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Sato, Hisashi*; Takayama, Yusuke; Suzuki, Hideaki*; Sato, Daisuke*
JAEA-Data/Code 2023-010, 47 Pages, 2023/09
JAEA-Data-Code-2023-010.pdf:1.45MB
When a high-level radioactive waste repository is constructed in a coastal area, it is necessary to fully evaluate the impact of seawater-based groundwater on engineered barriers, including buffer materials. In this report, one-dimensional saltwater infiltration tests were conducted to obtain data to understand the impact of seawater-based groundwater on the migration phenomena of water and solutes in the buffer material during the transient period. As a result, it was confirmed that the infiltration rate increased as the NaCl concentration in the infiltration solution increased. And it was confirmed that the water content ratio distribution changed as the NaCl concentration in the infiltration solution increased. As a result of analysis of the chloride ion concentration of the post-test specimens confirmed that chloride ion enrichment was occurred with infiltration. As a result of verifying the mechanism by which chloride ion enrichment occurs, it was confirmed that the phenomenon of chloride ion enrichment due to infiltration depends on the initial water content ratio.
Suzuki, Hideaki*; Takayama, Yusuke; Sato, Hisashi*; Watahiki, Takanori*; Sato, Daisuke*
JAEA-Research 2022-013, 41 Pages, 2023/03
JAEA-Research-2022-013.pdf:3.99MB
It is anticipated that the coupled thermal-hydraulic-mechanical and chemical (THMC) processes will occur, involving an interactive process with radioactive decay heat arising from the vitrified waste, infiltration of groundwater from the host rock into the buffer material, swelling pressure of buffer material due to its saturation and chemical reaction between bentonite and pore-water in the near-field of a geological disposal system for high-level radioactive waste repository. In order to evaluate these phenomena in the near-field, the THMC model has been developed. In this study, For the purpose of evaluating the near-field infiltration behavior in seawater-type groundwater environment, a hydraulic model was set in which the permeability of the buffer material change depending on the salt concentration in the pore-water. In order to evaluate the drying phenomenon of the buffer material due to waste heat, a temperature gradient water transfer model was set in consideration of the dependence of temperature and pore-water saturation. The THMC analysis of the in-situ experiment of engineered barrier system (EBS) experiment at the Horonobe Underground Research Laboratory was carried out. The validity of the model was then checked through comparison with measured data.
Mihara, Morihiro; ; Ueta, Shinzo*; *
JNC TN8430 99-011, 27 Pages, 1999/11
In radioactive waste disposal, compacted Na-bentonite has been proposed for a buffer material. However, Na-bentonite would change to Ca-bentonite in the long term period. The change of Na-bentonite to Ca-bentonite might cause the change in the data concerning with nuclides migration properties such as permeability, sorption and diffusion. In this study, effective diffusion coefficients of HTO, Cs, I and C in compacted Ca-bentonite which was changed from Na-bentonite, Kunigel V1, were obtained and were compared to published those of Kunigel V1. In addition, effective diffusion coefficients for compacted Ca-bentonite with syncetic sea system water, SW, were obtained in order to investigate effect of solution composition. The magnitude of effective diffusion coefficients in Ca-bentonite are arranged in smaller order as Cs
HTO
IC. It is estimated that their effective diffusion coefficients are same those of Na-bentonite. About effect of solution composition, effective diffusion coefficients of HTO in 1.8g/cm
dry density with SW were almost same values with distilled system water, DW. However, effective diffusion coefficients of HTO in lower density were smaller than values with DW. Regarding as effective diffusion coefficients of Cs in 1.8g/cm dry density, the effect of SW could not be observed as well as HTO. However, effective diffusion coefficients of I and C existing as an anion in pore water of bentonite increased by the reduction in the ion exclusion.
Yui, Mikazu; Sasamoto, Hiroshi; Randolph C Arthu*
JNC TN8400 99-030, 201 Pages, 1999/07
According to the Japanese program for research and development of high level radioactive waste (HLW) disposal defined by Atomic Energy Commission (AEC), the second progress report (i.e., H-12 report) for performance assessment (PA) of HLW disposal is to be published by the Japan Nuclear Cycle Development Institute (JNC) and submitted to the Japanese government before the year 2,000 (AEC, 1997). This report presents the establishment of generic groundwater chemical compositions for the PA supporting the H-12 report. The following five hypothetical groundwaters are categorized for PA based on the results of the first progress report (i.e., H-3 report) and binaly statistical analyses of the screened groundwater dataset: (1)FRHP(Fresh-Reducing-High-pH) groundwater (2)FRLP(Fresh-Reducing-Low-pH) groundwater (3)SRHP(Saline-Reducing-High-pH) groundwater (4)SRLP(Saline-Reducing-Low-pH) groundwater (5)MRNP(Mixing-Reducing-Neutral-pH) groundwater. In order to define representative groundwater compositions for the PA for the H-12 report, JNC has established the representativeness of the above five hypothetical groundwaters by considering the results of multivariate statistical analyses, data reliability, evidence for geochemical controls on groundwater chemistry and exclusion criteria for potential repository sites in Japan. As a result, the following hypothetical reference groundwaters are selected for the performance assessment analysis in H-12 report, respectively: (1)Reference Case groundwater: FRHP groundwater, and (2)Alternative Geological Environment Case groundwater: SRHP groundwater. In addition, JNC has consulted with overseas experts on the concepts used in groundwater evolution modeling. This modeling effort has focussed on simulating equilibrium water-rock interactions to predict groundwater compositions resulting from reactions between initial water compositions and rock mineral assemblages. These discussions have centered on recommendations for developing ...
PATRICIA F SALTE*; Sasamoto, Hiroshi; Apted, M. J.*; Yui, Mikazu
JNC TN8400 99-023, 231 Pages, 1999/05
The groundwater chemistry is one of important geological environment for performance assessment of high level radioactive disposal system. This report describes the results of geostatistical analysis of groundwater chemistry in Japan. Over 15,000 separate groundwater analyses have been collected of deep Japanese groundwaters for the purpose of evaluating the range of geochemical conditions for geological radioactive waste repositories in Japan. The significance to issues such as radioelement solubility limits, sorption, corrosion of overpack, behavior of compacted clay buffers, and many other factors involved in safety assessment. It is important therefore, that a small, but representative set of groundwater types be identified so that defensible models and data for generic repository performance assessment can be established. Principal component analysis (PCA) is used to categorize representative deep groundwater types from this extensive data set. PCA is a multi-variate statistical analysis technique, similar to factor analysis or eigenvector analysis, designed to provide the best possible resolution of the variability within multi-variate data sets. PCA allows the graphical inspection of the most important similarities (clustering) and differences among samples, based on simultaneous consideration of all variables in the dataset, in a low dimensionality plot. It also allows the analyst to determine the reasons behind any pattern that is observed. In this study, PCA has been aided by hierarchical cluster analysis (HCA), in which statistical indices of similarity among multiple samples are used to distinguish distinct clusters of samples. HCA allows the natural, a priori, grouping of data into clusters showing similar attributes and is graphically represented in a dendrogram Pirouette is the multivariate statistical software package used to conduct the PCA and HCA for the Japanese groundwater dataset. An audit of the initial 15,000 sample dataset on the ...
Wada, Ryutaro*; Nishimura, Tsutomu*; Fujiwara, Kazuo*; *; *
PNC TJ1058 97-002, 430 Pages, 1997/03
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