Natural analogue studies of engineered barrier materials at PNC TOKAI, JAPAN; Their framework and recent activities

None

亀井 玄人 ; 湯佐 泰久; 山形 順二*; 井上 邦博*

Kamei, Gento; Yusa, Yasuhisa; Yamagata, Junji*; Inoue, K.*

本資料は、第3回原子力先端研究国際シンポジウム(平成3年3月、於水戸)の報文集に掲載されたものである。人工バリアの長期耐久性評価のために行ったナチュラルアナログ研究について、1.ナチュラルアナログとは何か、2.その必要性、3.調査対象選定のための考え方、4.研究の構成、について述べた。具体的成果として、1.玄武岩質ガラスの風化変質(廃棄物ガラスの変質のアナログ)、2.土中埋設鋼管(緩衝材に包まれた鉄製オーバーパックのアナログ)、2.火成岩体の貫入によるベントナイトのイライト化(緩衝材の変質のアナログ)、4.コンクリート構造物の地下水又は海水による変質(バックフィル材等としてのセメントの化学的変質のアナログ)の4項目について記述した。本資料は、共同発表者の湯佐による外部発表許可済資料(2KA 29,80-02-131)に、その後の知見を加えてまとめなおしたものである。

Long-term extrapolations concerning the safety of a nuclear waste repository cannot be satisfactorily made on the sole basis of short-term laboratory tests. Natural analogues, which are the only means by which very slow mechanisms can be identified and by which long-term predictions of models can be tested for pertinence. Our studies for the assessment of long-term durability of engineered barrier materials are outlined. Materials of young age and with simple history are the most suitable for these studies as: (1)properties of the materials tend to deteriorate over the longer term; and (2)detailed quantitative data on the term and on the environmental conditions can be obtained. The framework of our studies includes: (1)clarification of alteration phenomena,(2)examination or the environmental conditions, and (3)support experiments. The following four materials and their alteration phenomena were selected: (1)Weathering alteration of basaltic glass (as vitrified waste form) : Basaltic glasses within 2800 years, from the Fuji and the Izu-Ohshima, were studied. (2)Corrosion of iron in soil (as overpack): corrosion of Industrial materials, gas/water service pipes of carbon steel or cast iron embedded in soil for the range from 20 to 110 years, were studied as analogy of alteration of iron in bentonite. (3)Illitization of smectite associated with contact metamorphism (as buffer material): A lateral variation of smectite to smectite/illite mixed-layer minerals, found in the aureole of the rhyolite intrusion, were studied. (4)Alteration of cement (as buffer or backfill material): Concrete components of fabrications with a known age were studied.