Measurement of radioactive gaseous effluents from voloxidation and dissolution of spent nuclear fuel

Laboratory-scale tests gave data on the release of tritium, 14C, 85Kr, and 129I as radioactive gases from spent nuclear fuels during voloxidation and dissolution. Voloxidation, a proposed reprocessing step, is intended to remove tritium from fuel by oxidation of UO2 to U3O8 prior to dissolution of the fuel with nitric acid. 14C, 85Kr, and 129I may be evolved in both steps. Quantitative data from the tests may be used in designing off-gas treatment processes and equipment. The tests were performed in a shielded cell with a combination voloxidizer-dissolver. With a recirculating off-gas system, tritium and 14C were trapped on molecular sieves; 129I was trapped on silver-exchanged zeolite. 85Kr was measured by online gamma-ray counting. Zircaloy-clad UO2 fuels from H. B. Robinson-2, Oconee-1, and Saxton reactors, with burnups from approximately 100 to approximately 28,000 MWD/MTHM, were tested. The results confirm that voloxidation released most of the tritium but only small fractions of the 14C, 85Kr, and 129I; the remainder of these radioactive gases evolved when the voloxidized fuels were dissolved. Voloxidation off-gases typically contained >99.8% of the tritium, 17 to 22% of the 14C, 7 to 17% of the 85Kr, and <8% of the 129I. Tritium evolved as HTO, with <0.1% as HT