MXPA99007942A - A nuclear plant - Google Patents

Abstract

A nuclear reactor plant with a light water reactor, comprises a containment (1) having an upper space (2) and a lower space (3). The lower space is separated from the upper space by a separating member (4) and arranged to house a cooling medium (16). Furthermore, the plant comprises a reactor vessel (9) housing a reactor core (10) and provided in the upper space (2). The separating member (4) comprises a portion (7) which is arranged to be located at such a position that the surface of the portion (7) facing the lower space (3) is in contact with said cooling medium (16). The reactor vessel is provided above said portion (7).

Description

A NUCLEAR PLANT BACKGROUND OF THE INVENTION AND PREVIOUS TECHNIQUE The present invention relates to a nuclear reactor plant with an ordinary water nuclear reactor, comprising a confinement having an upper space and a lower space, which is separated from the upper space by a member separator and which is arranged to house a cooling medium, and a safety container of the nuclear reactor which houses a reactor core and which is provided in the upper space. Said nuclear reactor plants are known and have been proven to work in a satisfactory manner. However, if the reactor core for any reason reaches such a temperature that the fuel begins to fuse and the geometry of the core changes, it may happen that the core falls out of its original position and penetrates the bottom of the nuclear reactor's safety container. say, the so-called core merger. In this case, the nucleus will fall on the lower surface of the confinement. As long as the confinement is intact and the core can be maintained within the confinement, there is no real risk that the radioactivity in a larger amount will escape into the environment. However, if the nucleus is fused through confinement, the risk for such a leak is imminent. Different measures have been proposed to avoid this risk. One measure is to spray coolant on the core located on the bottom surface. However, said cooling from above may be insufficient, for a longer period of time, to prevent in a secure manner that any part of the core penetrates the confinement. Another proposed measure is to let the core fall into a pool of water provided below the safety container of the nuclear reactor. Another measure, which has been proposed, is to let the core fall into a container having double walls between which a cooling medium circulates to cool the core.

BRIEF DESCRIPTION OF THE INVENTION The object of the present invention is to provide a way to deal with a core that has fallen through the surface of the nuclear reactor safety container in such a way that the risk of radioactive emissions into the environment can be reduced. . This object is obtained by the reactor plant initially defined and characterized in that the separating member comprises a portion which is arranged to be located in such a position that the surface of the portion facing the lower space is in contact with the medium cooling, and that the safety container of the nuclear reactor is provided above that portion. By such a design of the reactor plant, which allows the feature that such portion is immersed in a cooling medium, the core in a possible core melt will fall on talc portion. Whereupon, the following essential advantages are obtained, on the one hand that the core in a passive manner is cooled from below by the fact that the lower surface of the portion is in contact with the cooling medium in the lower space and by another side that is provided another barrier that can be penetrated by the core before it reaches the surface of the confinement floor. In addition, if the core penetrates the portion anyway, the entire floor surface of the confinement is available to the core, i.e. the core can be distributed over a large area covered by such cooling means. Advantageously, the portion may comprise a surface arranged in such a way that the cooling medium can flow along the surface and remove the heat from such a portion. In such a way, one can ensure an efficient cooling from below the core which has fallen to a possible core melt, since the cooling medium flows along the surface and cools it by natural recirculation. According to another embodiment of the invention, the spacer member comprises a wall portion extending upwardly from and surrounding the portion such that the portion and the wall portion form a cavity of the spacer member. In such a case, the core in case of a possible core fusion will be located in a delimited space and it is also possible to let the wall portion be cooled from the outside by such cooling means in the lower space. In addition, it is possible to fill the cavity with water before the melt reaches such a portion, allowing the cooling to be improved.

