention provides a schematic diagram of a passive waste heat removal system for a lead-bismuth pile with secondary cooling.

[0019] In the diagram: 1-Cooling water tank, 2-Condenser, 3-Isolation valve, 4-Excess heat exchanger, 5-Pressure relief valve, 6-Core, 7-Hot pool, 8-Steam generator, 9-Main pump, 10-Cold pool. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0021] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., refer to the orientation or positional relationship shown in the accompanying drawings, and are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or a connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] like Figure 1 As shown, the present invention provides a passive residual heat removal system for a secondary cooling type of lead-bismuth reactor, comprising a cooling water tank 1, a condenser 2, an isolation valve 3, a residual heat exchanger 4, a pressure relief valve 5, and a reactor coolant system. The reactor coolant system includes a reactor core 6, a hot pool 7, a steam generator 8, a main pump 9, and a cold pool 10. The reactor core 6 is immersed in a pool-type lead-bismuth reactor coolant. Below the reactor core 6 is the cold pool 10, and above the reactor core 6 is the hot pool 7. The steam generator 8 is immersed in the pool-type lead-bismuth reactor coolant. The reactor secondary loop feedwater system sends feedwater to the steam generator 8, generating steam which is then sent to the turbine. The hot pool 7 and the cold pool 10 are connected by the main pump 9, which provides the coolant. The exchange of heat between the reactor core and the reactor core is as follows: The condenser 2 is submerged in the cooling water tank 1. The condenser 2 is connected to the isolation valve 3 through the condensate pipe. The isolation valve 3 is connected to the residual heat exchanger 4 through the condensate pipe. The residual heat exchanger 4 is connected to the tee through the steam pipe. The tee is connected to the pressure relief valve 5 and the condenser 2 respectively. The residual heat exchanger 4 is immersed in the pool-type lead-bismuth reactor coolant system. After the coolant in the pool-type lead-bismuth reactor coolant system is heated by the reactor core 6, its temperature rises and it enters the hot pool 7. It flows sequentially through the upper part of the residual heat exchanger 4, the steam generator 8, and the lower part of the residual heat exchanger 4. Then, after being given a head by the main pump 9, it enters the cold pool 10 and re-enters the reactor core 6 to complete the coolant circulation process.

[0024] The water capacity of the cooling water tank 1 needs to be designed and validated based on the owner's requirements and the operating parameters of the lead-bismuth stack to ensure that the target of non-interference is met within the specified time. The cooling water tank 1 needs to be placed above the coolant system, and the height between the cooling water tank 1 and the coolant system needs to be determined based on the passive exhaust cooling capacity and flow rate.

[0025] The condenser 2 is a wall-type heat exchanger used to transfer the core waste heat to the cooling water tank 1. Its form can be tube bundle type, shell and tube type, spiral tube type, or C-type tube type.

[0026] The isolation valve 3 is used to isolate the passive residual heat removal system from the coolant system during normal reactor operation. In the event of a reactor accident, the isolation valve 3 opens, the passive residual heat removal system activates, and removes residual heat from the reactor core. Considering both single-cause and common-cause failures, the isolation valve 3 requires redundant design.

[0027] The waste heat exchanger 4 is a partitioned heat exchanger to prevent the lead-bismuth coolant and the passive waste heat removal system cooling water from mixing and contacting, thus avoiding radioactive material leakage. The waste heat exchanger 4 employs a secondary cooling method, fixed to the tube sheet of the lead-bismuth reactor coolant system. Its upper half is located in the hot pool 7, and its lower half in the cold pool 10. This allows the coolant in the hot pool 7 to exchange heat with water vapor, and the coolant in the cold pool 10 to exchange heat with cooling water and the steam-water two-phase flow. This reduces structural stress, avoids violent boiling or flash evaporation caused by large temperature differences in the lead-bismuth coolant and the passive waste heat removal system cooling water, and alleviates the pressure shock caused by cooling water vaporization. The waste heat exchanger 4 can be a tube bundle type, a shell-and-tube type, a spiral tube type, or a bayonet tube type. In this embodiment, a bayonet tube heat exchanger is used, which has a larger outer wall surface with a larger heat exchange area, and the outer tube annular cavity of the vapor space can buffer the pressure fluctuations caused by cooling water vaporization.

