Phébus-FP: Results and significance for plant safety in Switzerland

Phébus-FP is a multi-national collaborative programme comprising four integral and one debris bed melting and fission product release experiments. The integral experiments simulate the heat-up, degradation and fission product release and transport, thermal hydraulic response, aerosol behaviour and iodine chemistry in the containment. The total programme, including interpretation effort, runs from 1993 to ca. 2007. The experiments demonstrated new characteristics of core degradation, fission product and iodine chemistry and accident integral behaviour. PSI has participated extensively through planning support, interpretation of data from the experiments and analyses of the results to establish confidence in the models being used for plant application. A significant part of the PSI effort was performed to interpret the significance of silver iodide as an effective retention agent under typical reactor conditions. The conclusions are of an interim nature, since the data reduction and interpretation are not yet complete. The significance of the Phébus results for plant safety will be fully realised only after successful benchmarking of the computer codes against Phébus, and application to plant sequences. Such work remains in progress within the Phébus project and in various national programmes.