OSMOSE Program: Main issues and R and D for material fabrication

OSMOSE (from the French acronym for 'OScillations in Minerve of isOtopes in 'Eupraxic' Spectra') is a major CEA program. Its purpose is to measure by means of sample containing the studied actinides that are oscillated inside the MINERVE facility, the integral absorption cross section of the principal actinide isotopes in thermal (MOX and UOx neutron spectra), epithermal and fast neutron spectra. The fabrication of the 'Minerve Actinides' samples have to meet strict technical requirements. The material is a dense actinide or ThO2-doped UnatO2 ceramic in the form of pellets inside double Zircaloy cladding. These constraints made it necessary to develop nuclear material and ceramic fabrication processes ensuring a final densification exceeding 95% TD, a homogeneous dopant distribution in the ceramic, and minimal pollution of the fabricated materials. The R and D program led to the specification of two fabrication processes capable of obtaining the basic materials with a high density (95.5%TD for UnatO2) with a uniform dopant distribution in the sample while controlling the sample pollution. Work is now in progress to specify the relevant chemical analysis means and methods, to test the essential fabrication equipment -particularly the hot cell furnace - and to qualify the YAG laser welding process for the cladding tubes. (authors)