Emergency cooling system and method for reactor pressure vessel of ocean nuclear power platform

Abstract

The invention discloses an emergency cooling system and method for a reactor pressure vessel of an ocean nuclear power platform, and the system comprises a pressure vessel external cooling system which comprises a metal or alloy plate and an emergency cooling channel, the metal or alloy plate is arranged between the reactor pressure vessel and the pressure vessel supporting structure surrounding the reactor pressure vessel; the emergency cooling channel is arranged at the bottom of the pressure vessel lower sealing head. And the bottom cooling channel is of a double-layer bottom closed structure, is arranged below the pressure container, and comprises a double-layer bottom platform plate and a double-layer bottom coaming. And the water taking system is communicated with the bottom cooling channel through a pipeline. And the exhaust system is communicated with the bottom cooling channel through a pipeline. According to the invention, the inherent characteristic of low melting point of specific metal is utilized, lead absorbs heat and melts at the initial stage of an accident and coats the lower sealing head of the reactor pressure vessel, an emergency cooling channel is established, the heat of a reactor core is passively transmitted to seawater, and further deterioration of the accident is prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of marine nuclear power platforms, and in particular to a passive emergency cooling system and method for a reactor pressure vessel of a marine nuclear power platform. Background Art

[0002] As my country continues to develop marine resources, the demand for stable, reliable, and large-capacity offshore electricity and heat supply has become more urgent. Since the energy density of nuclear fuel is much higher than that of traditional fossil energy, offshore nuclear power platforms can provide energy supply for remote islands and resource-scarce areas, safeguarding marine energy and having good market prospects.

[0003] The external marine environment faced by offshore nuclear power platforms is more complex than that of land-based nuclear power plants. Due to limited conditions, they cannot be equipped with sufficient emergency resources like land-based nuclear power plants. The risk of nuclear accidents is theoretically higher than that of land-based nuclear power plants. They may also be deployed in remote waters, and accident rescue is far more difficult than for ordinary nuclear power plants.

[0004] At present, mature marine nuclear power platforms all adopt pressurized water reactor design, and the average temperature of the primary coolant is about 300℃. For severe accidents, the time sequence of core melting is different for different pressurized water reactors and different accident sequences, but they all have similar core melting processes. When the core is exposed, the highest core temperature is the saturation temperature of the primary coolant, which is about 350℃, and the core temperature begins to rise gradually. When the core outlet temperature reaches about 650℃, the entry condition for severe accident management is reached, and the core can be assumed to begin to melt. At this time, zirconium begins to oxidize, and the highest core temperature is about 1200℃. When the core melts to form a core debris bed and a molten pool, the highest core temperature is about 2200℃. The molten material will accumulate on the lower head of the reactor pressure vessel due to gravity. At this time, if there is no emergency heat conduction measure, the molten material will continue to melt through the lower head, causing the reactor pressure vessel to fail, resulting in a large amount of radioactive material released into the containment. The risk of releasing into the environment is extremely high, causing marine environmental pollution and international disputes. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a passive emergency cooling system and method for a reactor pressure vessel of an offshore nuclear power platform. By utilizing the inherent characteristic of low melting point of metallic lead, the lead absorbs heat and melts in the early stage of an accident and covers the lower head of the reactor pressure vessel, thereby establishing an emergency cooling channel and passively transferring the heat of the core to the seawater, thereby preventing the accident from further deteriorating, ensuring long-term cooling of the core, preventing damage to the boundary barrier of the reactor pressure vessel, and effectively preventing failure of the containment barrier.

[0006] The objective of the present invention is achieved through the following technical solutions: an emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform, comprising:

[0007] The external cooling system of the pressure vessel comprises a metal or alloy plate and an emergency cooling channel, wherein the metal or alloy plate is arranged between the reactor pressure vessel and the pressure vessel supporting structure surrounding the reactor pressure vessel; the emergency cooling channel is arranged at the bottom of the lower head of the pressure vessel; and a container connected to the metal or metal plate is arranged below the emergency cooling channel.

