Method for restoring operation of marine power reactor in LOCA accident

Abstract

The present invention relates to a method for restoring the operation of a marine power reactor in a LOCA accident. The method for restoring the operation includes the steps of: shutting down the power reactor and closing the normal feedwater system on the secondary side; starting the PRHR system; introducing seawater into the compartment housing the pressure vessel to flood the lower head; after the break in the LOCA accident is isolated, inflating the compartment to drain the introduced seawater; shutting down the PRHR system, reopening the normal feedwater system on the secondary side; and starting the power reactor. The present invention can effectively alleviate the rapid rise of the core temperature after the accident occurs and can gradually achieve partial or full power restoration of the power reactor.

Description

Technical Field

[0001] The present invention relates to the technical field of reactor engineering simulation, and particularly to a method for the recovery operation of a marine power reactor in a LOCA accident. Background Art

[0002] A LOCA accident (Loss Of Coolant Accident) is a serious situation that may occur during the operation of a nuclear reactor. The LOCA accident is mainly due to a failure such as a rupture in the pipeline or equipment of the primary coolant system, resulting in a large amount of coolant leaking from the rupture into the containment. The large loss of coolant will cause the cooling capacity of the reactor core to drop sharply, and then lead to a sharp rise in the core temperature. If effective measures are not taken in time, the core temperature may exceed the design temperature limit of the fuel element, causing the cladding of the fuel element to be damaged, and radioactive substances will be released into the coolant, triggering a serious accident.

[0003] Especially after a LOCA accident occurs in a marine power reactor, it is usually difficult to obtain water sources that meet the requirements of reactor operation in a timely manner. This makes it impossible for the reactor to operate at power according to the original operation mode even after the breach is isolated through damage control measures after a LOCA accident, thereby making it difficult to restore the marine power. Summary of the Invention

[0004] In view of the above problems of the prior art, the present invention proposes a method for the recovery operation of a marine power reactor in a LOCA accident, which can effectively alleviate the rapid rise of the core temperature after the accident and can gradually achieve partial or full power recovery of the power reactor.

[0005] Specifically, the present invention proposes a method for the recovery operation of a marine power reactor in a LOCA accident. The marine power reactor includes a pressure vessel disposed in an independent compartment. The pressure vessel includes a lower head and a cylindrical body, and the bottom end of the cylindrical body is connected to the lower head. A basket is provided in the cylindrical body for suspending the reactor core. A downward channel for the coolant is formed between the basket and the inner wall of the cylindrical body, and a PRHR system is provided in the downward channel. An upward channel for the coolant passing through the active area of the reactor core is formed in the basket. The method for the recovery operation includes the steps of:

[0006] Shut down the power reactor and close the normal feedwater system on the secondary side;

[0007] Start the PRHR system;

[0008] Introduce seawater into the compartment accommodating the pressure vessel to submerge the lower head;

[0009] After the break in the LOCA accident is isolated, the compartment is inflated to drain the introduced seawater;

[0010] Shut down the PRHR system and reopen the normal feedwater system on the secondary side;

[0011] Start the power reactor.

[0012] According to an embodiment of the present invention, an air inlet is provided at the top of the compartment, and a drain outlet is provided at the bottom of the compartment. The method includes inflating the compartment through the air inlet to press the seawater out of the compartment through the drain outlet.

[0013] According to an embodiment of the present invention, after reopening the normal feedwater system on the secondary side, the heat generated by the core is brought to the steam turbine through the primary-secondary heat exchanger of the PRHR system for work.

[0014] According to an embodiment of the present invention, after reopening the normal feedwater system on the secondary side, a three-dimensional natural circulation is formed in the core and the upper plenum region of the core, and a three-dimensional natural circulation is formed in the downcomer under the cooling effect of the primary-secondary heat exchanger.

[0015] According to an embodiment of the present invention, heat exchange is performed between the two three-dimensional natural circulations through the shroud.

[0016] According to an embodiment of the present invention, when a three-dimensional natural circulation is formed in the core and the upper plenum region above the core, mass transfer is achieved inside the core and the lower head. The refrigerant carrying heat flows downward from the core into the lower head and transfers the heat to the refrigerant in the lower head in contact therewith.

