OXIDATION OF URANIUM IN STEAM

The steam oxidation rates of U-metal foil and bar stock have been meas ured thermogravimetrically between 473 and 823 K. Both materials exhib ited Arrhenius-type behaviour in their steam oxidation rates below 573 -623 K, with activation energies of 46.9 +/- 3.3 kJ mol-1 for U foil b elow 623 K and 58.0 +/- 3.8 kJ mol-1 for U bar stock below 573 K. Howe ver, a significant rate reduction was observed at higher temperatures. In all cases, the oxidation products were uraninite-structured UO2-x compounds. Non-adherent oxide layers were formed on bar samples below approximately 573 K, becoming increasingly adherent at higher temperat ures. Similarly, the oxide layers produced on foil samples below appro ximately 623 K had highly porous cellular structures, whereas the laye rs formed at higher temperatures were significantly more dense. For bo th materials, the fall in oxidation rate above 573-623 K was attribute d to reduced steam ingress to the underlying metal caused by the incre asingly protective surface oxide.