The French "Institut de Radioprotection et de Sûreté Nucléaire" (IRSN) has worked for many years in the field of source term studies. In particular, the international in-pile Phebus FP (FP for fission product) programme was developed and performed by the IRSN at Cadarache with the support of the European Commission. This programme, composed of five integral tests, is devoted to the study of LWR severe accident, in particular for core degradation and source term. Phebus results provided experimental data of high interest for source term evaluation in the field of fission product release from the fuel, transport in the reactor coolant system and behaviour in the containment. This programme of integral experiments evidenced some gaps in the phenomenological knowledge on important safety issues, such as :
- iodine chemistry in the reactor coolant system and the containment,
- fission product release for high burn-up and MOX fuel,
- degradation and release processes in the presence of B4C control rod material,
- degradation and release processes in the presence of air, more particularly Ruthenium release (in case of air-ingress scenarios).
To complete the existing database, an additional Phebus test, FPT3, will be performed at the end of 2004 to provide data on B4C control rod effects on degradation, release and transport to the containment and additional data on iodine chemistry in the reactor coolant system and the containment.
In order to reduce remaining uncertainties, in parallel to integral tests, IRSN is currently developing out-of-pile experimental programmes, in accordance with priorities defined in the 5th Framework program of the EURSAFE project, dedicated to the study of:
- Iodine chemistry in the reactor coolant system (CHIP programme)
- Iodine chemistry in the containment (EPICUR programme)
- Ruthenium chemistry in the containment
- B4C rod degradation and release of degradation by-products (BECARRE programme)
- Oxidation of Zircaloy cladding under air (MOZART programme)
Other experimental programmes are under consideration; they concern:
- Quenching of degraded fuel rod (PRODHYG programme)
- Oxidation of U-O-Zr relocated mixtures resulting from fuel rod degradation (VIRTUOZ programme)
Outstanding results and open questions from Phebus FP programme will be described in the first part of the presentation. Objectives, description and planning of the out-of-pile programmes will be presented in the second part. Expected outcomes of these programmes with respect to reduction in uncertainties for source term evaluation will be discussed.