阅读说明：本技术 一种用于反应堆熔融物碎片床的注水冷却系统 (Water injection cooling system for reactor melt fragment bed ) 是由 黄政 张慧敏 孙婧 孙晓晖 周喆 李汉辰 王贺南 常愿 蔡盟利 雷宁博 李精精 于 2021-07-02 设计创作，主要内容包括：本发明属于核电厂反应堆安全系统技术领域,具体涉及一种用于反应堆熔融物碎片床的注水冷却系统,包括设置在安全壳(10)内部底端的堆坑内的集水底盘(4),冷却水(8)能够由集水底盘(4)的内部向上方涌出至集水底盘(4)的上表面。本分明能够在核电厂发生严重事故时将熔融物碎片床内的衰变热量快速有效地导出,并在长期阶段维持熔融物碎片床的可冷却性,从而保持安全壳结构的完整性,缓解事故后果。(The invention belongs to the technical field of nuclear power plant reactor safety systems, and particularly relates to a water injection cooling system for a reactor melt fragment bed, which comprises a water collecting chassis (4) arranged in a pit at the bottom end in a containment (10), wherein cooling water (8) can flow upwards from the inside of the water collecting chassis (4) to the upper surface of the water collecting chassis (4). The method can rapidly and effectively lead decay heat in the molten material fragment bed out when a severe accident occurs in a nuclear power plant, and maintain the coolability of the molten material fragment bed in a long-term stage, so that the integrity of a containment structure is maintained, and the accident consequence is relieved.)

1. A water injection cooling system for a reactor melt scrap bed, characterized by: including setting up water collection chassis (4) in the pit of the inside bottom of containment (10), cooling water (8) can by the inside of water collection chassis (4) upwards gushes out to the upper surface of water collection chassis (4).

2. A water injection cooling system for a reactor melt scrap bed as claimed in claim 1 wherein: still including setting up inside, the being used for of containment (10) storage water tank (1) of cooling water, the position of water tank (1) is higher than the position of water-collecting chassis (4), water tank (1) through downing line (2) with water-collecting chassis (4) intercommunication, the cooling water can be by gravity by water tank (1) process downing line (2) get into water-collecting chassis (4) inside and upwards gush out to the upper surface of water-collecting chassis (4).

3. A water injection cooling system for a reactor melt scrap bed as claimed in claim 2 wherein: the upper surface of the water collecting chassis (4) is provided with a plurality of injection nozzles (5), and the cooling water (8) in the water collecting chassis (4) flows out to the upper surface of the water collecting chassis (4) through the injection nozzles (5).

4. A water injection cooling system for a reactor melt scrap bed as claimed in claim 3 wherein: further comprising a sacrificial concrete material layer (6) covering the water collecting chassis (4) and the injection nozzle (5), the sacrificial concrete material layer (6) having a composition of Fe₂O₃And the like.

5. A water injection cooling system for a reactor melt scrap bed as claimed in claim 2 wherein: one end of the descending pipeline (2) is communicated with the bottom of the water tank (1), and the other end of the descending pipeline (2) is communicated with the side wall of the water collecting chassis (4).

6. A water injection cooling system for a reactor melt scrap bed as claimed in claim 5 wherein: the descending pipeline (2) is provided with a valve (3) which can be remotely controlled.

7. A water injection cooling system for a reactor melt scrap bed as claimed in claim 6 wherein: the descending pipelines (2) are uniformly distributed on the circumferential position of the water tank (1).

8. A water injection cooling system for a reactor melt scrap bed as claimed in claim 2 wherein: the water tank (1) is of an annular structure and is arranged close to the inner wall of the containment (10).

9. A water injection cooling system for a reactor melt scrap bed as claimed in claim 2 wherein: the injection nozzle (5) is made of high-temperature-resistant ceramic.

Technical Field

The invention belongs to the technical field of nuclear power plant reactor safety systems, and particularly relates to a water injection cooling system for a reactor melt fragment bed.

Background

In the event of a severe accident in a Light Water Reactor (LWR) nuclear power plant, the reactor core rapidly heats up due to loss of cooling capability, and causes melting of fuel assemblies and collapse of internals. The core melt then migrates and accumulates in the lower chamber of the reactor pressure vessel. If the reactor vessel wall is broken due to thermal shock, the core melt is injected from the break into the reactor pit. If the reactor pit is submerged by the cooling water, the sprayed high-temperature melt further generates strong physical and chemical action with the cooling water, is broken into fine particles and is deposited at the bottom of the pit, and thus a porous melt fragment bed is formed. After that, the bed of fragments of melt is continuously cooled and the decay heat carried by the particles of fragments is continuously discharged, so that the accident process can be finally and successfully terminated; otherwise, the fragment particles are heated and melted again to form a molten pool, so that the integrity of the concrete structure of the containment floor is threatened, and a large amount of radioactive substances can be released to the external environment.

