Development of fuel behavior analysis code for mechanical fuel cladding failure during reactivity insertion event in PWR

Abstract

Pellet-Cladding Mechanical Interaction (PCMI) failure is one of the failure mode which must be evaluated in nuclear fuel safety. PCMI is caused by mechanical load to the cladding due to fuel pellet expansion. Under high fuel burnup condition, the fuel cladding may become degraded by embrittlement under neutron-induced irradiation and hydrogen accumulation due to the waterside corrosion. In order to consider the further deterioration of the material with higher burnup, evaluation using mechanical indicators, e.g. strain and stress, might be required. As fuel burnup proceeds, cracks occur in the pellet due to an internal temperature gradient, which induces the fuel pellet relocation, and fission gas may be accumulated in the pellet and the gap between pellet and cladding. Cracks and fission gas may cause more deformation of the pellet under the power excursion than in low burnup condition. In this study, a transient model is developed, which can mechanistically evaluate the PCMI behavior, in particular, for fuel rods under higher burnup condition. The model is incorporated in a fuel behavior analysis code and verified by benchmarks with other similar codes. The PCMI predictability of this code is validated using the experimental test data.