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[HCG21-05] Verification study on borehole investigation technologies (1) Planning and management of the project
Keywords:radioactive waste, geological disposal, borehole investigation, Hayama Group, Miura Group
1. Introduction
Technologies for siting deep geological disposal repository for high-level radioactive waste etc. have been developed by the government and relevant research institutes. NUMO (Nuclear Waste Management Organization of Japan) recognized the importance of confirming in advance the applicability and issues of such technologies to Japan's diverse geological environment. We also recognized the importance of improving our own management capabilities in investigation planning, schedule/quality control, and analysis/evaluation of results, and developing human resources. Therefore, NUMO has been working with CRIEPI (Central Research Institute of Electric Power Industry) since 2006 to conduct the "verification study" through deep-deep borehole investigations (YDP-1 to 3) at CRIEPI Yokosuka site. The latest study aims to solve technical issues identified so far and to improve the management ability of NUMO staff through new borehole investigations (YDP-4). Technical issues include borehole wall collapse and diameter enlargement in the brittle Hayama Group, optimization of drilling technology to reduce core loss, confirmation of the effects of drilling mud on the geological environment data, and stratigraphic classification of accretionary complexes, improvement of hydraulic test and water sampling equipment for low-permeable rock, confirmation of applicability of unexamined measurement technology on physical, mechanical and thermal properties of rock and solute transportation characteristics including microbial community, and optimization of quality control/assurance technology for laboratory core tests. This paper reports on the planning and management.
2. Study Planning
In the planning of this study, we assumed as if this was the first deep borehole in the Preliminary [SH1] Investigations, and we comprehensively extracted data on geology, geological structure, hydrogeological characteristics, hydrochemical characteristics of groundwater, physical, mechanical, and thermal properties of rock mass and solute transport properties (including deep underground microbial communities. Based on this, the persons in charge of each discipline discussed the drilling length, drilling method, drilling mud, the purpose, method, and depth of data acquisition, including their effects on quality and cost. Further, in consideration of the above-mentioned technical issues, an investigation plan with two boreholes at the same location was formulated.
3. Management
The following shows the processes of management after the plan was formulated. When the drilling of the first hole was started, the predicted Miura Group was not encountered. Taking into account this fact etc. the plan was changed to extend the first hole from depth 420m to 720m and cancel the second hole. At that time, the impact of drilling mud and borehole tests on the geological environment and the priority of core sampling for laboratory tests were examined. Based on the results, the procedure from excavation to each borehole test was organized systematically. In addition, records were stored so that changes from the original plan and their background and reasons could be traced. As for progress control, we recognized the main events that affected the process and the period of stand-by and delays of the work. Through the above, we were able to understand the flow of boring surveys targeting brittle and swelling strata and the priority of conducting tests, and we were able to accumulate knowledge that can be reflected in future preliminary investigations.
4. Conclusion
Through this study, we were able to accumulate experience and knowledge on planning and management for the preliminary investigations. We will continue to confirm the applicability of the borehole investigation technologies, and based on the results, we will work to confirm and optimize the test method, and further improve management capabilities related to the quality and safety of investigations and tests.
Technologies for siting deep geological disposal repository for high-level radioactive waste etc. have been developed by the government and relevant research institutes. NUMO (Nuclear Waste Management Organization of Japan) recognized the importance of confirming in advance the applicability and issues of such technologies to Japan's diverse geological environment. We also recognized the importance of improving our own management capabilities in investigation planning, schedule/quality control, and analysis/evaluation of results, and developing human resources. Therefore, NUMO has been working with CRIEPI (Central Research Institute of Electric Power Industry) since 2006 to conduct the "verification study" through deep-deep borehole investigations (YDP-1 to 3) at CRIEPI Yokosuka site. The latest study aims to solve technical issues identified so far and to improve the management ability of NUMO staff through new borehole investigations (YDP-4). Technical issues include borehole wall collapse and diameter enlargement in the brittle Hayama Group, optimization of drilling technology to reduce core loss, confirmation of the effects of drilling mud on the geological environment data, and stratigraphic classification of accretionary complexes, improvement of hydraulic test and water sampling equipment for low-permeable rock, confirmation of applicability of unexamined measurement technology on physical, mechanical and thermal properties of rock and solute transportation characteristics including microbial community, and optimization of quality control/assurance technology for laboratory core tests. This paper reports on the planning and management.
2. Study Planning
In the planning of this study, we assumed as if this was the first deep borehole in the Preliminary [SH1] Investigations, and we comprehensively extracted data on geology, geological structure, hydrogeological characteristics, hydrochemical characteristics of groundwater, physical, mechanical, and thermal properties of rock mass and solute transport properties (including deep underground microbial communities. Based on this, the persons in charge of each discipline discussed the drilling length, drilling method, drilling mud, the purpose, method, and depth of data acquisition, including their effects on quality and cost. Further, in consideration of the above-mentioned technical issues, an investigation plan with two boreholes at the same location was formulated.
3. Management
The following shows the processes of management after the plan was formulated. When the drilling of the first hole was started, the predicted Miura Group was not encountered. Taking into account this fact etc. the plan was changed to extend the first hole from depth 420m to 720m and cancel the second hole. At that time, the impact of drilling mud and borehole tests on the geological environment and the priority of core sampling for laboratory tests were examined. Based on the results, the procedure from excavation to each borehole test was organized systematically. In addition, records were stored so that changes from the original plan and their background and reasons could be traced. As for progress control, we recognized the main events that affected the process and the period of stand-by and delays of the work. Through the above, we were able to understand the flow of boring surveys targeting brittle and swelling strata and the priority of conducting tests, and we were able to accumulate knowledge that can be reflected in future preliminary investigations.
4. Conclusion
Through this study, we were able to accumulate experience and knowledge on planning and management for the preliminary investigations. We will continue to confirm the applicability of the borehole investigation technologies, and based on the results, we will work to confirm and optimize the test method, and further improve management capabilities related to the quality and safety of investigations and tests.