Hydrogeological Characterization Based on Long Term Groundwater Pressure Monitoring

The Mizunami Underground Research Laboratory (MIU) is now under construction by the Japan Atomic Energy Agency in the Tono area of central Japan. The MIU project is being implemented in three overlapping Phases: Surface-based Investigation (Phase I), Construction (Phase II) and Operation (Phase III). The changes of groundwater pressure due to shaft excavation can be considered analogous to a large-scale pumping test. Therefore, there is the possibility that the site scale groundwater field (several km square) can be approximated by the long-term groundwater pressure monitoring data from Phase II. Based on the monitoring observations, hydrogeological characteristics were estimated using the s-log(t/r2) plot based on the Cooper-Jacob straight line method. Results of the s-log(t/r2) plots are as follows. The groundwater flow field around the MIU construction site is separated into domains by an impermeable fault. In other words, the fault is a hydraulic barrier. Hydraulic conductivity calculated from s-log(t/r2) plots are in the order of 1.0E−7(m/s). The above results from the long term monitoring during Phase II are a verification of the hydrogeological characteristics determined in the Phase I investigations.

TRU Recycling Options for Environmentally Friendly and Proliferation-Resistant Nuclear Fuel Cycle of FBR

The embodied challenges for introducing closed fuel cycle are utilizing advanced fuel reprocessing and fabrication facilities as well as nuclear nonproliferation aspect. Optimization target of advanced reactor design should be maintained properly to obtain high performance of safety, fuel breeding and reducing some long-lived and high level radioactivity of spent fuel by closed fuel cycle options. In this paper, the contribution of loading trans-uranium to the core performance, fuel production, and reduction of minor actinide in high level waste (HLW) have been investigated during reactor operation of large fast breeder reactor (FBR). Excess reactivity can be reduced by loading some minor actinide in the core which affect to the increase of fuel breeding capability, however, some small reduction values of breeding capability are obtained when minor actinides are loaded in the blanket regions. As a total composition, MA compositions are reduced by increasing operation time. Relatively smaller reduction value was obtained at end of operation by blanket regions (9%) than core regions (15%). In addition, adopting closed cycle of MA obtains better intrinsic aspect of nuclear nonproliferation based on the increase of even mass plutonium in the isotopic plutonium composition.

Low Alkaline Cement Used in the Construction of a Gallery in the Horonobe Underground Research Laboratory

In Japan, any high level radioactive waste (HLW) repository is to be constructed at over 300 m depth below surface. Tunnel support is used for safety during the construction and operation, and shotcrete and concrete lining are used as the tunnel support. Concrete is a composite material comprised of aggregate, cement and various admixtures. Low alkaline cement has been developed for the long term stability of the barrier systems whose performance could be negatively affected by highly alkaline conditions arising due to cement used in a repository. Japan Atomic Energy Agency (JAEA) has developed a low alkaline cement, named as HFSC (Highly Fly-ash Contained Silicafume Cement), containing over 60 wt% of silica-fume (SF) and fly-ash (FA). HFSC was used experimentally as the shotcrete material in construction of part of the 140m deep gallery in the Horonobe Underground Research Laboratory (URL). The objective of this experiment was to assess the performance of HFSC shotcrete in terms of mechanics, workability, durability, and so on. HFSC used in this experiment is composed of 40 wt% OPC (Ordinary Portland Cement), 20 wt% SF, and 40 wt% FA. This composition was determined based on mechanical testing of various mixes of the above components. Because of the low OPC content, the strength of HFSC tends to be lower than that of OPC. The total length of tunnel using HFSC shotcrete is about 73 m and about 500 m3 of HFSC was used. The workability of HFSC shotcrete was confirmed in this experimental construction.

Development of Characterization Technology for Fault Zone Hydrology

Several deep trenches were cut, and a number of geophysical surveys were conducted across the Wildcat Fault in the hills east of Berkeley, California. The Wildcat Fault is believed to be a strike-slip fault and a member of the Hayward Fault System, with over 10 km of displacement. So far, three boreholes of ∼ 150m deep have been core-drilled and borehole geophysical logs were conducted. The rocks are extensively sheared and fractured; gouges were observed at several depths and a thick cataclasitic zone was also observed. While confirming some earlier, published conclusions from shallow observations about Wildcat, some unexpected findings were encountered. Preliminary analysis indicates that Wildcat near the field site consists of multiple faults. The hydraulic test data suggest the dual properties of the hydrologic structure of the fault zone. A fourth borehole is planned to penetrate the main fault believed to lie in-between the holes. The main philosophy behind our approach for the hydrologic characterization of such a complex fractured system is to let the system take its own average and monitor a long term behavior instead of collecting a multitude of data at small length and time scales, or at a discrete fracture scale and to “up-scale,” which is extremely tenuous.

Current R & D Activities in the Study on Geosphere Stability

The Japanese islands are located in a tectonically active zone. The scientific base is required for assessing the geosphere stability for long-term isolation of radioactive waste in Japan. JAEA is promoting the establishment of investigation method for geotectonic events affecting geosphere stability and prediction model for the future changes of geological environments, that is necessary for site selection and safety assessment of the HLW geological disposal. For seismicity and faulting, detection techniques for active faults without topographic surface expression, such as using helium isotope ratios in hot spring gases or detection of hydrogen gas, and studies on the assessment of fault evolution have been developed. For volcanism and geothermal activity, heat sources for anomalous geothermal activity in non-volcanic regions are considered. Detection techniques for high-temperature fluids and magma deep underground, using geophysical and geochemical approaches, were constructed. For uplift, denudation and climatic/sea-level changes, a methodology to predict the future topographic change was developed. Also, for dating techniques as an essential part to proceed on these studies, C-14 and Be-10 dating using AMS and (U-Th)/He dating using QMS and ICP-MS have been developed. We are planning the establishment of assessment methods for geosphere stability including assessment of the activity of faults encountered in underground excavations, development of long-term prediction model of volcanism and hydrothermal activities, and hydrogeological analyses considering topographic change.

