Transition from slow deflagration to detonation

A literature search on the safety of nuclear power plants in the presence of external gas cloud explosions is reported. It includes literature up to the beginning of 1983. After presenting the current licensing situation in the Federal Republic of Germany, some recent work on damage analysis of real vapour cloud explosions is discussed. Experiments with real vapour clouds and free hydrogen-air clouds are reported. The transition from deflagration to detonation is discussed in several steps - the transition in long tubes when the flame is confined, in partially confined hydrogen-air clouds and the jet ignition of free gas clouds. The last two are large scale experiments done in the Prototype Nuclear Process Heat programme. The conclusions are that even partial confinement of a hydrogen-air cloud leads to pressure build-up, jet ignition of a gas cloud must be avoided, detonative ignition has to be excluded and turbulence generating structures, eg grids, only produce a local pressure build-up and do not lead to a transition from deflagration to detonation. (U.K.)