[0008] The melting point of the metal or alloy plate is higher than the temperature of the outer wall of the reactor pressure vessel and lower than the temperature of the pressure vessel when the core is exposed.

[0009] The bottom cooling channel is a double-bottom closed structure, which is arranged below the pressure vessel and includes a double-bottom platform plate and a double-bottom enclosure plate.

[0010] The water intake system is connected with the bottom cooling channel through a pipeline.

[0011] The exhaust system is connected with the bottom cooling channel through a pipeline.

[0012] Preferably, the metal or alloy plate is a lead plate.

[0013] Preferably, a thermal insulation layer is provided between the metal or alloy plate and the pressure vessel support structure.

[0014] Preferably, a gap is left between the emergency cooling channel and the lower head of the pressure vessel.

[0015] Preferably, the other end of the water intake system is connected to the sea valve box through a pipeline.

[0016] Preferably, the exhaust port of the exhaust system is arranged at the top of the bottom cooling channel.

[0017] Preferably, the water intake system and the exhaust system are provided with a plurality of opening and closing valves, all of which are arranged outside the containment vessel.

[0018] In addition to providing an emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform, the present invention further provides a method for emergency cooling of a reactor pressure vessel of an offshore nuclear power platform using the system, and the specific steps are as follows:

[0019] Step 1: When the marine nuclear power platform is operating normally, the pressure vessel external cooling system, bottom cooling channel, water intake system and exhaust system are in standby state, all valves are in closed state, and the bottom cooling channel is in closed state;

[0020] Step 2: After the accident, the temperature of the reactor pressure vessel rises abnormally, causing the metal or alloy plate outside the lower ring section of the pressure vessel to melt and flood the emergency cooling channel. Open the on-off valves on the water intake system and the exhaust system, and quickly inject seawater into the bottom cooling channel to extract the heat from the core.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The present invention provides a passive emergency cooling system and method for a reactor pressure vessel for an offshore nuclear power platform, wherein a lead plate is wrapped around the reactor pressure vessel. During normal operation, the temperature of the outer wall of the reactor pressure vessel is about 290°C, which will not cause the lead plate to melt. If the core is exposed after an accident, the temperature of the pressure vessel can reach 350°C, and the lead plate begins to melt, absorbing the heat of the core while flowing into the emergency cooling channel below the pressure vessel under the action of gravity. The molten lead completely covers the lower head of the reactor pressure vessel, and conducts the heat of the core to the bottom steel plate of the containment, and then passively transfers the heat to the seawater through heat conduction and heat convection in the bottom cooling channel, which can prevent the core temperature from further increasing, alleviate the consequences of the accident, and achieve long-term and reliable extraction of decay heat after the accident. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the standby state of the passive emergency cooling system of the reactor pressure vessel in an embodiment of the present invention;

[0024] Figure 2 It is a schematic diagram of the state of the passive emergency cooling system of the reactor pressure vessel under accident conditions in an embodiment of the present invention.

[0025] In the figure, 1 is an emergency cooling channel; 2 is a pressure vessel; 3 is a pressure vessel supporting structure; 4 is a lower head of the pressure vessel; 5 is a bottom cooling channel; 6 is a double-layer bottom platform plate; 7 is a double-layer bottom coaming; 8 is a lead plate; 9 is an insulation layer; 10 is a sea valve box; 11 is a containment shell; 12 is a lower ring section of the pressure vessel; 13 is a bottom suction grid; 14 is a sea valve; 15 is a containment shell water inlet isolation valve; 16 is a containment shell discharge isolation valve; 17 is a side exhaust ball valve; 18 is a side cabin; and 19 is a container. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0027] The technical solution of the present invention provides an emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform, comprising:

[0028] The external cooling system of the pressure vessel includes a metal or alloy plate and an emergency cooling channel 1, wherein the metal or alloy plate is arranged between the reactor pressure vessel 2 and the pressure vessel supporting structure 3 surrounding the reactor pressure vessel 2; the emergency cooling channel 1 is arranged at the bottom of the lower head 4 of the pressure vessel; and a container 19 connected to the metal or metal plate is arranged below the emergency cooling channel 1.

