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Journal Articles

Disruptive effects on a HLW repository due to uplift-erosion in the distant future

Miyahara, Kaname; Inagaki, Manabu; Kawamura, Makoto; Ebina, Takanori*; McKinley, I. G.*

Materials Research Society Symposium Proceedings, Vol.1193, p.177 - 184, 2009/05

Uplift and erosion cannot be generally precluded in Japan, therefore needs to be treated. In particular, uplift and erosion will cause major disruption of the engineered and natural barriers when the repository is exposed at the ground surface, although erosion of the repository should be excluded for very long times by careful siting and design. In Japan, uplift/erosion scenarios must be analysed, even if they occur far in the future as no assessment cut-off times have yet been defined. For this purpose, an argumentation method is being developed to allow sensible scenarios to be constructed. This paper discusses procedures to derive relevant conceptual models and resultant analyses in a credible manner which illustrates the effectiveness and robustness of the HLW disposal system, using relevant yardsticks based on natural radionuclide fluxes.

Journal Articles

Impact of silicon migration through buffer material on the lifetime of vitrified waste

Mitsui, Seiichiro; Makino, Hitoshi; Inagaki, Manabu; Ebina, Takanori*

Materials Research Society Symposium Proceedings, Vol.1193, p.397 - 404, 2009/05

The results of a sensitivity analysis for long-term glass dissolution taking into account Si release from the glass and its migration through the buffer material are presented to illustrate the impact of this near-field process on the lifetime of the vitrified waste. The lifetime of the glass estimated by the analysis showed a strong dependence on Si diffusion and distribution coefficients in the buffer material and groundwater flow rate in the EDZ. This indicates the significance of these parameters for the long-term evolution of vitrified waste. We also discuss the impact of glass hydration, which proceeds simultaneously with matrix dissolution considering Si release, on the lifetime of the vitrified waste. The results show that glass hydration is less important for the long-term evolution than matrix dissolution in an open system and it can be concluded that Si migration through the buffer material will be an important process for estimating the lifetime of the vitrified waste.

Journal Articles

Development of scenario analysis and database for quantitative analysis of microbial effects on the repository performance

Yoshikawa, Hideki; Inagaki, Manabu; Miyasaka, Iku*

Materials Research Society Symposium Proceedings, Vol.1193, p.375 - 380, 2009/05

The scenario analysis was performed for microbial effect on the performance assessment (PA) of high level radioactive waste disposal system based on recent literature review. The consideration for PA with these effects was clarified and important FEPs were selected in the point of safety function under various uncertainties for microbe information. It is clear that the biological effect on groundwater components evolution, which is caused by the microbial redox reaction, is one of the most important issues to assess on PA. And we developed a biological parameter database which has growth and metabolism data for interactive six microbial groups. The database composed some significant data like specific growth rate, maximum growth rate, constant decay rate, and experimental condition for model assessment.

Journal Articles

Measurement of HLW glass dissolution/alteration kinetics by using micro-reactor flow-through test method

Inagaki, Yaohiro*; Mitsui, Seiichiro; Makigaki, Hikaru*; Idemitsu, Kazuya*; Arima, Tatsumi*; Bamba, Tsunetaka; Noshita, Kenji*

Materials Research Society Symposium Proceedings, Vol.1193, p.219 - 228, 2009/05

We developed a new flow-through test method using micro-reactor, and applied it to measurement of the dissolution/alteration kinetics for a simulated HLW glass (P0798). In this method, a glass coupon is placed just on a Teflon plate having a micro-channel, and a solution is injected into the inlet of micro-channel by micro-syringe pump at a constant flow rate. The injected solution flows through the micro-channel reacting with the glass to the outlet, and the outlet solution is retrieved at certain intervals to be analyzed for determination of the dissolution/alteration rate. This method has some major features, i.e., simple test apparatus with compact size, high S/V ratio, sensitive/precise measurement of the glass dissolution/alteration rate, adequate glass shape for analysis of reacted glass surface, and so on. By use of this method the dissolution/alteration rate for P0798 was measured as a function of pH, temperature, flow rate, and time, and some available results were obtained to evaluate the dissolution/alteration kinetics.

Journal Articles

Measurement of initial dissolution rate of P0798 simulated HLW glass by using micro-reactor flow-through test method

Makigaki, Hikaru*; Inagaki, Yaohiro*; Idemitsu, Kazuya*; Arima, Tatsumi*; Mitsui, Seiichiro; Bamba, Tsunetaka; Noshita, Kenji*

Materials Research Society Symposium Proceedings, Vol.1193, p.307 - 314, 2009/05

By using micro-reactor flow-through test method we measured the initial dissolution rate of P0798 glass at 25$$^{circ}$$C as a function of pH between 5.6 and 12. The results showed that the initial dissolution rate determined by dissolution rate of Si has "V-shaped" pH dependency similar to R7T7 glass reported by CEA, France. We also measured the initial dissolution rate at pH 5.6 as a function of temperature between 25 and 90$$^{circ}$$C, and the activation energy was evaluated to be 51 kJ/mol, which value is slightly smaller than that of R7T7 glass at pH 9 reported by CEA. On the basis of these results and comparison, we discussed the dissolution kinetics of P0798 glass.

Journal Articles

Diffusion of cesium and iodine in compacted sodium montmorillonite under different saline conditions

Tachi, Yukio; Yotsuji, Kenji; Seida, Yoshimi; Yui, Mikazu

Materials Research Society Symposium Proceedings, Vol.1193, p.545 - 552, 2009/05

Diffusion of Cs and I in compacted montmorillonite were examined from the viewpoints of mechanistic understanding of salinity effects. The effective diffusivity and capacity factor for Cs and I were measured in compacted montmorillonite saturated with 0.01, 0.1 and 0.5M NaCl by through-diffusion experiments, coupled with multiple curve analysis including tracer depletion, breakthrough, and depth concentration curves. The De values obtained for Cs decreased as salinity increased, and those for I showed the opposite dependency. The distribution coefficient of Cs decreased as salinity increased. The diffusion and sorption parameters for Cs were also obtained by in-diffusion and batch sorption experiments, showing good agreement with those by the through-diffusion. The diffusion model based on electrical double layer theory predicted the salinity dependence of De reasonably well, the apparent diffusivity which includes sorption effect was also interpreted by the sorption coupled model.

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