KR20000029086A - Water nuclear reactor with in-built receptacle - Google Patents

Abstract

PURPOSE: A water nuclear reactor equipped with an integrated receptor, related to a pressurized water or abnormal boiling water reactor comprising a receptor collecting the debris of solid or liquid, corium, generated from the reactor core in the event of an abnormal fusion of the reactor, is provided. CONSTITUTION: A reactor core(12) and peripheral inside equipments are located in the center of a vessel(10). The reactor(12) consists of a multiplicity of nuclear fuel assemblies installed on a lower horizontal plate(14). The peripheral inside equipments, such as the reactor core(12), the lower horizontal plate(14) and a punched plate(16), etc., hang on the cylindric vertical wall surface by a support and guide device. A receptor(20), comprising a ring collector(32) to collect the whole of corium in the serious event of an abnormal fusion of the reactor core, is located inside of the vessel(10) and in the lower part of the reactor core(12). The receptor(20) comprises a flameproof brick layer(24) and a metal case(26).

Description

Water nuclear reactor with in-built receptacle

The present invention relates to pressurized water or boiling water reactors, which include a bowl-shaped receiver that collects solid or liquid debris, ie, "corium", that occurs in the core upon accidental melting of the core.

In reactors, many systems have been devised and developed over the past few years to prevent critical accidents causing partial or complete melting of the core.

In particular, FR-A-2 341 181 discloses a retainer provided at the bottom of the reactor to prevent the vessel from being punctured by corium formed during the core's sudden melting. Such a retainer comprises several horizontal plates at regular intervals, fixed to the wall of the container, intersected by openings in which the plates are staggered and whose edges protrude upward. In the event of an accident, the corium that flows through this opening continues to move to a bell-shaped distributor located in the center of the horizontal plate to reach the bottom of the container.

In addition, US-A-3 964 966 discloses a corium acceptor inside a reactor vessel, cooled by a liquid metal and disposed below the core. This receiver, made of steel, hangs directly on the lower horizontal plate supporting the core. The heat exchange pipe intersects the base of the receiver and extends upwards inside the receiver. This pipe is closed at its upper end and communicates with the interior of the receiver via a hole.

Despite the coupling structure of the receiver device mounted inside the vessel of the water reactor, there is a risk of accidental melting of the core due to the explosion. The corium fragments break into small particles while flowing to the bottom of the vessel. The water contained in the reactor vessel evaporates in contact with the small corium particles. A vapor film is formed around each of the particles, causing a high energy shock wave, making it easy to explode. This type of explosion cause is commonly referred to as a "vapor explosion."

Currently, the receiver devices described for collecting and storing corium at the bottom of the water reactor vessel are not designed to prevent vapor explosion. Also, these devices are not protected from the effects of an explosion. Although the possibility of interaction between evaporated water and corium is low, this type of explosion cannot be completely eliminated. Extremely strong pressure peaks resulting from an explosion can damage the prototype of the receiver device and reduce its capacity.

OBJECT OF THE INVENTION The present invention relates to pressurized or boiling water reactors having a corium collection device integrated with the vessel and having a design capable of preventing the occurrence of vapor explosions, thereby preserving the prototype of the receiving device in the event of an explosion.

1 is a vertical cross-sectional view of the bottom of a water reactor according to the present invention in which an receiver is integrated with a container in the event of an accident causing melting of the core.

According to the present invention, this object is a water reactor comprising a vessel and a core provided inside the vessel, the container comprising a bowl-shaped receiver which is provided in a vessel below the core and is formed of at least a portion of a refractory material. Corium formed during accidental melting of the core can be collected and filled with a porous mineral material that can be mixed with the corium to reduce the temperature of the corium to an equilibrium temperature below the melting point of the refractory material. It is achieved by a number reactor.

In reactors made in this way, the corium formed during the accidental melting of the core flows into porous mineral materials that do not contain water and splits into small particles. Thus, a state in which a vapor explosion can easily occur, that is, a state in which the vapor film surrounds each of the corium particles can be avoided. Therefore, such an explosion cannot occur and the prototype of the receiver is maintained.

This effect is further enhanced by gradually cooling the corium while it moves to the porous mineral material provided in the receiver. In this way damage to the receptor due to melting of the refractory material can also be prevented.

In one preferred embodiment of the present invention, a means for diffusing and dispersing corium, such as a grid or horizontal perforated plate, is arranged on top of the receiver with the porous mineral material.

