Estimation of 233U in process samples in presence of Pu(VI) and Th

An irradiated thoria-4% plutonia pellet piece was dissolved in standard THOREX dissolvent under reflux condition inside a shielded Glove box. Analysis of the Pu in this sample by thenoyl trifluoro acetone based solvent extraction showed that majority of the plutonium present was found to be in Pu(VI) form. Estimation of 233U formed due to breeding from 232Th necessitates quantitative separation of233U from Pu and thorium prior to radiometry. An extractive radiometric procedure was developed earlier in our laboratory using TOPO as extractant for estimation of 233U in presence of Pu and Th using oxalate as masking agent to take care of Pu(IV) and Th(IV). This method was found to give erroneous results when Pu was present in Pu(VI) form as conversion of Pu(VI) to Pu(IV) is a slow process and the masking of Pu(VI) with oxalate is not efficient. The present paper describes the development of a modified method to take care of the different valence states of Pu in the sample