LAUSR

ABSTRACT Measured isotopic compositions of UO2 and MOX fuel samples taken from irradiated light water reactor fuel assemblies were analyzed by CASMO5 coupled with a JENDL-4.0 base library to assess the uncertainties in the calculated isotopic compositions on heavy and fission product nuclides. The burnup calculations for the analysis were performed based on a single-assembly model taking into account the detail fuel assembly specifications and irradiation histories. For the MOX fuel samples, a multiple-assembly model was also adopted taking into account the effect of the surrounding UO2 fuel assemblies. The average and standard deviation of the biases (C/E − 1's (here C and E are calculated and measured results, respectively)) were calculated for each nuclide separately on the PWR and BWR UO2 fuel samples. The averaged biases for 235U, 236U, 239Pu, 240Pu, 241Pu and 242Pu were 2.7%, −0.9%, 0.3%, 0.7%, −2.4% and −1.7% for PWR UO2 samples, and 6.7%, −1.5%, 2.5%, −0.6%, 0.4% and −0.1% for BWR UO2 samples, respectively. The biases with the single-assembly model on the MOX fuel samples showed large positive values of 239Pu, and application of the multiple-assembly model reduced the biases as reported in our previous studies.