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

Abstract

Cs 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 > 800°C), 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 concrete structures where the temperature was not so high during the 1F accident. Results showed that the CsOH/concrete interaction at ~200°C occurred in water-insoluble Cs–(Al, Fe)–Si–O deposits and water-soluble phases, i.e., Cs carbonate hydrate and possibly Cs₂SiO₃ if Al and Fe are absent. 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 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.