Treament and Separation of Radioactive Fission Products Tritium, Rare Gases and Iodine in Nuclear Fuel Reprocessing Plants

摘要

In order to keep the local aNd worldwide radiation burden on the population well below the natural background level over the long term, it is necessary to limit the emissions of volatile radioactive fission products released in reprocessing plants in particular. The main nuclides concerned are krypton-35, iodine-129, iodine-131 and tritium.nBefore a suitable means of separating these radionuclides can be devised, their characteristics must be analyzed. The followingassumptions were made for the subsequent work in this field:n- All of the fission preduct rare gases are released into the off-gas.n- The majority of the tritium remains in the aqueous phase as HTO.n- Iodine appears both in the aqueous phase. in the off-gas, forming inorganic and organic compounds.nRare gases must therefore only be separated from the process off-gases of the head-end of the Purex and Thores processes. If further fission gas separation is required (approx. 90 %), it is sufficient to purify the dis-solver off-gas. It more stringent requirements are imposed (99 % retention), the shear off gas or the burner off-gas produced during LWR and HTR element reprocessing respectively must be included in the system also. To achieve high decontamination factors, the quantity of off-gas should be kept as law as possible, which can be accomplished by suitable dissolver design (locking systems and smokeless dissolution). Also, the off-gas must be fairly thoroughly precleaned, depending on the separation equipment employed (off-gas conditioning).