VERDON programme has been launched by the CEA as a follow-up of VERCORS programme. It addresses the consequences of a degradation of fuel elements in contact with air following penetration of the vessel after the meltdown of part of the reactor core or the dewatering of a spent fuel storage pit, especially the release and chemical behaviour of ruthenium (tests of release of fission products have been held under EPICUR programme as well).
The data base on Ru release under air ingress conditions from irradiated PWR fuel rods was still scarce, as in the VERCORS programme, few tests have been performed in very oxidising conditions and more particularly under air ingress with significant amount of air. In this context, VERDON programme included specific air ingress test on a genuine irradiated UO2 fuel sample in its original cladding. As in VERCORS programme, the sample has been previously reirradiated at low power in a MTR reactor, in order to rebuild the inventory of short halflife fission products (including 103Ru). This test has been conducted in a new dedicated hot cell. The aim was not only to measure the release of fission products, but also to study their deposit on thermal gradient tubes and their potential revolatilisation induced by air injection. Compared to VERCORS, VERDON included by more detailed examinations of the fuel sample before and after the tests, using microanalytical techniques, such as SEM, EPMA and SIMS in order to determine the location of the fission products within the various phases as well as the corresponding compounds if possible. This gave better understanding of the mechanisms, which promote fission products release in such situations, as well as supported the associated modelling. VERDON programme is a part of the International Source Term Programme, which is composed of separate effect tests aiming at reducing uncertainties in severe accident analyses.
Facility is in operation.