A new phenomenological criterion for pellet-cladding interaction rupture

International audienceThis study is concerned with structural integrity assessment of Pressure Water Reactor's (PWR) fuel rods under pellet-cladding interaction (PCI) loading condition. An important experimental and research cooperative program between EDF, AREVA-NP and the Atomic Energy Commission CEA is achieved in order to get a better understanding of the mechanisms possibly leading to PCI failure, as well as to qualify a PCI resistant rod design. The objectives of this work are: first, to improve the understanding of the pellet mechanical properties impact on cladding local loading with 3D simulations results, and second, to propose a new phenomenological rupture criterion for a better assessment of the failure risk. In this study fuel behaviour modelling under nominal and transient loading conditions is achieved with a multi-dimensional simulation tool called ALCYONE, included in the new fuel software PLEIADES currently co-developed by the CEA and EDF. Cladding loading due to mechanical interaction during power transient stage is first analysed through pellet-cladding interfacial stresses computed in the 3D simulation. Then, a 2D model is proposed in order to establish a correlation between interfacial loading and stress concentration in the cladding. In order to assess the failure risk under PCI a phenomenological criterion based on the membrane circumferential stress in the cladding and shear stresses at pellet-cladding interface is proposed. To compute the shear loading at pellet-cladding interface a new parameter (called $W_{r \theta}$) is introduced. Based on 3D calculations of PCI, it is shown in this paper that pellet fracture properties can have a significant effect on PCI loading