Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The reduction of mixed NiO-U₃O₈ oxides of various composition by hydrogen was studied in the temperature range 350-590 °C using the thermogravimetric method. An addition of nickel oxide in the amount of few per cent increases the reduction rate of U₃O₈ and substantially decreases the initial temperature of its reduction. The reduction of pure U₃O₈ proceeds with a maximum and steeply decreasing rate in the region of the oxide composition U₃O₈ → UO_2.59 and with a constant rate in the region UO_2.59 → UO_2.25. In the heterogeneous two-component system the reduction rate increases with the increasing content of nickel oxide. The reduction of the stoichiometric NiO is retarded by a small homophaseous addition of U₃O₈. Radiation oxidation of U⁴⁺ ions proceeds during the pre-irradiation of the samples with gamma radiation at a dose of 1 MGy and the reduction rate of samples with a surplus of U₃O₈ is decreased. With the increasing content of nickel oxide the negative effect of radiation is continuously changed into a positive effect (an increase of the reduction rate). The reduction kinetics of irradiated samples is in both homogeneous extreme regions of composition governed by the adsorption processes and in the heterogeneous region it depends on the radiation-induced defects with strongly temperature-dependent stability.