Geological Disposal Of High-level Radioactive Waste Research Articles

ICONE19-44182 Necessary Contents of Public Outreach for High Level Radioactive Waste Disposal

Nuclear power generation is one of the solutions for global warming. However, the nuclear power generation technology can not be completed unless the disposal method of the radioactive waste is decided. Various actions are performed about the High Level Radioactive Waste (HLW) disposal in particular in each country. However, planning of HLW disposal site was not successful, except Finland and Sweden. In Japan, geological disposal of HLW was selected. The operating body and the capital management body are also decided. Up to the present, no municipality apply the disposal site candidate. An important social element for HLW disposal is careful explanation and communication for municipality. For this purpose, a symposium to explain necessity of HLW is held in each district in Japan. The symposium is not successful, because of lack of carefulness to local situation considered. In this study, we evaluates the questionnaire by the symposium attendee to extract the idea and requests by the local people. With these questionnaire, the responsibility of the government should be more enhanced. Also, the detail answer to the people's questions are needed. Using these knowledge, the HLW disposal social acceptance has been discussed.

Numerical modeling of the regional ground water flow in Beishan area, Gansu Province

The characterization of the regional ground water flow system is very important to high-level radioactive waste geological disposal. The Beishan area, located in northwestern Gansu Province, China, is selected as a potential site for disposal repository. The area includes about 100000 km2 and has complicated hydrogeological conditions, which greatly increase the computational effort of regional ground water flow models. In order to reduce computing time, parallel computing scheme was applied to regional ground water flow simulation. Models with over one million cells were used to simulate how the faults and different recharge conditions impact regional ground water flow, both in steady and transient state. The results of this study provide regional ground water flow information for site characterization of the potential high-level radioactive waste disposal.

Study on risk communication by using Web system for the social consensus toward HLW final disposal

The web site that has illustrated characters to navigate information pertaining to unfamiliar issue such as high-level radioactive waste geological disposal is an effective method. However, since the information was provided mainly from a pro-nuclear power generation group, it resulted in frustration for the web site user because viewpoints outside the group were not considered nor the explanations were based on only rational aspects, the persuasive explanation based on technical viewpoints in other words. To close this communication gap, this research aims to enhance a better sense of involvement and social collaboration by creating an interactive communication model promoting emotional acceptance and independent thinking with Web system. This purpose was accomplished by the dialog-mode explanation and the scenarios with norm activation theory supported by facial expressions of the illustrated navigators to stimulate the emotional involvement of viewers and the specialists' reliable response on the electrical bulletin board system, then we conducted preparatory experiments concerning its effects and assessed its affectiveness by making this model available over the Internet.

ＤＬＶＯ理論に基づく地下水中でのモンモリロナイトゲルからの粒子の分散に関する評価

Theoretical study has been performed to clarify the ability of colloid release form the montmorillonite gel by the flowing groundwater. Evaluation of montmorillonite colloidal particles release from the bentonite buffer material is important for the performance assessment of radioactive waste disposal because the colloids may influence the radionuclide transport. In this study, the minimum groundwater flow rate required to tear off montmorillonite particles from surface of bentonite buffer was estimated from the shear stress on the gel front, which was calculated by the DLVO theory. The estimated shear force was converted to corresponding groundwater velocity by using Stoke's equation. The results indicated that groundwater velocity in a range of about 10−5 to 10−4 m/s would be necessary to release montmorillonite particles. This range is higher than the groundwater flow velocity found generally in deep geological media in Japan. This study suggests that the effect of montmorillonite particles release from the bentonite buffer on radionuclide transport is likely to be negligible in the performance assessment of high-level radioactive waste geological disposal.

Long-term stability of flow-path structure in crystalline rocks distributed in an orogenic belt, Japan

