SURFACE ANALYSES OF CsOH CHEMISORBED ON CONCRETE AND AGGREGATE AT AROUND 200OC

抄録

Information of Cs distribution is important for decommissioning of the Fukushima Daiichi Nuclear Power Station (1F). Several experimental studies confirmed the Cs retention on stainless steels by chemical reaction at high temperatures (commonly > 800 oC), but the Cs retention on non-metallic materials, such as concrete and thermal insulators, was not fully understood though they are used with large quantity in light water reactors. This study demonstrated that Cs might be deposited and retained on the concrete structure where the temperature was not so high during the 1F accident. It was revealed that the CsOH/concrete interaction at around 200 oC resulted in the formation of water-insoluble Cs-(Al,Fe)-Si-O deposits and water-soluble phases, i.e., cesium carbonate hydrate and possibly cesium silicate, if Al and Fe are not present. CsOH might be trapped on concrete by chemical reaction with CaCO₃ to form Cs₂CO₃ hydrate, and with aluminosilicate and SiO₂(quartz) to form Cs-Al-Si-O and Cs-Si-O deposits, respectively. This output will be useful for elucidating the trapping mechanism that caused an extremely high radioactivity on concrete shield plugs at 1F, and for developing an effective decommissioning practice for concrete structure.