Deep Geological Environment Research Articles

In-situ experiments for the determination of rock properties and behaviour at the Meuse/Haute Marne Centre

Andra is in charge of studying the feasibility of a disposal facility for long- lived high-level nuclear waste (LL-HLW) in a deep geological environment. With this aim, dedicated experiments have been carried out for several years at the Meuse/Haute Marne Underground Research Laboratory excavated in a 500 m deep argillaceous rock formation. These experiments include determining the feasibility of the excavation of disposal cells for LL-HLW, consisting of 40 meter long, 70 cm in diameter, horizontal cased micro tunnels. The hydro mechanical impact of the excavation of such openings on the rock mass behaviour is continuously monitored as well as their mean term mechanical behaviour. Since LL-HLW produce heat, the impact of temperature on the surrounding rock mass and on the micro tunnel steel casing will also be studied. Specific instrumentation has been developed to study this impact. The first step of the micro- tunnel excavation tests, carried out in 2009, has led to improving the excavation method and the drilling machine. These improvements will be tested in the next step of the excavation tests planned for 2010. The THM experiment dedicated to studying the behaviour of the rock mass under thermal solicitation started early 2010. The behaviour of a steel casing in contact with the rock mass and under thermal solicitation will be studied in an experiment scheduled to start in September 2010.

深地層の科学的研究における地質環境調査のノウハウ・判断根拠等の分析・整理

深地層の科学的研究における地質環境調査のノウハウ・判断根拠等の分析・整理

Effects of shield brine on the safe disposal of waste in deep geologic environments

The salinity of groundwater increases with depth in the Canadian Shield (up to 1.3 kg/L of density). The existence of brine can be critically important for the safe geologic disposal of radioactive wastes, as dense brine can significantly retard the upward migration of radionuclides released from repositories. Static and flushing conditions of the deep brine are analyzed using a U-tube analogy model. Velocity reduction due to the presence of dense brine is derived under flushing conditions. A set of illustrative numerical simulations in a two-dimensional cross section is presented to demonstrate that dense brine can significantly influence regional groundwater flow patterns in a shield environment. It is implied from the results that (1) the existence of Shield brine can be an indicator of a hydrogeologically stable environment, (2) activities near ground surface may not perturb the stable groundwater environment in the deep brine region, and thus, (3) the deep brine region can be considered as a candidate geologic site for the safe disposal of waste. In addition to brine, other issues associated with long-term waste disposal, such as geological, glacial and seismic events, may need to be considered for the safe storage of spent nuclear fuel in a shield environment.

深地層の科学的研究における地質環境調査のノウハウ・判断根拠等の分析・整理

深地層の科学的研究における地質環境調査のノウハウ・判断根拠等の分析・整理

A method for determining both diffusion and sorption coefficients of rock medium within a few days by adopting a micro-reactor technique

Abstract Migration properties characterized by physico-chemical factors such as distribution coefficient (Kd) and diffusion coefficient (De) are of great concern in performance assessment of high-level radioactive waste disposal in a deep geologic environment. These coefficients are normally obtained with different sample geometries using conventional methods, i.e., crushed samples by the batch sorption method for Kd determination and block samples by the through-diffusion method for De. A size dependence on both Kd and De has been reported and an additional correction due to size difference is required to maintain consistency of the data set. A fast method was developed, hereafter referred to as the micro-channel method, to determine both the sorption coefficient (Rd) and De using non-crushed rock sample by adopting the micro-reactor technique. In this method, a radionuclide solution is injected into a micro-channel (20 mm length, 4 mm width, 160 μm depth), which is in contact with a plate-shaped rock sample. A part of the injected radionuclide can diffuse into the rock matrix and/or adsorb on the rock surface and this results in an inlet-outlet concentration difference. A breakthrough curve is easily obtained with a short observation period because the injection amount is extremely small and is comparable to that escaping by diffusion into the matrix. The breakthrough curve is analyzed by a two-dimensional diffusion-advection equation to evaluate Rd and De. In the present study, tritiated water (specific activity, 1.2 × 104 Bq/mL; pH, 6) was injected into the micro-channel, and the breakthrough curve of 3H obtained. A series of experiments was carried out by changing the flow rate of the tritiated water (2.6 × 10−5–7.7 × 10−4 m/s). Rock samples were biotite granite from the Makabe area, Japan. The diffusion coefficient evaluated by least squares fitting to the numerical solutions (De = 1.5 × 10−11 m2/s) agreed well with that obtained by the through-diffusion method (1.3 × 10−11 m2/s). The breakthrough curve of Cs ([Cs] = 1.0 × 10−7 mol/L, pH 6) labeled with 134Cs (specific activity adjusted to 4.9 × 101 Bq/mL) was also obtained. A nearly constant Rd value (5.5 × 10−2 m3/kg) was found when the flow rate was less than 2.5 × 10−4 m/s. This implied that the sorption equilibrium is reached and Kd is obtained by the present method. This value was almost identical to Kd obtained by the batch sorption method (5.0 × 10−2 m3/kg), but the testing period was very different; 1 day and 7 days, respectively. It is concluded that application of the micro-channel method provided advantages when compared with the conventional methods.

