DISSOLUTION RESIDUES OF HIGHLY BURNT NUCLEAR-FUELS

After dissolution of spent LWR fuel and conditioning of the dissolver solution for reprocessing, residues of varying composition are obtaine d. In the nuclear fuel reprocessing plant at Karlsruhe the residues co ntain 60-84% fines. In order to study their structure and composition samples from different dissolution campaigns were collected. One sampl e was prepared for characterisation by different surface analytical te chniques and four samples were dissolved and analysed for their isotop ic and elemental composition. Scanning electron microscopy and X-ray m icroanalysis showed two phases, a metallic phase mainly composed of Mo , Ru and Rh and an oxidic phase with the main components Zr and Mo, bu t containing also significant amounts of Pu. The analysis of the disso lved fines by isotope dilution mass spectrometry and inductively coupl ed plasma mass spectrometry revealed Mo to be the main component. Rela tively high levels of Zr and Pu and low levels of Rh, Ru and Pd sugges t that most of these fine residues had reprecipitated from the dissolv er solution.