Thermodynamic evaluation of the solidification phase of molten core–concrete under estimated Fukushima Daiichi nuclear power plant accident conditions

Abstract

The solidification phases of molten core-concrete under the estimated molten coreconcrete interaction (MCCI) conditions in the Fukushima Daiichi Nuclear Power Plant Unit 1 were predicted using the thermodynamic equilibrium calculation tool, FactSage 6.2, and the NUCLEA database in order to contribute toward the 1F decommissioning work and to understand the accident progression via the analytical results for the 1F MCCI products. We showed that most of the U and Zr in the molten core-concrete forms (U,Zr)O 2 and (Zr,U)SiO 4 , and the formation of other phases with these elements is limited. However, the formation of (Zr,U)SiO 4 requires a relatively long time because it involves a change in the crystal structure from fcc-(U,Zr)O 2 to tet-(U,Zr)O 2 , followed by the formation of (Zr,U)SiO 4 by reaction with SiO 2. Therefore, the formation of (Zr,U)SiO 4 is limited under quenching conditions. Other common phases are the oxide phases, CaAl 2 Si 2 O 8 , SiO 2 , and CaSiO 3 , and the metallic phases of the Fe-Si and Fe-Ni alloys. The solidification phenomenon of the crust under quenching conditions and that of the molten pool under thermodynamic equilibrium conditions in the 1F MCCI progression are discussed.

Corium Experimental Thermodynamics: A Review and Some Perspectives

“…Few data were reported in the ISTC CORPHAD and PRECOS Projects and they need to be completed. The future studies should also focus on the interaction between corium and basaltic concrete, employed for the basemats of the units of the Fukushima Daichi site [166].…”

Investigating the mechanical behaviour of Fukushima MCCI using synchrotron Xray tomography and digital volume correlation

“…Full details of the simulant MCCI synthesis and characterisation are given in Ding et al 20 . The batched compositions were based on estimations of the relative proportions of core materials and concrete, previously reported in the literature and through discussion with personnel at the Japan Atomic Energy Agency 42,43 . The as-batched reagent stoichiometry included SiO 2 , CaO and Al 2 O 3 as components of the sand-rich cement mortar utilised in the reactor construction, Fe 2 O 3 and 316 stainless steel (Fe/Cr 18 /Ni 10 /Mo 3 )) to represent the steel components of the reactor units and (U,Zr,Ce)O 2 as an oxidised fuel/cladding surrogate (with Ce acting as a surrogate for Pu from mixed-oxide fuel within Unit 3).…”