The Second Progress Report (referred to as H12), documenting the progress made since the publication of the first progress report in 1992, was submitted to the Atomic Energy Commission of Japan (AEC) on 26 November 1999. The objective of H12 is to demonstrate the technical feasibility and reliability of the specified disposal concept for the high-level radioactive waste (HLW) in more rigorous and transparent manner. The report was expected to provide technical basis for the repository siting and regulatory processes as assigned by the AEC's "Guidelines on Research and Development Relating to Geological Disposal of High-Level Radioactive Waste in Japan".
The results of research and development discussed in H12 was summarized as follows:
It has been confirmed that stable geological environments are widely distributed in Japan in which an engineered barrier system constructed at depth can be expected to maintain its integrity for a long period of time, and which also function as a natural barrier to retard radionuclide migration.
Work in Japan and elsewhere has provided an extensive body of data and experience which allows confidence that an appropriate repository can be designed for any suitable host rock. Following site selection, the information required to support such design work and to establish a rational site development and management plan has been outlined.
The long-term safety of a repository system has been evaluated by a rigorous performance assessment methodology which includes a comprehensive evaluation of uncertainties. Despite extensive uncertainty at the present stage of the Japanese program, it has been demonstrated that a HLW repository would lead to negligible doses calculated to be below the guidelines established in other countries.

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The geological environment has two main functions in terms of ensuring the safety of geological disposal of high-level radioactive waste. One relates to the fundamental long-term stability of the site and the other to the properties of the host rock formations and groundwaters which facilitate the emplacement of the engineered barrier system and act as a natural barrier. In this connection, the feasibility of selecting a geological environment in Japan which is appropriate for geological disposal was discussed, based on findings obtained from case studies and field measurements.
Considering long-term stability of the site, it is important to understand the effects and spatial distributions of the natural phenomena such as fault movement, volcanic activity, uplift/denudation and climatic/sea-level changes. Fault movement and volcanic activity are relatively localized phenomena, and can be avoided by considering only areas that are sufficiently remote from existing volcanoes and major active faults for these phenomena to have a negligible probability of causing significant effects. Uplift/denudation and climatic/sea-level changes are gradual phenomena and are more ubiquitous. It is, nevertheless, possible to estimate future trends by extrapolating the past changes into the future, and then to identify areas that may not be affected significantly by such phenomena.
Considering the properties of the host rocks and groundwaters, it can be understood, from the presently available data, that deep groundwater in Japan generally flows slowly and its chemistry is in a reduced state. The data also suggest that deep rock masses, where the ground temperature is acceptably low and the rock pressure is almost homogeneous, are widely located throughout Japan.
Based on the examination of the geological environment in Japan, it is possible to discuss the requirements for the geological environment to be considered and the investigations to be performed during the site selection procedure.

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From the viewpoint of confidence building, it is very important to guarantee the quality of data for evaluating properties of the geological environment. To guarantee the quality of data, measurement with extremely well-known and repeatable precision and supporting documentation, that is able to explain the process of obtaining the data, are required.
The Japan Nuclear Cycle Development Institute (JNC) has been developing investigation techniques for deep geological environments in crystalline rock.
To date, drilling techniques and investigation equipment, such as a borehole sparker source for cross-hole seismic tomography, hydraulic test equipment and a groundwater sampler that meet the above mentioned requirements, have been developed. A hydraulic test sequence to confirm repeatability of measurement results and a groundwater sampling method to evaluate drilling fluid effects were also developed. The feasibility and usefulness of these investigation techniques were evaluated through ongoing geoscientific R&D programmes carried out in the Tono region, central Japan.
This paper is focused on techniques for groundwater investigation and describes investigation techniques developed by the JNC to evaluate hydrogeological and hydrochemical properties of rock and groundwater deep underground.

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The design requirements for the engineered barrier system (EBS) and the disposal facility in general were clarified based on currently available technologies. Realistic and reliable data and analysis techniques were used to derive specifications for the EBS and the other components of the disposal facility, also taking economic aspects into consideration.
The practical feasibility of designing and emplacing the EBS and constructing the disposal facility was examined for a wide range of physical rock properties. The impact on barrier performance of different materials and overpack and buffer dimensions was investigated and the results of preliminary calculations were used to modify the design specifications. Bentonite mixed with quartz sand was selected as the buffer material, which could bring about a reduction in costs without compromising performance.
The mechanical stability of tunnels was investigated based on data obtained from relevant geological environments. Rough estimates were then made of the depth range in which construction of the disposal facility is feasible. In addition, a design concept for efficient emplacement of the vitrified waste and layout of the tunnels was developed based on thermal analyses. It was shown that construction of the disposal system, emplacement of the waste forms and backfilling of the tunnels can be realized using currently available technologies or technological advances which are expected in the near future.
One objective of management of the disposal site is to collect and evaluate technical information to support decisions on permanent closure of the repository. In addition, monitoring the effects of repository construction and operation on the geological environment, as well as assessing the quality of emplacement of the engineered barriers, are primary elements of operational phase management.

