3D Modeling of PCI-SCC in Alcyone Fuel Performance Code

The paper presents the latest developments in ALCYONE fuel performance code concerning the modelling of pellet cladding interaction (PCI) and clad failure caused by iodine-induced stress corrosion cracking (I-SCC). ALCYONE includes a 3D finite element model to describe the thermo-mechanical behaviour of a fuel pellet fragment and its frictional contact with the surrounding cladding. ALCYONE provides a precise evaluation of the temperature and stress state across the clad wall during power transients that can lead to clad failure by I-SCC. The application of an I-SCC crack propagation model in the 3D simulations of PCI with ALCYONE is of primary interest in the paper. A series of power ramps performed in the OSIRIS materials test reactor are analyzed. The calculated times to failure by PCI induced I-SCC are compared to in-reactor measurements, which shows a good agreement each other. Advanced simulations of non-failed rods during power ramps are then proposed to analyze the potential reasons for the clad resistance to I-SCC in relation to the build-up of a suitable chemical environment at the clad inner wall. The simulations include thermodynamic equilibrium calculations of the uranium dioxide matrix with the fission products (FP) of interest for I-SCC (I, Cs, Te) that are coupled to the fission gas release model (MARGARET) of ALCYONE. They illustrate the importance of a correct assessment of the chemical conditions at the triple point with respect to I-SCC crack propagation modelling. (author)