USE OF HIGHLY SELECTIVE ION EXCHANGERS FOR MINIMIZATION OF WASTEVOLUMES

摘要

Treatment of liquid radwaste by highly selective ion exchangers separates essentially only the radioactiveelements from the inactive substances for storage and disposal. Even in high salt solutions only theradioactive target nuclides are removed and concentrated to a very small volume, and the inactiveelements are left in the liquid. After this kind of treatment the processed liquid can either be released orrecategorized for easier treatment with less expensive system.Conventional ion exchange materials, e.g. zeolites and organic resins, have been used for years fortreatment of different liquids. Relatively low selectivity factors have limited their efficient use. Three newhighly selective ion exchangers have been introduced to the market: CsTreat? for removal of cesium,SrTreat? for strontium, and CoTreat for cobalt and other corrosion products. Selectivity factors of thesenew materials are on much higher levels than for the conventional ones. Several industrial applicationsutilizing these new materials have already proven their efficiency. Typically decontamination factors ofseveral thousands can be achieved. Because of high selectivity, large proportion of the ion exchangecapacity of the media (from 0.35 meq/g to 5 meq/g) can be utilized for removal of radioactive elementsto treat very large volume of liquid using a very small volume of the media.Selective removal of radionuclides reduces the volume of wastes in storage and final disposal. The firstapplication for CsTreat in the Loviisa NPP in Finland treated 700 m3 of high-salt evaporatorconcentrates with 80 liters of CsTreat. After this several new processes, including mobile treatmentunits, were based on these ion exchangers both for low-salt and high-salt liquids. One application wasconstructed for treatment of reprocessing liquid to remove both cesium and strontium from highly acidicwaste.High volume reduction of waste leads to high concentrations of radioactive elements in the final waste.Highly selective ion exchangers can be utilized in many different ways. Most efficient way is to usecompact columns with volume of 2-12 liters. Used ion exchange columns are very easy to dispose of inconcrete containers. In the Loviisa NPP 12 pieces of columns with volume of 8 liters each are closedinto one concrete container with inner diameter of one cubic meter.