Development and qualification of the LOCA analysis system CUPIDON-DEMETER

As a support to the power reactor safety analysis, codes describing PWR-type fuel behaviour under LOCA conditions have been developed by CEA under the sponsorship of IPSN (Institute for Nuclear Safety and Safeguards). These codes are CUPIDON for unirradiated single fuel rod and DEMETER devoted to the prediction of the behaviour of a whole assembly. An extensive qualification program is underway. The main models: heat transfer, zircaloy oxidation and cladding deformation and rupture, have been separately benchmarked using PHEBUS experiments, German and Japanese transient tests and EDGAR transient tests. Qualification with global tests FLASH and PHEBUS is now underway. From the first calculations, it is concluded that CUPIDON gives a fair account of the behaviour of the rods tested in FLASH and PHEBUS. The new developments of the codes will mainly include: the influence of azimuthal differences of cladding temperature on zircaloy creep rate; the influence of the irradiation effect on mechanical behaviour if it proves significant; the introduction of a subchannel flow blockage index, using in particular PHEBUS phase II results. (author)