The off-gas composition upon dissolution of different types of non-irradiated nuclear fuels (UC, U 2 C 3 , U0 2 , (U,Pu)C and (U,Pu)0 2 ) in HNOj has been measured and the influence of dissolution parameters such as dissolution temperature, nitric acid molarity, fuel density and composition has been studied.For fast dissolutions less off-gas, especially N0 2 , is produced than for slow ones. No CO could be measured for the carbide dissolutions and NO is the most important constituent in the off-gas. For oxides and sesquicarbides, the N0 2 is the predominant species. Carbides are dissolved much faster than oxides and they don't leave any residue, but the solution stays dark and a slight N0 2 and C0 2 evolution continues after the dissolution is complete. This can be ascribed to the destruction of the organic compounds (mellitic acid, oxalic acid etc.) formed during dissolution.A nitric acid concentration of 6 Μ and temperatures of 80 -90 °C are optimum conditions to dissolve fuel materials in a reasonable time with a low nitrogen oxide content in the ofT-gas. The activation energy calculated from the Arrhenius plot was found to be 43.5 kJ/mol for UC. For U0 2 two values for activation energy were found, 64.1 kJ/mol if the fuel pellets are pressed from U 3 0 8 powder and 54.8 kJ/mol if the pellets are made from U0 2 powder.
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