模擬廃液を用いたセメント固化体の物性評価試験

Physical Property Evaluation Testing of Cement-Solidified Products Prepared from Simulated Liquid Waste

久保 美和*; 佐々木 忠志*

Kubo, Yoshikazu*; Sasaki, Tadashi*

低放射性廃棄物処理技術開発施設(LWTF)では、再処理施設で発生する硝酸ナトリウムを含む低放射性廃液を廃棄体化する方法として、セメント固化処理法を検討している。硝酸塩廃液の固化: 高温での固化は、セメントの急激な水和反応を生じさせ、混練時の急結や流動性低下を引き起こした。しかしながら、流動性を向上させる分散剤の添加およびセメントの硬化に必要な硬化液添加量の変更により、80C程度で固化可能であることを確認した。これにより、想定しているセメント固化方法が硝酸塩廃液に適用できることを確認した。スラリ廃液の固化: スラリ廃液の固化では、流動性の低下および圧縮強度の低下現象が見られた。これは廃液に含まれるリン酸塩の影響によるものと考えられ、リン酸塩濃度を0g/Lとするスラリ修正廃液の場合であれば、廃液温度80C、濃縮度65wt%で、塩充填率50wt%の固化が可能であることを確認した。NaNO、NaHCO、NaSOの含有量増加はそれぞれ、硬化遅延、圧縮強度の低下、流動性の低下を引き起こすことがわかった。なお、リン酸塩を単独で固化する場合は、含水塩(NaPO・8HO)として塩充填率50wt%(無水塩換算の塩充填率: 26.6wt%)の固化が可能であった。

In the low level radioactive waste treatment facility (LWTF), the cement solidification process is being studied on its applicability as a method for preparing waste packages from sodium-nitrate-containing low-level liquid waste generated at reprocessing plants. Solidification of nitrate solution waste: Solidification in a high temperature caused a rapid hydration reaction of cement, resulting in rapid hardening during the mixing process and a drop in fluidity. However, it has been confirmed that liquid waste can be solidified at 80C or so by adding a dispersing agent to improve fluidity and changing the amount of hardening solution to be added for cement hardening. This has verified that the cement solidification process under contemplation is applicable to nitrate-containing liquid waste. Solidification of slurry waste: In solidifying slurry waste, a fall in fluidity and a fall in compressive strength were observed. It is considered that this is attributed to the effects of phosphate contained in the liquid waste. In the case of slurry waste whose phosphate concentration is adjusted to 0g/L, it has been verified that solidified products whose salt mixing ratio is 50wt% can be prepared when the liquid waste temperature is 80C and the degree of concentration is 65wt%. It has been revealed that increases in the NaNO, NaHCO, and NaSO contents cause a delay in cement hardening, a fall in compressive strength, and a fall in fluidity, respectively. It has also been revealed that when liquid waste containing phosphate alone is solidified, solidified products whose salt mixing ratio is 50wt% in terms of hydrate salt (NaPO 8HO) (26.6wt% in terms of anhydrate salt) can be prepared.