Overview on drying technologies for radioactive evaporation concentrates

Radioactive waste water is normally treated by evaporation resulting in evaporation concentrates with solid contents in the range of 15 to 30% by weight. Typical compositions of evaporation concentrates depend on the type of the nuclear power plant (especially BWR or PNW) and the time of arising (operational phase, phases of intervention such as major repair and maintenance). Main components can be boron acids, sulfates, chlorides, nitrates, chemicals from decontamination procedures. Evaporation concentrates from BWRs are free from boron acids, whereas those from PWRs contain boron acids up to 30% by weight. In Germany today, mainly two types of conditioning facilities are used to transform liquid evaporation concentrates that contain boron acids into the solid state: one stationary facility, called ROBE, and one facility that can be operated mobile as well as stationary, called FAVORIT. Both processes can be described as drying below atmospheric pressure (vacuum) supported by indirect heating. All products fulfill the requirements for final and interim storage as far as they are defined today in Germany. The products from the thin-film evaporation process are very similar to those from the ROBE-system concerning density and humidity. Products from the spray drying process and the fluidized bed drying andmore » granulation process are different. Mobile plants must fulfill certain geometric conditions (e.g. transportation in 20 feet-containers). Maximum heights and masses are also restricted due to the working situation in nuclear power plants. First concepts have been developed and will undergo further review.« less