[0017] According to an embodiment of the present invention, when a three-dimensional natural circulation is formed in the core and the upper plenum region above the core, mass transfer is achieved inside the downcomer and the lower head. The refrigerant carrying heat flows downward from the downcomer into the lower head and transfers the heat to the refrigerant in the lower head in contact therewith.

[0018] According to an embodiment of the present invention, the step of starting the power reactor includes: gradually increasing the core power to enter the low-power operation recovery mode.

[0019] According to an embodiment of the present invention, the PRHR system includes a primary-secondary heat exchanger, and surface modification technology is carried out on the surface of the primary-secondary heat exchanger to enhance the condensation efficiency.

[0020] According to an embodiment of the present invention, two-dimensional or three-dimensional structures are etched on the surface of the primary-secondary heat exchanger.

[0021] A method for the recovery operation of a marine power reactor during a LOCA accident provided by the present invention effectively alleviates the rapid rise of the core temperature after the accident by starting the PRHR system and introducing seawater to flood the bottom of the lower head; and after isolating the break, the introduced seawater is drained, the PRHR system is closed, and the normal feedwater system on the secondary side is reopened to gradually achieve partial or full power recovery of the power reactor.

[0022] It should be understood that the above general description and the following detailed description of the present invention are both exemplary and explanatory, and are intended to provide further explanation of the present invention. Brief Description of the Drawings

[0023] Including the drawings is to provide further explanation of the present invention. They are incorporated and constitute a part of this application. The drawings show embodiments of the present invention and, together with this specification, serve to explain the principles of the present invention. In the drawings:

[0024] Figure 1 Shows the structure of a pressure vessel and a schematic diagram of the shutdown state of an embodiment of the present invention.

[0025] Figure 2 Shows a flowchart of a method for the recovery operation of a marine power reactor during a LOCA accident according to an embodiment of the present invention.

[0026] Figure 3 Shows the structure of a pressure vessel and a schematic diagram of the state in the low-power operation recovery mode of an embodiment of the present invention. Detailed Description of the Embodiments

[0027] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other.

[0028] Next, the technical solutions in the embodiments of this application will be clearly and completely described in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way restricts this application and its application or use. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of this application.

[0029] Note that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly dictates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0030] Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and values set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for the sake of convenience of description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationships. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the specification. In all the examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, further discussion thereof is not required in subsequent drawings.

[0031] In the description of the present application, it should be understood that the orientation or positional relationships indicated by orientation words such as "front, rear, upper, lower, left, right", "lateral, vertical, perpendicular, horizontal", and "top, bottom" are generally based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description. Without contrary description, these orientation words do not indicate and imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and thus should not be construed as limiting the protection scope of the present application; the orientation words "inside, outside" refer to the inside and outside relative to the contour of each component itself.

[0032] In addition, it should be noted that the use of terms such as "first" and "second" to define components is only for the convenience of distinguishing the corresponding components. Without further statement, the above terms have no special meanings, and thus should not be construed as limiting the protection scope of the present application. In addition, although the terms used in the present application are selected from well-known and commonly used terms, some of the terms mentioned in the specification of the present application may be selected by the applicant according to his or her judgment, and their detailed meanings are described in the relevant parts of this description. In addition, it is required to understand the present application not only through the actual terms used, but also through the meanings implied by each term.

[0033] Figure 1The structural and shutdown state schematic diagrams of a pressure vessel according to an embodiment of the present invention are shown. As shown in the figure, a marine power reactor includes a pressure vessel 100 disposed in an independent compartment. The pressure vessel 100 includes a lower head 101 and a cylindrical body 102. The bottom end of the cylindrical body 102 is connected to the lower head 101. A basket 103 is provided inside the cylindrical body 102 for suspending the reactor core 104. A downward channel 105 for refrigerant is formed between the basket 103 and the inner wall of the cylindrical body 102, and a PRHR (Passive Residual Heat Removal system) system 106 is provided in the downward channel 105 for effectively cooling the refrigerant. An upward channel 107 for refrigerant passing through the active region of the reactor core 104 is formed inside the basket 103, and the refrigerant absorbs heat in the upward channel 107. In the pressure vessel 100 of the marine power reactor, the refrigerant first flows downward in the downward channel 105 and enters the lower head 101. During this process, the refrigerant releases a part of its heat and exchanges heat with the surrounding environment. Then, the refrigerant enters the upward channel 107 from the lower head 101. In the upward channel 107, the refrigerant passes through the active region of the reactor core 104 and absorbs the heat generated by the reactor core 104. In this way, the refrigerant completes a cycle process inside the pressure vessel 100, realizing the alternation of heat release and heat absorption. Under normal conditions, through continuous circulation, the refrigerant continuously takes away the heat of the reactor core 104, maintaining the reactor core 104 within a safe temperature range and ensuring the stable operation of the marine power reactor, providing a reliable power source for the ship. However, after a LOCA accident occurs, a break occurs in the pipeline or equipment, resulting in a large amount of coolant leaking from the break, causing the water level of the refrigerant in the containment to decrease.

