JP4276145B2 - Production method of bentonite artificial barrier material - Google Patents
Production method of bentonite artificial barrier material Download PDFInfo
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- JP4276145B2 JP4276145B2 JP2004224262A JP2004224262A JP4276145B2 JP 4276145 B2 JP4276145 B2 JP 4276145B2 JP 2004224262 A JP2004224262 A JP 2004224262A JP 2004224262 A JP2004224262 A JP 2004224262A JP 4276145 B2 JP4276145 B2 JP 4276145B2
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- bentonite
- barrier material
- compaction
- aqueous solution
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Description
本発明は，放射性廃棄物地層処分事業等におけるベントナイト系人工バリア材料の製作
法に関する。
The present invention relates to a method for producing a bentonite-based artificial barrier material in a radioactive waste geological disposal project or the like.
放射性廃棄物地層処分場事業における現行の余裕深度処分概念では，底部ベントナイト層の構築方法として動的締固め方法が，また，ベントナイトプラグ或いはコンクリートピ
ット側部のベントナイト層等の構築方法としてはベントナイトブロックの積上げで構築する方法が検討されている。この場合，ベントナイト系人工バリア材料の要求性能は乾燥密
度１.６Ｍｇ／ｍ3程度が現状で想定されており，ブロックでは，作業性の面から１辺が
０.５〜１ｍ程度の立方体になると考えられている。
Under the current marginal depth disposal concept in the radioactive waste geological disposal site project, the dynamic compaction method is used as the bottom bentonite layer construction method, and the bentonite block is used as the construction method for the bentonite plug or the bentonite layer on the concrete pit side. A method of building by building up is being studied. In this case, the required performance of bentonite-based artificial barrier materials is currently assumed to be a dry density of about 1.6 Mg / m 3 , and the block is a cube with one side of about 0.5 to 1 m in terms of workability. It is considered.
このようなベントナイト系バリア材料を製作するには，最も一般的には，ベントナイト粉体に所定の含水比となるまで加水し，動的に若しくは静的に締固めることになる。動的
締固めでは振動ローラが，また静的締固めでは大型ジャッキが代表的な機械である。
In order to manufacture such a bentonite-based barrier material, most commonly, the bentonite powder is hydrated to a predetermined moisture content and compacted dynamically or statically. Vibrating rollers are typical machines for dynamic compaction, and large jacks are typical machines for static compaction.
例えば乾燥密度が１.６Ｍｇ／ｍ3のベントナイト系人工バリア材料を動的締固め法で構築する場合には，狭い処分坑道内で大型の振動ローラーを使用することになり，作業性
や安全性が劣ることが考えられる。また，１辺が０.５〜１ｍ程度のベントナイトブロックを静的締固め法で製作するには，２０００ｔｆクラスのジャッキが必要となり，放射性
廃棄物地層処分坑道に必要なブロックを大量に生産することを考えると，ベントナイトブロックの製造プラントはかなり大規模なものになる。したがって，いずれにしても，締固
めのための負荷は相当なものになると予想される。
For example, when a bentonite-based artificial barrier material with a dry density of 1.6 Mg / m 3 is constructed by dynamic compaction, a large vibrating roller is used in a narrow disposal tunnel, which improves workability and safety. May be inferior. In addition, to produce bentonite blocks with a side of about 0.5 to 1 m by static compaction, a 2000 tf-class jack is required, and a large number of blocks required for radioactive waste geological disposal tunnels are produced. Therefore, the bentonite block manufacturing plant will be quite large. In any case, therefore, the compacting load is expected to be substantial.
他方，締固め前にベントナイト材料の含水比調整を行うのが好ましいが，その加水によってベントナイトが膨潤し，この膨潤圧が締固めのための付与圧力を高める結果，締固め
の負荷をさらに増大させることになる。
On the other hand, it is preferable to adjust the moisture content of the bentonite material before compaction, but the bentonite swells due to its addition, and this swelling pressure increases the applied pressure for compaction, which further increases the compaction load. It will be.
