The transmutation methods to reduce the burden of high level radioactive waste had been compared to identify the most suitable method for this purpose. The results showed that the molten salt reactor (MSR) was suggested to be an effective transmutation system. Based on this result, a new concept of Integral Molten Salt Fast Reactor (IMSFR) as a highly efficient transmutation system for transuranium elements has been proposed in this study; the system consists of a combination of an MSR fuelled with chloride molten salt fuel and the chloride-based pyrochemical processing subsystem. In this system MSR fuel can be transferred between the reactor core and the pyrochemical processing subsystem without chemical form change.

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A novel pyroprocess is proposed to recover actinides from spent nuclear fuels, in which a liquid Ga is used as the key electrode material to achieve a high actinide/lanthanide separation efficiency. To evaluate the proposed pyroprocess, it is necessary to clarify the separation performance in the system of LiCl-KCl/liquid Ga electrode. In this study, an electrochemical actinides recovery was conducted by galvanostatic electrolysis of the liquid Ga electrode in LiCl-KCl melts containing both actinides (U, Pu and Am) and lanthanides (Ce, Nd, La and Gd) chlorides at 773 K. The obtained Ga alloy after the electrolysis was analyzed quantitatively to calculate the separation factors of Pu and Am based on Ce. The calculated separation factors in LiCl-KCl/liquid Ga electrode system were more than 10 times higher than those in LiCl-KCl/liquid Cd system.

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Benzo-18-crown-6 ether resin was synthesized with the carrier of porous fine silica beads. By using synthesized crown ether resin packed in glass columns, ⁴⁸Ca enrichment was studied. A high speed chromatography experiment was conducted at the band migration speed of 48 m day^-1. In spite of the high speed of migration, enrichment of ⁴⁸Ca was observed at the front boundary of the displacement type chromatography. Comparing with previously reported experiments of 1 m 3 m and 200 m migrations, we confirmed that separation coefficient ε slightly decreases with increase in the band velocity. In addition, the enriched zone was found to increase with increase in the migration length. The observed relation shows that the width of the enriched zone is proportional to square root of the migration length.

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A rapid and convenient chemical separation method for determining ⁹⁰Sr activity in aerosol samples using Empore™ Strontium Rad Disks was established. The method employ ed solid-phase extraction and ion-exchange chromatography, and achieved a Sr yield of > 80%. Furthermore, it completely eliminated ²¹⁰Pb, which interferes with ⁹⁰Sr radiation counting. Sample pretreatment, chemical separation and Cherenkov light measurement required approximately 4 h, 2.5 h, and 14 days, respectively, to achieve a detection limit of 0.004 Bq. Using the developed method, the ⁹⁰Sr concentration and ⁹⁰Sr/¹³⁷Cs activity ratio in aerosol samples collected after the Fukushima nuclear accident were determined.

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