Accuracy of MA transmutation calculation with MA specimens irradiated in the experimental fast reactor "JOYO"

not registered; Takeda, Toshikazu*; not registered; Kitada, Takanori; Aoyama, Takafumi 

The accuracy to calculate the transmutation of minor actinides (MAs) was evaluated using MA specimens irradiated in the Experimental Fast Reactor JOYO. The Np transmutation characteristics were analyzed in this study. The transmutation ratio of Np was calculated by the one point burnup calculation code "ORIGEN2." The neutron fluxes which were input to "ORIGEN2" were calculated with the JOYO core management code system "MAGI" and "CITATION", both are based on three dimensional diffusion theory with 7 energy group. The continuous energy Monte-Carlo code "MVP" was introduced in order to evaluate the detail flux distribution inside the subassembly. The neutron flux obtained by a radiometric dose analysis without Np dosimeter was also used for the transmutation calculation. By comparing the flux distributions by MVP with and without the geometric heterogeneity in a subassembly, it was found that there had little effect on the calculation of Np transmutation near the core center of JOYO Mark-II. Calculated Np transmutation ratio with neutron fluxes by the MAGI and CITATION were 30% larger than that obtained from the -ray spectrum measurement, whereas the calculated value with the adjusted neutron flux by a radiometric dose analysis was about 1220% larger than the measured value. It is apparently due to an overestimation of the neutron fluxes by the MAGI and CITATION. As it was also found that there were large uncertainties in the adjusted neutron flux and the measured Np transmutation ratio, further investigation is required. As a result of this study, the points to be considered were found to improve the accuracy of the analysis.