Integral Experiments on Critical Irradiation of ²³⁷Np and ²⁴¹Am Foils at Kyoto University Critical Assembly

At the Kyoto University Critical Assembly (KUCA), critical irradiation experiments on ²³⁷Np and ²⁴¹Am foils are carried out in the neutron hard spectrum core. For nuclear transmutation of minor actinides, special attention is paid to determining ²³⁷Np and ²⁴¹Am fission reaction rates and to ²³⁷Np capture reaction rates in the KUCA hard spectrum core. In the back-to-back (BTB) fission chamber, two nuclide foils (test: ²³⁷Np or ²⁴¹Am; reference: ²³⁵U) are set closely to each other to measure the aforementioned fission reaction rates. Interestingly, the experimental ²³⁷Np and ²⁴¹Am fission and capture reaction rates are attained by critical irradiation at low W reactor power for 1 h in the core and are successfully deduced through signals from the BTB fission chamber (fission) and the gamma-ray detection (capture) after the irradiation, respectively, together with MCNP calculations.