Preparation of bulk‐nanostructured UO 2 pellets using high‐pressure spark plasma sintering for LWR fuel safety assessment

Nuclear fuel undergoes a significant restructuration during its lifetime in the nuclear reactor. Especially at the rim of the pellet, large UO 2 grains disintegrate into a nanosized material. In this paper, we focus on the preparation of bulk UO 2 with grain sizes below 100 nm to investigate the physico‐chemical properties of this so‐called “high burn up structure” ( HBS ). Preparation of bulk nanocrystalline materials is a challenge that can be overcome using the high‐pressure spark plasma sintering ( HP SPS ) technique. In‐house developed HP SPS with 500 MPa applied pressure was used for compaction of 11 nm UO 2 powder obtained by oxalate conversion. The procedure yielded dense (>90%) compacts with grain size as low as 34 nm for samples sintered at 800°C.