[0034] Figure 2 The flowchart of a method for the resumed operation of a marine power reactor in a LOCA accident according to an embodiment of the present invention is shown. As shown in the figure, a method for the resumed operation of a marine power reactor in a LOCA accident provided by the present invention includes the steps:

[0035] S1. Shut down the power reactor and the normal feed water system on the secondary side. During a LOCA accident, shutting down the power reactor is to stop the chain reaction and reduce the heat generation in the reactor core 104. When the power reactor is operating normally, a large amount of heat is generated through the fission reaction of nuclear fuel. After a LOCA accident occurs, the loss of coolant has deteriorated the cooling environment of the reactor core 104. Continuing to maintain the chain reaction will cause the temperature of the reactor core 104 to rise continuously, further exacerbating the severity of the accident. By inserting control rods or other means to shut down the power reactor, heat generation can be reduced from the source, which is the first step in alleviating the accident. It should be noted that the normal feed water system on the secondary side mainly delivers feed water to the secondary side of the steam generator to take away the heat transferred from the primary side and generate steam to drive the steam turbine for power generation. Shutting it down during a LOCA accident is because the normal operating conditions of the secondary loop system are damaged. If water continues to be supplied to the secondary side of the steam generator, abnormal heat exchange caused by the loss of primary side coolant may cause equipment such as the steam generator to bear abnormal thermal stress and pressure changes.

[0036] S2. Start the PRHR system 106. This can help remove the decay heat of the reactor core 104 and prevent the temperature of the reactor core 104 from being too high. Decay heat is the heat continuously generated due to the decay process of radionuclides after the chain reaction of nuclear fuel stops. When the high-temperature refrigerant passes through the PRHR system 106, heat is transferred from the refrigerant to the heat exchange tubes of the PRHR system 106 by heat conduction. The operation of the PRHR system 106 can buy time for the repair of the LOCA accident. During the operation of the PRHR system 106, it can temporarily undertake part of the cooling task of the normal feed water system on the secondary side to relieve the burden of the normal feed water system on the secondary side.

[0037] S3. Introduce seawater into the compartment housing the pressure vessel 100 to flood the lower head 101. When the lower head 101 is flooded with seawater, it can directly cool the lower head 101. The lower head 101 is an important part of the refrigerant circulation path. Cooling the lower head 101 can indirectly cool the refrigerant inside it. Because there is heat transfer between the lower head 101 and the refrigerant, the lower-temperature seawater absorbs the heat of the lower head 101, so that the temperature of the refrigerant can be effectively reduced during the process of entering and leaving the lower head 101. This helps to maintain the refrigerant within a suitable temperature range, better achieve the cooling of the reactor core 104, and prevent the temperature of the reactor core 104 from being too high. Using seawater to flood the pit where the lower head 101 is located is a relatively simple and effective cooling method. Compared with some complex active cooling equipment and systems, this method can reduce the dependence on complex mechanical devices to a certain extent.

[0038] Steps S2 and S3 are used to mitigate the rapid increase in the temperature of the reactor core 104 after an accident, mainly by reducing the temperature of the refrigerant through the PRHR system 106 and introducing seawater, so that the refrigerant can continuously absorb the residual heat of the reactor core 104 and effectively control the rate of water level drop in the pressure vessel 100.

[0039] S4. After the break in the LOCA accident is isolated, the compartment is inflated to discharge the introduced seawater. When the power reactor needs to resume operation, the heat transfer effect of the lower head 101 is weakened and the equipment is restored to a relatively dry operating environment.