[0028] The pressure relief valve 5 is used to prevent excessive pressure caused by the rapid vaporization of cooling water in the circuit during the initial stage of an accident, which would generate a large amount of steam. The pressure relief valve 5 must be a safety-grade pressure relief valve, capable of automatic reseating and closing, and must be permissible to frequent opening and closing.

[0029] The working principle of this invention is as follows:

[0030] When a reactor accident occurs, a shutdown signal triggers an emergency shutdown. The main feedwater pipeline and main steam pipeline isolation valves of steam generator 8 are closed, and the passive residual heat removal system is activated. At this time, the coolant in the reactor coolant system, under the influence of the density difference between the main pump or cold pool area and the hot pool area, establishes a circulation flow: "Core 6 - Hot Pool Area 7 - Upper Part of Residual Heat Exchanger 4 - Steam Generator 8 - Lower Part of Residual Heat Exchanger 4 - Main Pump 9 - Cold Pool Area 10". As it flows through residual heat exchanger 4, it transfers the core residual heat to the cooling water in residual heat exchanger 4, and ultimately to the cooling water tank 1 and the atmosphere. The specific implementation process of activating the passive residual heat removal system is as follows:

[0031] The reactor shutdown signal triggered an emergency shutdown, which in turn triggered the opening of isolation valve 3, and the passive residual heat removal system was activated.

[0032] When the passive waste heat removal system is put into operation, the condenser 2 and the condensate pipe contain cooling water, and the steam pipe of the passive waste heat removal system contains water vapor. Under the action of gravity, a gravity-driven passive circulation is established, and the cooling water in the condenser 2 and the condensate pipe flows downward into the waste heat removal heat exchanger 4 by gravity.

[0033] Cooling water descends from the central tube of the exhaust heat exchanger 4 to the bottom and exchanges heat with the primary coolant. It then vaporizes into water vapor within the outer annular cavity of the steam space in the exhaust heat exchanger 4 and enters the steam pipe. The water vapor flows through the steam pipe to the condenser 2. The outer wall of the exhaust heat exchanger 4 contacts the primary coolant for heat exchange. The upper half of the exhaust heat exchanger 4 has a high-temperature steam zone and a high-temperature hot pool 7 on its inner and outer sides, respectively. The lower half has a lower-temperature cooling water zone containing two phases and a lower-temperature cold pool 10 on its inner and outer sides, achieving equivalent counter-current heat exchange.

[0034] The condenser 2 exchanges heat fully with the cooling water tank 1, condensing water vapor into cooling water, which flows to the waste heat exchanger 4, completing the cooling water circulation of the closed passive waste heat discharge system.

[0035] After the passive residual heat removal system is in stable operation, the condenser 2 and the condensate pipe contain cooling water, while the steam pipe contains water vapor. There is still a large density difference between the two sides. Under the action of gravity, the passive circulation of the process is achieved without relying on external moving parts, thus realizing the removal of core residual heat and ensuring reactor safety.

[0036] During the above operation, if the steam output is high and causes the pressure in the passive waste heat removal system to be too high, the pressure relief valve 5 will open to release pressure when the pressure reaches the set value for opening, until the system pressure drops to the set value for closing / reseating. This ensures that the pressure in the passive waste heat removal system is within the allowable range and prevents system damage.

