Transmission electron microscopy investigation of neutron irradiated Si and ZrN coated UMo particles prepared using FIB

Two fuel plates, containing Si and ZrN coated U-Mo fuel particles dispersed in an Al matrix, were irradiated in the BR2 reactor of SCKCEN to a burn-up of ~70% 235U. Five samples were prepared by INL using focused ion beam milling and transported to SCKCEN for transmission electron microscopy (TEM) investigation. Two samples were taken from the Si coated U-Mo fuel particles at a burn-up of ~42% and ~66% 235U and three samples from the ZrN coated U-Mo at a burn-up of ~42%, ~52% and ~66% 235U. The evolution of the coating, fuel structure, fission products and the formation of interaction layers are discussed. Both coatings appear to be an effective barrier against fuel matrix interaction and only on the samples having received the highest burn-up and power, the formation of an interaction between Al and U(Mo) can be observed on those locations where breaches in the coatings were formed during plate fabrication.