Hirohide Kofuji

MOX Co-deposition Tests at RIAR for SF Reprocessing Optimization

The Oxide Electrowinning method has been studied as one of the candidate dry reprocessing concepts of the future fuel cycle systems. On the MOX co-deposition process, the main process of that method, some fundamental experiments have been performed to confirm its feasibility. In the experiments, several parameters were set to study the suitable electrolysis condition to obtain desired granule of MOX. The concentrations of uranium, plutonium, fission products(FP) simulators, and corrosion products(CP) simulators were adopted as the parameters. The blowing gas composition (O2, Cl2, Ar) during the electrolysis was also set as the variable condition. Through these experiments, it was clarified that the partial pressure of chlorine gas during electrolysis was important to obtain MOX granule with high Pu concentration (about 30%) without generating bottom precipitation in melt. Finally, adequacy of the process control method for MOX co-electrolysis was confirmed through the test using spent fast reactor(FR) fuel.

Am, Cm recovery from genuine HLLW by extraction chromatography

The extraction chromatography experiments for Am(III) and Cm(III) recovery from genuine HLLW were carried out in order to demonstrate modified 2 flow-sheets using CMPO/SiO2-P and HDEHP/SiO2-P adsorbents for obtaining DTPA-free MA(III) product solution. The first flow-sheet achieved about 90% MA(III) recovery with more than 103 of decontamination factor for 155Eu. However, further modification is necessary for separation of light lanthanides. Purification of MA(III) from both of heavy and light lanthanides was successfully done by the 2nd flow-sheet although recovery yields of MA(III) was almost the same with the current flow-sheet i.e. 70%. The recovery yield is expected to be improved by some optimizations in operation conditions such as column length, flow rate of the mobile phase and etc.

Optimization of Chemical Composition in the Iron Phosphate Glass as the Matrix of High Level Waste Generated From Pyroprocessing

As part of ongoing research and development of nuclear waste disposal techniques suitable for the pyrochemical processing system [1], iron-phosphate glass was examined as an alternative waste form for high level waste generated from the electro-refining process [2]. To enhance the waste element content in the glass matrix and improve the durability of the waste form, optimization experiments of the glass composition were performed, and the effects of other additional transition metal oxides were determined. From the surface analysis of iron phosphate glass, a leaching mechanism was assumed for various elements contained in the glass matrix. We have selected suitable a glass composition for the treatment of radioactive waste generated from the spent electrolytes of pyrochemical processing.Copyright

Separation of Lanthanoid Phosphates From the Spent Electrolyte of Pyroprocessing

This study is carried out to make the pyroprocessing hold a competitive advantage from the viewpoint of environmental load reduction and economical improvement. As one of the measures is to reduce the volume of the high-level radioactive waste, the phosphate conversion method is applied for removal of fission products from the melt as spent electrolyte in this paper. Though the removing target elements in the medium are alkali metals, alkaline earth metals and lanthanoid elements, only lanthanoid elements and lithium form the insoluble phosphates by reaction with Li3 PO4 or K3 PO4 . Therefore, as the first step, the precipitation experiment was carried out to observe the behaviours of elements which form the insoluble precipitates as double salts other than simple salts. Then the filtration was experimented to remove lanthanoid precipitates in the spent electrolyte using Fe2 O3 -P2 O5 glass system as a filtlation medium which is compatible material with the glassification. The result of separation of lanthanoid precipitates by filtration was effective and attained almost 100%.Copyright

Effect of Pulse Electrolysis on Morphology of Co-Deposited MOX Granules

In the oxide electrowinning method of nuclear fuel recycling, the applicability of the pulse electrolysis methodto the mixed-oxide (MOX) codeposition process was evaluated. Several experiments were conducted involving uranium, plutonium, and elements simulating fission products (FPs) or corrosion products (CPs). Through these experiments, the effects of impurities and electrolysis pulse waveforms on the deposit were clarified. In particular, the difference between the dissolution kinetics of UO2 and PUO2 during the period in which current was stopped was found to be the most important factor influencing the deposition behaviors. As a result, pulse electrolysis conditions, which could restrain Pu enrichment of the deposited MOX, were confirmed. Furthermore, it was found that the elemental distribution in the MOX granule obtained by pulse electrolysis was homogenized, which is well suited for nuclear fuel fabrication. Finally, a qualitative model of the pulse electrolysis reaction near the field of the cathode surface is proposed.