A mechanistic approach of the sintering of nuclear fuel ceramics

The CEA and the COGEMA, as part of their effort to model the different stag es of the MOX fuel fabrication process, have specifically worked, on the si ntering stage. A physical mechanistic model of MOX fuel sintering is propos ed, as well as the numerical schemes that will lead to the achievement of t he corresponding software tool. The model takes into account surface diffus ion, grain boundary diffusion, volume diffusion, exchanges between solid an d gas, as well as the mechanical strains of grains. The scale at which conc entrations and strains are taken into account is smaller than grain size (0 .1 mum for green pellets and 10 mum for sintered ones). The numerical resol ution schemes of this problem have been conceived, and are also presented. They mainly consist of relaxation procedures to uncouple partial derivative mass conservation equations, flux balances along interfaces, non-linear po tential equality conditions at interfaces, and Navier-Lame equations over e ach grain. A code (SALAMMBO) is under construction, based on the latter; on ce validated by experimental and parametric tests, this code will describe Pu distribution, grain and pore size distribution, and local density of the pellets as functions of the sintering conditions, thus enabling further de velopments of the fabrication process such as the obtention of advanced mic rostructures of improved MOX fuels. (C) 2001 Elsevier Science B.V. All righ ts reserved.