Conventional secondary nuclear power plant designs do not have mitigation measures specifically directed to off-stack smelt debris bed cooling. The mitigation strategies of the third generation advanced nuclear power plants for the out-of-pile melt fragment bed can be roughly divided into two types: one is the melt reactor pressure vessel internal retention (IVR) strategy, represented by us AP1000, which maintains the integrity of the reactor pressure vessel by flooding the pit to cool the reactor pressure vessel outer wall surface under accident conditions. However, the mitigation measures are only directed to the melt in the reactor pressure vessel, and once the reactor pressure vessel fails, the melt outside the reactor pressure vessel cannot be further cooled; furthermore, IVR strategies cannot be applied to more powerful heap types due to limitations in external cooling capacity. Another type is the Core catcher (Core catcher) design represented by french EPR (see fig. 1) and russian VVER (see fig. 2), whose basic principle is to first mix the sprayed high temperature melt with the sacrificial material concrete, then spread it on a steel plate precoated with high temperature inert material, and then to perform cooling by injecting cooling water from the top of the melt to submerge the melt. The core catcher strategy also has its own limitations. On the one hand, the cooling water is submerged from the top to the bottom of the molten material fragment bed, and a large amount of steam generated in the cooling process flows from the bottom to the top. Since the two fluids flow in opposite directions, there is a possibility that the cooling water cannot permeate down into the interior of the melt chips effectively due to the obstruction of the upward vapor flow (referred to as the CCFL phenomenon). Especially the area near the bottom, it is likely difficult to obtain efficient cooling. On the other hand, the results of the existing experimental study and program calculation also show that: the coolability of the melt chip bed, with cooling water flooded from the top, is largely dependent on the height of the formed melt chip bed. Thus, if the bed of molten material fragments is not effectively spread during the formation process, it may result in the bed of molten material fragments eventually not being cooled effectively.

Disclosure of Invention

The invention aims to provide a high-efficiency passive cooling system aiming at a molten substance fragment bed formed in a pit under a severe accident of a nuclear power plant, which is used for quickly and effectively guiding decay heat in the molten substance fragment bed out and maintaining the coolability of the molten substance fragment bed in a long-term stage, thereby maintaining the integrity of a containment structure and relieving accident consequences.

In order to achieve the purpose, the invention adopts the technical scheme that the water injection cooling system for the reactor molten material fragment bed comprises a water collecting chassis arranged in a pit at the bottom end in the containment, and cooling water can flow upwards from the inside of the water collecting chassis to the upper surface of the water collecting chassis.

Further, still including setting up the containment is inside, be used for the storage the water tank of cooling water, the position of water tank is higher than the position on water collection chassis, the water tank pass through the descending pipeline with water collection chassis intercommunication, cooling water can be passed through gravity by the water tank process the descending pipeline gets into water collection chassis is inside and upwards gush out extremely the upper surface on water collection chassis.

Furthermore, a plurality of injection nozzles are arranged on the upper surface of the water collecting chassis, and the cooling water in the water collecting chassis flows out to the upper surface of the water collecting chassis through the injection nozzles.

Further, the water-collecting device also comprises a sacrificial concrete material layer which covers the water-collecting chassis and the injection nozzle, and the component of the sacrificial concrete material layer is Fe₂O₃。

Furthermore, one end of the descending pipeline is communicated with the bottom of the water tank, and the other end of the descending pipeline is communicated with the side wall of the water collecting chassis.

Furthermore, a valve capable of being remotely controlled is arranged on the descending pipeline.

Furthermore, the descending pipelines are uniformly distributed on the circumferential position of the water tank.

Furthermore, the water tank is of an annular structure and is arranged close to the inner wall of the containment.

Furthermore, the material of the injection nozzle is high-temperature-resistant ceramic.

The invention has the beneficial effects that:

1. accident consequences after the retention (IVR) strategy in the pressure vessel of the molten material reactor is invalid are considered, corresponding relieving measures are provided, and the capability and the safety of the nuclear power plant for dealing with serious accidents are further improved.

2. The melt scrap bed is cooled by a passive means under the accident condition, a safety-level power supply and an active pump are not needed, the system and equipment are simplified, the inherent safety of the nuclear power plant is improved, and the economy is guaranteed.

3. The mode of injecting water from the bottom instead of the traditional mode of flooding water from the top is adopted, so that the phenomenon that the injected cooling water is blocked by reversely flowing steam is avoided, the limitation of the CCFL phenomenon is overcome, and the infiltration capacity and the cooling efficiency of the cooling water are effectively improved.

4. The cooling capacity is primarily dependent on the flow rate of the cooling water bottom injection rather than the height of the debris bed being determinative of cooling as in the top submerged version, thereby reducing the need for flattening during melt formation and improving coolability.