In this preferred embodiment of the invention, the porous mineral material is preferably a foamed ceramic comprising about 99% silica. The porosity of the mineral material provided in the receiver means a capacity capable of retaining a large amount of corium inside the receiver. Such porosity is preferably about 63% to about 80%.

The receiver is preferably separated from the bottom of the vessel by a space that allows water to circulate upwardly around the receiver. This circulation of water helps to cool the receiver, thus contributing to maintaining the prototype of the receiver.

The receiver may be hemispherical as needed or may consist of a hemisphere mounted on the cylinder.

In a preferred embodiment of the invention, the refractory material is arranged inside a steel case which is also part of the receiver in the form of a brick.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings, but the scope of the present invention is not limited thereto.

EXAMPLE

The embodiment shown in FIG. 1 relates to a pressurized water reactor. However, as already pointed out, the present invention is not limited to this type of reactor, but applies to all general number reactors. Thus, it can be applied to boiling water reactors.

Referring to Fig. 1, reference numeral 10 denotes a reactor vessel. Only the bottom of the container is shown in the figure. In the center of the vessel 10 is provided a core 12 and a peripheral internal device.

The core 12 typically consists of a plurality of nuclear fuel assemblies arranged vertically side by side. This assembly lies on the lower horizontal plate 14. This horizontal plate 14 is perforated so that the coolant contained in the vessel is circulated into these assemblies and is adjacent to the nuclear fuel assembly. The perforated distribution feed plate 16, which preferably has a convex bottom, is generally fixed below the horizontal plate 14.

The core 12 and peripheral internals such as the lower horizontal plate 14 and the perforated plate 16 are hooked to the cylindrical vertical wall of the container 10 by the support and guide device 18.

The core 12 and its peripheral internals may be formed in any shape other than that shown in the drawings, within the scope of the present invention.

According to the present invention, as shown in FIG. 1, the receiving receiver 20 is located inside the vessel 10 and also below the core 12. More precisely, the receiver 20 is located between the perforated plate 16 and the convex bottom of the generally hemispherical vessel 10.

Receptor 20 is designed to collect corium upon sudden melting of core 12. The term " corium " refers to a molten mass produced in the event of an accident and generally encompasses the fuel and its cladding and the cladding of the internal structures associated with the reactor control rods and the core 12. The receiver 20 is designed and arranged to collect all of the corium in the event of a serious accident in which the core 12 melts.

In the preferred embodiment of the present invention shown in FIG. 1, the receiver 20 is separated from the bottom of the container 10 by an upward passage space between the upper end around the container and the container 10. As indicated by the arrows in FIG. 1, circulation of water contained in the reactor vessel occurs through this space 22. When an accident occurs, the circulation of water is caused by natural convection in this space. The circulation of water produces an effect of cooling the receiver 20.

Receptor 20 includes one or more layers of bricks 24 of refractory material. This material is selected from as high a melting point as possible and with good chemical compatibility with corium. In particular, zirconium-based ceramic materials are preferred, which have the advantage of being widely used in the industry.

As shown in FIG. 1, the bricks 24 are arranged in parallel and preferably have adjacent complement ends of, for example, U- or dovetail shapes that engage each other.

Receptor 20 further includes a metal case 26 having a brick 24 therein. This metal case 26 may in particular be made of stainless steel. This includes an inner surface layer and an outer surface layer that completely applies brick 24. The case 26 also includes an upper flange connecting the upper ends of the inner surface layer and outer surface layer of the receiver 20 to each other.

The upper flange of the metal case 26 is used to hang the receiver 20 into the container 10. In this case, the upper flange is caught on the support 28 provided inside the container 10 as shown in FIG.

As a variant or supplement, a radial reinforcement (not shown) oriented radially about the vertical axis of the container 10 can be inserted into the space 22 separating the container from the receiver 20. In this case, the radial reinforcement has holes for circulating water in the space 22.

As shown in the embodiment, the receiver 20 is substantially hemispherical and coincides with the bottom of the vessel 10.

In a variant of the not shown embodiment, this substantially hemispherical shape may be extended upwards by a cylindrical portion centered on the vertical axis of the container 10. Such a device may be chosen especially if the receiver is formed only of the hemispherical portion, if the total amount of corium formed during the catastrophic event exceeds the capacity that the receiver 20 can accommodate. The assessment of the capacity that can be accommodated inside the receiver 20 is made in consideration of the porous mineral material 30 inside the receiver, which is described in more detail below.

