INDUSTRIAL-SCALE REMOVAL OF CESIUM WITH HEXACYANOFERRATE EXCHANGER - PROCESS-DEVELOPMENT

An industrial scale process utilizing hexacyanoferrate-based ion excha ngers was developed for the selective separation of radioactive cesium from nuclear waste solutions. This process was put into operation at the Loviisa Nuclear Power Plant (NPP) (pressurized water reactor, VVER -440), Finland, at the end of 1991, and it has shown superiority to an y other cesium separation method used at present at nuclear plants. Th is paper summarizes the work that was carried out in the development o f this process. In the first phase of the work, the performance of sev eral cesium-specific precipitants and ion exchangers (eg., zeolites an d hexacyanoferrates) was tested by laboratory experiments. Based on th ese initial tests, two precipitants, sodium hexanitrocobaltate and tun gstophosphoric acid, and two hexacyanoferrate exchangers were chosen f or pilot-scale experiments. These experiments showed that the hexacyan oferrate ion exchangers were the most efficient materials for the remo val of Cs-137 and Cs-134 and were suitable for large-scale column oper ation. With hexacyanoferrates, decontamination factors (DFs) of severa l thousands and volume reduction factors (VRFs) in the range of 2000 t o 10 000, were obtained for Cs-137 and Cs-134. By using the cesium-spe cific precipitants, DFs and VRFs on the order of 100 were feasible in the Loviisa concentrates. After the pilot experiments, an exchanger ba sed on hexacyanoferrate was chosen to be used in the full-scale cesium -separation plant constructed at the Loviisa NPP.