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Fission gas release from irradiated UO2 fuel : Development of new mechanistic code MFPR and applications



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R.Dubourg (1), M.S. Veshchunov (2), G.Nicaise (1), V.E. Shestak (2) , V.Tarasov (2).
8th International Conférence on CANDU Fuel 21/09/03 au 24/09/03 Honey Harbour, Ontario


MFPR code is a mechanistic code developed in collaboration between IBRAE (Russia) and IRSN (France). It describes both intra and inter-granular fission gas behaviour in different realistic situations such as inreactor irradiation regime or LOCA transients or high temperature annealing modes. It includes improvements in the classical re-solution effects, from irradiation and from thermal effects. A new formulation of the grain growth model is proposed. The main specificity concerns the strong interaction between intra-granular gas and point or extended defects. The vacancy model included in the code allows self-consistent calculation of bubble nucleation factor, realistic description of grain bubble relaxation and implementation of model for enhanced bubble mobility in the vacancy field created at the end of annealing regime. The dislocation creep model, implemented for annealing regime, explains the observed burst release during high temperature ramps.

Examples are given on ADAGIO, FLASH and VERCORS experiments, giving satisfying results. Further improvements are proposed concerning the grain growth model, dislocation model which might be extended to irradiation regime and the thermal resolution model.

(1) : IRSN
(2) : IBRAE