XANES study on novel mixed valent A₂U₄O₁₂(A=K, Rb or Tl) uranates

Abstract

Alkali metal (Na, K, Rb, and Cs) uranates are likely to form in operating or transient reactor conditions by interaction of coolant/fission products with uranium oxide fuel. The valency of uranium in uranates formed in reactor operating conditions plays an important role in migration of fission products as well as in uranium diffusion in the fuel and thus determines fuel behavior during reactor operation. X-ray absorption near edge structure (XANES) measurements on uranates K₂U₄O₁₂, Rb₂U₄O₁₂, and Tl₂U₄O₁₂ have been made to determine the valency of uranium in these compounds. XANES analysis reveals that uranium is present in mixed valence state in these compounds, as U(V) and U(VI). The ratio of uranium (V) to (VI) states (determined from XANES analysis), in all the compounds, does not conform to 1:1 as required by their chemical formula. The reason for this mismatch may be the instability of U(V) state during sample preparation in these compounds as well as reference compounds.