Crystallographic study of Si and ZrN coated U-Mo atomised particles and of their interaction with al under thermal annealing

A new type of high density fuel is needed for the conversion of research and test reactors from high to lower enriched uranium. The most promising one is a dispersion of atomized uranium-molybdenum (U-Mo) particles in an Al matrix. However, during in-pile irradiation the growth of an interaction layer between the U-Mo and the Al matrix strongly limits the fuel's performance. To improve the in-pile behaviour, the U-Mo particles can be coated with protective layers. The SELENIUM (Surface Engineering of Low ENrIched Uranium-Molybdenum) fuel development project consists of the production, irradiation and post-irradiation examination of 2 flat, full-size dispersion fuel plates containing respectively Si and ZrN coated U-Mo atomized powder dispersed in a pure Al matrix. In this paper X-ray diffraction analyses of the Si and ZrN layers after deposition, fuel plate manufacturing and thermal annealing are reported. It was found for the U-Mo particles coated with ZrN (thickness 1 μm), that the layer is crystalline, and exhibits lower density than the theoretical one. Fuel plate manufacturing does not strongly influence these crystallographic features. For the U-Mo particles coated with Si (thickness 0.6 μm), the measurements of the as received material suggest an amorphous state of the deposited layer. Fuel plate manufacturing strongly modifies its composition: Si reacts with the U-Mo particles and the Al matrix to grow U(Al, Si)₃ and U ₃Si₅ phases. Finally both coatings have shown excellent performances under thermal treatment by limiting drastically the U-Mo/Al interdiffusion.