A review of multiphysics coupling numerical modeling techniques for risk assessment in geological disposal of high-level radioactive waste.

At present, in the geological disposal domain of high-level radioactive waste, little is known about microorganisms in deep underground geological environment in our country. This paper introduces some interactions between microbiological and geological disposal of high-level radioactive waste. There is a huge biosphere in the deep underground, mainly held by extremophiles. Microorganisms can influence the waste geological disposal environment in two aspects. On the one hand, the storehouse security will be confronted with serious problems of microorganisms because of their material corrosion capability. The main species of corrosion microorganisms include sulfate reducing bacteria, sulfur-oxidizing bacteria, saprophytic bacteria, iron bacteria and fungi. About research development on interactions between microbiological and geological disposal of high-level radioactive waste in China and abroad, foreign countries started early. Specialized research field has been formed and many achievements has been made by a series of research in Sweden, US, France, Canada, and so on. But relevant study is very few in our country. Therefore, there are special necessity and urgency to carry out this research.

The geological disposal of high-level radioactive waste (hereinafter referred to "geological disposal") is a long-term, complex, and systematic scientific project, whose data and information resources in the research and development ((hereinafter referred to ”R&D”) process provide the significant support for R&D of geological disposal system, and lay a foundation for the long-term stability and safety assessment of repository site. However, the data related to the research and engineering in the sitting of the geological disposal repositories is more complicated (including multi-source, multi-dimension and changeable), the requirements for the data accuracy and comprehensive application has become much higher than before, which lead to the fact that the data model design of geo-information database for the disposal repository are facing more serious challenges.In the essay, data resources of the pre-selected areas of the repository has been comprehensive controlled and systematic analyzed. According to deeply understanding of the application requirements, the research work has made a solution for the key technical problems including reasonable classification system of multi-source data entity, complex logic relations and effective physical storage structures. The new solution has broken through data classification and conventional spatial data the organization model applied in the traditional industry, realized the data organization and integration with the unit of data entities and spatial relationship, which were independent, holonomic and with application significant features in HLW geological disposal. The reasonable, feasible and flexible data conceptual models, logical models and physical models have been established so as to ensure the effective integration and facilitate application development of multi-source data in pre-selected areas for geological disposal.

The geological disposal of high-level radioactive waste is concerned with the systematic characteristics of the long-time scale of groundwater. As part of the china site investigations and research associated with the disposal of high-level radioactive waste, the paleogroundwater in deep boreholes have been employed in order to characterize groundwater flow in the fractured bedrock at Jijicao preselected site. By obtaining the deep groundwater samples from deep borehole, this study focused on krypton isotope data, the groundwater mixing and relationship were analyzed, and the paleogroundwater dating results were corrected. It found that the age of deep groundwater is 25ka and 46ka, the characteristics of slow groundwater circulation rate and long residence time are conductive to the safe disposal of high-level radioactive waste.

A core concern in the research on deep geological disposal of high-level radioactive waste is the migration of radionuclides in geological bodies. Most studies on radionuclide migration consider the role of only the rock fissures without incorporating the influence of the rock matrix. In this paper, the rock mass for geological disposal of high-level radioactive waste is regarded as a fissure-pore medium. Considering the influences of radionuclide diffusion and fluid transport on radionuclide migration in the process of disposal, the governing equation of radionuclide migration and evolution in the pore-fissure medium is established. The numerical scheme of the governing equation is given based on the mixed finite volume method (FVM), using our program solution module written in C++. On this basis, the numerical test model with fissures was developed, which analyzed the radionuclide migration law in clayey rocks under various fissure and rock matrix diffusion coefficients and hydraulic conductivities. The simulation results are compared with finite element method results, revealing the superiority of the mixed FVM method in solving problems of radionuclide migration in discontinuous geological bodies containing hiatuses, mutations, and fissures. The study provides a theoretical basis for evaluating the safety, feasibility, and suitability of geological disposal repositories for high-level radioactive waste in terms of radionuclide migration.

