Development and Verification of the Thermal Behavior Analysis Code for MA Containing MOX Fuels

In order to develop a minor actinide (MA) containing MOX (MA-MOX) fuel design method, the analysis models to predict irradiation behavior of MA-MOX fuel have to be developed and the accuracy of the irradiation behavior analysis code should be evaluated with the results of post-irradiation examinations (PIEs) for MA-MOX fuels. In this study, we developed the computer module TRANSIT (Thermal Property and Vapor Pressure Analysis Module for Minor Actinide Containing MOX Fuel) to compute thermal properties of MA-MOX fuel. TRANSIT can give thermal conductivity, melting temperature and vapor pressures of MA-MOX. By using this module, we improved the thermal behavior analysis code DIRAD and developed the DIRAD-TRANSIT code system to compute the irradiation behavior of MA-MOX fuel. This system was verified with the results of PIEs for the conventional MOX fuels and the MA-MOX fuels irradiated in the experimental fast reactor JOYO. As the result of the verification, we determined that the DIRAD-TRANSIT code system would precisely predict the fuel thermal behavior, i.e. fuel temperature and fuel restructuring, for oxide fuels containing several percent minor actinides.