Experimental Validation for Pin-wise Isotope Prediction Methodology

Currently, nuclear spent fuel has been many issues. In order to solve this issue, many assessment has to be required; criticality, shielding and decay heat etc. Isotopic composition of spent fuel is essential for these assessment. Until now, spent fuel isotopic composition was calculated in unit of assembly. For detail information in unit of fuel pin, pin-wise isotope prediction methodology was developed. At time to develop this methodology, validation was not complicated. Therefore, verification for this methodology was performed in this study. Pin-wise isotope prediction was validated by comparing with OECD/NEA experimental data. Among OECD/NEA experimental data, Takahama Unit 3, Calvert Cliffs Unit 1 and Ohi Unit 1&2 was used for validation. 5% was set as objective error and error was expended up to 30% for isotope which has low impact on criticality. Impact on criticality was evaluated by number density and importance. Major isotopes satisfied the objective error and two parameter was calculated for isotopes with 30% error. As a results, most isotopes had low number density. Therefore, it was expected that these isotopes has low effect on criticality. Although ¹³⁷Cs, ¹⁴⁴Nd, ⁹⁰Sr were relatively high number density, it is forecasted that they also had small influence because of low cross-section. Unlike them, there were isotope to overestimate. they had a short half-life than half-life of other isotopes. For these isotopes, radioactive decay happens during cooling time. this reason make error large. About this problem, additional studied will be required in the future