Plutonium heterogeneity in MOX fuel: A quantitative analysis

(U,Pu)O2 mixed oxide (MOX) fuel has been irradiated in thermal as well as fast reactors in India for Pu utilization. MOX fuels are conventionally fabricated through the powder metallurgical route in conformance with the quality specifications. Homogeneity of fissile material in MOX fuel is a crucial characteristic which affects its performance in reactor as well as post irradiation dissolution for reprocessing. The relative richness and spatial extent of Pu rich agglomerates in the fuel matrix are the two important parameters to be controlled during fabrication to ensure homogeneity in the fuel. Gamma auto radiography is one of the routinely used inspection techniques for quality control of PFBR fuels for homogeneity. A new method based on image analysis and spectrophotometric analysis of the gamma auto radiographs has been developed for quantitative characterisation of fuel heterogeneity. The method could be used to estimate the relative Pu richness and size of the agglomerate in the fuel.