Nuclear reactor containments

The containment for a nuclear reactor comprises a pre-stressed concrete structure having a steel lined cavity with a substantially hemispherical base and housing a primary vessel for containing a nuclear reactor core and ancillary equipment generally submerged in liquid coolant, the primary vessel being suspended by attachment at its rim to a roof lining and to steel anchors in a concrete roof structure. Cooling is provided for the upper peripheral region of the primary vessel and is so arranged that, in operation of the nuclear reactor the cooling effect increases progressively upwards to a maximum at the attachment of the primary vessel with the roof lining. The cooling system serves to reduce the temperature of the primary vessel in the region above the surface of the liquid coolant so that stresses at the attachment of the rim with the roof lining are low. Cooling associated with the roof lining of the cavity consists of a layer of concrete of higher thermal conductivity than the concrete of the structure through which cooling fluid can be conducted. (U.K.)