CN112201372A

CN112201372A - Method for realizing retention of molten material in reactor core of nuclear reactor

Info

Publication number: CN112201372A
Application number: CN202011109117.5A
Authority: CN
Inventors: 王佳赟; 黄高峰; 曹臻; 方立凯; 曹克美; 芦苇; 黄兴冠
Original assignee: Shanghai Nuclear Engineering Research and Design Institute Co Ltd
Current assignee: Shanghai Nuclear Engineering Research and Design Institute Co Ltd
Priority date: 2020-10-16
Filing date: 2020-10-16
Publication date: 2021-01-08
Anticipated expiration: 2040-10-16
Also published as: CN112201372B

Abstract

The invention provides a method for realizing reactor core melt retention in a severe accident situation of a nuclear reactor, which has the following characteristics: by arranging a reasonable containment submergible area, cooling measures and the coolant loading of a reactor primary loop, under the accident condition of reactor core melting, the containment submergible area is submerged to a specific height by using the coolant of the primary loop, and meanwhile, coolant circulation is formed in the containment, so that decay heat is removed, the integrity of a pressure vessel is maintained, and the retention in the molten material pressure vessel is realized. According to the method for retaining in the melt pressure container, the reactor cavity is submerged by adopting the primary loop water source, the retaining in the melt pressure container can be automatically realized without manual intervention, the safety level of a reactor can be effectively improved, the release of a large amount of radioactive substances to the environment is avoided, and the public health is protected.

Description

Method for realizing retention of molten material in reactor core of nuclear reactor

Technical Field

The invention relates to a method for retaining reactor melt, in particular to a method for retaining reactor core melt in the case of a severe accident of a nuclear reactor.

Background

For nuclear reactors, after a fission reaction has occurred, even if the nuclear reaction has ceased, the nuclear fuel still produces a significant amount of heat, i.e., decay heat, and thus three basic safety functions need to be followed during nuclear power plant set-up: reactor shutdown, decay heat removal, and radioactive containment.

Under normal conditions, decay heat is continuously removed by the waste heat discharge system after the reactor is shut down, and the nuclear fuel is ensured to be intact. However, in case of an accident, if a special safety facility fails accidentally, a primary loop of the reactor loses coolant continuously, and then the reactor core is exposed, so that the decay heat of the reactor core cannot be effectively led out, and the nuclear fuel is heated until the nuclear fuel is melted, namely serious accidents of the nuclear power plant, such as the accident of the Sanli island in 1979, the accident of the Fudao in 2011, and the like, occur. Without effective measures, the molten core will further melt through the pressure vessel and even through the containment floor, breaking through the safety barrier, resulting in the release of radioactive material to the environment.

In order to avoid such situations, the third generation nuclear power technology focuses on the prevention and mitigation of serious accidents, and a series of measures are taken to maintain the cooling of the melt and maintain the integrity of the containment. The use of a pressure vessel to achieve melt retention is one of the measures and also one of the solutions to achieve retention.

A large-scale third-generation passive power plant is provided with a built-in refueling water tank, and under the accident condition, a corresponding valve is opened by utilizing an automatic or manual triggering signal, and water in the water tank is injected into a reactor cavity by utilizing gravity to realize submergence. This solution requires the aid of a water tank and the need to actuate a valve, which can cause a retention measure to be unsuccessful when a signal occurs or the valve fails.

Chinese patent CN202887747U discloses an active and passive combined reactor cavity water injection system, which is provided with a refueling water tank outside a containment and a passive water tank inside the containment, wherein water in the refueling water tank realizes reactor cavity water injection by an active water injection pump, and a plurality of valves are also controlled on a water injection path; the passive water tank realizes passive water injection by controlling the opening and closing of a valve (depending on the power supply of a storage battery). The scheme needs to realize water injection by depending on an active pump or a valve powered by a storage battery, and measures are disabled under the condition that the power supply is lost or the valve cannot be opened due to signal or failure.

Chinese patent CN200920260693.2 discloses a reactor cavity water injection system for nuclear power system, which is a method of directly injecting an independent water source into a water injection cavity at the lower part of a reactor cavity through a water inlet pipeline by a power device. Likewise, the system will not function when power is lost or the valves on the lines fail.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for realizing the retention of core melt in a nuclear reactor under the condition of a serious accident. Specifically, by reasonably setting the water content of the reactor core and the containment flooding area and cooling the upper area of the containment, the pressure vessel can be flooded automatically by using the coolant in the primary loop of the reactor under the condition of the melting of the reactor core of the nuclear power plant, and the coolant circulation is realized in the containment, so that decay heat is continuously brought out, the retention in the molten material pressure vessel is realized, other signals, the assistance of equipment and any manual intervention are not needed, and the safety and the economical efficiency of the reactor are improved.