[0040] S5. Shut down the PRHR system 106 and restart the normal feedwater system on the secondary side. Since the PRHR system 106 mainly functions to remove residual heat in emergency situations. When the power reactor needs to resume normal operation, shutting down the PRHR system 106 can avoid unnecessary interference with the system under normal operating conditions, ensure that the operating parameters of the system are more stable, and facilitate precise control and adjustment. Starting the normal feedwater system on the secondary side can provide a stable cooling water source for the system. The normal feedwater system on the secondary side is specially designed to provide appropriate water volume and pressure according to the operating requirements of the system. During the restart phase, the reactor core 104 still generates a large amount of heat, and reliable cooling means are required to maintain the temperature within the safe range. The normal feedwater system on the secondary side can effectively remove the heat generated by the reactor core 104 through heat exchange and other means to ensure the safe operation of the reactor.

[0041] S6. Start the power reactor, mainly by gradually increasing the power of the reactor core 104 to enter the low-power operation restart mode.

[0042] In some examples, refer to Figure 1, the PRHR system 106 includes a primary-secondary heat exchanger 108. The primary-secondary heat exchanger 108 transfers heat to the external environment or other heat dissipation devices through natural convection. The primary-secondary heat exchanger 108 transfers the heat on the primary side to the secondary side. The primary-secondary heat exchanger 108 is generally a spiral tube heat exchanger, with the secondary side inside the tube and the primary side outside the tube. The refrigerant in the pressure vessel 100 runs outside the tube, and the refrigerant medium runs inside the tube, exchanging heat with the external system. The primary-secondary heat exchanger 108 condenses the water vapor on the primary side, and relies on the condensed water generated by the water vapor to supplement the water level in the pressure vessel 100. This process helps to balance the pressure in the system. When the water level rises, part of the space in the pressure vessel 100 is occupied by liquid water, and the space of the gaseous part decreases relatively, thereby reducing the internal pressure. This can effectively relieve the excessive pressure that may occur in the pressure vessel 100 and ensure the safe and stable operation of the system. Further, surface modification technology is carried out on the surface of the primary-secondary heat exchanger 108 to enhance the condensation efficiency. Effectively condensing the water vapor on the primary side is crucial for controlling the water level and pressure inside the pressure vessel 100. The surface modification technology mainly changes the physical or chemical properties of the heat exchanger surface, so that more heat can be transferred from the primary side to the secondary side, thereby improving its condensation ability for water vapor and further improving the thermal efficiency of the entire system. The surface modification technology includes coating technology, surface roughening treatment, etc.

[0043] Preferably, two-dimensional or three-dimensional structures are etched on the surface of the primary-secondary heat exchanger 108. The two-dimensional or three-dimensional etched structures can significantly increase the surface area of the heat exchanger. A larger surface area means more space for water vapor to contact and condense on the surface. The two-dimensional or three-dimensional etched structures can also guide the flow of the fluid and improve the hydrodynamic performance. For example, the microgroove structure can guide the flow direction of the condensed water, enabling it to drain from the heat exchanger surface faster and reducing the flow resistance.

[0044] In some examples, an air inlet is provided at the top of the compartment, and a drain outlet is provided at the bottom of the compartment. The compartment is inflated through the air inlet to press the seawater out of the compartment through the drain outlet. After an emergency such as a LOCA accident occurs, seawater is introduced to cool the lower head 101. Once the break is isolated, it is necessary to quickly drain the seawater in the compartment to restore the normal operation of the marine power reactor. By inflating the compartment through the top air inlet, the pressure of the gas can be used to quickly press the seawater out of the bottom drain outlet. This method can empty the seawater in the compartment in a relatively short time and improve the recovery speed.

