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[en] JNFL have developed the vitrification technology of a high level liquid waste with a modification in discharge performance of the noble metal by changing the bottom structure and adding heating means. Cold test was conducted by using a full scale mock-up melter which introduced the new vitrification technology. In the cold test, we confirmed the discharge performance of the noble metal. (author)

[en] This paper describes the development of the advanced melter in Rokkasho Reprocessing Plant (RRP). This advanced melter is a Liquid Fed Joule heated ceramic melter, and the design of the advanced melter is largely different from the existing one. For the confirmation of the advanced melter performances, the full-scale inactive test was planned to be divided into 2 phases according to the test purposes. The phase-I test had been performed from Nov. 2013 to Feb. 2014, and it was confirmed that the advanced melter had good performances compared with the existing melter. And then, the phase-II test has been performed from Nov. 2014, and the good results are acquired in severe conditions, without periodical washing operation, with increasing glass production rate, etc. (author)

[en] Electrical and rheological properties of glass which contains various concentrations of simulated fission products were measured as a function of temperature and holding time. Homogeneous samples of glass containing simulated fission products were made from glass beads and simulated high level waste solution in a large scale melter. The viscosity of the glass decreased with temperature. When the glass included the deposit of noble metals which are not soluble in glass, the glass showed non-Newtonian behavior. The viscosity of the glass increased with the holding time because the deposit of noble metal settled on the bottom. Impedance of the glass was measured using parallel plate electrodes made from platinum at various frequencies. The impedance of glass was determined mainly by the concentration of sodium rather than noble metals. However, the impedance of glass including noble metal decreased with the holding time. This is because noble metals that settled on the bottom formed an electrically conducting layer. After measurement, glass on the bottom was analyzed by SEM. Agglomerated particles of ruthenium dioxide and palladium-tellurium alloy were observed. (author)

[en] The redox condition of simulated high-level waste (HLW) glass was investigated by thermodynamic calculations for the phase equilibrium of crystalline phases composed of platinum group elements (PGE, Pd, Rh, and Ru) based on the thermodynamic data for Pd-Rh-Ru and (Ru,Rh)O₂ solid solutions. Phase equilibrium calculation indicates that the stability field of the Pd-rich metal phase with an FCC structure and the (Ru,Rh)O₂ phase is nearly independent of the relative abundances of Pd, Rh, and Ru. Thermodynamic calculation for rhodium partitioning between Pd-Rh-Ru and (Ru,Rh)O₂ can provide the temperature and oxygen fugacity conditions under which these phases are stable. The redox condition of HLW glasses retrieved from a full-scale mock-up melter (KMOC) in JAEA, Tokai, Japan, was evaluated by comparing the results of chemical composition analysis for PGE crystalline phases in the glasses with those of phase equilibrium and/or thermodynamic calculations. The obtained results suggest that the oxygen fugacity is higher than the atmospheric condition (f_O2 > 0.21) for the glass retrieved in a normal melter operation, while it is lower at 10^-1.5-10^-2.0 for the PGE-rich residual glass retrieved from the melter after glass draining. The calculated f_O2 values are consistent with the redox condition estimated from Ce³⁺/Ce⁴⁺ ratios of KMOC glasses reported previously. (author)

[en] Phase equilibrium experiments for the simulated high-level waste (HLW) glass containing palladium, rhodium and ruthenium discharged from a full scale mock up melter have been carried out between 1073 and 1473 K under air and CO_2 atmosphere. The chemical compositions of Pd-Rh-Ru-Te (Pd metal phase) and (Ru, Rh)O_2 (Ru oxide phase) solid solutions and glass matrix were measured by electron probe micro analysis. Palladium content in the Pd metal phase decreased and ruthenium content in the Ru oxide phase increased with increasing temperature and decreasing oxygen fugacity due to progressive reduction of rhodium. The chemical compositions of these crystalline phases are independent of that of borosilicate glass matrix. Partition coefficient of rhodium between Pd metal phase and Ru oxide phase (K_R_h) can be expressed by ln K_R_h = 27264/T - 18.372 + ln f_o_2 were T and f_o_2 represent absolute temperature and oxygen fugacity. Based on the comparison of crystal compositions in the HLW glass with experimental results, it can be expected that the HLW glass examined in this study had been equilibrated in the temperature range from 1273 to 1373 K and oxygen fugacity close to that of air just before discharging from the melter. (author)

[en] The molten state of simulated high-level waste glass and the behavior of ruthenium element in the melt were investigated by using synchrotron radiation based X-ray imaging technique. Melting, generating and moving of bubbles, condensation and sedimentation of ruthenium element were observed dynamically in continuous 12-bit gray-scale images from the CCD camera. X-ray intensity was obtained easily by digitalizing gray-scale values in the image. The existence of ruthenium element, which is one of the most important insoluble residues in the recycle process of spent nuclear fuels, is emphasized as a black color in the CCD image at X-ray energy higher than the Ru K-edge. The position sensitive imaging X-ray absorption fine structure (XAFS) measurement was also performed to clarify a chemical state of ruthenium element in the melt. (author)

[en] The partitioning of rhodium and ruthenium between Pd–Rh–Ru alloy with a face-centered cubic (FCC) structure and (Ru,Rh)O_2 solid solution has been investigated between 1273 and 1573 K at atmospheric oxygen fugacity. The rhodium and ruthenium contents in FCC increase, while the RhO_2 content in (Ru,Rh)O_2 decreases with increasing temperature due to progressive reduction of the system. Based on the experimental results and previously reported thermodynamic data, the thermodynamic mixing properties of FCC phase and (Ru,Rh)O_2 have been calibrated in an internally consistent manner. Phase equilibrium of platinum grope metals in an HLW glass was calculated by using the obtained thermodynamic parameters.

[en] The distribution and chemical state of the Ru element in the simulated high-level waste glass were examined by using the synchrotron radiation-based X-ray imaging technique. An X-ray CCD camera instead of an ion chamber was used to determine the transmitted X-ray intensity in the imaging measurement. Spectra of the X-ray absorption fine structure with position sensitivity were obtained by analyzing the gray-scale value of each pixel in the X-ray CCD image. We confirmed the position sensitivity in the imaging XAFS technique by analyzing a test sample, in which RuO₂ and Ru metal powders were scattered at random. We successfully obtained information on the Ru distribution and the chemical state (oxide or metal) of each small Ru-rich spot in the sample. The imaging XAFS technique was applied to the simulated high-level waste glass samples. It was concluded from the analyzed imaging XAFS spectra that the Ru element scattered in the glass sample exists as oxide RuO₂. (author)

[en] The shear rate dependency of the viscosity of three simulated high-level radioactive waste glasses containing 0, 1.2 and 4.5 wt% platinum group metals (PGMs) was examined at a temperature range of 1173–1473 K by a rotating viscometer. Shear stress when the shear rate equals zero, i.e. yield stress, was also measured by capillary method. The viscosity of the glass containing no PGM was shear rate-independent Newtonian fluid. On the other hand, the apparent viscosity of the glasses containing PGMs increased with decreasing shear rate, and nonzero amount of yield stresses were detected from both glasses. The viscosity and yield stress of the glass containing 4.5 wt% PGMs was roughly one to two orders of magnitude greater than the glass containing 1.2 wt% PGMs. These viscoplastic properties were numerically expressed by Casson equation