In the spent nuclear fuel reprocessing, uranium and plutonium are recovered by Tri-butyl phosphate (TBP) extractant. After recovering uranium and plutonium, high level liquid waste (HLLW) containing a lots of fission products and minor actinides is vitrified to store stable. However, long time surveillance is required until the vitrified waste decreases hazard level safety, due to mainly the minor actinide long half-life. In order to reduce the hazard level drastically, a lot of research for recovering MA and transmutation have been studying.
The Japan Atomic Energy Agency (JAEA) has started to develop a new flowsheet to recover MA from HLLW. The new flowsheet, we named it the Hybrid process, is combined with solvent extraction and the low pressure loss extraction chromatography techniques. In the solvent extraction process, TBP extractant is used for recovering MA with Lanthanides (Ln) by increasing the concentration of TBP and NO3-. After back extraction, MA can be separated from Ln by using NTAamide adsorbent in the extraction chromatography.
In this study, the cold tests of solvent extraction by using TBP were conducted. In order to recover MA and Ln from HLLW, concentration of TBP must be increased than that of 30% in the PUREX process. However, by increasing the concentration of TBP, separation becomes harder due to the difference of density between the solvent and aqueous solution changes small. Thus, the centrifugal contactor which has high separation performance than the mixer settler or the pulse column, was used in this study.
In the separation performance test, the centrifugal contactor could mix and separate 50% TBP-n dodecane with 3M nitric acid solution stably. Also, the centrifugal contactor could work on high O/A ratio condition, which means the ratio of organic phase flowrate against the aqueous phase flowrate.
The flowsheet test was conducted by using the cold elements. Ln could be separated from the simulated HLLW solution with good decontamination performance against the other elements.