Definition of a process for the recovery of ultra traces of Pu238 from a 300 Kg depleted uranium batch

In order to measure the half life of the double beta decay of U238, a process for the recovery of trace amounts of Pu238 (about 30 000 atoms) from a 300 kg batch of depleted uranium has been studied and tested. The process includes a Pu (IV) valency adjustment step with nitrous oxide, followed by nine chromatographic cycles (plutonium decontamination factor up to 1011 have been achieved for Th, Pa and U). The procedure to realize the alpha spectrometry measurement has also been defined. Full scale apparatus have been set in the CRN facility near STRASBOURG. The first part of the experiment (U238 purification before one year aging and measurement of the extracted Pu238 traces) has been realized. The results of the Pu traces counting allows the validation of the chemical process but also show an important Pu238 contamination certainly a consequence of the TCHERNOBYL accident. (author). 76 refs., 63 tabs., 49 figs