Separation of Radioactive Strontium from Alkaline Nuclear Waste Solutions with the Highly Effective Ion Exchanger SrTreat

SrTreat is an inorganic ion exchanger whose structure is based on a sodium titanate. It is available in granular form and is suitable for use in packed-bed operations. This exchanger has proved to be highly effective in the removal of radioactive strontium from alkaline nuclear waste solutions. SrTreat was used for the first time in an industrial-scale separation process in 1996 in Murmansk, Russia. During that operation 2500 bed volumes of low-active (22 kBq/l) waste solution with a moderate salt concentration was decontaminated from 90Sr with an average decontamination factor of 7400. The exchanger is especially suited for the decontamination of alkaline concentrated sodium nitrate solutions that are characteristic of neutralized stored wastes from some nuclear-fuel-reprocessing plants.At the Japanese Atomic Energy Research Institute (JAERI), a new radionuclide-removal system, successfully utilizing SrTreat for the removal of 90Sr (7.4 GBq/l) from a neutralized alkaline reprocessing waste solution, was commissioned in the summer of 1997. In the laboratory-scale tests with a JAERI simulant, adjusted to pH 10 and having 2.4 mol/l of NaNO3, strontium could be removed from more than 1000 bed volumes with an SrTreat column, thereby obtaining a decontamination factor between 2000 and 15 000. In addition to the performance of SrTreat columns in strontium removal, basic studies on the ion exchange equilibrium of strontium on SrTreat and the effects of pH and interfering cations on strontium exchange are discussed.