Okumura Taiga, Yamaguchi Noriko, Dohi Terumi, Iijima Kazuki, Kogure Toshihiro
Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
Institute for Agro-Environmental Sciences, NARO, 3-1-3 Kannondai, Tsukuba, Japan.
Microscopy (Oxf). 2019 Jun 1;68(3):234-242. doi: 10.1093/jmicro/dfz004.
Radiocesium-bearing microparticles (CsMPs), consisting substantially of silicate glass, were released to the environment during the Fukushima Daiichi Nuclear Power Plant accident in March 2011. Since the CsMPs were formed inside the damaged reactors during the accident, we investigate the inner structures of several CsMPs by transmission electron microscopy to understand the events within the reactors. Elemental mapping of the CsMPs shows a distinct radial distribution of Cs with a higher concentration near the surface of the CsMPs, implying that Cs was in a gaseous state in the reactor atmosphere and diffused into the glass matrix after formation of the glass particles. In some CsMPs, Zn and Fe also showed a similar radial distribution to Cs, suggesting that those elements may have diffused outward where Cs was abundant. In addition, submicron crystals were present as inclusions in several of the CsMPs and were identified as chromium spinels ((Fe2+,Zn)(Cr,Fe3+)2O4), acanthite (Ag2S), molybdenite (MoS2) and hessite (Ag2Te). The spinels contained ferrous iron (Fe2+), suggesting that the atmosphere inside the reactors was reductive to some extent. Also, boron was not detected in the glass matrix of the CsMPs despite using electron energy-loss spectroscopy, indicating that most of the control rods made of B4C might have created a eutectic alloy without vaporization. These detailed investigations of the inner structures in the CsMPs may offer information on the damaged reactors that are difficult to access because of the high radiation fields.
含放射性铯的微粒（CsMPs）主要由硅酸盐玻璃构成，在2011年3月福岛第一核电站事故期间释放到了环境中。由于CsMPs是在事故期间于受损反应堆内部形成的，我们通过透射电子显微镜研究了几个CsMPs的内部结构，以了解反应堆内发生的情况。CsMPs的元素映射显示Cs呈明显的径向分布，在CsMPs表面附近浓度较高，这意味着Cs在反应堆气氛中呈气态，并在玻璃颗粒形成后扩散到玻璃基质中。在一些CsMPs中，Zn和Fe也呈现出与Cs相似的径向分布，表明这些元素可能在Cs含量丰富的地方向外扩散。此外，亚微米晶体作为夹杂物存在于几个CsMPs中，经鉴定为铬尖晶石（(Fe2+,Zn)(Cr,Fe3+)2O4）、辉银矿（Ag2S）、辉钼矿（MoS2）和碲银矿（Ag2Te）。尖晶石含有亚铁（Fe2+），这表明反应堆内部的气氛在一定程度上是还原性的。此外，尽管使用了电子能量损失谱，但在CsMPs的玻璃基质中未检测到硼，这表明大多数由B4C制成的控制棒可能形成了一种共晶合金而未汽化。对CsMPs内部结构的这些详细研究可能会提供有关因高辐射场而难以进入的受损反应堆的信息。
