Munetaka Myochin

Integrated Experiments of Electrometallurgical Pyroprocessing Using Plutonium Oxide

Electrometallurgical pyroprocessing is a promising technology to realize actinide fuel cycle. Integrated experiments to demonstrate electrometallurgical pyroprocessing of PuO2 in continuous operation were carried out. In each test, 10–20 g of PuO2 was reacted with Li reductant to form metal product. The reduction products were charged in an anode basket of the electrorefiner with LiCl-KCl-UCl3 electrolyte. Using the anode, deposition of uranium on the solid cathode was carried out when PuCl3/UCl3 concentration ratio was low. After the Pu/U ratio in the salt electrolyte was increased enough, Pu and U were recovered simultaneously on a liquid cadmium cathode. By heating up the deposits for distillation of the salt and the cadmium, U metal or Pu-U alloyed metal was obtained as residues in the crucible. It was the first result to demonstrate the recovery of metal actinides in the continuous operation of pyroprocessing of oxide fuels.

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.

Redox equilibria of Pu4+/Pu3+ and PuO22+/Pu4+ couples in molten NaCl-CsCl eutectic as measured by absorption spectrophotometry

Abstract In order to enhance the understanding of redox reactions of plutonium ions in molten NaCl-CsCl eutectic, absorption spectrophotometry was performed for Pu3+, Pu4+, and PuO22+ in molten NaCl-CsCl at 923 K by controlling the flow-rate ratio of Cl2 and Ar or O2 in the ventilating mixture gas. Based upon the relations of the measured rest potentials to the concentration ratios of [Pu4+]/[Pu3+] and [PuO22+]/[Pu4+], the redox potentials of Pu4+/Pu3+ and PuO22+/Pu4+ couples in molten NaCl-CsCl eutectic at 923 K were estimated.

Electro-deposition behavior of minor actinides with liquid cadmium cathodes

Transuranic elements have been simultaneously electro-deposited on a liquid cadmium cathode and decontaminated from fission products dissolved in molten 3LiCl-2KCl in the electrorefining of a pyrochemical reprocessing. Some lab-scale electrolysis experiments were carried out using uranium, plutonium and minor actinide elements in order to evaluate the performance of liquid cadmium cathodes. The results of several experiment confirmed that neptunium, americium and curium could be recovered together with Pu by the liquid cadmium cathodes through electrolysis operation. The separation factors of minor actinide vs. Pu were estimated to be about 0.5 to 2.5 and those of rare earth element vs. total actinides 18 to 32.

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.

In Situ X-Ray Diffraction Measurement of Electrodeposition Process in Molten Salts

In-situ X-ray diffraction (XRD) method has been developed for the observation of elctrodeposition process in molten NaCl-2CsCl salt to investigate the mechanism of pyrochemical process of nuclear fuel reprocessing system. In this paper, the scattered X-ray beam from electrodepositing nickel in NaCl-2CsCl melt was measured by the reflection mode at BL19B2 beamline of SPring-8 as the preliminary experiment. The time dependence of the electrodepositing nickel in NaCl-2CsCl melt at 923K was investigated by the in-situ XRD measurements.