ベントナイト緩衝材の流出特性の評価(II)

Evaluation of the outflow characteristic of bentonite buffer material (II)

松本 一浩*; 棚井 憲治 

Matsumoto, Kazuhiro*; Tanai, Kenji

高レベル放射性廃棄物の地層処分における人工バリア埋設後においては、緩衝材の物理的安定性に影響を及ぼす事象の一つとして、緩衝材の流出挙動が考えられる。緩衝材の流出挙動は、岩盤亀裂中への侵入現象と、亀裂へ侵入したベントナイトゲルの地下水による侵食現象の二つの現象によるものと考えられており、この現象を実験により定量的に把握する必要がある。前報では、緩衝材の流出挙動に関する基礎的な一部のデータ取得を行った。本報では、緩衝材の流出挙動をより詳細に把握するために、緩衝材流出挙動試験設備(BENTFLOW)を用い、ベントナイト供試体の仕様(乾燥密度、ケイ砂混合率)および亀裂幅、また亀裂内流速をパラメータとして実験を実施し、データの拡充を行った。

The outflow behaviour of bentonite buffer material was experiment to assess the physical stability in the geological disposal system, the parameters of experiment are the dry density of bentonite, mixtures ratio silica sand, fracture width, and flow velocity. The outflow phenomena were identified as extrusion and erosion, and the experimental results are as follows; (1) Extrusion (a) The proportional coefficient obtained from the relation between time and extrusion distance was arranged by the relation with effective clay density. The experimental eguation of the proportional coefficient is as follows; A=6.758710exp(5.7261d)exp((6.1598+(-0.5398d)+(-0.9272d))) (b)By model experiment, the density distribution into fracture was measured. The density distribution of an extrusion region obtained 0.8-0.2 Mg m. The average dry density into fracture of bentonite gel was about 0.4 Mg m below. (c) The influence of density of bentonite/sand mixtures material (30 wt%, 1.6 Mg m) by the extrusion phenomenon was calculated. It was assumed that the average fracture density is about eight fractures parameter. The reduction in density of the bentonite/sand mixtures material is about 4.5% (1.527 Mg m) of the initial value after 10, 000 years. (2) Erosion (a) The colloid concentration and the particle size in drainage liquid were measured as parameter of flow velocity into fracture. The result of measurement, colloid concentration decreased with the increase in the flow velocity. Moreover, the particle size of colloid became large. (b)In the case of average flow velocity 1E-5 m s, the colloid was generated in drainage liquid. Therefore, the flow velocity for occurrence of erosion was suggested smaller than 1E-5 m s.