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Some Aspects of Natural Analogue Studies for Assessment of Long-Term Durability of Engineered Barrier Materials; Recent Activities at PNC Tokai, Japan

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湯佐 泰久; 亀井 玄人 ; 新井 隆

Yusa, Yasuhisa; not registered; Arai, Takashi

本研究は天然の類似試料の長期変質挙動を調べる事により、人工バリア材の長期耐久性を評価することを目的とする。I. 対象試料の選定:天然の歴史試料は古いほどさまざまな要因が重複し、その環境条件も複雑でかつ変化し、把握できにくくなる。また、変質期間に関する情報も得られにくくなる。したがって、比較的若い、単純な履歴の試料を研究することとした。II. 研究の構成:(1)変質現象の調査、(2)環境条件の把握、(3)(組成差や環境条件の差を比較するための)サポート実験、を本研究の構成とする。III. 調査例:人工バリア材、すなわち、(1)廃棄物ガラス、(2)オーバーパック、(3)緩衝材、(4)埋め戻し材、の耐久性評価のために、それぞれ、(1)玄武岩質ガラスの風化変質、(2)炭素鋼の土壌腐食、(3)熱(接触)変成作用によるスメクタイトのイライト化作用、(4)コンクリート構造材の化学的劣化、の研究を実施している。なお、本論文はCEC主催第4回ナチュラルアナログ ワーキンググループミーテング(1990年6月 Scotland Pitlochry)での発表をまとめたものであり、CEC report n0 EUR 13014 ENとして製本・公表される予定である。

This paper contains an overview of analogue studies for the assessment of long-term durability of engineered barrier materials at PNC Tokai. Materials of young age and with simple history are the most suitable for study as: (1)properties of the materials tend to deteriorate over longer historical time intervals; and (2) detailed quantitative data on time intervals and environmental conditions are more likely to be available. The following materials and their alteration phenomena were selected: (1)weathering alteration of basaltic glass (as vitrified waste form), (2)corrosion of iron in soil (as overpack), (3)illitization of smectite associated with contact metamorphism (as buffer material), (4)alteration of cement (as buffer or backfill material). (1)Weathering alteration of basaltic glass: Basaltic g1asses, from the Fuji and the Izu-Ohshima pyroclastic fall deposits were studied. The observations were made: (a)Climatological conditions have not varied significantly during the last three thousand years. Therefore, values for temperature, amount, and chemistry of ground water are quantified. (b)The cases studied could be regarded as leaching experiments in groundwater, using mass balances in water-g1ass interaction. (c)Although the groundwater is of Ca(Mg)-HCO$$_{3}$$ type in the Fuji area and of Na-Cl type in the Izu-Ohshima, similar alteration ratios (2$$sim$$ 3$$mu$$m/1000yr) were obtained. (2)Corrosion of iron in soil: Industrial materials, such as gas/water service pipes of carbon steel or cast iron embedded in soil for 20 $$sim$$ 110 years, were selected for an analogue study of corrosion of iron in bentonite. The maximum corrosion rates obtained so far fall in the range of 0.04$$sim$$0.09 mm/yr. (3)Illitization of smectite associated with contact metamorphism: In the Murakami bentonite deposit in central Japan, lateral variation of smectite to smectite/illite mixed-layer minerals are found in the aureole of the rhyolite intrusion body. Conversion of smectite to the

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