したがって，本発明はベントナイトを締固めて高密度のベントナイト系バリア材料とす
るさいの締固め負荷を低減することを目的したものである。
Accordingly, an object of the present invention is to reduce the compaction load when compacting bentonite to form a high-density bentonite-based barrier material.
本発明は，前記の課題を解決する手段として，締固め前のベントナイトの含水比調整時に，水にかえて，ベントナイトの層間陽イオンと同種のイオンを含む水溶液を用いる点に特徴がある。 The present invention provides, as means for solving the above problems, when the water content ratio adjustment compaction before bentonite, instead of water, is characterized in that Ru with an aqueous solution containing ions of the interlayer cations of the same type as bentonite.
すなわち本発明によれば，ベントナイトの含水比を調整してからベントナイトを締固めるさいに，当該ベントナイトの層間陽イオンと同種の陽イオンを含む水溶液を前記の含水
比の調整に用いることを特徴とするベントナイト系人工バリア材料の製作法を提供する。そのさい，例えばベントナイトがＮａ型ベントナイトである場合には，陽イオンを含む水
溶液としてＮａイオンを含む水溶液を使用し，ベントナイトがＣａ型ベントナイトである
場合にはＣａイオンを含む水溶液を使用する。
That is, according to the present invention, when the bentonite is compacted after adjusting the moisture content of bentonite, an aqueous solution containing the same kind of cation as the interlayer cation of the bentonite is used for adjusting the moisture content. A method for producing bentonite-based artificial barrier materials is provided. At that time, for example, when the bentonite is Na-type bentonite, an aqueous solution containing Na ions is used as the aqueous solution containing cations, and when the bentonite is Ca-type bentonite, an aqueous solution containing Ca ions is used.
放射性廃棄物地層処分場事業におけるベントナイトバリアの構築において，底部ベントナイト層のように現場締固め施工を行う場合でも，或いはコンクリートピット側部のよう
に締固めたベントナイトブロックを積み上げる場合でも，所要の要求密度に達するように均一にベントナイトを締固めることが必要であり，このためには，適正な含水比のベント
ナイトに適正な締固め圧力を作用させることが肝要である。しかし，ベントナイト粉体に加水すると膨潤を起こすので，その膨潤圧と締固め圧力が作用・反作用の関係になり，実
際にベントナイトが所要密度に圧密されるための圧力は，膨潤圧が高いとその分だけ大きくなる。また，ベントナイトの膨潤は経時変化するので，加水時点と締固め時点との違い
によっても締固め圧力が微妙に異なることになる。
In building a bentonite barrier in a radioactive waste geological disposal site project, it is necessary to meet the requirements even when performing on-site compaction work like the bottom bentonite layer or when building up compacted bentonite blocks like the concrete pit side. It is necessary to compact the bentonite uniformly so as to reach the density. To this end, it is important to apply an appropriate compaction pressure to the bentonite having an appropriate water content. However, since water swells when bentonite powder is added, the swelling pressure and compaction pressure have a relationship of action and reaction. In fact, the pressure for consolidating bentonite to the required density is higher when the swelling pressure is higher. It gets bigger by the minute. In addition, since the swelling of bentonite changes with time, the compaction pressure differs slightly depending on the difference between the time of hydration and the time of compaction.
本発明者らは，ベントナイトの層間陽イオンと同種の陽イオンを含む水溶液を含水比調整のための添加水に使用すると膨潤圧を抑制できる結果，所要の密度に圧密するための締固め圧を低減できることを見い出した。 As a result of suppressing the swelling pressure when using an aqueous solution containing a cation of the same kind as the interlayer cation of bentonite as an additive water for adjusting the water content ratio, the inventors have set a compaction pressure for consolidating to a required density. I found that it can be reduced .