[0045] In some examples, the secondary normal feedwater system is started, and the heat generated by the reactor core 104 is carried to the steam turbine through the primary-secondary heat exchanger 108 for work. Specifically, the primary-secondary heat exchanger 108 of the PRHR system 106 disconnects the heat exchange with the previous external system and switches to the heat exchange with the steam turbine. When the secondary normal feedwater system is started, a continuous supply of feedwater will be delivered to the primary-secondary heat exchanger 108. At this time, the power of the reactor core 104 gradually increases, and the heat of the reactor core 104 can be efficiently transferred to the feedwater on the secondary side, causing the temperature of the originally cooler water to continuously rise, and then turning into high-temperature water or even high-temperature steam. After heat exchange, the refrigerant enters the steam turbine and starts to expand, pushing the blades of the steam turbine to rotate at high speed with a powerful pressure. The rotational movement of the blades is transmitted to other related equipment, such as a generator, through a transmission shaft, thereby realizing the output of mechanical energy and completing the key energy conversion process from the thermal energy generated by the reactor core 104 to the mechanical energy output by the steam turbine, ultimately providing partial power for the ship to conduct self-rescue.

[0046] Figure 3 The state schematic diagram of a pressure vessel and the low-power operation recovery mode according to an embodiment of the present invention is shown. Now, in combination with Figure 1 and Figure 3The specific process of step S5 is described as follows. In some examples, after the secondary normal feedwater system is started, a three-dimensional natural circulation is formed in the core 104 and the upper plenum 109 area above the core 104. The upper plenum 109 is an important spatial area within the reactor pressure vessel 100, which is directly connected to the core 104 and is a chamber structure located above the core 104 and enclosed by the shroud 103 and the upper fluctuating plate 110 above. The riser 107 is located within the upper plenum 109, and the riser 107 is a channel system composed of fuel assemblies, support structures, etc. In the normal state without a LOCA accident, the coolant passing through the active region of the core 104 flows upward into the riser 107 within the upper plenum 109, and the coolant absorbs heat in the riser 107. In the method for resuming operation during a LOCA accident, when the secondary normal feedwater system starts to operate, water is transported to the primary-secondary heat exchanger 108 for heat exchange. In the core 104 area, nuclear reactions continuously generate heat. Due to the temperature difference, the water around the core 104 is heated, and the density of the water after the temperature rises becomes smaller. Under the action of buoyancy, this hot water moves upward and enters the upper plenum 109 area. Referring to the upward arrow between the core 104 and the upper plenum 109 area, this upward arrow indicates the upward movement of the hot water. The upper plenum 109 is similar to a "transfer station" for heat convergence and distribution. The hot water accumulates here, making the upper region of the upper plenum 109 have a higher temperature. Relatively colder water, under the action of gravity, replenishes the bottom of the core 104 from the surrounding or other parts of the system. This exchange of hot and cold fluids unfolds in three-dimensional space, forming a complex natural circulation. Referring to the downward arrow near the inner side of the shroud 103 at the edge of the core 104 and the upper plenum 109, this downward arrow indicates the downward movement of the cold water. In this three-dimensional natural circulation process where hot water moves upward and cold water moves downward, there is not only vertical flow in the up and down directions but also horizontal flow. The horizontal flow is mainly due to temperature differences and fluid pressure differences at different positions. For example, at the edge and the center of the core 104, due to the uneven heat distribution, the temperature and density of the water are different, thus triggering horizontal fluid exchange. This three-dimensional natural circulation can ensure that the heat generated by the core 104 is taken away in a timely manner and maintain the temperature of the core 104 within a safe range.

[0047] Meanwhile, under the cooling effect of the primary-secondary heat exchanger 108, a natural circulation is formed in the downcomer 105. When the primary-secondary heat exchanger 108 starts to exert its cooling effect, the temperature of the coolant near it will be affected first and decrease. In the downcomer 105, there is originally a temperature difference in the coolant. The coolant closer to the primary-secondary heat exchanger 108 has a relatively lower temperature, while the part farther away from it has a higher temperature. Due to the principle of thermal expansion and contraction, the coolant with a higher temperature has a smaller density, and the coolant with a lower temperature has a larger density. Under the action of gravity, the coolant with a larger density will naturally flow downward. Refer toFigure 3 In the primary-secondary heat exchanger 108, there is a downward arrow indicating the downward flow of the refrigerant. The refrigerant with a higher temperature and lower density near the side of the hanging basket 103 will move upward under the action of buoyancy, as shown by the upward arrow outside the hanging basket 103, to fill the space vacated by the downward flow. In this way, a three-dimensional natural circulation is formed in the downward channel 105. This three-dimensional natural circulation is like an automatically regulated heat transfer chain, enabling the refrigerant to continuously flow in the downward channel 105, transferring heat orderly to the primary-secondary heat exchanger 108 for exchange and cooling, thereby ensuring the heat balance of the entire system. Moreover, the formation of the three-dimensional natural circulation does not require additional power drive and can operate stably relying on its own physical characteristics. This not only reduces energy consumption but also improves the reliability of the system operation, ensuring the partial power recovery of the marine power reactor.