According to another embodiment of the invention, a connection capable of being opened is provided to extend between the cooling means in the lower space and the cavity and to allow supply of the cooling medium to the cavity. In such a way it is possible to cool the core not only from below through the portion but also by direct supply of a cooling medium on the core. With this, the connection capable of being opened can comprise a conduit extending through the wall portion. In this way, the core can also be cooled from below, for example, by a cooling medium that flows above the core. In addition, the connection capable of being opened can comprise a portion of guns arranged to melt at a predetermined temperature and with this the connection will be able to open. In such a manner, the additional cooling will take effect as soon as the sufficiently high temperature has been achieved by the fuse portion. With this, the fuse portion can be comprised by said portion, which likewise involves the flow of the cooling medium into the cavity from below.

According to another embodiment of the invention, the lower space comprises a bottom surface formed by the lower limit wall of the confinement, said portion being provided at a distance from the bottom surface, wherein at least one support plate essentially vertical extends between the portion and the bottom surface. According to another embodiment of the invention, at least one channel extends through the separate member and connects the upper and lower spaces. The channel has a hole in the lower space, which is arranged to be located in the cooling means. By means of the channel, the possible discharge of steam into the upper space, which can lead to an increase in pressure therein, will be transported downward into the lower space and condensed in such cooling medium. According to an advantageous embodiment, the connection capable of being opened has a hole in the cavity, which is provided at a lower level than the orifice of the channel. In this way, it is ensured that the pressure of the cooling medium in the connection capable of opening will be sufficiently high to allow the cooling medium to flow through the connection capable of opening and into the cavity, and in such a way that the The core can be cooled at the same time as the water vapor above the core can be cooled by the cooler cooling medium in the lower space. In order to ensure efficient cooling of the core for a longer period of time, means may be provided for cooling such cooling medium in the lower space. Other features and advantages of the present invention will be more obvious from the following description of the different embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be explained in more detail by means of the modalities, defined by means of the example and with reference to the accompanying drawings, in which Figure 1 describes a section through a nuclear reactor plant according to the present invention.

DETAILED DESCRIPTION OF THE DIFFERENT MODALITIES The invention relates to a nuclear reactor plant with an ordinary water nuclear reactor, ie a reactor which may comprise a boiling water nuclear reactor, BR, or a pressurized water nuclear reactor. , PWR, and which uses water as a cooling medium and moderator. Figure 1 schematically describes a nuclear reactor plant comprising a confinement 1 housing an upper space 2 and a lower space 3, which are separated from each other by means of a spacer member 4 in the form of an intermediate wall. The intermediate wall 4 comprises a substantially peripheral planar portion and a cavity 6 centrally provided and defined by a lower portion 7 and a wall portion 8 extending around the lower portion 7 connecting this portion 7 to the peripheral portion 5. A Nuclear reactor safety container 9 is provided in the head space 2 and in such a way that at least a part extends downwardly into the cavity 6. In FIG., the core of the reactor contained in the safety container of the nuclear reactor 9 is described schematically.

