A Phase-Field Description of Brittle Crack Propagation in Nuclear Fuels
Résumé
The fuel element of most Pressurized Water Reactors are made of a stack of uranium dioxide pellets where
heat-generating nuclear fission reactions take place and a zirconium alloy cladding which constitutes a guarantee
against dispersion of fissile material and fission products. Modelling the in-reactor behaviour of such fuel elements
is made complex by the myriad of coupled, nonlinear, chemical, mechanical, thermal and microstructural changes
that take place within the fuel. From the mechanical point of view alone, various contributions must be taken into
account, such as brittle fracture of the fuel pellets at reactor start-up, thermally and radiation induced viscoplasticity,
swelling due to fission products, pellet-cladding mechanical interaction (PCMI), etc. The cracking of pressurised
water reactor fuel pellets has the two main consequences on the macroscopic mechanical behaviour of the fuel rod:
firstly, to relieve the stress in the pellet, upon which the majority of the mechanical and physico-chemical
phenomena are dependent, and secondly, to lead to pellet fragmentation. Taking fuel cracking into account is
therefore necessary to adequately predict the mechanical loading of the cladding during the course of an
irradiation. Simulating these phenomena is challenging both from a numerical standpoint and from the point of view
of the physical phenomena involved. As a result of this, advanced and robust numerical techniques are necessary,
especially in large-scale fuel performance. Our presentation will focus on the treatment of the fuel cracking through
a phase-field approach using the finite element solver Cast3M, developed by CEA, and also the first steps to deal
with unstable crack propagation in a quasi-static point of view