[0048] In some examples, heat exchange occurs between the two natural circulations through the hanging basket 103. Looking at the three-dimensional natural circulation in the core 104 and the upper chamber 109 region, the high-temperature fluid carrying the heat generated by the core 104 moves upward into the upper chamber 109, and these high-temperature fluids are in close contact with the hanging basket 103. The hanging basket 103 has good heat conduction performance, and it can quickly conduct the absorbed heat to the refrigerant in the downward channel 105 in contact with it, enabling the heat to be effectively transferred from the circulation system inside the hanging basket 103 with a higher temperature to the circulation system outside the hanging basket 103 with a lower temperature. This heat exchange connects the two relatively independent natural circulation systems with each other, forming a complete heat exchange network. Through the heat conduction of the hanging basket 103, the system can utilize and distribute heat more efficiently, avoiding local heat accumulation. This natural heat exchange method utilizes the temperature difference and fluid motion characteristics of the two circulation systems themselves, without the need for additional complex power devices to drive heat exchange, improving the reliability and economy of the system. And this heat exchange mechanism can ensure that the heat of the core 104 can be taken away in time, maintaining the temperature of the core 104 within a safe range and ensuring the partial power recovery of the marine power reactor.

[0049] In some examples, mass transfer is achieved inside the core 104 and the lower head 101. The core 104 is the core area where nuclear reactions occur. During the continuous progress of nuclear reactions, a large amount of heat is generated, and at the same time, various changes in the state of matter and the migration of substances also occur. Inside the core 104, the coolant absorbs heat, its temperature rises and its state changes, and some of its components will also undergo corresponding physical and chemical changes. The core 104 and the lower head 101 are connected and communicated through a specific structure, enabling mass transfer between the two. For example, the high-temperature coolant flows downward from the core 104 area into the lower head 101. During this process, the heat carried by the coolant is transferred downward as the coolant flows. The lower head 101 receives the coolant from the core 104, and its heat will continue to be transferred to the surrounding environment or other media in contact with it. This mass transfer inside the core 104 and the lower head 101 helps to maintain the stability of the thermal-hydraulic state of the core 104, timely transfer the heat generated by the core 104, etc. through the lower head 101, avoid excessive heat accumulation affecting the safety of the core 104, and at the same time ensure the reasonable flow and distribution of substances in this area.

[0050] In some examples, mass transfer is achieved inside the downcomer 105 and the lower head 101. The coolant in the downcomer 105 has its own flow characteristics and thermal-hydraulic state, and it continuously circulates in the channel to achieve heat transfer. When the coolant flows downward along the downcomer 105, it will eventually flow into the lower head 101. Inside the lower head 101, the coolant from the downcomer 105 interacts with the substances originally in the lower head 101 to achieve mass transfer. For example, the coolant flowing in from the downcomer 105 brings certain heat, possible impurities, and different chemical substance components, etc., which will mix and exchange with the substances already in the lower head 101. At the same time, the substances in the lower head 101 will also affect the coolant flowing in, such as changing its temperature and composition ratio. Moreover, the flow state and temperature change of the coolant in the lower head 101 will in turn affect the mass transfer process between it and the downcomer 105. This mass transfer inside the downcomer 105 and the lower head 101 can further optimize the heat transfer path of the entire system, ensure that the coolant continuously adjusts its thermal-hydraulic and material states during the circulation process, work better in coordination, efficiently carry away the heat generated by the core 104, and maintain the stable operation of each part of the system under appropriate temperature, pressure, and material composition conditions, playing an indispensable role in the partial power recovery of the ship power reactor.

