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)

Abstract

The Phébus FP1ASN – Autorité de Sûreté Nucléaire (French nuclear safety authority); ASTEC – Accident Source Term Evaluation Code; BIP – Behavior of Iodine Program; CHRS – Containment Heat Removal System; EPR – European Pressurised water Reactor); FP – Fission Products; IRSN – Institut de Radioprotection et de Sûreté Nucléaire; ISTP – International Source Term Program; L2 PSA – Level 2 Probabilistic Safety Assessment; LB-LOCA – Large Break Loss of Coolant Accident; MER – Modèle d’Evaluation des Rejets – acronym in French for « Models for Release Evaluations »; NPP – Nuclear Power Plants; PWR – Pressurized Water Reactor; RCS – Reactor Coolant System; SAMG – Severe Accident Management Guidelines; STEM – OECD Source Term Evaluation and Mitigation program; THAI – Thermal-hydraulics, Hydrogen, Aerosols and Iodine.1 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.