Distribution equilibrium of nitrous acid in reprocessing solution

The distribution coefficient of nitrous acid (HNO2) has been measured under PUREX conditions with the parameters of HNO3, TBP and uranium concentrations. FIA (Flow Injection Analysis) was applied to the measurement of HNO2 concentration to simplify the operation and to shorten the required analysis time. That enables us to avoid the decomposition of HNO2 in sample solution. The following results are obtained. The distribution coefficient of HNO2 in 30%TBP/normal dodecane(nDD)-HNO3 has the maximum value of about 35 at 0.1mol/l HNO3, is proportional to TBP concentration in organic phase, and is inversely proportional to uranium concentration in 30%TBP/nDD at 3mol/l HNO3. Furthermore, the distribution coefficient of HNO2 is dependent on the concentration of hydrogen ion, but is independent of HNO2 and NO3- concentrations. There is not difference between the distribution coefficient of HNO2 using sodium nitrite solution and that using NOx gas. A new formula is proposed to estimate the distribution coefficient of HNO2 under PUREX conditions. The formula is expressed by the concentrations of hydrogen ion in aqueous phase and free-TBP in organic phase. (author)