SIMULATION OF RIA TRANSIENTS ON MOX FUEL RODS WITH ALCYONE FUEL PERFORMANCE CODE

Abstract

International audienceAs regards Reactivity-Initiated Accidents (RIAs), the ALCYONE multidimensional fuel performance code co-developed by CEA, EDF and Framatome within the PLEIADES software environment is intended to predictively simulate the response of a fuel rod by taking account of mechanisms in a way that models the physics as closely as possible, encompassing all possible stages of the transient (PCMI and post-DNB phases) as well as various fuel/cladding material types and irradiation conditions of interest. Validated for PWR-UO2 fuels, it is now being adapted to simulate the behaviour of Zircaloy-4-based claddings shrouding MOX fuel pellets. ALCYONE V1.4 RIA-related features and modelling are first presented. The constitutive model for the oxide fuel includes cracking in tension, thermal creep and grain-boundary cracking. The modelling of grain-boundary cracking-induced fission gas release (the dominant release mechanism in RIAs) and swelling are discussed in this paper. Simulations of RIA transients performed on MOX fuel rods from the French CABRI REP-Na programme in flowing sodium coolant conditions are then compared to relevant experimental results. This paper shows to what extent ALCYONE-starting from base irradiation conditions it itself computes-is currently ready to simulate and analyse further tests on MOX fuel to be performed under prototypical PWR conditions within the CABRI International Programme. The homogeneous modelling gives satisfactory results. An alternative and heterogeneous approach may be a complementary path towards a more local description of the MOX fuel behaviour under RIA conditions: if both heterogeneous and homogeneous approaches will give the same information and results at the macroscopic level, the heterogeneous one will enable to understand, via numerical simulations, what happens at lower (meso-and microscopic) scales