As high-beta-gamma-LLW (low-alpha-ILW) has high nuclide concentration, it is necessary for safe disposal to avoid direct human contact to the waste.
  This report describes whether the existence of high-beta-gamma-LLW repository can be detected or not, if underground space utilization is planned at the area of the closed repository in the relatively deep space in the future.
  Based on survey items prior to utilization in relatively deep areas, the possibility of anomaly finding is considered in three stages on present technologies. For these three stages are as follows :
(1) by records (or in mind),
(2) by geophysical prospecting, and
(3) by construction control.
  As the result, one can reveal the existence of the repository in one or some stage(s), that is, one can avoid the direct human contact to the disposed waste, even if he plans to utilize a underground repository space.

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  In the present paper, pH of the aqueous solution contacting hydrated low-alkalinity cement was measured and the chemical mechanism to maintain the moderate pH was discussed.
  The low-alkalinity cement was prepared by mixing 3CaO・3Al₂O₃・CaSO₄ containing clinker, anhydrite and blast furnace slag. Solubility of hydrated cement paste was measured to investigate the effect of blast furnace slag. The Measured pH of the liquid phase contacting hydrated cement paste was in the range of 10.4 to 12.3 after 66 weeks. The composition of the hydrated cement paste was estimated from the chemical composition of the cement. The Measured pH of the liquid phase was compared with that evaluated from the chemical composition of hydrated cement and from the solubility data of calcium silicate hydrate (C-S-H gel). It was found that the measured pH agrees well with the evaluated pH.

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  The high pH condition of aqueous solutions in the radioactive waste repository, which keeps the solubility of many radionuclides low, can be achieved by dissolution of cementitious materials. In order to clarify the mechanism to maintain this high pH for long time, we investigated the dissolution phenomena of synthesized C₃S(C₃S:3CaO・SiO₂) hydrate.
  In the present research, leaching test was conducted by changing the ratio of mass of C₃S hydrate to mass of leaching water (Liquid/solid ratio) from 10～2000(wt/wt). C₃S hydrate were contacted with deionized water and set in the sealed bottle. After the lapse of the pre-determined time, the solid was separated from the solution. The value of pH and concentrations of Ca and Si in the aqueous phase were measured. The solid phase was characterized by using XRD, DTA/TG and ²⁹Si-NMR.
  It was found that the pH and Ca concentration in the aqueous phase were converged into a constant value, which was in agreement with these reported by Greenberg et al.[1], with the leaching time. From the results of XRD and DTA/TG analysis on the solid phase and the Ca concentration in the aqueous phase, it was confirmed that Ca(OH)₂ was preferentially dissolved when the liquid/solid ratio was 10 or 100(wt/wt), and C-S-H as well as Ca(OH)₂ was dissolved when the liquid/solid ratio was 500(wt/wt) or more. NMR results showed that structure of silicate anion of the C-S-H became longer when the liquid/solid ratio was 500(wt/wt) or more. This indicates that leaching of C₃S hydrate therefore results in polymerization of C-S-H. This research will contribute to improve the evaluating method for the long-term performance of the repository, because the change of C-S-H structure effects the dissolution and sorption of radionuclides.

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  In geological disposal, it is necessary to prevent shaft, tunnel and their environs to be a main passage of radioactive nuclide transfer by sealing system combined backfill, plug and grout. This paper shows an example of design of sealing system. Since calcium ion from concrete tunnel support is considered to change the property of sealing material, the effect of concrete is evaluated by experimental study.

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  Recent studies estimate that a half of living carbon in the earth may exist in subsurface environment. Deep subsurface microbial communities have recently received increased attention. There are strong but circumstantial indications of microbial life widespread at depth in the crust of the Earth. This communication presents preliminary information about the subsurface bacterial abundance. Abundances of total and selected bacteria in the interstitial water of granite and sedimentary rocks up to 1000 m deep were determined. Maximum abundance of 10⁵～10⁶ cells/ml was observed in the granite and sedimentary rock waters, respectively. Iron-oxidizing/reducing bacteria were detected at depths having specific pH and oxidation/reduction potential (Eh). Those pH and Eh regimes were corresponding to the Fe²⁺/Fe(OH)₃ or FeS₂/Fe²⁺, FeS₂/FeCO₃ interface conditions. It is implied that these bacteria are involved in geochemical processes such as precipitation, dissolution and cycling of sulfur, iron, and related elements.

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  Outlines of the special number of “execution techniques for high level radioactive waste disposal” are described, in which disposal works such as disposal site selection, geological investigation, facilities design, performance assessment, facilities construction, waste placement, facilities closure and etc are studies at desk work.

