Takanori Kunimaru

Unique distribution of deep groundwater bacteria constrained by geological setting

We collected groundwater samples at depths of up to 482 m from three boreholes drilled into sedimentary rock within two formations in Hokkaido, Japan. The prokaryotic community in each subsurface groundwater sample was analysed by microscopic counts and cloning-sequencing the 16S rRNA genes. On total direct counts, there were between 4.61 × 10(4) and 5.06 × 10(6) prokaryote cells ml(-1) in the samples, which is similar to the numbers observed at the marine subsurface. However, the vertical distribution of the prokaryotes did not show a simple decrease in abundance with increasing depth. A high abundance of cells with significant amounts of RNA was identified in the domain Bacteria using fluorescence in situ hybridization, with a high frequency of dividing cells at the transition zone between the two sedimentary rock formations. Cloning-sequencing analysis showed the predominance of γ-Proteobacteria at this transition zone at 281-312 m. The horizontal heterogeneity of the microbial distribution in the subsurface environment was also demonstrated by a relatively high density of members of the domain Archaea in borehole HDB-4, drilled only 1.5 km northeast of HDB-6 and in the same formation.

Development of the Quality Management System for Borehole Investigations: Part 1—Quality Assurance and Quality Control Methodology for Hydraulic Packer Testing

A quality assurance and quality control (QA/QC) system for the hydraulic packer tests has been established based on the surface-based investigations at JAEA’s underground research laboratories in Mizunami and Horonobe. The established QA/QC system covers field investigations (data acquisition) and data analysis. For the field investigations, the adopted procedure is selection of a test section based on a detail fluid logging and checking with tally list, followed by inspection of test tools such as pressure transducers and shut-in valves, etc., test method selection using a “sequential hydraulic test” for deciding appropriate method, and finally data quality confirmation by pressure changes and derivatives on a log-log plots during testing. Test event logs should also be described during testing for traceability. For the test data analysis, a quick analysis for rough estimation of hydraulic parameters, and a detailed analysis using type curve and/or numerical analyses are conducted stepwise. The established QA/QC system has been applied to the recent borehole investigations and its efficiency has been confirmed.© 2010 ASME

Development of a Quality Management System (QMS) for Borehole Investigations: Part 2—Evaluation of Applicability of QMS Methodology for the Hydrochemical Dataset

An appropriate QMS, which is among the first tools required for repository site characterisation, will save on effort by reducing errors and the requirement to resample and reanalyse–but this can only be guaranteed by continuously assessing if the system is truly fit-for-purpose and amending it as necessary based on the practical experience of the end-users on-site. A QA audit of hydrochemical datasets for boreholes HDB-1–11 from Horonobe URL project by JAEA has been carried out by the application of a formal QA analysis which is based on the methodology previously employed for groundwaters during the recent site characterisation programme in Sweden. This methodology has been successfully applied to the groundwaters of the fractured crystalline rocks of the Fennoscandian Shield and has now been adapted and applied to some of the ground- and porewaters of the Horonobe URL area. This paper will present this system in the context of the Japanese national programme and elucidate improvements made during hands-on application of the borehole investigation QMS. Further improvements foreseen for the future will also be discussed with a view of removing inter-operator variability as much as is possible. Only then can confidence be placed in URL project or repository site hydrochemical datasets.Copyright

Technical Know-How of Selection Process for the Horonobe Underground Research Laboratory Area and Site

This study demonstrates the selection process for the Horonobe URL based on surveys of existing information and geophysical surveys on a regional scale. In addition, preliminary requirements on the geological environment, safety (during construction of the underground facility) and social and environmental constraints were taken into consideration. The technical know-how utilised through the experiences for the site selection is described here. The proposed Horonobe URL site required the existence of argillaceous sedimentary formations and associated groundwater. Further fundamental requirements were appropriate rock mechanical properties and low gas content in the host rock to meet safe underground construction and operation regulations. This led to a stepwise narrowing down from several potential URL areas located completely within the Horonobe District to one candidate URL area and, finally, to a specific URL site. In the URL investigation area (ca. 3 km × 3 km) the main surface-based investigations were conducted as the first step to choosing the actual URL site. This was selected based on establishing fundamental factors related to the geological environment, safety and societal issues. This paper provides an outline of the process utilised in selecting the URL site by taking into consideration technical and social requirements. Thus stepwise approach and experience in selecting the URL site will be applicable when NUMO needs to select a site through literature surveys, and preliminary and detailed investigations in the future.Copyright

Study on the Estimation Error Caused by Using One-Dimensional Model for the Evaluation of Dipole Tracer Test

In-situ tracer tests are a valuable approach to obtain parameters for a performance assessment of nuclear waste repository. A one-dimensional model is simple and is commonly used to identify radionuclide transport parameters by fitting breakthrough curves simulated using the model to those obtained from tracer tests. However, this method can increase uncertainty and introduce errors in the estimated parameters. In particular, such uncertainties and errors will be significant when evaluating parameters for tests conducted in a dipole (two-dimensional) flow field between injection and withdrawal wells. This paper describes a numerical analysis investigation into the effects of various experimental conditions on parameters estimated using a one-dimensional model for cases involving tracer tests in a two-dimensional fracture plane. Results show that longitudinal dispersivity tends to be overestimated by the one-dimensional model analysis. This overestimation is the result of several factors: smaller pumping rate, larger dipole ratio, stronger heterogeneity of the fracture hydraulic conductivity, and greater orthogonally-oriented background groundwater flow. Such information will help us to better plan and design tracer tests at underground research laboratories located in both Mizunami in central Japan and Horonobe in northern Japan. Understanding appropriate experimental conditions will help decrease the uncertainty in the results of tracer tests.Copyright

Development of Comprehensive Techniques for Coastal Site Characterisation: Part 3—Conceptualisation of Long-Term Geosphere Evolution

A critical issue for building confidence in the long-term safety of geological disposal is to demonstrate the stability of the geosphere, taking into account its likely future evolution. An ongoing collaborative programme aims to establish comprehensive techniques for characterising the overall evolution of coastal sites through studying the palaeohydrogeological evolution in the coastal system around the Horonobe area, Hokkaido, northern Japan. Information on natural events and processes related to the palaeohydrogelogical evolution of the area have been integrated into the chronological tables and conceptual models that indicates the temporal and spatial sequences of the events and processes, such as climatic and sea-level changes, palaeogeography, and geomorphological and geological evolution in the area. The methodology for conceptualisation of the geosphere evolution will be applied to other analogous coastal areas on Japan’s western seaboard to produce comprehensive techniques to support understanding the geosphere evolution of potential coastal sites for deep geological repositories.Copyright