Evolution of radionuclide transport and retardation processes in uplifting granitic rocks, Part 1; Key processes, conceptual models and scenario

Metcalfe, R.*; Tachi, Yukio; Sasao, Eiji; Kawama, Daisuke*

Science of the Total Environment, 957, p.177375_1 - 177375_17, 2024/12

https://doi.org/10.1016/j.scitotenv.2024.177375

A safety case for an underground radioactive waste repository must show that groundwater will not in future transport radionuclides from the repository to the near-surface environment (the biosphere) in harmful quantities. Safety cases are developed step-wise throughout a programme to site and develop a repository. At early stages, before a site is selected, safety cases are generic and based on simplified safety assessment models of the disposal system that have conservative parameter values. Later, when site-specific conditions are known, more realistic models are needed for the long-term geo-environmental evolution and their impacts on radionuclide migration/retention. Uplift is one such environmental change, which may be particularly important in countries near active tectonic plate boundaries, such as Japan. Here we review the state of knowledge about how the properties of fractured granitic rocks evolve during uplift, based on studies in Japan. Hence, we present conceptual models and a generic scenario for mass transport and retardation processes in uplifting granitic rocks as a basis for realistic numerical models to underpin safety assessment.

Rapid and long-lasting bedrock flow-path sealing by a "concretion-forming resin"; Results from evaluation tests in an Underground Research Laboratory, Horonobe, Japan

Yoshida, Hidekazu*; Yamamoto, Koshi*; Asahara, Yoshihiro*; Maruyama, Ippei*; Karukaya, Koichi*; Saito, Akane*; Matsui, Hiroya; Mochizuki, Akihito; Katsuta, Nagayoshi*; Metcalfe, R.*

Powering the Energy Transition through Subsurface Collaboration; Proceedings of the 1st Energy Geoscience Conference (Energy Geoscience Conference Series, 1), 20 Pages, 2024/00

A capability to permanently seal fluid flow-paths in bedrock, such as natural faults/fractures, and damaged zones around boreholes/excavations, is needed to ensure the long-term safety and effectiveness of many underground activities. Cementitious materials are commonly used as seals, however these materials unavoidably undergo physical and chemical degradation, therefore potentially decreasing seal durability. In order to solve these problems, a more durable sealing method using concretion-forming resin has been developed by learning from natural calcite (CaCO) concretion formation. The sealing capability of resin was tested by experiments on bedrock flow-paths in an underground research laboratory (URL), Hokkaido, Japan. The results showed a decrease the permeability rapidly down to 1/1,000 of the initial permeability due to calcite precipitation over a period of one year. During the experiment inland earthquakes occurred with foci below the URL (depths 2-7 km and maximum magnitude 5.4). Due to the earthquakes the hydraulic conductivities of the flow-paths sealed initially by concretion-forming resin increased. However, these flow-paths subsequently resealed rapidly, and within a few months recovered the same hydraulic conductivities as before the earthquakes. This new technique for rapidly producing long-lasting seals against fluid flow through rocks will be applicable to many kinds of underground activities.

Effects of -radiation on a direct disposal system for spent nuclear fuel, 2; Review of research into safety assessments of direct disposal of spent nuclear fuel in Europe and North America

Kitamura, Akira; Takase, Hiroyasu*; Metcalfe, R.*; Penfold, J.*

Journal of Nuclear Science and Technology, 53(1), p.19 - 33, 2016/01

https://doi.org/10.1080/00223131.2015.1014874

Not only geological disposal of vitrified waste generated by spent fuel (SF) reprocessing, but also the possibility of disposing of SF itself in deep geological strata (hereinafter "direct disposal of SF") may be considered in the Japanese geological disposal program. In the case of direct disposal of SF, the radioactivity of the waste is higher and the potential effects of the radiation are greater. Specific examples of the possible effects of radiation include: increased amounts of canister corrosion; generation of oxidizing chemical species in conjunction with radiation degradation of groundwater and accompanying oxidation of reducing groundwater; and increase in the dissolution rate and the solubility of SF. Therefore, the influences of radiation, which are not expected to be significant in the case of geological disposal of vitrified waste, must be considered in safety assessments for direct disposal of SF. Focusing especially on the effects of -radiation in safety assessment, this study has reviewed safety assessments in countries other than Japan that are planning direct disposal of SF. The review has identified issues relevant to safety assessment for the direct disposal of SF in Japan.