[0051] In some examples, the pipes running through the pressure vessel 100 are arranged as high as possible, and the aperture diameters of the pipes are controlled. In this way, after a LOCA accident, the size of the pipe break can be controlled to be relatively small, and the position of the break is relatively high, so that the refrigerant loss rate is relatively slow, which is conducive to implementing the method for the ship power reactor to resume operation in a LOCA accident provided by the present invention.

[0052] It should be noted that usually after a LOCA accident, the loss of the system water inventory in the pressure vessel 100 is large, and the primary side flow holes are already exposed. After closing the PRHR system 106 and starting the secondary side normal feed water system in step S5, the core 104 cannot be started according to the normal process in step S6. Therefore, a low-power restoration operation mode is adopted, and through the aforementioned different flow and heat transfer methods, the ship can resume the power to move forward at a low speed. In less cases, if the loss of the system water inventory is small and the primary side flow holes are still submerged, after closing the PRHR system 106 and starting the secondary side normal feed water system in step S5, the core 104 can be started normally, and a single-phase natural circulation is formed in the flow channels of the core 104 - upper plenum 109 - primary-secondary heat exchanger 108 - downcomer 105 on the primary side, so that the secondary side can absorb the heat of the core 104 and generate steam to drive the steam turbine to do work.

[0053] It will be apparent to those skilled in the art that various modifications and variations can be made to the above exemplary embodiments of the present invention without departing from the spirit and scope of the present invention. Therefore, it is intended that the present invention cover modifications and variations falling within the scope of the appended claims and their equivalent technical solutions.

Claims

1. A method for the resumption of operation of a marine power reactor in a LOCA accident. The marine power reactor includes a pressure vessel disposed in an independent compartment. The pressure vessel includes a lower head and a cylinder body, and the bottom end of the cylinder body is connected to the lower head. A basket is provided in the cylinder body for suspending the reactor core. A downward channel for the refrigerant is formed between the basket and the inner wall of the cylinder body. A PRHR system is provided in the downward channel. An upward channel for the refrigerant passing through the active region of the reactor core is formed in the basket. The method for resumption of operation includes the steps: Shut down the power reactor and close the secondary side normal feed water system; Start the PRHR system; Introduce seawater into the compartment accommodating the pressure vessel so that the seawater submerges the lower head; After the break in the LOCA accident is isolated, inflate the compartment to discharge the introduced seawater; An air inlet is provided at the top of the compartment, and a drain outlet is provided at the bottom of the compartment. The method includes inflating the compartment through the air inlet to press the seawater out of the compartment through the drain outlet; Close the PRHR system, reopen the secondary side normal feed water system, form a three-dimensional natural circulation in the reactor core and the upper chamber region above the reactor core, and form a three-dimensional natural circulation in the downward channel under the cooling action of a primary-secondary side heat exchanger; Start the power reactor.

2. The method for resuming operation according to claim 1, wherein, After reopening the secondary side normal feed water system, take the heat generated by the reactor core to the steam turbine through the primary-secondary side heat exchanger of the PRHR system for work.

3. The method for resuming operation according to claim 2, characterized in that, The two three-dimensional natural circulations exchange heat through the basket.

4. The method for resuming operation according to claim 3, wherein When a three-dimensional natural circulation is formed in the reactor core and the upper chamber region above the reactor core, mass transfer is realized inside the reactor core and the lower head. The refrigerant carrying heat flows downward from the reactor core into the lower head and transfers the heat to the refrigerant in the lower head in contact therewith.

5. The method for resuming operation according to claim 3, wherein When a three-dimensional natural circulation is formed in the reactor core and the upper chamber region above the reactor core, mass transfer is realized inside the downward channel and the lower head. The refrigerant carrying heat flows downward from the downward channel into the lower head and transfers the heat to the refrigerant in the lower head in contact therewith.

6. The method for resuming operation according to claim 1, characterized in that, The step of starting the power reactor includes: gradually increasing the reactor core power to enter the low-power operation resumption mode.

7. The method for resuming operation according to claim 1, characterized in that, The PRHR system includes a primary-secondary side heat exchanger, and surface modification technology is carried out on the surface of the primary-secondary side heat exchanger to enhance the condensation efficiency.

8. The method for resuming operation according to claim 7, characterized in that, Etch two-dimensional or three-dimensional structures on the surface of the primary-secondary side heat exchanger.

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