Time-dependent surface modification of uranium oxides exposed to water plasma

Abstract

Thin UO2 films exposed to water plasma under UHV conditions have been shown to be interesting models for radiation induced oxidative dissolution of spent nuclear fuel. This is partly attributed...

Mixed H2O/H2 plasma-induced redox reactions of thin uranium oxide films under UHV conditions

“…This was attributed to the atomic hydrogen, being also being present in the pure water plasma. The effect is, though, very weak and longer exposure times than used in the present study are needed (30-60 min [27]) to observe a partial reduction of U(VI) into U(V). For mixed H 2 O/H 2 plasma, the reduction becomes more pronounced.…”

“…For longer exposures, U(VI) is slowly reduced back to U(V). These findings were discussed in detail and a simple kinetic model was developed to describe the dynamics of the process [27]. While we previously only used this methodology for exposures to pure water plasma [28], we have there extended in the present study the experimental conditions by using mixed H 2 O/H 2 plasma.…”

An Alternative Conceptual Model for the Spent Nuclear Fuel–Water Interaction in Deep Geologic Disposal Conditions

“…The authors propose that such a process would explain the absence of oxidants and oxidized uranium during the long-term leaching tests mentioned in Section 3, and leads to the overall recombination of oxidizing species in solution back to water. The formation of U(V) and subsequent reduction was recently observed at the surface of a thin UO 2 film exposed to plasma in vacuum at 400 • C [34,35]. The authors also mention the formation of a surface-bound •OH radical as an intermediate species involved in the oxidation of the UO 2 surface [34,35,69].…”

“…The formation of U(V) and subsequent reduction was recently observed at the surface of a thin UO 2 film exposed to plasma in vacuum at 400 • C [34,35]. The authors also mention the formation of a surface-bound •OH radical as an intermediate species involved in the oxidation of the UO 2 surface [34,35,69].…”

“…The proposed explanations above typically invoke an oxidizing first step due to oxidizing radiolytic species, of which H 2 O 2 is claimed to be the most important, although recently the role of •OH radicals has also been mentioned [9,[34][35][36]. The role of the intrinsic ionizing radiation from spent fuel and the effects on the solid and at the spent fuel-water interface are not included in the current conceptual model.…”