At the Loviisa Nuclear Power Station (NPS) all liquid waste, i.e., spent resins and evaporator concentrates, have been stored in a large tank storage facility. Dominating radionuclides in the evaporator concentrates have been Cs-134 and Cs-137. By removing cesium from the waste, purified liquid can be released within licensed release limits, and cobalt as a second dominating nuclide is left in a small waste volume on the bottom of the tank. Since 1985, the use of inorganic hexacyanoferrate-based materials for purification of cesium has been studied. A full-scale system for cesium removal, called the IVO-CsTreat System, was constructed in 1990 to 1991. A method to produce the ion exchanger in granular form in industrial scale was developed, and the facility to produce it was constructed. The ion exchange material was produced in 1991, and the full-scale purification facility was commissioned at the Loviisa NPS in October 1991. In the test run, 253 m3 of concentrate was purified between October 31, 1991 and June 11, 1992 with three ion exchange columns, each with a volume of 8 l. A volume reduction factor of over 10 000 was achieved as the ratio of liquid and ion exchanger volume. The decontamination factor for cesium was approximately 2000.
