New capabilities of simulating fission product transport in circuits with ASTEC/SOPHAEROS v.1.3

Modelling the behaviour of fission product (FP) in a nuclear reactor coolant system (RCS) undergoing a hypothetical severe accident is an important step in the evaluation of radioactive release outside a nuclear power plant. The SOPHAEROS module, part of the ASTEC system, aims at simulating main FP vapour and aerosol phenomena in the RCS. New capabilities of the module are here presented, such as chemistry computation and extended circuit configuration. After a description of the models, two applications are presented. The first one is a complete severe accident sequence considering all the RCS loops. It shows a non-negligible FP retention in all the loops and outlines the need for a deterministic approach to better account of all the RCS and not only the main estimated path for FP release. The second application is focused on a complex part of the RCS generally simplified in all the FP transport model: the reactor vessel upper plenum. FP retention in this volume is not well estimated. The SOPHAEROS code applied to this volume shows that FP retention is under-estimated, possibly leading to over conservative results.