Use of groundwater lifetime expectancy for the performance assessment of a deep geologic waste repository: 1. Theory, illustrations, and implications

Long‐term solutions for the disposal of toxic wastes usually involve isolation of the wastes in a deep subsurface geologic environment. In the case of spent nuclear fuel, if radionuclide leakage occurs from the engineered barrier, the geological medium represents the ultimate barrier that is relied upon to ensure safety. Consequently, an evaluation of radionuclide travel times from a repository to the biosphere is critically important in a performance assessment analysis. In this study, we develop a travel time framework based on the concept of groundwater lifetime expectancy as a safety indicator. Lifetime expectancy characterizes the time that radionuclides will spend in the subsurface after their release from the repository and prior to discharging into the biosphere. The probability density function of lifetime expectancy is computed throughout the host rock by solving the backward‐in‐time solute transport adjoint equation subject to a properly posed set of boundary conditions. It can then be used to define optimal repository locations. The risk associated with selected sites can be evaluated by simulating an appropriate contaminant release history. The utility of the method is illustrated by means of analytical and numerical examples, which focus on the effect of fracture networks on the uncertainty of evaluated lifetime expectancy.

Comparative Analysis of Results From Deterministic Calculations of the Release of Radioactivity From Geological Disposal of Spent Fuel in Crystalline Rocks

AbstractThis paper presents results from deterministic calculations of radionuclide migration in a deep geological environment. The concept assumes single canister with spent nuclear fuel situated in bentonite (near-field) and surrounded by crystalline host rock (far-field). The results are presented in the form of release rates from the near-field and far-field, which contains also a part of advective release from the system of two single fractures. Additionally, radiological risk is evaluated in the form of dose rates for a water drinking scenario for an exposed population group. The analyses have been done by using the methodologies and computer codes used at the Institute for Energy EC-JRC in the Netherlands and the Mining Institute KSC RAS in Russia.

Countermeasures Planned for Reducing Water Inflow into Deep Shafts at the Mizunami Underground Research Laboratory

The Mizunami Underground Research Laboratory (MIU) is currently being constructed. The MIU design consists of two 1,000 m-deep shafts with several research galleries. The goals of the MIU project are to establish techniques for investigation, analysis and assessment of deep geological environments, and to develop a range of engineering expertise for application in deep underground excavations in crystalline rocks such as granite. The diameter of the Main and the Ventilation Shafts are 6.5 m and 4.5 m, respectively. Horizontal tunnels to connect the shafts will be excavated at 100 m depth intervals. The Middle Stage, at about 500 m in depth, and the Main Stage, at about 1,000 m in depth, will be the main locations for scientific investigations. The Main and the Ventilation Shafts were 180 m and 191 m deep, respectively, in November 2006. During construction, water inflow into the shafts has been increasing and affecting the project progress. In order to reduce the water inflow into the shafts, pre- and post-excavation grouting has been planned. A post-excavation grouting test has been undertaken in the Ventilation Shaft and the applicability of several techniques has been evaluated. This paper describes an outline of the MIU project, its work plan and the results of the post-excavation grouting test.

天然現象に対する深部地質環境の応答：北海道北部，幌延地域を事例とした地下水の流動状態の長期的変遷

天然現象に対する深部地質環境の応答：北海道北部，幌延地域を事例とした地下水の流動状態の長期的変遷

Anaerobic and aerobic sorption of cesium and selenium on mudrock

This study is focused on sorption and determination of distribution ratios (Rd) of cesium and selenium on mudrock, which is the potential host rock for waste disposal in Taiwan. Batch tests including sorption kinetic and isotherms tests have been performed in synthetic groundwater at aerobic and anaerobic conditions which might be found in the deep geologic environment. It is found that Rd for sorption of cesium did not have an obvious difference in both conditions with various contact time. However, Rd in anaerobic condition for sorption of selenium was greater than that in aerobic condition. Selenium is a redox sensitive element and its solubility in reducing conditions is controlled by the formation of metallic or precipitable selenium. It demonstrated variation of Rd with time in both conditions for Se sorption kinetic experiments was equal (10 ml/g) and indicated a part formation (10%) of precipitable selenium (Se 0 , FeSe or FeSe 2 ) in the solution. Moreover, it was not enough to form precipitable selenium completely in reducing condition as to insufficient experimental period (2 weeks) and in the presence of Fe 2+ . The Freundlich and Langmuir isotherm for the concentration ranges (i.e., 10 –3 –10 –7 M) conducted in both conditions seem to be adequate to quantitatively describe the sorption of cesium and selenium, respectively.