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The second progress report, H12, documented research and development progress for the high-level waste disposal made since the publication of the earlier the first progress report (H3) in 1992. The concept of geological disposal in Japan is similar to that considered in other countries, being based on a system of multiple passive barriers consisting of the geological environment and an engineered barrier system. The disposal system considered is generic, in the sense that no single rock type and no siting area have so far been identified. H12 performance assessment provided a test for the robustness of the system concept based on intentional siting and design, taking account of a wide range of Japan's geological environment. The assessment included a comprehensive evaluation of uncertainty and potentially detrimental factors, including perturbations due to external events and processes. Despite the considerable uncertainty at the current stage of the Japanese program, a safety case that is adequate for the aims of the assessment can be made by a strategy of employing conservatism where there is uncertainty and stressing the reliability and effectiveness of the performance of the near field. The aim of this paper is to summarize arguments that should build confidence in the findings of the H12 assessment.

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Second Progress Report on Research and Development for the Geological Disposal of HLW in Japan was published in 2000 by Japan Nuclear Cycle Development Institute. The issue presents basic technical feasibility of safe HLW disposal on Japan. The issue, however, lacks discussion about realistic time frame for geological stability assessment, and treating of instability in geoscientific models, because candidate repository sites have not yet selected in Japan. This paper present short conceptional discussion of the time frames and instability in geoscientific models and propose some time frames and instability treating process.
Methods of geological prediction are classified into seven groups: (1) Prediction by extrapolation, (2) Prediction by analogy, (3) Prediction by probability, (4) Prediction by experiment, (5) Prediction by conceptual model, (6) Prediction by numerical simulation, and (7) Prediction by safety assessment model.
Geologic future prediction should be cross-checked by several different methods. However, only geological evidence from the earth's history of nearly five billion years can verify long-range predictions for subterranean containment of waste which are usually based on short-range experiments and numerical modeling.
On the geologically unstable Japanese archipelago, Japan is making extensive efforts for prediction of earthquakes and volcanic eruptions to reduce geological hazards. Long-range geological prediction is investigated for safe disposal of nuclear waste and for subterranean sequestration of CO₂.

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Groundwater is faced to seawater in the end of its flow system. The shape of the interface of the fresh groundwater and salt water is discussed by Ghyben-Herzberg Low, in the previous studies. However, the groundwater push out the interface to the off-shore side than the low expected and the fresh groundwater flows even in the marine bottom (beneath of the marine bottom). This study summarized the previous studies for the interface and review the data of recent works. Distribution of submarine groundwater discharge and the shape of the seawater / freshwater interface is related strongly each other. The understanding of the groundwater flow property in the bottom end of its flow system will be useful for the development of water resources and evaluation for the environments.

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The relation between the mass transport rate and the spatial distribution of retardation coefficient, R_d, has been examined by using two-dimensional (2-D), advection-dispersion model. In the calculated breakthrough curves, this study focused on the peak height and its arrival time. To compare them easily, the dimensionless mean residence time was always set at unity. In the results, as the R_d values were distributed perpendicular to the flow direction, the peak height and its arrival time strongly depended on the R_d distribution. This study, for simplicity, considered two kinds of R_d layers and assumed that the small R_d and the large were arranged parallel to one another. The smaller the alternation frequency of the layers became, the higher peak and the shorter arrival-time the breakthrough curve showed. In contrast, when the frequency was large enough, the peak-arrival time almost agreed with the homogeneous case. Further, this study confirmed that the variation of the skewness of R_d had no appreciable influence on the whole mass transport rate. When the 2-D distribution of R_d was described by, e.g., log-normal distribution, the average mass transport rates showed agreement with those on the other probability density functions defined by the same set of the arithmetic mean and the standard deviation of R_d. These tendencies mentioned above were confirmed in the range of Peclet number from 10 to 10² for the dimensionless standard deviation at least up to around 1.

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In this paper, firstly, we describe the detail of the methodology for the stress measurement using the AE and DRA methods. Secondly, we show the two case studies of stress measurement using the AE and DRA methods to evaluate the possibility to measure in situ stresses using rock core samples obtained from underground excavation area.
In one of the case studies, rock cores were obtained from horizontal boreholes drilled into the wall of a drift excavated in soft sedimentary rock. This allowed the vertical stress variation with distance from the drift wall to be determined up to a depth of 5 m. The vertical stresses determined using rock cores varied with distance and reached a maximum of 4 ∼ 5 MPa at a distance of 2 ∼ 2.5 m from the drift, when the highest concentration of stress was expected. The vertical stress variation was consistent with calculations by the three dimensional FEM program, ANSYS. Furthermore, the stress measured by the over coring method just nearly agreed with the stress determined by the AE and DRA methods. The AE and DRA methods described in this paper should be applicable to in situ stress measurement with reasonable accuracy even in soft sedimentary rock. A delay time of up to 101 days did not affect the determination of in situ stress in soft sedimentary rock.
The other case study has been focused on full stress tensor determination from a single oriented cored rock. Core was obtained from an HI cell measurement hole at Cannington mine in Australia to establish whether the complete stress tensor could be determined from AE and DRA test data. The rockmass at Cannington mine is geologically very complex, and different stress magnitudes and orientation were calculated by the HI cell even within adjacent locations along a hole axis. Two test sites were analyzed for stress measurements using cored rock. The orientation of the estimated stresses appears to match the localized orebody orientation very well. The main principal stress was found to be parallel to the orebody strike. The intermediate principal stress was parallel to the dip, while the minor principal stress was normal to the orebody. Given that the predominant geological structures in the mine are a set of strike slip faults oriented 70 / 330 and that the general slickensides on these are sub-horizontal, the conclusion that the principal stress is parallel to the strike of the orebody is geologically sound.

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