Post irradiation examination of thoria-plutonia mixed oxide fuel in Indian hot cells

Mixed oxide (MOX) fuel clusters containing ThO₂+4%PuO₂, and ThO₂+6.75%PuO₂ fuel pins were irradiated in the pressurized water loop of the Indian research reactor CIRUS, to burn up in the range of 20 GWd/T(HM). The ThO₂+4%PuO₂ fuel elements had free standing cladding made of Zircaloy-2 and the ThO₂+6.75%PuO₂ had collapsible Zircaloy-2 cladding. The fuel clusters had performed well during irradiation with no apparent indications of failure. The techniques used for the post irradiation examination (PIE) of these fuels in the hot cells included visual examination, fuel pin diameter measurements, leak testing, gamma scanning, gamma spectrometry, ultrasonic testing, eddy current testing, ceramography, metallography, beta gamma autoradiography and measurement of released fission gases. Micro hardness measurement of cladding and evaluation of mechanical properties using ring tension test were also carried out. This paper elaborates on the techniques and the results of the PIE carried out on ThO₂+4%PuO₂ fuel. (author)