The reactor plant described is of the so-called boiling water type and comprises a steam duct 11 which extends outwardly from the confinement 1 to a turbine plant to generate electric power. From the turbine plant, a water supply line 12 extends through the confinement 1 back into the safety container of the nuclear reactor 9. Above the confinement 1, there is another space 13 which is arranged to accommodate different pools , for example a pool with water in which the fuel rods can be provided during the repair and replacement of fuel. A number of channels 14, called extraction tubes, are provided between the upper space 2 and the lower space 3. It should be noted that one of the channels 14 is merely described in Figure 1. The confinement 1 comprises a lower limiting wall 15 which it forms an essentially flat bottom surface of the lower space 3. The lower space 3 is arranged to receive cooling means 16, for example * water. In addition, the lower space 3 is arranged to receive the amount of cooling means 16 such that the orifice of the channel 14 in the lower space 3 is located in the cooling means 16. On the other hand, in Figure 1 a device The heat exchanger 17 is schematically described, which is arranged to be connected to an external cooling circuit for cooling the cooling medium 16. Further, the flat portion 15 comprises at least one one way valve which is arranged to open a connection if the pressure in the lower space is higher than the pressure in the upper space 2 to be able to equalize the pressure both in space 2 and in space 3. In addition, in Figure 1 a connection capable of opening 18 in the form of pipe conduit between the cavity 6 and the lower space 3. The connection capable of opening 18 can comprise a valve member that allows automatic opening in a core fusion. The connection capable of opening 18 may also comprise a fuse fuse, which at a temperature increased to a predetermined level melts and opens the connection 18. On the other hand, a connection capable of opening 19 may be provided in the portion 7, which may also comprise a valve member or a fusion fuse that melts at a predetermined temperature and that opens the connection 19 in such a way that the cooling means 16 can flow through into the cavity 6. As seen from FIG. Figure 1, in a boiling water nuclear reactor the open-able connections 18 and 19 are provided at a lower level and in the orifice of the channel 14. Due to the cooling, by the heat-inducing device 17, the pressure in the upper space 2 is somewhat higher than in the lower space 3, comparing the liquid level slightly lower in the channel 14 than the lower space 3. In a possible vapor leak in the In the upper space 2, the steam will thus be transported downwardly through the channel 14 and condensed in the cooling medium 16. The lower space 3 and the cooling means 16 present inside it consequently form the so-called condensation pool . The lower portion 7 in the cavity 6 comprises a lower surface which is immersed in the cooling means 16 and which allows the natural flow of the cooling medium along the surface. Said flow can be improved if the surface is, for example, convex. It can also be essentially flat and inclined in some way in relation to the horizontal plane. Also other shapes of the surfaces are possible to be able to increase the flow of the cooling medium and with this the cooling in the portion 7. The lower portion 7 can be made of different types of material. For example, it can be mentioned that it can comprise a steel plate, the lower surface of which is placed in direct contact with the cooling means 16 in the lower space 3. Thus, a satisfactory heat transfer between the cavity 6 and the increase means 16 is ensured. In addition, vertical support plates 20 can be provided between the lower portion 7 and the lower boundary wall 15 of the confinement 1. These support plates 20 can be provided for example with a star configuration and radially extending. The purpose of the support plates 20 is on the one hand to increase the heat transfer surface of the lower portion 7 and on the other hand to form a support for the lower portion 7 and to absorb the forces that may arise for example from explosions. Possible vapor in the cavity 6. The support plates 20 are designed and positioned in such a way that they do not alter the flow of the cooling medium 16 along the lower portion 7. If the reactor core 10 for any reason reaches a Increased temperature and begins to melt, and with this its position is lost in the safety container of the nuclear reactor 9 and falls against and through the bottom of the safety container of the nuclear reactor 9, the core 10 changes geometrically in such a way, * that it will be placed in the lower portion 7. Since the lower portion 7 and the wall portion 8 are cooled from outside by the cooling means 16, the portion 7 at least during advantageous conditions so in a passive way it will resist the heat developed by the core 10 that has fallen. The cooling of the core will be improved by the direct supply of the cooling medium 16 to the core via the connection capable of opening 18 and / or the connection capable of opening 19. Since the orifice of the channel 14 is located above the connections 18, 19 it is ensured that the pressure of the cooling medium 16 can always overcome the pressure prevailing in the upper space 3 and in particular in the cavity 6 in such a way that the cooling means 16 flows inwardly through the connections 18 and 19. Further, in a possible core melt, the design of the cavity 6 and its bottom 7 will cause the core heat, which has fallen into the cavity, to be transferred to the cooling medium 16 via the bottom 7 of such so that the pressure in the lower space 3 increases and is higher than the pressure in the upper space 2. However, at the same time the cooling medium will be supplied to the core via the connections 18 and 19 at least while the pressure in the lower space 3 is higher than in the upper space 2. The cooling medium, which in this way supplies the core which has fallen, will evaporate, which increases the pressure in the upper space 2 of such Thus, the downward blowing is carried out through the channels 14. Consequently, the conditions are not always stable and the gas generated by the dropped core will be stored both in space 2 and in space 3 in such a way that sustains a reduction in total pressure. If the cooling is not sufficient, the core after a time will melt through the lower portion 7 and will fall into the cooling medium 16 in the lower space 3. As can be seen in Figure 1, the bottom surface of the lower space 3 has a significantly larger area than lower portion 7 and whereby the core can be spread over a larger area on the bottom surface. During the passage of the molten core through the portion 7, it will be divided and in this way the cooling effect is increased. Consequently, these factors will result in a more efficient cooling of the core by means of the cooling means 16 and with this it is also possible to prevent the core from penetrating the lower limit wall 15 of the confinement 1. By the arrangement according to the invention, another barrier in a core fusion possible in this way can be provided. This design may have an essential significance in order to ensure that there is no leakage of radioactivity to the environment outside confinement 1. It should also be noted that the arrangement according to the invention is completely based on passive measures, that is, does not imply the fusion of pumps or other actively driven members in order to ensure the integrity of the confinement 1 in a possible core fusion.

The present invention is not limited to the described embodiment but may be varied and modified within the scope of the following claims. For example, it should be noted that the plant can comprise either one of the connections capable of opening 18 and 19, both of these or none. It is also possible to provide more open-able connections that extend around the wall portion 8. Although. the described modality refers to a boiling water nuclear reactor, it should also be noted that the principles according to the invention can also be applied to the so-called nuclear pressurized water reactor.

Claims (12)

1. A nuclear reactor plant with an ordinary water nuclea-r reactor comprising a confinement having an upper space and a lower space, which is separated from the upper space by a separating member and which is arranged to house a cooling medium and a safety container of the nuclear reactor housing a refractor core and provided in the head space, characterized in that the spacer member comprises a portion which is arranged to be located in such a position that the surface of the portion faces the lower space and is in contact with the cooling medium, and that the safety container of the nuclear receiver is provided above such portion.

2. The nuclear reactor plant according to claim 1, characterized in that the portion comprises a surface arranged in such a way that the cooling medium can flow along the surface and remove heat from such portion.

3. The nuclear reactor plant according to any of the rei indications 1 and 2, characterized in that the separating member comprises a wall portion that extends upwards and surrounds the portion such that the portion and the wall portion form a cavity of the sperm member.

4. The nuclear reactor plant according to claim 3, characterized in that the connection capable of being opened is provided to extend between the cooling medium in the lower space and the cavity and to allow the supply of such cooling medium to the cavity.

5. The nuclear reactor plant according to claim 4, characterized in that the connection capable of opening comprising a conductor extending through the wall portion.

6. The nuclear reactor plant according to any of claims 4 and 5, characterized in that the connection capable of being opened comprises a fuse portion arranged to melt at a predetermined temperature and thereby open the connection capable of being opened.

7. The nuclear reactor plant according to claim 6, characterized in that the fuse portion is comprised by such portion.

8. The nuclear reactor plant according to any of claims 4 to 6, characterized in that the connection capable of being opened comprises a valve member.

9. The nuclear reactor plant according to any of the preceding claims, characterized in that the lower space comprises a bottom surface formed by the lower limiting wall of the confinement, said portion being provided at a distance from the bottom surface, and that by at least one essentially vertical support plate extends between the portion and the bottom surface.

10. The nuclear reactor plant according to any of the preceding claims, characterized in that at least one channel extends through the separating member and connects the upper and lower spaces, and that such channel has a hole in the lower space , which is arranged to be located in the cooling medium.

11. The nuclear reactor plant according to claims 4 and 10, characterized in that the connection capable of being opened has a hole in the cavity, which is provided at a lower level than the orifice of the channel.

12. The nuclear reactor plant according to any of the preceding claims, characterized by the means arranged to cool such cooling medium in the lower space.