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  The making high activity of the high-level radioactive waste disposal business shall be fully started after establishing of the implementing organization which is planned around 2000. Considering each step of disposal business, in this study, the implementation procedure for a series of disposal business such as the selection of the disposal site, the construction and operation of the disposal facility, the closure and decomrnissioning of the disposal facility and the management after closure, which are carried forward by the implementation body is discussed in detail from the technical viewpoint and an example of the master schedule is proposed.
  Furthermore, we investigate and propose the concept of the geological disposal which becomes important in carrying forward to making of the business of the disposal, such as the present site selection smoothly, the fundamental idea of the safe securing for disposal, the basic idea to get trust to the disposal technique and the geological environmental condition which is the basic condition of this whole study for the disposal business making.

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  Strategy and contents of investigation and evaluation for site selection of high level radioactive waste disposal was discussed with regard to the required condition for safety assessment and design of facility according to the planned master schedule of high level radioactive waste disposal. Definite investigation program including the content, process, accuracy etc. was made up for the proposed geological conditions.

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  Ensuring the physical integrity of engineered barriers for an extremely long time period is necessary for geological disposal of high-level radioactive wastes.
  This report describes the design process and the designed configurations of both overpack and buffer as engineered barriers. Manufacturing procedure, quality control and inspection methods are also summarized.
  Carbon steel was selected as a structural material of the overpack and the specification of the overpack was determined assuming disposal in the depths of 1000m below surface of crystalline rock site.
  The mixture of bentonite and sand (80% sodium bentonite and 20% silica sand by mass) was selected as material for a buffer from mainly its permeability and characteristics of self-sealing of a gap occurred in construction work.
  Welding method of a lid onto the main body of the overpack, uniting method of a corrosion-resistance layer and the structural component in the case of a composite overpack and manufacturing procedures of both blocks-type and monolithic-type buffers are also investigated.

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  The design conditions of ground facility for high level radioactive waste disposal were shown under considering of construction and operating of the ground facility and manufacturing of the engineered barrier system. Overpacksystem, which include the process of waste reception, encapsulation and inspection, were considered. Then the process flow and the design of facility of Overpacksystem were presented. Father more, The manufacturing and inspection systems of buffer materials were studied. Then the process flow was shown. The out line of the incidental facilities was shown. That is the manufacturing facility of the backfiring material, the central operation center, the ventilation facility for the ground facility, the draining facility, the utility facility, the safety management facility, the field of soil excavated and the concrete's batcher plant. Finally, the layout of whole facility and the bird-eye view was shown.

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  In Japan, several kinds of techniques needed for high-level radioactive waste disposal have been researched and developed for the deep underground rock formation which is distributed from several hundreds meter to one thousand meter below the surface. In order to confirm roughly the feasibility on the construction of disposal, as a first step in this study, a fundamental design concept of the underground facilities necessary to dispose of about 37,800 waste forms is discussed, and the depth and scale of the disposal facilities are estimated. Furthermore, an example of the basic layout design for disposal facilities finally is demonstrated under the above discussion.
  In the second step, we discussed the more detail design, such as the shape and dimension of tunnels, the types and materials for tunnel timbering, the minimum distance between adjacent tunnels or waste forms and the ventilation and drainage system. Furthermore, we demonstrate an example of the detailed layout design of total disposal facilities under the above discussion.
  We also investigated the some construction techniques such as the excavation method, the carrying out method of excavated rocks, the grouting method for rocks around tunnels and the grouting materials and the equipment for ventilation, air-cooling and drainage in tunnels, and then propose roughly a method for construction management based on the present available techniques.

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  Based on the principle of radiation protection, we studied the handling and emplacement procedure of waste and buffer material. We showed the handling flow diagram, conceptual drawings of handling and emplacement facility in two cases of emplacement ; vertical emplacement in pit and horizontal emplacement in tunnel. The procedure and material for backfilling and plugging have been studied and the optimum method of current technologies is selected. Regarding the tunnel supporting, the removal of concrete supporting mainly was studied. Finally, we showed our view of monitoring before and after the close of disposal facility.

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  Scenarios for the geological disposal of high-level wastes were constructed in order to assess the safety of the HLW disposal and the performance of the repositories. The list of features, events, and processes (FEP) related to the disposal and their influence on others, called process influence diagram (PID), were utilized to construct the scenarios. As a result, the scenario involved in groundwater flow can be divided into a reference scenario and alternative scenarios. In addition, the latter are composed of upheaval/erosion, submergence, permanent glacial epoch, permanent interglacial epoch, and higher-temperature inclination with depth. According to the scenario analysis, the performance assessments of barriers were conducted for a sedimentary rock area and granitoid rock area. The results showed that a lower individual dose resulting from the disposal was obtained for the sedimentary rock area because of the higher values of porosity and distribution coefficients in the sedimentary rock area than those in the granitoid rock area. In addition, the dose for the upheaval/erosion scenario gave rise to the highest value.

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