PROPOSAL FOR A FUTURE PHÉBUS TEST ON AIR INGRESS
R. Zeyen1, A. Mailliat2, B. Clément3, SN Annual Conference, Alicante.
The main issues for reactor safety in case of severe accident sequences are the containment integrity and the characteristics of the Source Term. Since the TMI2 accident, in March 79, the progress of research has made it possible to estimate the potential consequences of a rather large spectrum of severe accidents sequences. Nevertheless, there are still issues about Source Term which remain unaddressed and which impact on the reliability of the present estimates. Especially, one of the uncertainties is related to ruthenium source term evaluation in case of air ingress in a reactor pressure vessel both in shutdown events and whenever vessel penetration takes place in a non-inerted containment. Ruthenium source term is also a pending issue for accidents involving loss of coolant from a spent fuel storage pool and for some fuel handling accidents. In such air ingress situations, there are several experimental evidences that ruthenium is released from the reactor core as a volatile fission product and one of the ruthenium compounds may be still volatile in the containment conditions. It must also be pointed out that ruthenium radio-toxicity is comparable with the iodine one in the short term and the cesium one in the mid term. This analysis led IRSN and the EC Joint Research Centre to promote a new programme test named PHEBUS STLOC1 to be conducted in the Phébus facility after completion of the present Phébus-FP programme. Its main objective is the consequence on source term of air ingress on a degrading core. Test preparatory studies were made, mainly focused on reactor scenario analyses and literature search on ruthenium behaviour. It was decided, through expert recommendations, that the STLOC-1 test would simulate air ingress after melt-through of the reactor pressure vessel lower head, as well as the oxidation of fission products previously deposited, which, in certain cases may lead to their re-vaporisation. Within this presentation the PHEBUS STLOC1 experimental facility will be explained and some indications given on potential programme partners.