For the precise calculation of the burnup of minor actinide isotopes, a code system-SWAT has been developed. This system analyzes burnup problems with neutron spectrum that depends on the type of a reactor and the irradiation history, using latest evaluated nuclear data files JENDL-3 or ENDF/B-VI. The post irradiation test in TRINO and the recent experiment in typical PWRs in Japan were analyzed with SWAT. These analyses show that the results of U and Pu for high burnup fuels almost agree with experimental results but those for middle burnup fuels do not agree with them. The results for Am and Cm isotopes still have large discrepancy. The average C/E of 243Am is ∼0.79, and that of 244Cm is ~0.70 for high burnup (~33,000 MWd/tU) samples. For middle burnup (~25,000 MWd/tU) samples, the C/E for 244Cm is over 2.0. The discrepancy is partially explained by considering the power peaking history of first cycle and second cycle.
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