Containment behaviour in Phebus FP

Abstract The international Phebus FP (fission product) programme investigated core degradation and radioactive product release originating from a core melt-down accident in Light Water Reactors. Five integral in-pile tests were performed at Cadarache. During these tests, the main processes which affect the severe degradation of fuel and control rods, the release of fission products and control materials, their transport through the reactor coolant circuit as well as their deposition as aerosols in the containment vessel were assessed. Various physico-chemical processes such as aerosol agglomeration and various deposition modes, such as gravitational settling, diffusiophoresis and deposition on the stainless steel walls were analysed during each test considering containment components dimensioned to guarantee conditions representing as far as possible the reactor case. The radiochemistry of fission products in the sump and the gaseous atmosphere of the containment were scrutinized in order to determine volatile forms of fission products, which could be released to the environment due to a containment leakage or a deliberate venting during an accident. The experimental data base obtained contains a wealth of information to validate the computer codes used for safety and accident management assessment. Observations made in Phebus-FP containment vessel led to a thorough understanding of the in-containment source term and its coupling with thermal hydraulics under unsaturated but condensing atmospheres. This paper summarizes the main results of interest concerning the containment vessel experimental data obtained during the whole PHEBUS FP programme.