Hiroshi Kamizono

Durability of an La2Zr2O7 waste form containing various amounts of simulated HLW elements

Durability of an La2Zr2O7 waste form containing various amounts of simulated HLW elements was examined at 90°C in three kinds of solutions. In HCl solution of pH = 1, the leach rateof La, Nd and Ce from the La2Zr2O7 waste form decreased with increasing concentration of Nd and Ce which were solved in La2Zr2O7 yielding solid solutions. In deionized water of pH = 5.6 and NaOH solution of pH = 10 however, such a compositional effect on rates was not observed because of the formation of hydroxides or carbonates on the surface of the solid.

Segregation of the elements of the platinum group in a simulated high-level waste glass

Segregation of the elements of the platinum group occurred during vitrification of the borosilicate glass containing 20 wt% simulated high-level waste oxides. The segregated materials were composed of two crystalline phases: one was the solid solution of ruthenium and rhodium dioxides and the other was that of palladium and rhodium metals also with tellurium. The segregated materials were not distributed homogeneously throughout the glass: (i) on the surface of the glass, there occurred palladium, rhodium and tellurium alloy alone; and (ii) at the inner part of the glass, the agglomerates of the two phases were concentrated in one part and dispersed in the other.

Thermal shock resistance of a simulated high-level waste glass

Abstract Thermal shock resistance of a simulated high-level waste glass was examined by water quenching in the range of the temperature difference up to 600°C. The observation of cracks revealed that there existed two critical temperature differences. One was the threshold temperature difference of 74°C above which surface cracks appeared. The other was the temperature difference of 600°C at which cracks were propagated markedly and the specimen broke down into many pieces. In the range of the temperature difference of 74°C to 600°C, the surface area of cracks on the surface of the quenched specimens increased with increasing temperature difference. However, the fractional release of sodium and cesium from the quenched specimens was almost constant in the range of the temperature difference up to 500°C, and it increased markedly at the temperature difference of 600°C. These facts indicate that sodium and cesium do not leach out from the cracks when the separation of fracture surfaces is small.

Volatilization of cesium from nuclear waste glass in a canister

Volatilization of /sup 134/Cs from simulated high-level waste glass in a canister during several reheatings up to a maximum of 1000/sup 0/C was examined. The results showed that the temperature dependence of the amount of /sup 134/Cs suspended in the air inside the canister could be divided into two categories. As the temperature was increased above 500/sup 0/C, the amount of /sup 134/Cs suspended in the air inside the canister also increased. On the other hand, for temperatures <500/sup 0/C, the amount of /sup 134/Cs suspended in the air inside the canister had an almost constant value after several reheatings up to a maximum of 1000/sup 0/C. In this case, the air contamination by cesium-bearing material inside the canister is considered to be significant even at waste storage temperatures <500/sup 0/C.

Accelerated Leach Tests of SRL-165 High-Level Waste Glass in Deionized Water

Accelerated short-term leach tests in a laboratory are neccessary in order to estimate, with reasonable accuracy, the long-term leaching behavior of high-level waste glass. In the present study, static leach tests of an SRL-165 high-level waste glass were carried out in deionized water at two different glass-surface-area to solution-volume ratios (SA/V-ratio), namely 0.85 and 0.079 cm−1 at 90°C, and 0.85 cm−1 at 40°C. First, an equation was examined which related Si-concentrations with time, temperature and SA/V-ratio under the present static conditions. The parameter determined at 90°C, 0.85 cm−1 can be used to calculate the Si-concentration at 40°C, 0.85 cm−1. Second, at the low SA/V- ratio of 0.079 cm−1, the concentrations of Ca and Mg in the leachates peaked and then decreased a little. The equation used above does not explain the variation of the concentrations of Ca and Mg at a low SA/V-ratio. The precipitation of Ca and Mg onto the glass surface is probably caused by the adsorption efficiency of th...

Congruent dissolution of high-level waste glass in synthetic groundwater

Abstract Four kinds of synthetic groundwater which resemble one type of Japanese groundwater were prepared. Simulated high-level waste glass was leached in the synthetic groundwater at 70°C for up to 49 days and at 20°C for one year. It was found that the leaching of the high-level waste glass could be characterized as congruent in the synthetic groundwater and incongruent in deionized water. The chemistry of the synthetic groundwater causes the congruent leaching which is likely to occur in deep geologic disposal sites.

Continouos-flow leach tests of simulated high-level waste glass in synthetic basalt groundwater

Abstract Continuous-flow leach tests have been carried out on simulated high-level waste glass in synthetic Grande Ronde basalt groundwater at 90 °C for up to 180 d. Preliminary results obtained without irradiation are described here as reference data for later comparison with those from future experiments with irradiation. The time-dependence of the concentrations of silicon is traced, and the maximum concentration at the plateau is estimated. It is concluded from the results that, above a linear flow rate of 0.1 cm/d, the normalized leach rates of silicon tend to level off at about 6 μg · cm −2 · d −1 which is the maximum value under the present flow conditions.

Durability of High-Level Waste Glass in Flowing Groundwater Under Gamma-Irradiation

Durability of simulated high-level waste glass in continuously-flow J-13 tuff groundwater has been examined at 90 C under gamma-irradiation. The results obtained are compared with those without gamma-irradiation. The effects of groundwater radiolysis on the glass durability are discussed based on the Eh-pH excursion obtained in the present system. It is found that the groundwater tends to be reduced under gamma-irradiation, however, this may not influence the solubility of multivalent cations leached from the glass.

Effects of some glass additives on nuclear waste glass durability in water

Borosilicate glass is a candidate material for immobilizing high-level waste (HLW) stemming from the reprocessing of spent fuels used for nuclear power generation. The borosilicate glass containing HLW, which is called HLW glass, will be stored on the land surface for several tens of years and then disposed of in deep geologic formations. The contact of HLW glass with ground water in deep geologic disposal sites is the primary concern of this paper, because it is a first step for radionuclides in the glass to be released into the biosphere. The durability of HLW glass in ground water is fairly good for the purpose of safe disposal. However, if the leach rate of the HLW glass is reduced by four orders of magnitude to 10 .9 g cm -2 day -1, the glass can hold its integrity even after a considerable amount of 237Np with a half-life of 2.14 × 106 years decays in the glass. In this study, we try to improve the durability of the glass as much as possible. For this purpose, the effects of some glass additives on nuclear waste glass durability in water are examined. For example, Fe203 is used as a glass additive, since it has been

Effects of carbonate and sulphate ions in synthetic groundwater on high-level waste glass leaching

Etude de la precipitation lente de quelques elements sur la surface du verre ou dans les lessivats, en utilisant un verre de borosilicate contenant 11,7% de dechets simules