Drawings

FIG. 1 is a schematic diagram of part of a third generation nuclear power plant core catcher system (French EPR) of the background of the invention;

FIG. 2 is a schematic diagram of a core catcher system of a third generation nuclear power plant of the background of the present invention (Russian VVER);

FIG. 3 is a schematic diagram of a water flooding cooling system for a reactor melt debris bed (including the positional relationship of containment 10 and core 11) according to an embodiment of the present invention;

FIG. 4 is a schematic perspective view of a water injection cooling system for a reactor melt scrap bed according to embodiments of the present invention;

FIG. 5 is a schematic diagram of the operation of a water injection cooling system for a reactor melt scrap bed according to the embodiments of the present invention;

in the figure: 1-water tank, 2-descending pipeline, 3-valve, 4-water collecting chassis, 5-injection nozzle, 6-sacrificial concrete material layer, 7-melt fragment bed, 8-cooling water, 9-steam, 10-containment vessel and 11-reactor pressure vessel.

Detailed Description

The invention is further described below with reference to the figures and examples.

As shown in fig. 3 and 4, the water injection cooling system for the reactor molten material fragment bed provided by the invention comprises a water collecting chassis 4 arranged in a pit at the bottom end inside a containment 10, and cooling water 8 can flow upwards from the inside of the water collecting chassis 4 to the upper surface of the water collecting chassis 4.

Still including setting up at the inside water tank 1 that is used for the storage cooling water of containment 10, the position of water tank 1 is higher than the position of the chassis 4 that catchments, and water tank 1 is through descending pipeline 2 and the chassis 4 intercommunication that catchments, and the cooling water can be gushed out to the upper surface of the chassis 4 that catchments upwards inside by water tank 1 through descending pipeline 2 entering the chassis 4 that catchments through gravity.

The upper surface of the water collecting chassis 4 is provided with a plurality of injection nozzles 5, and cooling water 8 in the water collecting chassis 4 is gushed out to the upper surface of the water collecting chassis 4 through the injection nozzles 5.

Further comprising a sacrificial concrete material layer 6 covering the water collecting bottom plate 4 and the filling nozzle 5, wherein the sacrificial concrete material layer 6 is Fe₂O₃Etc. for mixing with the injected high temperature melt, thereby reducing its temperature and power density, protecting the mechanical structural integrity of the injection nozzle 5.

One end of the descending pipeline 2 is communicated with the bottom of the water tank 1, and the other end of the descending pipeline 2 is communicated with the side wall of the water collecting chassis 4.

The descending pipeline 2 is provided with a valve 3 capable of being remotely controlled, and the valve is in a closed state when in normal operation, and is opened after receiving a signal of the damage of the reactor pressure vessel or an instruction of an operator after an accident occurs.

The downer lines 2 are several and evenly distributed over the circumferential position of the tank 1 (a total of 4 separate series of downer lines 2 are shown in fig. 4, for example only).

The water tank 1 is of an annular structure and is arranged close to the inner wall of the containment 10.

The material of the injection nozzle 5 is high temperature resistant ceramic, and the injection nozzle 5 is used for injecting cooling water into the molten material fragment bed in the pile pit.

Finally, the practical application of the water injection cooling system for reactor melt scrap bed provided by the present invention is described:

referring to fig. 5, when a severe accident of core melting occurs in a nuclear power plant and the wall surface of the reactor pressure vessel 11 is damaged, a large amount of high-temperature core melt is injected into the bottom reactor pit and reacts strongly with the cooling water. On the one hand, a bed of smelt fragments 7 formed by the breaking up of the high temperature smelt is deposited into the reactor pit and is brought into contact with and mixed with the layer of sacrificial concrete material 6, reducing the temperature and energy density of the smelt by mutual physicochemical action. On the other hand, when receiving a reactor pressure vessel breakage or an operator instruction, the control valves 3 on all the descent pipelines 2 of the system are simultaneously opened, and then the cooling water 8 stored in the water tank 1 flows into and converges to the water collection chassis 4 through the descent pipelines 2 under the action of gravity, and then permeates upwards through the injection nozzles 5 at the upper part to be injected into the pores in the mixed sacrificial concrete material layer 6 and the molten mass fragment bed 7. The cooling water 8 is heated by the fragment particles to generate steam 9, and the steam 9 flows upwards to take away heat in the melt fragment bed 7, so that the temperature of the melt fragment bed is reduced, and finally, the melt fragment bed is cooled and maintained. In particular, since the flow direction of the cooling water 8 and the steam 9 is the same, the upward osmotic flow of the cooling water 8 is not hindered by the steam 9, thereby facilitating the cooling of the melt chip bed 7 more. The water injection cooling system for the reactor melt fragment bed can be used for dealing with the serious accident process after the reactor pressure vessel 11 fails and relieving accident consequences.

The device according to the present invention is not limited to the embodiments described in the specific embodiments, and those skilled in the art can derive other embodiments according to the technical solutions of the present invention, and also belong to the technical innovation scope of the present invention.