Modeling of low enrichment uranium fuels for research and test reactors

Abstract

During the last decade, a considerable international effort to develop a low enriched uranium fuel for research and test reactors with high uranium density has been underway. UMo-based alloys are the best candidates for achieving this conversion although several failures in U-Mo dispersion fuel plates like pillowing and large porosities have been reported during irradiation experiments, introducing obstacles to further developments. In this chapter we apply the BFS method to model the behavior of the interface Al/UMo_x and the interdiffusion of additives, as Si and Ge, added to the Al matrix, in order to identify the driving forces responsible for the observed effects. The basis features characterizing the real system are identified in this modeling effort as are: the trend to interfacial compound formation, the Al “stopping power” of increasing Mo concentration, the depletion of Si in the Al matrix and the reduced diffusion of Al into UMo with high Si concentration. These and other basic questions must be answered in order to have a better understanding of the basic behavior of this fuel previous to its qualification. While the approach presented in this chapter is relevant to other applications as well, it is important to highlight the influence that modeling techniques can have in problems of high technological importance, and the benefits arising from virtual experiments and detailed understanding from simple atomistic approaches.