High temperature reaction between UO and sea salt deposit

Takano, Masahide ; Nishi, Tsuyoshi; Kurata, Masaki ; Amaya, Masaki  ; Nagase, Fumihisa 

In the severe accident at Fukushima Daiichi Nuclear Power Station, the seawater was pumped into the cores. When the seawater is vaporized on the hot fuel debris, the various salts like chlorides and sulphates are deposited. In this work, the reactivity between UO and the sea salt was examined in the temperature range from 815 to 1198 C, to characterize the impacts of seawater on the chemical form of fuel debris. The pelletized mixture of UO and the salt heated for 30 min in argon flow yielded mainly MgO and UO, whose lattice parameter is much smaller than that of stoichiometric UO. It was found that calcium decomposed from the sulphate could dissolve into UO to form solid solution. However, by the analyses on the UO pellets heated with the salt at 913 and 1002 C for 3 h, the reaction was found to be limited at the UO/salt deposit interface. The evolution of corrosive gases by the volatilization and thermal decomposition of the salt would be another aspect of importance for the structural materials and chemical form of the volatile fission products in the core.