Development of radiochemical separation technology

This project was aimed at the radiochemical test of partitioning technologies of long-lived radionuclides and its evaluation by using a simulated and multi- component radioactive waste containing Am, Np, Tc, U and so on. Target goals of recovery yields for Am and Np, and those for Tc, Cs and Sr were chosen as 99% and 95%, respectively. The work scopes and contents were, as follows. 1) In the radiolytic performance test and evaluation of partitioning technologies for LLN, (1) Continuous electrolytic denitration system was developed. Decomposition mechanism of nitric acid and formic acid, and co-precipitation of transient elements were examined. (2) Sequential separation system of Tc, Np and U with enhancing the Tc extraction yield was developed, and its radiolytic capability was evaluated. (3) Radiolytic evaluation of mutual-separation for Am and RE by Zr-DEHPA/NDD was performed in a batch and a multi-stages continuous system, respectively. (4) Organic-inorganic composite ion-exchangers for the removal of heat generating radionuclides were synthesised, and the continuous removal of Cs and Sr was conformed by a composite ion-exchanger packed column. 2) In the radiolytic characteristics of materials with irradiation dose, chemical compositions and compounds of degradation products were qualitatively analysed, and their radiolysis mechanisms were elucidated. Conditions of the 3rd phase formation and the complex reaction between degradation products and metal ions were also established. 3) Finally, RE oxides were prepared by a microwave heating and a microwave heating/combustion synthesis, respectively. Thermal decomposition of RE nitrate and morphology of prepared RE oxide were examined. All results will be used as the fundamental data for the advanced partitioning technology to be performed in the next stage