[0029] The melting point of the metal or alloy plate is higher than the temperature of the outer wall of the reactor pressure vessel 2 and lower than the temperature of the pressure vessel 2 when the core 5 is exposed.

[0030] The bottom cooling channel 5 is a double-bottom closed structure, which is arranged below the pressure vessel 2 and includes a double-bottom platform plate 6 and a double-bottom enclosure plate 7 .

[0031] The water intake system is connected to the bottom cooling channel 5 through a pipeline.

[0032] The exhaust system is connected to the bottom cooling channel 5 through a pipeline.

[0033] The present invention transforms the reactor pressure vessel 2 and the double bottom structure at the bottom of the marine nuclear power platform to form an emergency cooling channel and a bottom cooling channel 5. When the temperature of the reactor pressure vessel 2 rises abnormally, they can be put into use in a passive manner to ensure long-term cooling of the core.

[0034] In the present invention, a bottom cooling channel 5 is arranged at the bottom of the marine nuclear power platform. The double bottom structure of the platform below the pressure vessel 2 is utilized to arrange a double bottom enclosure 7 so as to enclose the double bottom into a closed space to form the bottom cooling channel 5 .

[0035] like Figure 1 As shown, in one embodiment of the present invention, the metal or alloy plate is preferably a lead plate 8. In this embodiment, the melting point of lead is 327.85°C, the boiling point is 1749.85°C, the chemical stability is good, it is basically inert, and it hardly reacts with water and air, and it has high thermal conductivity, which can effectively remove heat in a relatively small system. In this embodiment, by setting up an external cooling system for the pressure vessel, the pressure vessel support structure 3 surrounding the reactor pressure vessel 2 is used to partially cover the lead plate 8 with the lower ring section 12 of the pressure vessel, and an insulation layer 9 is provided between the lead plate 8 and the support structure 3 to reduce heat loss during normal operation. A container 19 is provided at the lower part of the reactor pressure vessel lower head 4, and a certain gap is left between the container 19 and the pressure vessel lower head 4 to form an emergency cooling channel. The number of lead plates covered by the lower ring section should be sufficient to ensure that the emergency cooling channel is filled after melting.

[0036] like Figure 1As shown, in one embodiment of the present invention, the other end of the water intake system is connected to the sea chest 10 through a pipeline. After an accident, seawater is introduced into the bottom cooling channel 5 through the sea chest 10, the air is discharged and filled with seawater, and the seawater in the emergency cooling channel 1 can conduct heat to the bottom cooling channel 5 through the steel structure below the pressure vessel 2, and then lead it out to the seawater through the lower double bottom platform plate 6. In this embodiment, the bottom cooling channel 5 is directly connected to the seawater through the bottom sea chest 10 of the platform side cabin. In this embodiment, the water intake system includes a sea chest 10 connected to the water intake pipeline, a bottom suction grille 13 arranged at the bottom of the sea chest 10, a sea valve 14 arranged at the outlet of the sea chest 1, and a containment water inlet isolation valve 15 arranged on the water intake pipeline outside the containment, and the water intake pipeline is connected to the sea valve 10 and the bottom cooling channel 5. The upper layer of the double bottom platform plate 5 is the containment bottom plate, and the lower layer is the hull outer plate.

