Assurance of environmental safety through containment

In the initial years of nuclear power stations, safety strategy focused on ''design basis accidents'' which incorporated a broad scenario of accident possibilities, and which acted as an envelope for all accidents taken into account during the licensing procedure. The later sixties began consideration of accidents beyond the design basis accidents. These severe accidents could be assumed to be the result of an accident coupled with an independent and extensive failure of protection and safety systems. Containments and their safeguard systems have been designed for radiation source terms which could only occur under some severe accident conditions. However, containments to date have not been designed for the mechanical and thermal loads that could accompany severe accidents. Containments will be capable of accommodating the effects of severe accidents with relatively modest changes to the present containment designs, many of which changes are already contemplated in the next generation plants