X-ray tomography study on the crushing strength and irradiation behaviour of dedicated tristructural isotropic nuclear fuel particles at 1000 °C

Two types of dedicated Tristructural isotropic (TRISO) nuclear fuel partides, PyC-1 (Kernel/Buffer/PyC) and PyC-2 (Kernel/Buffer/SiC/PyC) from PYCASSO (rocarbon irradiation for creep and swelling/shrinkage of objects) neutron irradiation experiments, were studied. For unirradiated particles, crushing experiments using a unique hot cell, combined with in situ X-ray computed micro-tomography (XCT) imaging, were conducted at room temperature (RT) and at 1000 degrees C. Although the SiC layer on the particles is presumed to provide 'mechanical stability' to the TRISO particles, results showed a remarkable reduction (-45%) in the crushing strength of the PyC-2 partides at 1000 degrees C compared to RT. The fracture patterns of the two types of partides, both at the contact zone and on subsequent propagation, differ significantly at RT and 1000 degrees C. Further, irradiated particles (irradiation temperature: 1000 +/- 20 degrees C; irradiation doses: 1.08-1.23 dpa and 1.49-1.51 dpa) were imaged by XCT: 250 PyC-1 partides and 223 PyC-2 particles were studied in total and the change in radius/layer thickness in each type was examined. It was found that the buffer densification was lower in PyC-1 particles compared to PyC-2 partides, and the PyC layer shrank in the PyC-1 particles, whereas it expanded in PyC-2. Results are discussed in terms of how the residual stresses can impact the high-temperature and post-irradiation behavior of these particles. (C) 2019 The Authors. Published by Elsevier Ltd.