Effect of Technetium on Stability of U(Ⅳ) and Hydrazine in PUREX Process

In this research, the oxidation reaction of U(Ⅳ)-hydrazine catalyzed by technetium in nitric acid was studied by spectrophotometry. The results show that temperature and technetium concentration are the main factors affecting the oxidation rate of U(Ⅳ). The reaction order for technetium is 1.23, and the reaction activation E_a is 79.2 kJ/mol. A zero-order reaction characteristic for U(Ⅳ) is observed with average reaction rate constant 1.60×10^-4 min^-1. The concentration of hydrazine has little effect on the oxidation rate of U(Ⅳ) catalyzed by technetium. In Tc-U(Ⅳ)-hydrazine system, U(Ⅳ) and hydrazine are oxidated simultaneously. At first, U(Ⅳ) is oxidated completely, and subsequently, the hydrazine is oxidated completely soon. Compared to the system of Tc-hydrazine，the oxidation rate of hydrazine containing U(Ⅳ) is a little slower, and U(Ⅳ) shows both acceleration and inhibition impact on oxidation of hydrazine catalyzed by technetium in nitric acid. In Tc-U(Ⅳ)-Pu(Ⅲ)-hydrazine system, Pu(Ⅲ) is stable for less than 45 min when the concentration of technetium is 0.005 mol/L.