Recent status of radiochemical analysis of irradiated trans-uranium targets

Koyama, Shinichi  ; Osaka, Masahiko  ; Mitsugashira, Toshiaki

We have developed a sequential radiochemical separation method (SRCS) in order to isolate each trans-uranium element (TRU) contained in a TRU target (or fuel) irradiated in the experimental fast reactor JOYO. The chemical separation procedures for SRCS consist of the following steps. (1) Target dissolution with a 8M of HNO solution including hydrogen peroxides as a valence control reagents for Pu and Np to their tetravalent states. (2) Sequential elution of main fission products (FPs) including trivalent actinides (An(III)) and lanthanides (Ln(III)) by washing the anion exchange resin column with 8M HNO. (3) Elution of U(VI) from the same column with 8M HNO and the change the effluent to 11.6M HCl. (4) Elution of Pu(III) from the same column by reducing Pu(IV) to Pu(III) with 11.6M HCl-0.1M NHI solution. (5) Group separation for Ln(III) and An(III) by using tertiary pyridine-type anion exchange resin embedded in silica bead. (6) Mutual separation of Am(III) and Cm(III), also for each lanthanide, by anion exchange resin. For the step 5 and 6, the effluent used was 3/7(v/v) mixture of methanol and HCl and 9/1(v/v) mixture of methanol and 0.013M HNO, respectively. The decontamination factor of Pu for the isolated Np was much higher than 10. The isotopic composition of isolated trans-uranium was determined mainly by thermal ionization mass spectroscopy. The SRCS sheet was applied to the analyses of MOX fuels irradiated in the experimental fast reactor JOYO. On the basis of isotope analysis, the transmutation and incineration behavior (T-I behavior) of trans-uranium nuclides were elucidated.