Progress on rock mechanics research of Beishan granite for geological disposal of high-level radioactive waste in China

Numerical modeling of site-scale groundwater flow with stochastic parameterized hydraulic conductivity fields for geological disposal of high-level radioactive waste in China

Thermo-hydro-mechanical behavior of clay rock for deep geological disposal of high-level radioactive waste

A deterministic safety assessment methodology has been developed to evaluate long-term radiological consequences associated with geologic disposal of high-level radioactive waste, and to demonstrate a generic feasibility of geologic disposal. An exposure scenario considered here is based on a normal evolution scenario which excludes events attributable to probabilistic alterations in the environment. A computer code system GSRW thus developed is based on a non site-specific model, and consists of a set of sub-modules for calculating the release of radionuclides from engineered barriers, the transport of radionuclides in and through the geo- sphere, the behavior of radionuclides in the biosphere, and radiation exposures of the public. In order to identify the important parameters of the assessment models, an automated procedure for sensitivity analysis based on the Differential Algebra method has been developed to apply to the GSRW.

To ensure the safety of geological disposal of high-level radioactive waste, in-situ experiments have been carried out to examine the behavior of rocks in underground research laboratories (URLs). At the Meuse/Haute-Marne URL in France, the French National Radioactive Waste Management Agency (Andra) has been assessing the Callovo-Oxfordian claystone (COx) as potential host rock of geological disposal by subjecting the COx to in-situ heating mimicking exothermic radioactive waste. Results of the in-situ experiments are used to validate and bolster the numerical simulators for predicting the thermo-hydromechanically (THM) coupled behavior of the COx. The numerical simulators are, however, yet to be tested for predicting the failure and fracture development of the COx during heating, which is of paramount importance to the safety of the geological disposal. In this research, we modelled a recently carried out in-situ experiment at the Meuse/Haute-Marne URL using the TOUGH-FLAC simulator to predict the failure and fracture development of the COx during heating. The objectives are to examine the effects of (i) the weak bedding planes, (ii) the softening rate of matrix/weak plane strengths, and (iii) the stiffness anisotropy of the COx on the development of shear and tensile fractures during heating. Results show that considering failure along the weak planes enabled accurate predictions of fracture development. Also, fracture development intensified at a softening rate beyond a threshold level and the geometry of fractures was significantly affected by the stiffness anisotropy. These results will help boost the reliability of the safety and performance assessment of geological disposal in claystone.

A deterministic safety assessment methodology has been developed to evaluate long-tern1 radiological consequences associated with geologic disposal of high-level radioactive waste, and to demonstrate a generic feasibility of geologic disposal. An exposure scenario considered here is based on a normal evolution scenario which excludes events attributable to probabilistic alterations in the environment. A computer code system GSRW thus developed is based on a non site-specific model, and consists of a set of sub-modules for calculating the release of radionuclides from engineered barriers, the transport of radionuclides in and through the geo-sphere, the behavior of radionuclides in the biosphere, and radiation exposures of the public. In order to identify the important parameters of the assessment models, an automated procedure for sensitivity analysis based on the Differential Algebra method has been developed to apply to the GSRW.

Geological disposal of high-level radioactive waste is a worldwide problem. Currently, China is at a critical stage of site selection for an underground laboratory that will be used for field tests of geological disposal. A large amount of multidisciplinary research data has been acquired in the previous site selection processes. Therefore, an integrated geo-information database, called the geo-information database for a pre-selected area (PAGD), and a data management system were specifically designed to facilitate the management of these data. First, an integrated geo-information model was designed to manage the multidisciplinary data. Second, a robust metadata manager was developed for metadata management. Finally, a data management system with B/S and C/S hybrid architecture was developed and realized based on the integrated geo-information database. As a result, a few hundred GB of data from numerous different disciplines were stored and managed successfully.

The program for disposal of high-level and transuranic radioactive waste in the United States calls for establishment of a mined repository in geologic formations that will provide for retrievability of the waste for 50 years. The goal of radioactive waste isolation in mined repositories is to prevent unacceptable concentrations of radionuclides from migrating to the accessible environment. Early concepts of high-level radioactive waste disposal assumed that containment of the waste by the enclosing rock would be virtually complete. With the application of broader scientific and engineering disciplines, specifically geology and hydrology to the study of prospective environments for waste disposal, the realization came that total isolation of the waste in the immediate vicinity of the repository will be difficult to ensure, and this includes geological and hydrological methods used for predicting conditions or events that may prevail during the extremely long time required for waste isolation. Some of the earth processes that are of major concern during the waste-isolation storage time include: (1) rates of radionuclide transport in the ground-water flow system which, in turn, reflect chemical reactions of radionuclides with ground water and earth materials; (2) climatic changes; and (3) tectonic and associated erosional events. To compensate for the limitations in our knowledge, the current rationale for waste isolation emphasizes the need for a series of independent barriers to radionuclide migrations. Multiplicity of these barriers, both engineered and natural, will compensate for uncertainties in predicting natural or man-induced conditions and events that may occur during the time required for waste isolation.

