Kozai Naofumi, Sato Junya, Osugi Takeshi, Shimoyama Iwao, Sekine Yurina, Sakamoto Fuminori, Ohnuki Toshihiko
Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan.
Nuclear Backend Technology Center, JAEA, Tokai, Ibaraki 319-1194, Japan.
J Hazard Mater. 2021 Aug 15;416:125965. doi: 10.1016/j.jhazmat.2021.125965. Epub 2021 Apr 27.
This study contributes toward developing measures for the disposal of radiocesium-contaminated sewage sludge ash (SSA). Here, we prepared two types of solidified bodies containing 30 wt% radiocesium-bearing SSA. The material used for the two solidified bodies were alkaline-reacted metakaolinite (geopolymer) and ordinary Portland cement (OPC). Cement has been used for solidification of low-level radioactive wastes, and geopolymer is a candidate of cement alternative materials. The characteristics of these solidified bodies were investigated by various aspects including mechanical strength, transformation of SSA components during solidification, and radiocesium confinement ability by leaching test. The compressive strength of geopolymer- and OPC-solidified bodies at 30 wt% SSA content was more than 40 MPa. After static leaching test at 60 °C, Cs was hardly leached out from the geopolymer-solidified bodies containing SSA at 30 wt% to ultrapure water (<0.1%), whereas more than 30% Cs was leached from the OPC-solidified bodies containing SSA at 30 wt% even though only ~9% of Cs in the SSA is soluble. These results strongly indicate that geopolymer is far superior to OPC for solidifying radiocesium-bearing SSA.
本研究有助于制定放射性铯污染污泥灰（SSA）的处置措施。在此，我们制备了两种含有30 wt%含放射性铯SSA的固化体。用于这两种固化体的材料分别是碱反应偏高岭土（地质聚合物）和普通硅酸盐水泥（OPC）。水泥已用于低水平放射性废物的固化，地质聚合物是水泥替代材料的候选者。通过包括机械强度、固化过程中SSA成分的转变以及通过浸出试验测定的放射性铯限制能力等多个方面对这些固化体的特性进行了研究。在SSA含量为30 wt%时，地质聚合物和OPC固化体的抗压强度均超过40 MPa。在60°C下进行静态浸出试验后，含30 wt% SSA的地质聚合物固化体中的铯几乎不向超纯水浸出（<0.1%），而含30 wt% SSA的OPC固化体中即使SSA中只有约9%的铯可溶，仍有超过30%的铯被浸出。这些结果有力地表明，在固化含放射性铯的SSA方面，地质聚合物远优于OPC。