大規模地下施設の建設に伴う周辺地下水環境の変化

The Japan Atomic Energy Agency (JAEA) is constructing the Mizunami Underground Research Laboratory at Mizunami, Japan to establish general techniques for the assessment of the deep geological environment. The facility including two 1,000 m shafts and sub-stages at 100 m depths between two shafts is currently under construction in the sedimentary rocks. This study aims to evaluate the environmental changes around a large underground facility. To this end, hydrochemical changes in response to shaft excavation are assessed based on the observation of hydraulic head and groundwater chemistry around the facility. The observations indicated that rock formations with low hydraulic conductivity act as barriers to hydraulic disturbances, while higher conductivity zones provide a preferential flow path. Groundwater flow to the drifts creates chemical changes by mixing among chemically different groundwaters in higher conductivity zones. It is therefore meaningful to monitor the water pressure and chemistry at highly conductive rock formations during construction and operation of underground facilities. These investigations will provide the basic information on hydrochemical buffer capacity of the natural environment. Furthermore, observations suggest that grouting of conductive rock formations is important for maintaining the groundwater at near preconstruction levels so as to retain the buffer capacity of the rock formations used for safety assessment.

Sorption of cesium on granite under aerobic and anaerobic conditions

This study focused on the determination of distribution coefficients (K d) of 137Cs under aerobic (∼21% O2) and anaerobic conditions (1−10 ppm O2) which might be found in the deep geologic environment. The anaerobic conditions were simulated in a glove box filled with highly pure argon (99.9%). Both batch tests and solid-phase analyses, including X-ray diffraction, N2-BET surface area, and polar-microscopy/autoradiography were employed for analyzing the sorption of 137Cs on granite, which is the potential host rock for waste disposal in Taiwan. Before starting batch tests, the rock samples were placed in the glove box for one week, and the E h values of experimental liquids were periodically measured until the E h value decreased below 0 mV. The sorption of 137Cs was studied at various concentrations in synthetic groundwater. The Freundlich sorption isotherm seems to be adequate to quantitatively describe the sorption of Cs for the concentration ranges (i.e., 10-3−10-6 M) conducted in both conditions. The distribution coefficient (K) obtained from the two-week batch tests indicated no obvious difference in two systems and the values of K and n are similar. In addition, sorption onto a specific host rock was found to be dependent on its mineralogical components. The photos obtained from polar-microscopy/autoradiography analyses showed that biotite is the principal mineral component responsible for the sorption of 137Cs onto granite.

Determination of 90Sr / 238U ratio by double isotope dilution inductively coupled plasma mass spectrometer with multiple collection in spent nuclear fuel samples with in situ 90Sr / 90Zr separation in a collision-reaction cell

Strontium-90 is one of the most important fission products generated in nuclear industry. In the research field concerning nuclear waste disposal in deep geological environment, it is necessary to quantify accurately and precisely its concentration (or the 90Sr / 238U atomic ratio) in irradiated fuels. To obtain accurate analysis of radioactive 90Sr, mass spectrometry associated with isotope dilution is the most appropriated method. But, in nuclear fuel samples the interference with 90Zr must be previously eliminated. An inductively coupled plasma mass spectrometer with multiple collection, equipped with an hexapole collision cell, has been used to eliminate the 90Sr / 90Zr interference by addition of oxygen in the collision cell as a reactant gas. Zr + ions are converted into ZrO +, whereas Sr + ions are not reactive. A mixed solution, prepared from a solution of enriched 84Sr and a solution of enriched 235U was then used to quantify the 90Sr / 238U ratio in spent fuel sample solutions using the double isotope dilution method. This paper shows the results, the reproducibility and the uncertainties that can be obtained with this method to quantify the 90Sr / 238U atomic ratio in an UOX (uranium oxide) and a MOX (mixed oxide) spent fuel samples using the collision cell of an inductively coupled plasma mass spectrometer with multiple collection to perform the 90Sr / 90Zr separation. A comparison with the results obtained by inductively coupled plasma mass spectrometer with multiple collection after a chemical separation of strontium from zirconium using a Sr spec resin (Eichrom) has been performed. Finally, to validate the analytical procedure developed, measurements of the same samples have been performed by thermal ionization mass spectrometry, used as an independent technique, after chemical separation of Sr.