In order to achieve the purpose, the invention adopts the following scheme: the lower part of the containment is provided with a floodable area which can collect liquid water in the containment, and the pressure vessel loaded with the reactor core is positioned in the floodable area. The floodable area has a reasonable free volume, and in case of an accident, the coolant lost from the primary circuit can be flooded to a height not lower than the height of the lower head of the pressure vessel. The upper part of the containment is provided with a cooling measure which can condense steam in the containment, and the floodable area is communicated with the upper space, so that on one hand, the steam generated in the floodable area at the lower part can enter the upper space of the containment, and on the other hand, the steam in the upper space can enter the floodable area after being condensed.

Preferably, a passive mode is adopted to cool the containment to remove energy in the containment, so that steam in the containment is condensed.

Furthermore, if the water level of the floodable area is high enough, a flow channel can be arranged outside the pressure container, and flow heat transfer is formed at the position close to the wall surface outside the pressure container by utilizing the pressure difference and the density difference generated by the vapor phase and the liquid phase in the flow channel so as to strengthen the heat exchange capacity of the outer wall surface under the flooding condition of the pressure container.

In a preferred embodiment of the invention, a method is provided for achieving stagnation in a molten metal pressure vessel, the reactor cavity being in the lower region of the containment vessel, belonging to the floodable region, and the reactor pressure vessel being in the reactor cavity, wherein in the event of an accident in a nuclear power plant, a primary circuit of the reactor is continuously deprived of coolant, resulting in core fuel being exposed and melted by decay heat. And the coolant of the primary loop enters the containment vessel and then is collected in the reactor cavity, is at least submerged to the height above the lower end enclosure of the pressure vessel, and cools the outer wall surface of the pressure vessel by the coolant of the primary loop. The coolant enters the containment vessel in a steam form after being heated and evaporated, and flows back to the reactor cavity after being condensed in the upper area of the containment vessel, so that closed circulation is realized, decay heat is continuously removed, and the integrity of the pressure vessel is maintained.

Therefore, the method for retaining the molten material in the pressure vessel can fully utilize the existing water source of the primary loop of the reactor by setting the reasonable safe shell submergible area, the free volume and the water content of the primary loop, can automatically remove the heat in the reactor core molten state without additional water replenishing measures, keeps the integrity of the pressure vessel, completely does not need manual intervention, and greatly improves the safety of a nuclear power plant.

Under the condition that the reactor core is submerged by water, the temperature of the reactor core cannot be increased sharply due to the strong heat exchange capacity and high latent heat of vaporization of the water. And under the condition that the reactor core is exposed, the reactor core loses effective cooling, water in a primary circuit enters the containment vessel in a liquid state or steam mode, steam is condensed in the containment vessel and finally collected to the reactor cavity at the lower part of the containment vessel, and the reactor cavity is submerged. The molten reactor core is transferred into the lower end enclosure of the pressure vessel under the action of gravity, the outer wall surface of the pressure vessel submerged by water has strong heat exchange capacity, two-phase heat transfer can be realized by means of vaporization of water, generated steam enters the containment vessel and is condensed again, and then flows back to the reactor cavity to realize closed circulation, so that heat is continuously taken out, the integrity of the pressure vessel is maintained, the uncontrollable diffusion of the molten reactor core is avoided, and the safety is improved.

The conception and the resulting technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, features and effects of the present invention.

Drawings

FIG. 1 is a schematic view of a preferred embodiment of the method of the present invention for achieving melt retention;

FIG. 2 is a schematic diagram of a preferred embodiment of the present invention for achieving melt retention.

Wherein: 100-a reactor core; 110-a reactor pressure vessel; 120-a conduit connected to a pressure vessel; 200-a containment vessel cavity; 210-a compartment within a containment; 220-containment internal compartment walls; 230-upper space in containment; 240-condensate collection and reflux apparatus in containment; 310-containment wall; 320-containment shielding structure; 330-air inlet on containment shield structure; 340-safety shell shielding structure top outlet

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in further detail below.

As shown in fig. 1, in a method for retaining molten core in a nuclear reactor in a severe accident situation, a floodable area 200 is provided at a lower portion of a containment vessel 310, and a cooling means is provided in an upper space 230 to condense water vapor therein. Liquid water in the containment vessel 310 can be collected to the floodable area 200 by a collection device and corresponding piping 240, and communication between the floodable area 200 and the upper space 230, the pressure vessel 110 is located in the floodable area 200, and when water from a primary circuit enters the containment vessel 310, the pressure vessel 110 can be flooded to a certain height. A circuit refers to the pressure-containing boundary formed by the pressure vessel 110 and its associated piping 120.

