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Dissolution behaviour of radiocaesium-bearing microparticles released from the Fukushima nuclear plant

福島原子力発電所事故により放出された放射性Cs含有微粒子の溶解挙動

奥村 大河*; 山口 紀子*; 土肥 輝美; 飯島 和毅; 小暮 敏博*

Okumura, Taiga*; Yamaguchi, Noriko*; Dohi, Terumi; Iijima, Kazuki; Kogure, Toshihiro*

福島第一原子力発電所事故により放出された放射性Csの一部は、珪酸塩ガラスを主体とする微粒子(CsMP)に含まれて飛散した。そこで我々は環境中から採取したCsMPの純水及び人工海水での溶解実験を行い、CsMPの溶解挙動や環境中での寿命を推定した。その結果、純水(ただしpHはおよそ5.5)ではCsMPの半径が0.011$$mu$$m/yの速度で減少するのに対し、海水中では0.130$$mu$$m/yであった。海水中での速い溶解速度はpHの違いによるものと考えられる。さらに純水での溶解実験前後のCsMPを電子顕微鏡により分析すると、サイズが小さくなり、形態も変化していた。一方、海水中で溶解されたCsMPの場合は、鉄とマグネシウムに富む板状の二次鉱物が表面を覆っていた。

Radiocesium-bearing microparticles (CsMPs) were released by the FDNPP accident. We conducted dissolution experiments of CsMPs by reaction with pure water absorbing CO $$_{2}$$ from the atmosphere and seawater. The activation energy for the dissolution of CsMPs was estimated to be 67 and 89 kJ/mol, and the dissolution rate at 13$$^{circ}$$C was 0.011 and 0.130 $$mu$$m/y for pure water and seawater, respectively. Probably the faster dissolution rate in seawater than in pure water is mainly owing to the difference in pH. The shapes of CsMPs dissolved in pure water were considerably altered. Tin oxide and iron oxide nanoparticulates were formed on their surfaces. Such features were similar to those observed in a CsMP collected recently in Fukushima Prefecture, indicating that dissolution of CsMPs is also occurring in the environment. In the case of CsMPs dissolved in seawater, a crust of secondary minerals rich in Mg and Fe was formed and the glass matrix became smaller inside the crust.

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パーセンタイル:10.66

分野:Multidisciplinary Sciences

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