Most evaluations of the contaminant retardation processes likely to be important in geological disposal (e.g. for high level radioactive waste (HLW)) consider only the present characteristics of fractures and associated mineral infills. Relatively little attention has been given to possible long-term changes in these features, and their influence on groundwater flow. The work reported here seeks to provide analogous evidence that such changes are not likely to be important and hence to improve confidence in the presently adopted evaluation methodology and its long-term applicability. In the orogenic belt that is formed by the Japanese islands, there are wide areas of crystalline rock. The rocks in each area have a distinctive age sequence which is partly reflected in the characteristics of the fracture systems and associated mineral fillings that occur. These characteristics generally imply that groundwater and solutes can be conducted through fracture networks, except in the cases of fault zones or crushed zones. The structural and mineralogical features of these networks readily illustrate how certain contaminants might react and be retarded by the fracture fillings and open pore geometry, due to chemical sorption and/or physical retardation. Here, we describe the fracture systems developed in crystalline rocks with different ages that are intruded into the Japanese orogenic belt. The aim is to build a model for the long-term fracturing process and hence to evaluate fracture ‘stability’. In particular, the comparisons are made between the fracture geometries and the frequencies observed in the 1.9–0.8 Ma Takidani Granodiorite (the youngest exposed pluton in the world), the ca. 67 Ma Toki Granite and the ca. 117 Ma Kurihashi Granodiorite located in central to northwest Japan. The observations show that all these crystalline rocks have similar fracture frequencies, with 1 to 2 fractures per meter in the massive part of rock bodies. Mineralogical studies and dating analyses of fracture fillings also suggest that fractures are relatively physically stable. Major new fractures tend not to be created in the massive part of rock bodies even when a pluton has been subjected to the regional stresses of plate movements with a duration of about 100 Ma. The results show the unique characteristics of the fracture forming process and the relatively stable geometries of fracture network systems in crystalline rocks distributed within the orogenic belt. This analogue also enables us to provide a model to build confidence in a technical approach applicable for modeling of hydrogeology and geology over long time scales under the orogenic stress field present in Japan. The model may also be useful for other stable tectonic settings as well as for a characterizing sites in crystalline rocks for the possible geological disposal of HLW and other toxic wastes.

高レベル放射性廃棄物処分操業時における安全・品質保証の考え方(NP4 核燃料サイクル・バックエンド技術)

Safety and quality assurance during operation must be the most important factors in High Level Radioactive Waste (HLW) disposal business. A HLW geological repository will be constructed more than 300m bellow surface, where have many constraints comparing with surface; space, temperature, humidity, water inflow and unexpected disasters, hi order to overcome or protect such issues, safety and quality assurance principles for facility design and process planning should be indispensable. Based on such understanding and features of HLW geological disposal, we have established 7-Principle with emphasizing integration of safety and quality manner during operation. Considering various EBS emplacement concepts, we can specify the most concerned issues for designing remote handling equipments and operational planning.

An analogue of long-term stability of flow-path structure in crystalline rocks distributed in the orogenic belt, Japan

In the orogenic belt, in the Japanese islands, crystalline rocks from the youngest to older ages and of different orders have been identified which have formed massive areas. The fracture system observed within these rock masses implies that the groundwater and solute can be conducted through the fracture's network. It is expected that the nuclides can be retarded due to chemical sorption and/or physical retardation by the fracture fillings and fracture open pore geometry. Most of the evaluation framework of the nuclides retardation process in the geological disposal of high level radioactive waste (HLW) is, however, basically taken into account in the present geological state, without changes of structural and mineralogical features, and in its influence on the groundwater flow system over a long period of time. This paper seeks analogous evidence that can provide the confidence of such evaluation methodology and its long-term applicability. Here, we describe the fracture system developed in the crystalline rock with the different ages intruded in the orogenic belt in order to build the long-term fracturing and its "stability" model. In particular, comparisons with the rock of 1.9–0.8 Ma Takidani Granodiorite (the youngest pluton in the world), ca. 67 Ma of Toki Granite and ca. 117 Ma Kurihashi Granodiorite located in central to northwest Japan suggest a unique characteristic of the fracture forming process and their relatively stable geometrical changing. This analogue enables us to provide a model to build the confidence of a safety context applicable for the geological setting under the orogenic field with a long-term scale. The model may also be useful for other stable tectonic settings as well as for a site characterisation methodology of crystalline rock for HLW geological disposal.

Evaluation of Long-Term Irradiation Field in Geological Disposal of High-Level Radioactive Wastes

Vitrified high-level radioactive waste (HLW) is subject to alpha, beta, gamma and neutron irradiation as a result of radionuclidedecay. Radiation can cause chemical and physical effects on HLW geological disposal system, in particular, engineered barrier system (EBS) which consists of vitrified waste, overpack container and surrounded buffer material. Alpha and beta radiation can be shielded completely by the overpack as long as it retains its containment function. Gamma and neutron radiation, on the other hand, will penetrate the overpack, and then enter the buffer material and the host rock. To assess radiation effects within the EBS for long time, it is essential to evaluate the evolution of irradiation field, quantitatively. Thus, radiation transport calculations were done to obtain dose rate, irradiation dose and absorbed dose in the irradiation field. In these calculations, vitrified waste, overpack, buffer and host rock were modeled with a same concentric cylinder.

