Characterization of Cs deposits formed by the interaction of simulated fission product CsOH in the gas phase and concrete at 200C

Luu, V. N. ; Nakajima, Kunihisa  

Cesium distribution is crucial for decommissioning Fukushima Daiichi Nuclear Power Station (1F). Several experimental studies confirmed Cs retention on stainless steels by performing chemical reactions at high temperatures (typically above 800C)), but the Cs retention on concrete, used in large quantities in light water reactors, is not fully understood. This study demonstrated that Cs might have been deposited and retained on the concrete structures where the temperature was not so high during the 1F accident. Results showed that the CsOH/concrete interaction at around 200C occurred in 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 CaCO to form CsCO hydrate, and with aluminosilicate and SiO(quartz) to form Cs-Al-Si-O and Cs-Si-O deposits, respectively. This output could help elucidate the trapping mechanism that caused extremely high radioactivity on concrete shield plugs at 1F and develop an effective decommissioning practice for concrete structures.