第4回 深部地質環境研究センター研究発表会講演要旨及びポスター発表概要

第4回 深部地質環境研究センター研究発表会講演要旨及びポスター発表概要

Representation of Fracture Zone Interpretation Uncertainty in 3D Geological Models of the Mizunami Underground Research Laboratory, Japan

ABSTRACTThe Japan Nuclear Cycle Development Institute (JNC) is undertaking research into the deep geological environment in Japan in the Tono area of Japan. In the Mizunami Underground Research Laboratory (MIU) Project, located in the Tono area, JNC is carrying out surface-based investigations and will excavate an Underground Research Laboratory (URL) in order to establish comprehensive techniques for investigating and characterising the geological environment. The MIU Project focuses on the investigation of the granitic rocks of the Toki Granite. The geological structure and hydrogeological properties of the Toki Granite are closely affected by the regional fracture zones and faults. The interpretation of these features is undertaken in 3D and directly linked into 3D hydrogeological models. Significant uncertainty exists in the 3D interpretation of the fracture zones, and geologists must make several assumptions regarding the 3D structure in order to develop the 3D interpretation. In order that these assumptions are communicated to the hydrogeologists, a methodology has been developed for representing uncertainty in the 3D geological models. An important part of the uncertainty representation, is the development of a fracture zone classification in which the uncertainty in both the presence and the geometry of the fracture zone is assigned. Other elements include the development of alternative models, visualisation of raw data, development of conceptual models, development of bounding models, and suitable quality assurance and archiving of modelling projects.

Migration characteristics of some chemical species in a granite fracture according to their chemical properties

Migration experiments were carried out in artificial rock fractures of 50×50 cm scale in order to understand the transport phenomena of contaminants in deep geological environment. The tracers used in this experiments were tritiated water, anion, polymers, and sorbing cations. The experimental study was focused on the interpretation of the retardation and matrix diffusion of the tracer in the fracture. To visualize migration phenomena, an organic dye, eosine, was used as a tracer. The migration plumes were taken with a digital camera as a function of time and stored as a digital image file. Computer simulation was performed not only for the hydraulic behavior such as distributions of pressure and flow vectors in the fracture but also for the migration plume and the elution curves. These simulation results were interpreted by comparing experimental ones, thus providing a way to understand migration behavior of tracers and interaction between rock and chemical species.

P23-08 高レベル放射性廃棄物処分の実施段階におけるサイクル機構での地層処分技術に関する研究開発

High-level radioactive waste (HLW) from the reprocessing of spent nuclear fuel is to be disposed of deeper than 300m below the ground surface in Japan and the operation of disposal is planed to start in 2033 to 2037. The JNC's program and examples of the recent progress on the R&D of geological disposal of the HLW are described in this paper. JNC will execute the basic R∿D to reflect the accomplishments to the implementation of disposal and safety regulation. The program covers three fields which are research on the deep geological environment, improving the reliability of disposal technologies and development of advanced safety assessment methods.

放射性廃棄物地層処分 花こう岩を対象とした深部地質環境の調査技術開発の課題と現状 測定データの品質保証の観点で構築した地下水調査法の提案

放射性廃棄物地層処分 花こう岩を対象とした深部地質環境の調査技術開発の課題と現状 測定データの品質保証の観点で構築した地下水調査法の提案

Grimsel 2000 – Status of International Projects at the Grimsel Test Site (GTS)

ABSTRACTDuring 17 years of cooperation, the Grimsel underground test site in the Swiss Alps has become established as a major center for study of the deep geological environment. The present Phase V of operation involves collaboration of 15 organizations from 9 countries.The 7 major projects currently running can be divided into 3 areas:- Confirmation of fundamental understanding and testing of models of processes identified to be significant in integrated performance assessment- Demonstration and optimization of site characterization technology- Demonstration of the technology for constructing and operating a deep repository in an efficient and quality assured manner.This sub-division of projects is somewhat simplistic as, wherever possible, large, long- running experiments are designed to achieve a number of goals. The paper will provide a summary of some projects running at Grimsel, an overview of the rationale behind the experimental concepts and a perspective on possible future work.

動燃式低水圧制御水理試験機(動燃式JFT)の原理と適用例

Resently, It is essentially necessary to obtain the hydraulic parameters of ground water in deep geological environment in order to contribute on the establisment to modelling of regional ground water flow.However, in-situ test method in the low permeable zone have not been developed. Hence we developed "New PNC Aquifer Test Method" with a single borehole and nonsteady state theory.This measurmentu nit was developedt o settlment four problem as follows,1 ) To prevent hydraulic destruction,2) Improvement of operating efficiency,3) To measure a pore water pressure in low permeability,4) To measure the coefficient of permeability in low permeable rock bed.When to make in-situ experiment, w e got a good result.The minimumc oefficiento f permeability on in-s i tu experiment was 8.5×10-9 c m/sec and the measurement was over within 6 hours