報告書番号

N09016

タイトル（和文）

幌延における堆積岩の特性研究(その2)－電力中央研究所／日本原子力研究開発機構共同研究 平成16～20年度成果報告－

タイトル（英文）

Study on Characteristics of Sedimentary Rock at the Horonobe Site(2)- Report of Collaboration Research between CRIEPI and JAEA -

概要 （図表や脚注は「報告書全文」に掲載しております）

高レベル放射性廃棄物処分に必要な地質環境特性に関わる調査・評価手法の開発・高度化のため、(財)電力中央研究所と（独）日本原子力研究開発機構は、幌延深地層研究センターにおいて共同研究を実施し、平成16～20年度の成果として以下を得た。堆積岩の続成作用と急速スレーキング(浸水崩壊)に関する検討の結果、声問層の珪藻質泥岩は急速スレーキングしなかった。-140m坑道の掘削影響領域の調査を行い影響範囲を推定した。岩石の化学的風化特性を検討し、酸化・溶解、水質変化で分帯ができた。岩石の物理特性を考慮した探査技術を検討し、変換解析法を用いて検討により、検層データと透水係数・一軸圧縮強度に相関性が認められた。コントロールボーリング技術の現地適用性を検討し、大曲断層が分布する箇所で孔長800mまで、ほぼ100％のコアを採取し、断層周辺の水理地質構造を明らかにした。地下水年代測定技術の現地適用性を検討し、 4Heと36Cl/Clの値から当地域の地下水が流動性に乏しく、堆積時からほぼ滞留している可能性が高いことがわかった。地質環境と微生物群集に関する基礎検討により、堆積岩の間隙中の微生物量は非常に少ないが、微生物種と地下の酸化還元環境とに関連があることが示唆された。

概要 （英文）

CRIEPI (Central Research Institute of Electric Power Industry) and JAEA (Japan Atomic Energy Agency) have been conducting a collaboration research to develop methodology for the characterization of geological environment since FY 2002. This report describes the results of the collaboration research in mainly from FY 2004 to FY 2008. As the collaboration research, the following research results were obtained.
(1)Study on the slaking property
We discovered the spherical silica (amorphous silica) in siliceous rock (Opalin chert) between the Koitoi and Wakkanai Formation. The permeability of this chert (10-12m/sec) decreases to compare with near depth diatomaceous mudstone (10-10m/sec). This diatomaceous mudstone dose not rapidly slakes. Excavated disturbed zone(EdZ) at -140m tunnel was estimated with drilled cores and gas flows from the tunnel wall.
(2)Study on the chemical weathering of the sedimentary rock
The weathering property was investigated of mudstone at an outcrop and east shaft. Weathering profile was divided oxidized, dissolved, transition and fresh zone. Oxidation was limited to the vicinity of surface.
(3)Study on the pore water extraction methodology.
Sample preparation under N2 condition before porewater squeezing to prevent oxidation showed that the squeezed porewater chemistry was affected by the sample storage period before squeezing.
(4)Study on exploration method considering the physical property of the rock.
The depth profile of the mechanical and permeability properties can be estimated by the results of physical logging in the borehole and laboratory measurements of core samples.
(5)Study on the applicability of the controlled drilling system to the Horonobe site
The controlled drilling system was applied to the Hokushin site and the Kami-horonobe site in the Horonobe town. At the Kami-horonobe site, the system was applied to drill the Omagari fault and characterize the hydro-geology around the fault. The controlled drilling was successfully done with around 100% of core recovery and hydro-geological characteristics was estimated.
(6) Groundwater dating
The results of estimation of groundwater age by 4^He and 36^Cl indicate groundwater in Wakkanai layer has been stagnant from sedimentation of Wakkanai formation.
(7) Microbial analyses of sedimentary rocks
To understand the relationship between microbial activity and geochemical conditions, we analyzed the microbial activity and diversity in sedimentary rocks from the east shaft of Horonobe underground research center. In the rocks, the abundance of microbes was lower, revealing simple microbial community. The fundamental data to understand the relationship between microbial activity, diversity and geochemical conditions were obtained.

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