Thorium cycle models into DIONISIO code: Species, thermomechanical behaviour and fission gas release

Abstract In this work we present the main developments made to include the thorium cycle in the DIONISIO fuel code. For this, models for species evolution, thermomechanical behaviour and fission gas release development are incorporated. First of all, a simplified neutronic behaviour model was developed, which adds the capability of simulating the whole cycle at the least possible computational cost. We start from the balance of nuclides in the thorium chain, considering fresh ThO 2 mixed with PuO 2 , which works as fissile species for the initial stages of operation. This simple model shows an acceptable performance in comparison with results from dedicated neutronic codes like CONDOR. Afterwards, the main thermal and mechanical parameters were adapted for thorium mixed oxide materials. For fission gas release, an existing model based on diffusion equations was also modified on the same way as thermomechanical parameters. Finally, results of the whole code with the included modifications were compared to some experiments over mixed fuels (Th,Pu)O 2 andl (Th,U)O 2 .