High-temperature Knudsen cell studies of cesium iodide in hyperstoichiometric uranium dioxide

The stability of cesium iodide in the presence of UO_2+x was investigated at temperatures up to 2300 K and for 0.00 < x < 0.29 in a Knudsen-cell mass-spectrometric apparatus. Heating of CsI and hyperstoichiometric urania, UO_2.29, to 900 K produced Cs₂U₄O₁₂ with a reaction yield of about 50%. Most of the unreated CsI starting material was volatilized below 1000 K. The decomposition of Cs₂U₄O₁₂ was observed between 1250 and 1800 K, producing atomic cesium observable in the mass spectrometer. At these temperatures, the oxygen potential of the chemical system appeared to be controlled by the UO_2+x.