Under normal operating conditions, the reactor core 100 generates heat and transfers the heat to the water in the pressure vessel 110, and the heat is transferred to the two circuits through the corresponding pipes 120 to realize circulation, thereby achieving the purpose of utilizing the core heat.

As shown in fig. 2, in case of accident, the failure of the dedicated system occurs due to accident, and no matter whether the pressure vessel 110 and the pipeline 120 connected thereto are breached, water in a loop will enter the containment vessel in a liquid or vapor state, and the reactor will be shut down under the action of the protection system, but due to decay heat, the reactor core still generates a large amount of heat. The heat continuously evaporates the residual water in the pressure vessel 110, so that the residual water enters the containment vessel from the breach or through the pressure protection device in a vapor state and/or a liquid state, the core is exposed and continuously heated, and finally the molten material is melted, and the molten material is transferred into the lower end enclosure of the pressure vessel under the action of gravity. The molten core 105 will heat the lower head wall of the pressure vessel 110. During an accident, as coolant in the primary loop continues to decrease, and this water enters the containment vessel in a vapor or liquid state, the vapor will condense at the containment wall 310, enter the cavity 200 through the passage 240 along with other liquid water, and accumulate in the cavity 200. When the core 100 melts, the volume of water in the cavity 200 has flooded at least to the level of the bottom head of the pressure vessel 100. The molten core 100 migrates into the lower head of the pressure vessel 100 to form a molten core 105, and the wall surface of the lower head of the pressure vessel 100 is heated. The water in the reactor cavity 200 is boiled under the heating of the wall surface of the lower end socket of the pressure vessel 100, and the steam enters the upper compartment 230 of the containment vessel along the channel and flows back after being condensed by the wall surface of the containment vessel 310, so that closed circulation is realized. Outside the containment 310, the air in the gap between the containment 310 and the shielding structure 320 is heated by the wall 310, the density of the heated air is reduced, the heated air generates an upward flow driving force and enters the atmosphere from the shielding structure outlet 340, and the cooler air enters the gap from the shielding structure inlet 330, so that the final heat discharge is realized. By means of the strong heat exchange capacity of two-phase heat transfer, the water in the containment vessel cavity 200 can continuously cool the wall surface of the pressure vessel 100 to maintain the integrity of the pressure vessel 100, so that the molten core 105 is retained in the pressure vessel 100, the threat to the containment vessel is avoided, and meanwhile, the release of a great amount of fission products to the environment is also avoided.

Compared with the prior art, the embodiment has the following beneficial effects:

1. according to the method for realizing reactor core melt retention under the condition of a serious accident of the nuclear reactor, the water filling amount of the primary loop and the submergible area of the containment vessel are reasonably set, the primary loop is submerged by adopting water, no additional water tank or water injection measure is needed, the system setting is simplified, and the economical efficiency is improved.

2. The method for realizing reactor core melt retention of the nuclear reactor under the condition of a serious accident provided by the embodiment makes full use of the existing water source of the primary circuit, realizes the purpose of ensuring safety under the condition of no manual intervention, and greatly improves the safety.

3. According to the method for realizing reactor core melt retention in the case of a severe accident of the nuclear reactor, the heat removal is preferably implemented in a passive mode, so that the long-term infinite heat removal can be realized, the possibility of releasing a large amount of radioactive substances is greatly reduced, and a better basis is provided for simplifying nuclear emergency.

It will be understood by those skilled in the art that various changes and modifications may be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that all such modifications and variations be included within the scope of the invention as determined by the appended claims and their equivalents.

Claims

1. A method for realizing reactor core melt retention in a severe accident situation of a nuclear reactor is characterized in that a containment submergible area and containment cooling measures are arranged, so that heat removal can be realized by a primary coolant under the situation of reactor core melting, and the integrity of a reactor pressure vessel is kept.

2. The method of claim 1 wherein the submergible region of the containment vessel is located in a lower portion of the containment vessel, and upon exposure and melting of the core, lost coolant from the primary circuit can flood the submergible region to a specified height.

3. The method of claim 2, wherein the reactor pressure vessel is located in a floodable area of the containment vessel, the flooding height being at least as high as and above a pressure vessel bottom head.

4. The method of claim 1 wherein the containment cooling means is located in an upper region of the containment vessel and removes heat and condenses steam within the containment vessel. The containment cooling measure can utilize the wall surface of the containment or can be provided with special cooling equipment.

5. The method as claimed in claim 1, 2 or 4, wherein the containment floodable area and the upper portion of the containment are communicated with each other, the steam generated in the containment floodable area can enter the upper space of the containment, and the liquid coolant condensed by the containment cooling means can enter the containment floodable area.