[0037] like Figure 1 As shown, in one embodiment of the present invention, the exhaust interface of the exhaust system is arranged at the top of the bottom cooling channel 1. In this embodiment, the exhaust system is arranged at the top of the bottom cooling channel 5. The exhaust interface is arranged at the top of the bottom cooling channel 15 to ensure that the seawater can completely submerge the double bottom, exhaust the gas inside the double bottom, and ensure the heat transfer efficiency; after the seawater fills the bottom cooling channel 5, the heat of the pressure vessel can be conducted to the bottom of the containment 11 through the lead, and then transmitted to the seawater through the cooling channel. In this embodiment, the exhaust system includes a containment discharge isolation valve 16 and a side exhaust ball valve 17 connected to the exhaust pipeline, wherein the containment discharge isolation valve 16 is arranged on the exhaust pipeline outside the containment 11, the exhaust pipeline extends from the side cabin 18 to above the waterline and then extends out of the side cabin, and the side exhaust ball valve 17 is arranged on the pipeline before the exhaust pipeline extends out of the side cabin 18.

[0038] like Figure 1 As shown, in one embodiment of the present invention, the water intake system and the exhaust system are provided with a plurality of opening and closing valves, all of which are arranged outside the containment 11. In this embodiment, the manual valves of the water intake and exhaust pipelines are arranged outside the containment 11 to reduce the radioactive irradiation of the valves and facilitate the operation of the equipment after the accident.

[0039] In addition to providing an emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform, the technical solution of the present invention further provides a method for emergency cooling of a reactor pressure vessel of an offshore nuclear power platform using the above system, and the specific steps are as follows:

[0040] Step 1: When the marine nuclear power platform is operating normally, the pressure vessel external cooling system, the bottom cooling channel 5, the water intake system and the exhaust system are in a standby state, each valve is in a closed state, and the bottom cooling channel 5 is in a closed state;

[0041] Step 2: After the accident, the temperature of the reactor pressure vessel 2 rises abnormally, causing the metal or alloy plate outside the lower ring section 12 of the pressure vessel to melt and submerge the emergency cooling channel 1. It can be judged that the core may be melted. At this time, open the on-off valves on the water intake system and the exhaust system, and quickly inject seawater into the bottom cooling channel 5 to extract the heat of the core and alleviate the consequences of serious accidents.

[0042] In one embodiment of the present invention, the structure of the emergency cooling system of the reactor pressure vessel of the marine nuclear power platform is as follows: Figure 1 As shown, the reactor pressure vessel 2 is in a normal operating state, and the sea valve 14, the containment water inlet isolation valve 15, the containment discharge isolation valve 16 and the side exhaust ball valve 17 are in a closed state.

[0043] When an accident occurs on an offshore nuclear power platform, if the temperature of the reactor pressure vessel 2 rises abnormally, causing the lead plate 8 covering the outside of the lower ring section of the reactor pressure vessel 2 to melt and flow into the emergency cooling channel 1, it can be determined that the core is exposed and there is a risk of core meltdown. If the temperature and pressure in the reactor pressure vessel 2 continue to rise and reach the set limit, the following operations need to be performed:

[0044] 1) Open the side exhaust ball valve 17, the containment discharge isolation valve 16, and the containment water inlet isolation valve 15 to connect the bottom cooling channel 5 with the external atmospheric space;

[0045] 2) Open the sea valve 14 on the sea valve box 10, and the seawater is sucked into the grid 13 from the bottom and enters the sea valve box 10, flows through the containment water inlet isolation valve 15 and enters the bottom cooling channel 5;

[0046] 3) Seawater is injected into the bottom cooling channel 5, and the gas therein is discharged. After the seawater is filled, the state of the emergency cooling system of the reactor pressure vessel of the marine nuclear power platform after being put into operation is as follows: Figure 2 shown.

[0047] 4) The decay heat of the reactor pressure vessel 2 is transmitted to the emergency cooling channel 1 filled with lead through the lower head. The heat of the emergency cooling channel 1 is conducted to the steel plate at the bottom of the containment by convection, and then to the seawater in the bottom cooling channel. The lower double-layer bottom platform plate 6 is in direct contact with the external seawater, dissipating the heat of the bottom cooling channel 5 into the seawater.

[0048] Through the above methods, the accident process can be effectively mitigated, the risk of core meltdown can be reduced, and the core heat can be exported to seawater in a long-term and reliable manner.

