With the exception of the mechanical annexe and turbine house, the buildings of the main power block are all designed to remain structurally intact, leak — tight {in the case of pressure-retaining parts) and functionally operable, to the extent required by their safety role, despite the occurrence of defined hazards including a safe shutdown earthquake. Because of its position close to the safety classified buildings, the mechanical annexe also has some capability for resisting an earthquake such that it will not fail and impair the functioning of the other buildings.

Other buildings designed to withstand seismic load­ings are the reserve ultimate heat sink auxiliary shut­down and diesel building, essential diesel buildings and the radioactive waste process and storage build­ing. The last-mentioned building is designed to retain liquid and solid wastes that may be spilled under the specified earthquake conditions.

The main building foundations are constructed of reinforced concrete. In the main power block, the reac­tor building, auxiliary and control building, fuel build­ing and the turbine house have separate foundations.

The buildings of the main power block are con­structed of reinforced concrete with some internal steel framing. The reactor building comprises the pre­stressed concrete primary containment vessel and its internal structures supporting the primary coolant sys­tem components. The containment base is of rein­forced concrete and contains a keyhole-shaped slot to accommodate the reactor pressure vessel and its instrument guide tubes. For leak tightness the con­crete containment structure has a 6 mm thick steel liner attached to its internal surfaces. Penetrations are provided for pipes and cables to enter the con­tainment and for man access. The two man access penetrations each incorporate two interlocked doors uuh an airlock between. There is an equipment hatch tor bringing large plant components into and out of the containment; this is provided for plant construc­tion, repair and replacement purposes. All these pene­trations are firmly anchored and sealed into the con­tainment wall. Except where it butts the auxiliary and fuel buildings, the containment is enclosed by a
steel-framed secondary containment enclosure build­ing, which provides for collection and filtration of leakages from the primary containment.

The containment is designed to contain the radio­active products and withstand the effects arising from postulated major reactor fault conditions such as a loss of coolant accident (LOCA). It also serves to protect the reactor primary coolant plant including the reactor vessel, steam generators, pressuriser and reactor coolant pumps. Massive reinforced concrete internal structures support the primary coolant plant within the containment. Structures embedded in these are designed to restrain the plant and prevent dam­age in the event of an earthquake and to limit dam­age due to postulated failure of major high pressure pipes. The concrete internal structures also function as radiation shields to shield operating and mainte­nance staff from excessive radiation exposure from the reactor coolant system components. The contain­ment internal height is 64 m, its internal diameter is 45.7 m, and its wall thickness is 1.3 m. It supports

within it a high level polar crane of 260 tonnes lifting capacity.