Static leach tests were conducted for simulated high-level waste (HLW) glass in CaCl₂/Ca(OH)₂ solutions to investigate the corrosion behavior of HLW glass under calcium-rich environments induced by cement based materials in geological repositories. Another series of leach tests were conducted in deionized water in the presence of iron to investigate the effects of iron over-pack on the glass corrosion.
  In CaCl₂/Ca(OH)₂ solutions, corrosion of the glass was inhibited during the test period compared to that in deionized water at the pH range of 6 - 11, while higher corrosion rate was observed in the initial stage of the test in Ca(OH)₂ solution at the initial pH of 12. However, the corrosion rate dropped due to a formation of calcium silicates that covered the surface of the glass.
  Under the condition that iron exists in the vicinity of the glass, glass corrosion was enhanced compared to that without iron throughout the testing period. In addition, an alteration layer including iron and silicon was observed at the interface between the glass surface and the iron after the leach tests, and thermodynamic calculation showed that formation of an iron silicate was favored under the chemical compositions of the leachate during the period. The enhancement of the glass corrosion was assumed to be accompanied with transformation of silica, a glass network former, into iron silicates.

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  Diatomaceous earth and siliceous rock are widespread in the areas along the Sea of Japan in Hokkaido Prefecture, Akita Prefecture, Noto Peninsula and Oki Islands. To construct underground structures in the siliceous rock mass, it is essential to understand its mechanical properties. In this study, siliceous mudstone of the Wakkanai formation obtained from the deep underground in Horonobe, Hokkaido was applied to various laboratory tests; uniaxial compression test, Brazilian tension test, drying shrinkage test and the test to investigate the time dependent behavior and strength recovery. The testing results showed that water has a huge effect on the deformation and failure of the siliceous mudstone; when the specimen is air dried in room temperature, the axial shrinkage strain reaches 0.9% and the strength is twice larger than that in wet condition. It was found that the siliceous mudstone exhibits the same degree of time dependent behavior and strength recovery as other rocks such as tuff and sandstone.

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  A gap surrounding the buffer material in an HLW repository should be filled in an appropriate way. Pellets made of bentonite are expected to be a candidate material for filling the gap. Using higher density bentonite pellets increases the probability that the gap is filled high density. Conventional methods of making bentonite pellets using compressive force are possible to high density pellets in response to the magnitude of compression. However, there are still room for improvement in terms of shape and ease of production. We have devised a newly method for making bentonite pellets using dry shrinkage. We have verified that spherical pellets could be made under high water content and plastic conditions. Subsequently, we have revealed that spherical pellets with a high water content would turn into high density pellets with a dry density of about 2.0Mg/m³ if treated appropriately in the drying process.

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