Use of Phébus FP and other FP programs for atmospheric radioactive release assessment in case of a severe accident in a PWR (deterministic and probabilistic approaches developed at IRSN)

• Deterministic and probabilistic approaches are used for Source Term evaluations.
• The Phébus FP results contribute to improve the Source Term evaluations for PWRs.
• Iodine and ruthenium behavior have a large impact on the Source Term consequences.
• Iodine oxide seems to be one of the major iodine species in releases.

The Phébus FP1 program had a major importance in the development of knowledge on severe accident in the international nuclear safety community and has been helpful for the validation of phenomenological assumptions related to the core melt accident progression and then for the validation of simulation tools.The paper presents the contribution of the Phébus FP program to the calculation of radioactive releases to the atmosphere for reference accident scenarios (named “reference Source Term”) in case of a severe accident in a French PWR. The system-level code ASTEC is used for these evaluations. This approach has then been completed by the probabilistic approach (L2 PSA) which includes calculations of radioactive release for a very large number of accident scenarios.Several years after the last Phébus FP experiment, the paper presents the status of the modeling used for these Source Term calculations, presents some important results, highlights the contribution of previous research programs and explains how more recent results from the ISTP project have also been taken into account.Further expectations for the next few years are presented in conclusion.