図１はＮａ系ベントナイト粉体を用いて直径１００ｍｍ×高さ５０ｍｍの円柱状のベントナイトブロックを作成したさいの本発明者らの行った代表的な試験結果を示したもので
ある。試験は，含水比調整用の液と含水比（実際にはベントナイトの液相／固相（％））を代えて，乾燥密度１.６Ｍｇ／ｍ3のベントナイトブロックに圧密するに要した最大締
固め応力（ＭＰａ）を測定した。
FIG. 1 shows a typical test result conducted by the present inventors when a columnar bentonite block having a diameter of 100 mm and a height of 50 mm was prepared using Na-based bentonite powder. The test was carried out with the maximum tightening required to consolidate to a bentonite block with a dry density of 1.6 Mg / m 3 instead of the water content adjustment liquid and the water content ratio (actually, the bentonite liquid phase / solid phase (%)). The consolidation stress (MPa) was measured.
図１の測定結果に見られるように，含水比調整用に蒸留水を用いた場合に比べて，３％ＮａＣｌ水溶液を用いた場合および無水エタノールを用いた場合には，最大締固め応力が
低下している。特に液／固（％）が約７％付近においてその傾向が顕著であり，最大締固
め応力がほぼ半減している。
As can be seen from the measurement results in Fig. 1, the maximum compaction stress decreases when 3% NaCl aqueous solution is used and when absolute ethanol is used, compared to when distilled water is used to adjust the water content ratio. is doing. In particular, the tendency is remarkable when the liquid / solid (%) is about 7%, and the maximum compaction stress is almost halved.
このような作用は，加水中のＮａイオンがＮａ系ベントナイトの膨潤を抑制したものと見ることができる。無水エタノールの場合には，ベントナイトの層間に入り込まない程度
の大きさの分子の液体であることから，同様にベントナイトの膨潤を抑制したものと見る
ことができる。
Such an action can be seen as Na ions in the water suppressing the swelling of Na-based bentonite. In the case of absolute ethanol, it can be considered that the swelling of bentonite is similarly suppressed because it is a molecular liquid that does not enter the bentonite layer.
このように，適切なイオンを含む水溶液をベントナイトの締固め前の調整液に用いると，ベントナイトの締固め圧力を低減することができることが明らかである。この原理により，本発明によれば，Ｎａ型ベントナイトの場合にはＮａイオンを含む水溶液，代表的にはＮａＣｌやＮａＨＣＯ3の水溶液を使用し，Ｃａ型ベントナイトのＣａイオンを含む水溶液，代表的にはＣａＣｌ2水溶液をベントナイト含水比調整用に使用して締固め圧力を低減させることができる。 Thus, using an aqueous solution containing appropriate ions in compaction before adjusting liquid bentonite, it is clear that it is possible to reduce the compaction pressure of bentonite. Based on this principle, according to the present invention, in the case of Na-type bentonite, an aqueous solution containing Na ions, typically an aqueous solution of NaCl or NaHCO 3 is used, and an aqueous solution containing Ca ions of Ca-type bentonite, typically Can reduce the compaction pressure by using a CaCl 2 aqueous solution for adjusting the moisture content of bentonite .
以上説明したように，本発明によると，ベントナイトの締固めに際して，その締固め圧力を含水比調整液の陽イオンの種類と濃度によって低減することができる。このため，ベントナイトの原位置での締固め作業或いはベントナイトブロックの作成において，その締固め負荷を低減することができる。そして，本発明で使用する含水比調整液は，処分坑道が閉鎖されたあとには地下水によって希釈されるので，最終的には蒸留水を使用して締固めた場合と同等の性能のベントナイト系人工バリア材料となり（図２），該バリア材料を変質させる等の問題もない。 As described above, according to the present invention, upon compaction of bentonite, it can be low reducing by the compaction pressure on the type and concentration of cations water content adjusted solution. For this reason, the compacting load in the in-situ compaction work or the creation of the bentonite block can be reduced. The water content ratio adjusting liquid used in the present invention is diluted with groundwater after the disposal tunnel is closed, so that the bentonite system having the same performance as that obtained when it is finally compacted with distilled water is used. artificial Ba becomes rear material (FIG. 2), there is no problem of changing the nature of the barrier material.
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