[0037] While those skilled in the art will recognize that the present invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention, the embodiments should be considered illustrative and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and therefore all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0038] Furthermore, it should be understood that although the present invention is described according to embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A passive waste heat removal system for secondary cooling of a lead-bismuth pile, characterized in that, The reactor includes a cooling water tank (1), a condenser (2), an isolation valve (3), a residual heat exchanger (4), a pressure relief valve (5), and a reactor coolant system. The reactor coolant system includes a reactor core (6), a hot pool (7), a steam generator (8), a main pump (9), and a cold pool (10). The reactor core (6) is immersed in a pool-type lead-bismuth reactor coolant. The cold pool (10) is below the reactor core (6), and the hot pool (7) is above the reactor core (6). The steam generator (8) is immersed in a pool-type lead-bismuth reactor coolant. The secondary feedwater system sends feedwater to the steam generator (8), generates steam, and sends it to the steam turbine. The hot pool (7) and the cold pool (10) exchange coolant through the main pump (9). The condenser (2) is submerged in the cooling water tank (1). The condenser (2) is connected to the isolation valve (3) through the condensate pipe. The isolation valve (3) is connected to the exhaust heat exchanger (4) through the condensate pipe. The exhaust heat exchanger (4) is connected to the tee through the steam pipe. The tee is connected to the pressure relief valve (5) and the condenser (2) respectively.

2. The passive waste heat removal system for secondary cooling of lead-bismuth piles according to claim 1, characterized in that, The residual heat exchanger (4) is immersed in the pool-type lead-bismuth reactor coolant system. After the coolant in the pool-type lead-bismuth reactor coolant system is heated by the reactor core (6), its temperature rises and it enters the hot pool (7). It flows sequentially through the upper part of the residual heat exchanger (4), the steam generator (8), and the lower part of the residual heat exchanger (4). Then, after being provided with head by the main pump (9), it enters the cold pool (10) and re-enters the reactor core (6) to complete the coolant circulation process.

3. The passive waste heat removal system for secondary cooling of lead-bismuth piles according to claim 1, characterized in that, The cooling water tank (1) is placed above the coolant system. The height between the cooling water tank (1) and the coolant system needs to be determined based on the passive exhaust cooling capacity and flow rate.

4. The passive waste heat removal system for secondary cooling of lead-bismuth piles according to claim 1, characterized in that, The condenser (2) is a partitioned heat exchanger used to transfer the core waste heat to the cooling water tank (1), including tube bundle type, shell and tube type, spiral tube type, and C-type tube type.

5. The passive waste heat removal system for secondary cooling of lead-bismuth piles according to claim 1, characterized in that, The residual heat exchanger (4) is a partitioned heat exchanger.

6. The passive waste heat removal system for secondary cooling of lead-bismuth piles according to claim 5, characterized in that, The residual heat exchanger (4) adopts a secondary cooling method and is fixed on the tube sheet of the lead-bismuth stack coolant system. Its upper half is located in the hot pool (7) and its lower half is located in the cold pool (10), so that the coolant in the hot pool (7) exchanges heat with water vapor, and the coolant in the cold pool (10) exchanges heat with cooling water and steam-water two-phase flow.

7. The passive waste heat removal system for secondary cooling of lead-bismuth piles according to claim 1, characterized in that, The reactor shutdown signal triggers an emergency shutdown, which opens the isolation valve (3), and the passive residual heat removal system is activated. When the passive residual heat removal system is activated, the condenser (2) and condensate pipes contain cooling water, and the steam pipes of the passive residual heat removal system contain steam. Under the action of gravity, a gravity-driven passive circulation is established. The cooling water in the condenser (2) and condensate pipes flows downward into the residual heat removal heat exchanger (4) by gravity. After the cooling water descends from the central tube of the residual heat removal heat exchanger (4) to the bottom and exchanges heat with the primary coolant, it vaporizes into water in the steam space of the residual heat removal heat exchanger (4). Steam enters the steam pipe, and water vapor flows to the condenser (2) in the steam pipe; the outer wall of the waste heat exchanger (4) contacts the primary loop coolant for heat exchange. The inner and outer sides of the upper part of the waste heat exchanger (4) are respectively the high temperature steam and the high temperature hot pool (7), and the inner and outer sides of the lower part are respectively the low temperature cooling water and the low temperature cold pool (10), realizing equivalent counter-current heat exchange; the condenser (2) and the cooling water tank (1) exchange heat fully, condensing the water vapor into cooling water, which flows to the waste heat exchanger (4), completing the cooling water circulation of the closed passive waste heat discharge system.

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