Procedure and Results of Decommissioning of R&D Facility of Uranium Fuel

From 1998 through 2005, the facilities for research and development (R&D) of uranium ore-dressing and uranium fuel etc. were decommissioned and soil contaminated by uranium was collected. All the pieces of apparatus in the nuclear facilities which might be contaminated with uranium were treated as radioactive wastes. At the time of the decommissioning activity, there was no specific value to judge as radioactive wastes. So MMC considered and adopted the pragmatic procedure to judge that soil was radioactive waste or not. During decommissioning facilities and collecting soil, the environmental monitoring was conducted. And it was confirmed that these activities had no influence on the surrounding areas. All decommissioning activities were finished with no difficulty. The wastes generated from the decommissioning activities were packed in the steel containers and have been stored safely in the storehouse built in the same area. In this report, the details of decommissioning activities are described.

Dry-Run of Site Investigation Planning Using the Manual for Preliminary Investigation in Japan

A stepwise site selection process has been adopted for geological disposal of HLW in Japan. Literature surveys, followed by preliminary investigations (PI) and, finally, detailed investigations in underground facilities will be carried out in the successive selection stages. In the PI stage, surface-based investigations such as borehole surveys and geophysical prospecting will be implemented. In order to conduct the PI appropriately and efficiently within a restricted timeframe and budget, planning and management of PI are very important. NUMO therefore compiled existing knowledge and experience in the planning and managing of investigations in the form of manuals to be used to improve and maintain internal expertise. The first editions of the two manuals were prepared on the basis of experience overseas, and then they were revised by taking geological environment, laws and regulation in Japan into consideration. This paper introduces the procedure of PI planning using the manual as well as the results of the dry-run, with the Yokosuka area as a hypothetical PI area, where the demonstration study is under way. Based on the dry-run, applicability of the manual is checked and, at the same time, further revisions are made to improve the content.

Regulatory Research for Geological Disposal of High-Level Radioactive Waste in Japan

The Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry (NISA) has renewed its regulatory role and its need for regulatory research on radioactive waste management, with recent circumstances of radioactive waste management in Japan being taken into consideration. In response, a technical supporting organization, the Japan Nuclear Energy Safety Organization (JNES), in 2009 released the five-year research plan “Regulatory Research Plan on Radioactive Waste Management 2010–2014”, in cooperation with the research institutes of the Japan Atomic Energy Agency (JAEA) and the National Institute of Advanced Industrial Science and Technology (AIST). The geological disposal research plan and the future research activities are outlined in this paper. JNES launched safety studies on geological disposal in 2003, the year it was established. JAEA and AIST joined as regulatory support research institutes in 2005. In October 2007, all three parties signed an agreement of cooperative study on geological disposal, which facilitated joint studies and exchanges of staff, data, and results. One of the ongoing joint studies has focused on regional-scale hydrogeological modeling using JAEA’s Horonobe Underground Research Laboratory.

Removal of Fission Products in the Spent Electrolyte Using Iron Phosphate Glass as a Sorbent

This study is carried out to make the pyroprocessing hold a competitive advantage from the viewpoint of environmental load reduction and economical improvement. As one of the measures to reduce the volume of the high-level radioactive waste (HLW), the phosphate conversion method is applied for removal of fission products (FP) from the melt, referring to the spent electrolyte in this paper. Among the removing target chlorides in the spent electrolyte i.e., alkali metals, alkaline earth metals and rare earth elements, only the rare earth elements and lithium form the precipitates as insoluble phosphates by reaction with Li3PO4. The sand filtration method was applied to separate FP precipitates from the spent electrolyte. The iron phosphate glass (IPG) powder, which is a compatible material for the immobilization of FP, was used as a filter medium. After filtration experiment, it was proven that insoluble FP could almost be completely removed from the spent electrolyte. Subsequently, we attempted to separate the dissolved FP from the spent electrolyte. The IPG was being used once again but this time as a sorbent instead. This is possible because the IPG has some unique characteristics, e.g., changing the valence of iron, which is one of its network modifiers due to its manufacturing temperature. Therefore, it would be likely to sorb some FP when the chemical condition of IPG is unstable. We produced three kinds of IPG under different manufacturing temperature and confirmed that those glasses could sorb FP as anticipated. According to the experimental result, its sorption efficiency of metal cations was attained at around 20–40%.

Adaptation of CCIM Technology for HLW Treatment: Results of Research and Development

Results of feasibility tests of application of Cold Crucible Inductive Melting (CCIM) technology to high level waste (HLW) treatment on examples of Savannah River Site, USA, and PA “Mayak”, Russia, HLW, carried out at SIA Radon, and results of design of new perspective bench-scale HLW vitrification facility are presented in this report. Full-scale low level waste (LLW) vitrification plant is under operation at Radon since 2003. Successful Radon experience aroused an interest to this technology from US DOE. Since 2001 Radon performed tests on vitrification of surrogates of various types of HLW stored at US DOE Sites. Process variables were determined and vitrified wastes were characterized in details. Since 2007 Radon was a subcontractor in the project on design and construction of a new CCIM based vitrification facility at PA “Mayak”. From preliminary tests on Mayak HLW surrogates the main technological features of CCIM process were determined and principles of the process control were formulated. Radon performed the design of the cold crucible and automated control system. On the base of analysis of previously and newly obtained data the main requirements to designing of cold crucible melters and auxiliary equipment, intended for actual HLW treatment, were worked out.