RECENT APPROACH IN TREATMENT OF LIQUID RADIOACTIVE WASTE: MEMBRANE METHODS
	
Grazyna Zakrzewska-Trznadel

Institute of Nuclear Chemistry and Technology
Dorodna 16, 03-195 Warsaw, Poland

The fuel cycle produces different types of radioactive waste. Radioactive waste is also generated during production and application of radioisotopes, as well as during processing of raw materials containing naturally occurring radioactive isotopes. All those wastes have to be treated and conditioned before safe storage or disposal to protect the human health and natural environment. The management of radioactive waste has to be reached with reasonable cost by implementing appropriate technologies. The processing requirements depend on the level of radioactivity and chemical and physical properties of the waste streams. Various methods are used to treat aqueous radioactive wastes, including evaporation, chemical precipitation  and ion exchange, as well as less developed solvent extraction, biotechnological processes and membrane methods. Although membrane processes are still considered as novel technologies in the field of radioactive waste treatment, many applications in nuclear centres and laboratories around the world are reported.
	At Department of Nuclear Methods of Process Engineering, Institute of Nuclear Chemistry and Technology, for many years membrane techniques are studied and considered as a possible application in radioactive wastes processing field. After some years of research reverse osmosis was applied at Institute of Atomic Energy (Department of Radioactive Waste Treatment) processing the radioactive wastes from all of Poland. The 3-stage RO plant supplements the existing waste processing system based on evaporator giving the possibility of initial concentration of liquid waste or final polishing of the condensate after evaporation. 
Intensive studies on ultrafiltration (UF) enhanced by sorption on different sorbents or complexation with chelating polymers are carried on. The ceramic membranes made from alumina, titania and zirconia are used in experiments. