Patent Number: 053435052
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A nuclear reactor core is located in a vessel 1 placed in a concrete walled well or shaft 2. The floor or foundation 3 extends beneath the well 2 and below the remainder of the power station. The recovery device is included in the floor 3 and comprises partitions 4 normally constituted by parallel steel plates defining narrow, elongated, empty volumes 5, which alternate with coolant channels 6. The coolant is normally water. Each of the coolant channels 6 is surmounted by a refractory concrete layer 7 and a continuous silica concrete layer 8 surmounts the refractory concrete layers 7, as well as the empty volumes 5. The silica concrete layer 8 can sufficiently deaden the shock of the falling molten material, while partly absorbing the heat thereof, so that the remainder of the recovery device is not exposed to excessive temperatures. As illustrated in FIG. 1, a refractory concrete enclosure 9 is placed at the bottom lateral sides of the well 2 and is in contact with the ends of the refractory concrete layers 7. It makes it possible to confine the molten mass preventing it from attacking the less resistant lateral walls of the well 2. The coolant channels 6 are connected by at least one pipe 10 common to a coolant source 11, which can be of a random nature such as a watercourse, an artificial lake or a sump of the power station. In the latter case it is conceivable that the sump would be empty during normal operation and would only be filled during an accident during which case the pipe 10 is open. However, it is more reliable to use permanently filled sumps and if then the water level is too high, valves 12 or other sealing devices can close the pipe 10 during normal periods. It is then advantageous for the valves 12 or said devices to open automatically, i.e. are controlled by a device sensitive to the temperature rise in the area of the coolant channels 6 or provided with fusible parts, which disintegrate when the neighbouring area is heated. An outlet 13, formed by at least one pipe opposite to the preceding pipe 10, makes it possible to freely give off the vapour produced by the heating process into the atmosphere. The operation of the recovery device in the case of an accident firstly involves the destruction of the continuous silica concrete layer 8 and then the molten material penetrates the empty volumes 5 without being able to attack the refractory concrete layers 7. This viscous molten material is then decelerated by the partitions 4 and only descends slowly, particularly as it is rapidly exposed to the cooling process, which significantly increases the molten material viscosity. The partitions 4 may be locally pierced by the very hot material, but this will not lead to any significant disturbance, because the material which comes into contact with the coolant will be exposed to an even faster cooling operation, which will solidify the material and transform it into a plug obstructing the opening. Therefore it is pointless to protect the partitions 4 by covering them with refractory material, which would significantly slow down the cooling process. The evacuation of the vapour permits a permanent and automatic replenishment of the cold coolant from the source 11 through the coolant channels 6, in order to compensate for the unbalance of the hydrostatic pressures. Circulation is purely natural and no pump or similar device is used. The aim is to solidify the core material when it is only occupying part of the empty volumes 5. However, if necessary, cooling can continue until the empty volumes 5 are completely filled. A refractory concrete plate 14 is located below the empty volumes 5 and the coolant channels 6 so as to provide a final protection for the floor 3 before it can be attacked. The rectilinear partitions 4 defining the channel-like empty volumes 5 have the advantage of permitting a significant cooling flow and a large heat absorption fluid volume. Moreover, the recovery device can be elongated in accordance with the slightly different construction shown in FIGS. 3 and 4. The refractory concrete enclosure 9 is supported by a foundation 15, which is also visible in FIG. 2, but which is in this case not continuous and instead has an interruption 16, whose width substantially corresponds to the internal diameter of the refractory concrete enclosure 9. The partitions 4 and the empty volumes 5, as well as the coolant channels 6 which they define, extend below the interruption 16 and out of the foundation 15 and the vertical of the well 2. This arrangement enables the molten core to spread to a greater extent and to be cooled more rapidly. The refractory concrete enclosure 9 is subject to a sufficiently small overhang to be permitted. FIG. 4 shows how the pipe 10 and the outlet 13 are connected to the ends of the coolant channels 6. The empty volumes 5 are isolated from the pipe 10 and the outlet 13 by the walls 17.