Key Aspects of the H12 Safety Case

ABSTRACTIn Japan, as outlined in the overall high-level radioactive waste (HLW) management program defined by the Japanese Atomic Energy Commission (AEC, 1994), HLW from reprocessing of spent nuclear fuel will be immobilized in a glass matrix and stored for a period of 30 to 50 years to allow cooling. It will then be disposed of in a deep geological formation. Pursuant to the overall HLW management program, an organization with responsibility for implementing HLW disposal will be established around the year 2000. This will be followed by site selection and characterization, demonstration of disposal technology, establishment of the necessary legal infrastructure, relevant licensing applications and repository construction, with the objective of starting repository operation by the 2030s and no later than the mid 2040s.The HLW disposal program is currently in the research and development (R&D) phase and the Japan Nuclear Cycle Development Institute (JNC) has been assigned as the leading organization responsible for R&D activities. The aim of the R&D activities at the current stage is to provide a scientific and technical basis for the geological disposal of HLW in Japan and to promote understanding of the safety concept not only in the scientific and technical community but also by the general public. One of the features of the R&D program is that its progress is documented at appropriate intervals, with a view to clearly determining the level of achievement of the program and to promote understanding and acceptance of the geological disposal strategy by the general public. As a major milestone, the Power Reactor and Nuclear Fuel Development Corporation (PNC, now JNC) submitted a first progress report, referred to as H3 (PNC, 1992), in September 1992.

Experimental Study of Gas Permeabilities and Breakthrough Pressures in Clays

ABSTRACTIn this study, gas migration experiments in unsaturated and saturated states were carried out to clarify the fundamental gas migration characteristics in compacted bentonite to be used for the geological disposal of high-level radioactive waste. In unsaturated experiments, the gas permeability for Japanese bentonite (Kunigel VI) as a function of degree of saturation was measured to examine the applicability of conventional two-phase flow models to compacted bentonite. The intrinsic permeability obtained in this study was about five orders of magnitude larger than that obtained in water permeation tests with the same density. The difference seems to originate from the change of pore structure due to the swelling phenomenon of the bentonite. Since these effects have not been evaluated quantitatively yet, various relative gas permeability functions of conventional two-phase flow models were applied as a first approximation.Saturated experiments designed to simulate the gas migration phenomenon in a repository for the waste were carried out to obtain relationship between breakthrough and swelling pressures using Kunigel VI and French Fo-Ca clay in saturation state. The reproducibility of the breakthrough pressure was also examined for Kunigel VI bentonite. The breakthrough pressure was almost the same as swelling pressure irrespective of the type of clay. As to the reproducibility of breakthrough pressure, it was observed that first and second breakthrough pressures were almost the same for Kunigel VI specimens with the dry densities of 1.7 and 1.8 g/cm3.

Effect of Dry Density on Activation Energy for Diffusion of Strontium in Compacted Sodium Montmorillonite

ABSTRACTFor performance assessments of geological disposal of high-level radioactive waste, activation energies for the diffusion of strontium ions and the basal spacings of compacted sodium montmorillonite in the water-saturated state were determined.Basal spacings determined by XRD indicated changes in the interlamellar space from a three-water layer hydrate state to a two-water layer hydrate state as the dry density of the montmorillonite increased from 1.0 to 1.8 Mg m-3. Activation energies from 17.3 to 30.8 kJ mol-1 for the apparent diffusion coefficients of strontium ions were obtained. The lower activation energies than for diffusion of strontium ions in free water were determined for montmorillonite specimens of lower dry density (1.2 Mg m-3 and below), while the higher activation energies were at higher dry densities (1.4 Mg m-3 and above).These findings cannot be explained by changes in only the geometric parameters, which the pore water diffusion model is based upon. Possible explanations for the dry density dependence of the activation energy are the changes of the temperature dependence of the distribution coefficients and/or of the diffusion process with increasing dry density

Effects of biotite distribution on cesium diffusion in granite

Diffusion coefficients of Cs + in biotite granite were determined from 5° to 70°C using an initial solution concentration of <0.1 ppm. A formation factor of ∼5·10 −4 was obtained with deuterium diffusion experiments. Data fitting with a simple diffusion equation considering non-linear sorption gave effective diffusion coefficients of Cs + from 10 −8 to 5·10 −7 cm 2 s −1 at various temperatures. The complex diffusion profiles with one to three diffusion coefficients were described by assuming the sorbing mineral biotite had a heterogeneous distribution. This assumption enabled pore diffusion control to be investigated at concentrations of <0.1 ppm. The maximum intrinsic surface diffusion coefficient derived from the literature was estimated to be on the order of 10 −7 cm 2 s −1, and established the range of the diffusion coefficient under various concentration conditions. A simple calculation of Cs + matrix diffusion retardation using a one-dimensional single fracture model showed the importance of determining an accurate diffusion coefficient by considering mineral distribution in the rock. In addition, the Cs + concentration affects the surface diffusion contribution and must be adequately considered to accurately analyze long-lived 135Cs transportation in rock formations when the single fracture model is applied to the safety analysis of high-level radioactive waste geological disposal.