[0049] The embodiments of the present invention utilize the inherent characteristics of lead's low melting point and a passive method to safely and reliably extract the decay heat of the core in the harsh scenario of power outage after an accident. By utilizing the low melting point of lead, the high temperature of the pressure vessel at the beginning of the accident melts the lead and fills the emergency cooling channel to form a channel for the pressure vessel to conduct heat to the outside; by utilizing the seawater level difference, cooling seawater is passively introduced to flood the bottom cooling channel in the double bottom; by utilizing heat conduction and heat convection, the reactor decay heat is passively transferred to the outer plate at the bottom of the platform, and the core heat is reliably extracted to the seawater for a long time.

[0050] The present invention makes efficient use of the original space and structure of the marine nuclear power platform, and utilizes the existing pressure vessel support structure, double bottom structure, sea valve box and other structures and equipment. Only limited sealing panels, lead blocks, pipelines and valves need to be added to implement the present solution, which occupies less resources and has high space utilization.

[0051] The lead plate coated on the outer wall of the pressure vessel in the embodiment of the present invention can be used as a primary shielding component during normal operation, effectively shielding the radiation source of the core and reducing the weight of the primary shielding.

[0052] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An emergency cooling system for reactor pressure vessels of marine nuclear power platforms, Features: The system comprises: A pressure vessel external cooling system, comprising a metal or alloy plate and an emergency cooling channel (1), wherein the metal or alloy plate is arranged between a reactor pressure vessel (2) and a pressure vessel support structure (3) surrounding the reactor pressure vessel (2); the emergency cooling channel (1) is arranged at the bottom of a lower head (4) of the pressure vessel; and a container (19) connected to the metal or metal plate is arranged below the emergency cooling channel (1); The melting point of the metal or alloy plate is higher than the temperature of the outer wall of the reactor pressure vessel (2) and lower than the temperature of the pressure vessel (2) when the core (5) is exposed; The bottom cooling channel (5) is a double-layer bottom closed structure, arranged below the pressure vessel (2), and comprises a double-layer bottom platform plate (6) and a double-layer bottom enclosure plate (7); A water intake system connected to the bottom cooling channel (5) through a pipeline; The exhaust system is connected to the bottom cooling passage (5) through a pipeline.

2. An emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform as claimed in claim 1, Features: The metal or alloy plate is preferably a lead plate (8).

3. An emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform as claimed in claim 2, Features: A thermal insulation layer (9) is provided between the metal or alloy plate and the pressure vessel support structure (3).

4. An emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform as claimed in claim 3, Features: A gap is left between the emergency cooling channel (1) and the lower head (4) of the pressure vessel.

5. An emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform as claimed in claim 4, Features: The other end of the water intake system is connected to the sea valve box (10) through a pipeline.

6. An emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform as claimed in claim 5, Features: The exhaust port of the exhaust system is arranged at the top of the bottom cooling channel (1).

7. An emergency cooling system for a reactor pressure vessel of an offshore nuclear power platform as claimed in claim 6, Features: The water intake system and the exhaust system are provided with a plurality of opening and closing valves, all of which are arranged outside the containment vessel (11).

8. An emergency cooling method for a reactor pressure vessel of an offshore nuclear power platform, Features: The system according to any one of claims 1 to 7 is used to perform emergency cooling on the reactor pressure vessel of an offshore nuclear power platform, and the specific steps are as follows: Step 1: When the marine nuclear power platform is operating normally, the pressure vessel external cooling system, the bottom cooling channel (5), the water intake system and the exhaust system are in a standby state, each valve is in a closed state, and the bottom cooling channel (5) is in a closed state; Step 2: After the accident, the temperature of the reactor pressure vessel (2) rises abnormally, causing the metal or alloy plate outside the lower ring section (12) of the pressure vessel to melt and flood the emergency cooling channel (1). The on-off valves on the water intake system and the exhaust system are opened, and seawater is quickly injected into the bottom cooling channel (5) to extract the heat from the core (5).

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