Location preferences of fission products in high density U(Mo) dispersion fuel element

Abstract

The development of fuels with low 235U enrichment has become valuable over the course of the last twenty years, being of special interest fuels with high density of U(Mo) dispersion in Al matrices. The aim is to replace high enriched fuel by low enriched one with relative U/Utot contents less than 0.2. Experimental evidence of U(Mo) under irradiation1–4 show the existence of an interaction layer (IL) between UMo and the Al matrix. The IL growth influences the mechanical integrity of the plates, generating a structural weakness. Swelling accumulation can ultimate lead to fuel plate failure. Characterization of the IL with different rates of fuel burn-up shows the presence of fission products (FP).5 In this way, Sr, Cs, Nd, La, Ce and Xe have been detected by electron probe microanalysis (EPMA), electron microscopy (SEM) and energy dispersive x-ray microanalysis (EDX).6 Other works have confirmed the nucleation and growth of fission gas bubbles (swelling) in the aluminum matrix.7,8 The FP accumulation has been observed by Huet et al.,2 in the IL and aluminum matrix interface. FP implantation in Al matrices has been measured by EPMA, and Nd content has been estimated through Xe presence in the precipitation and formation of bubbles2 for the swelling effect. From another point of view, the irradiation of fuel plates of UMo show that the formation of the IL depends on the fission rate, and the swelling, on the other hand, depends on the burn-up or the fission density.9 Similar concepts have been reported regarding the FP-induced swelling,10 and the acceleration of swelling due to the influence of recrystallized phases of UMo.11 In agreement with experimental researches focusing on the influence of the FP in the IL, in the present work the configurational energy has been calculated, based on the functional density theory (DFT), of the disordered phases bcc U(Mo), bcc U(Mo, FP), fcc U(Mo)Al3, fcc U(Mo,FP)Al3, fcc Al and fcc Al(FP). The selected FP are Nd, Ce, La and Pr. The code used is VASP.12,13 In order to simulate disordered solutions the Special Quasi Random Structures (SQRS)14,15 was employed.