PWR degraded core analysis

A review is given of the various phenomena involved in degraded core accidents and the ensuing transport of fission products from the fuel to the primary circuit and the containment. Information has been gathered from world-wide published sources on the relevant physical and chemical phenomena and no one particular reactor or site is referred to. The most significant accident sequences from the three major PWR risk studies are reviewed. The condition and behaviour of water reactor fuel during normal operation and at the start of degraded core accidents is described. The generation of hydrogen from the Zircaloy-steam and the steel-steam reactions is reviewed. A discussion follows on the way in which the core deforms and finally melts after loss of coolant. Debris relocation studies are reported and containment integrity assessed. Finally the behaviour of fission product elements during the course of a PWR degraded core accident is considered. (U.K.)