Cracking of Cr-coated accident-tolerant fuel during normal operation and under power-ramping conditions

摘要

In this paper, an analysis is presented for the cracking of Cr-coated Zircaloy claddings proposed for use in accident-tolerant fuels (ATF). Tensile hoop stresses are induced in the coating by pellet-cladding interaction (PCI), which results from the fuel swelling under normal operation, or from additional thermal expansion of the fuel after power ramping. The hoop stress is limited by the stress relaxation associated with dislocation glide that dominates the thermal creep in the coating. The energy-release rate for crack channeling has also been calculated, and it increases almost linearly with the thickness of the coating. By comparing this energy-release rate with the toughness of Cr, we can develop a design map for the maximum coating thickness required to avoid fracture at different levels of ramped power. We also propose a design protocol for coatings based on a simplified fracture analysis, which allows existing PCI codes to be leveraged.