Long-term stability of fracture systems and their behaviour as flow paths in uplifting granitic rocks from the Japanese orogenic field

Yoshida, Hidekazu*; Metcalfe, R.*; Ishibashi, Masayuki; Minami, Masayo*

Geofluids, 13(1), p.45 - 55, 2013/02

https://doi.org/10.1111/gfl.12008

In granitic rocks fracture networks provide pathways for groundwater flow and solute transport that need to be understood to assess the long-term performance of deep underground environment. In order to clarify the long-term processes, Japanese plutons of different ages were studied. Detailed investigation of in-situ fracture fillings sampled from a depth of 300 meters was carried out to clarify the fracturing and mineral infilling processes. Different plutons show identical episodes, consisting of: brittle tensile fracturing (Stage I); relatively rapid uplifting accompanied by hydrothermal water circulation that produced fracture fillings (Stage II); and a period of low-temperature meteoric water circulation (Stage III). The paragenesis of carbon isotopic compositions of carbonate minerals show that there were distinct episodes of mineral precipitation. The evolution of fillings identified here enable development of a model of fracturing and persistence of fluid conducting systems.

Proposal for quality assessment method of groundwater chemistry for hydrochemical investigation

Mizuno, Takashi; Metcalfe, R.*; Iwatsuki, Teruki; Mie, Hideki*

Chikasui Gakkai-Shi, 49(2), p.139 - 152, 2007/05

https://doi.org/10.5917/jagh1987.49.139

Hydrochemical studies are generally conducted based on chemical data of groundwater samples. Various methodologies exist for obtaining samples and for assessing the quality of the collected sample. This study is aimed at establishing a methodology for quality assessment of chemical data obtained from groundwater samples using a method known as Evidence Support Logic. In this study, pH data of groundwater obtained from several boreholes were assessed using this method. The results showed that 23 out of 63 samples satisfied the applied quality criteria. When plotted, the data from the 23 samples show a constant value from top to bottom of investigation area when compared to a plot using data from all samples. These results indicate that the quality assessment method demonstrated by this study is applicable to groundwater studies and that by considering the sample quality it will be possible to develop a clearer interpretation of the deep underground geochemical environment.

The Hydrogeochemistry of argillaceous rock formations at the Horonobe URL site, Japan

Hama, Katsuhiro; Kunimaru, Takanori; Metcalfe, R.*

Proceedings of 2nd International Meeting on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, p.399 - 400, 2005/03

The current status of the hydrogeochemical study has been presented.

Sensitivity analysis to the geochemical parameters of the groundwater

Metcalfe, R.*; Savage, D.*; Bath, A. H.*; Walker, C.*

JNC TJ7400 2004-013, 148 Pages, 2004/03

JNC-TJ7400-2004-013.pdf:6.11MB

This report describes calculations of the solubilities of elements that are relevant to Performance Assessment in the groundwaters of the Tono area.

Project to develop a coupled geochemical/hydrogeological model of the Tono area

Sugita, Kenichiro*; Metcalfe, R.*

JNC TJ7400 2005-073, 181 Pages, 2003/03

JNC-TJ7400-2005-073.PDF:7.43MB

This document is the report of a project to develop a coupled geochemical/hydrogeological model of the groundwater system in the Tono area of Gifu ken, central Japan. a major outcome of the work has been identify alternative possible origins for the Na-(Ca)-Cl dominated groundwater salinity in the southern part of the study area.

Geochemical Methods for Interpreting Groundwater Flow around Tono and Their Generic Relevance to Site Selection, Site Characterization and Performance Assessment -A Final Report on a JNC International Fellowship

Metcalfe, R.

JNC TN7440 2002-002, 377 Pages, 2002/02

JNC-TN7440-2002-002.pdf:17.96MB

This report presents work undertaken by Richard Metcalfe, during a JNC International Fellowship, between 1 March1999 and 28 February 2002. During this period, the main purpose of the work was continuous review and appraisal of geochemical studies being done by the Japan Nuclear Cycle Development Institute (JNC) and contribution to a range of specific geochemical sutdies. This involved workng closely with Japanese colleagues at Tono Geoscience Center (TGC). These actvities were very broad in scope and produced a wide range of different outputs. However, a dominant theme was the application of geochemical information to understand past and present grounwater flow. The present report aims to compile those outputs from the Fellowship that deal with this theme.

Development of a method for the classification of groundwater sample quality

Mizuno, Takashi; Metcalfe, R.*; Mie, Hideki; Iwatsuki, Teruki

no journal, , 

no abstracts in English