The disposal of the Nation`s spent nuclear fuel and high-level waste has been studied for many years. The Nuclear Waste Policy Act of 1982 and the subsequent Nuclear Waste Policy Amendments Act (NWPAA) of 1987 provide the legislative framework under which the Department of Energy (DOE) must operate when evaluating potential sites for the geologic disposal of spent nuclear fuel and high-level waste. Additionally, the DOE must comply with regulations published by the Environmental Protection Agency (EPA) in 40 CFR 191, ``Environmental Radiation Protection Standards for Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes`` and the Nuclear Regulatory Commission (NRC) in 10 CFR 60. ``Disposal of High-Level Radioactive Wastes in Geologic Repositories.`` The DOE also operates under its own regulation, 10 CFR 960. ``General Guidelines for the Recommendation of Sites for Nuclear Waste Repositories.`` The DOE has devoted considerable resources to this pro gram, which is managed by the Office of Civilian Radioactive Waste Management (OCRWM). Disposal of spent nuclear fuel and high-level waste in a geologic repository has never before been done anywhere in the world. Since this is a first-of-a-kind facility, extreme care must be taken to ensure that all environmental and public health standards are met during its required long life. Yucca Mountain was designated by the NWPAA as the sole site to be characterized for the disposal of spent nuclear fuel and high-level waste (see ``Description of the Yucca Mountain Site``). It is important to recognize that Yucca Mountain has not been chosen for a permanent disposal site or repository. Rather, it is the candidate site to be characterized to determine whether or not it meets the myriad requirements set forth in existing regulations for the long-term disposal of spent nuclear fuel and high-level waste. 8 figs.

In the 1980s, HADES (High-Activity Disposal Experimental Site) was the first underground research laboratory (URL) dedicated to the study of the geological disposal of radioactive waste in a deep clay formation, the Boom Clay. It was not until the early 2000s, after a siting process, that ANDRA implemented the Meuse/Haute-Marne URL, in the Callovo-Oxfordian formation at a depth of about 500 m in order to develop the Cigéo project (French industrial centre for geological disposal). ANDRA therefore relied heavily on the work carried out in HADES, through numerous co-operation projects (participation in in situ experiments) both between ANDRA and ONDRAF/NIRAS and SCK CEN (EURIDICE) and/or with Mont Terri consortium, and within European projects (CLIPEX, RESEAL, etc.). This was driven by a dual objective: (1) to prepare its own experimental programmes in the Meuse/Haute-Marne underground laboratory (methodology, experimental devices and protocols, etc.); and (2) to acquire general knowledge on the behaviour of argillaceous rocks, in particular in terms of similarity and differences between the various argillaceous rocks. This paper illustrates the contribution of HADES to the ANDRA programme. This concerns the characterization of the claystone behaviour, host rock and swelling clay-based seals (hydromechanical, thermo-hydromechanical, excavation damaged zone, etc.), and the design and the behaviour of underground structures and seals in deep clay formation (constructability, lining/support, etc.).

In Japan, the implementation of the high-level radioactive waste (HLW) disposal is one of urgent issues in the situation that Japan will continue the use of nuclear power. But, the lay people may not have the sufficient amount of information and knowledge about HLW disposal to hold their opinions about this issue. In this research, in order to clarify what opinions they will have with enough information and knowledge, we had the face-to-face dialogues about the HLW disposal with 2 or 3 lay persons. The dialogues were conducted 11 times with different lay persons’ groups. In these dialogues, after the lay participants had a certain amount of knowledge about HLW disposal, they became to talk about their opinions to the HLW disposal program in Japan. These opinions included the doubt against the open solicitation to select the siting area in the HLW disposal program of Japan, the emotion like NIMBY, the indication of lack of public relations about HLW disposal, and so on.