In order to effectively collect the entirety of the corium generated by the core 12 during the catastrophic event into the receiver 20, a ring collector 32 may be provided above the receiver upper end as shown in FIG. This collector 32 may in particular overlie the upper flange of the receiver 20 via a cross-beam structure 33.

The upper surface of the collector 32 extends upwardly adjacent the wall surface of the vessel 10 and has a hopper shape that is curved inwardly. More precisely, the walls of the collector 32 and the vessel 10 to prevent the fragments and flow of the molten core from penetrating into the space 22 provided between the receiver 20 and the bottom of the vessel 10. The allowable distance between is a few centimeters.

According to one of the basic features of the present invention as described above, the receiver 20 is filled with a porous mineral material 30. This porous mineral material can be mixed with the corium formed during the accidental melting of the core 12 and from materials that can lower the temperature of the corium to an equilibrium temperature below the melting point of the brick 24 formed of the refractory material. Is selected. The water-free mineral substance 30 is mixed with corium to prevent the precondition of vapor explosion from occurring. This is because the water-free mineral material 30 prevents the formation of a vapor film around each of the corium particles formed by the cleavage of the corium as it flows into the receiver 20. Thus, the risk of receptor damage due to vapor explosion is virtually excluded.

The porous mineral material 30 filled with the receiver 20 is preferably a foamed ceramic containing about 99% silica. This type of material gradually cools the corium while it moves into the receiver 20. Thus, the temperature of corium is stabilized below the melting point of the refractory material forming brick 24.

In this way, it is possible to prevent the receptor 20 from being damaged by the melting of the refractory bricks.

The porosity of the mineral material 30 is determined in sufficient capacity to collect the entirety of the corium formed by melting of the core 12 into the receiver 20. The porosity of the material to reduce the flow rate of the corium and to sufficiently cool it while the corium flows is about 63% to 80%.

As shown in FIG. 1, it is desirable to have a means for diffusing and dispersing the corium on top of the receiver 20 comprising the porous mineral material 30. Such means may in particular consist of a horizontal perforated plate 34 or a horizontal grid.

A flow path 36 of corium is shown which is caused by melting of the core in the event of a serious accident. When the corium falls over the perforated plate 34, the corium is dispersed throughout the width of the receiver 20 through the holes in the plate. Corium then breaks up inside the porous mineral material 30 which does not contain water.

The present invention is not limited to the above embodiment. As already pointed out, the present invention can be applied to any type of nuclear reactor regardless of the arrangement of the core and surrounding internal structures. In addition, the shape and structure of the receiver may differ from that described above. It is also preferred to have a space 22, a corium diffusion means and a ring collector 32, although in some cases they may be omitted. Finally, the porous mineral material is preferably a silica-based foamed ceramic as described above, but may vary from case to case.

As mentioned above, the mineral substance eliminates the risk of vapor explosion. By the mineral material 30 the flow of corium is slowed and cooled to a temperature below the melting point of the refractory brick 24. In addition, the corium is cooled by a circulation of water designed to naturally convection inside the space 22, as in the general receiver 20. Thus, the receiver 20 can maintain a circular shape in an optimal state.

Claims (10)

A water reactor comprising a vessel and a core provided within the vessel, the reactor comprising a bowl-shaped receiver provided below the core in the vessel and at least partially formed of a refractory material, the receiver being capable of accidental melting of the core. A reactor characterized in that it is filled with a porous mineral material which can collect the corium formed during the wake up and mix with the corium to lower the temperature of the corium to an equilibrium temperature below the melting point of the refractory material. The reactor of claim 1, wherein the means for diffusing and dispersing corium is disposed above the receiver comprising the porous mineral material. 3. The nuclear reactor of Claim 2, wherein the means for diffusing and dispersing the corium comprises a grid or a horizontal perforated plate. The reactor of claim 1 wherein the porous mineral material is a foamed ceramic. The reactor of claim 4, wherein the foamed ceramic comprises about 99% silica. The reactor of claim 1, wherein the porous mineral material has a porosity of about 63% to about 80%. The reactor of claim 1, wherein the receiver is separated from the bottom of the vessel by an upward passage space for circulation of water. The reactor of claim 1, wherein the receiver is hemispherical. The reactor of claim 1, wherein the receiver comprises a hemisphere mounted on a cylinder portion. The reactor of claim 1, wherein the receiver comprises a metal case in which the brick of the refractory material is stored.