Evaluation of 237Np transmutation characteristics with chemical analysis of Neptunium dosimeter irradiated in 'Joyo'

The purpose of this study is to evaluate transmutation characteristics such as dependence of 237Np transmutation rate to neutron energy spectrum and neutron fluences. Analysis of the Neptunium dosimeter, in which was irradiated in the experimental fast reactor 'Joyo', was carried out by applying the technique for analysis of minor actinide nuclides in irradiated MOX fuel. It is necessary to remove Vanadium before analysis of Neptunium dosimeter because NpO2 powder was enclosed in Neptunium dosimeter that was made of Vanadium capsule. The result of analysis and evaluations are as follows. (1) In order to recover Neptunium sample completely, sample was dissolved with capsule before removing the Vanadium from sample solution. Sample treatment method of whole capsule dissolution for chemical analysis of Neptunium dosimeter was established. (2) 237Np, Plutonium isotopes, 241Am and 137Cs in the dosimeter were analyzed using the method of whole capsule dissolution, alpha spectrometry, gamma spectrometry and isotopic dilution mass spectrometry. Transmutation rate of 237Np was calculated using the analyzed value. Tendency of transmutation rate was certified, which is higher fission ratio at the center and higher capture ratio at both upper and lower end. (3) Transmutation rate with error was evaluated by neutron fluences considering the neutron energy spectrum, and calculated value by 'MAGI' code was agreed well with analysis value. Dependence of transmutation rate of 237Np to neutron energy spectrum was certified. (author)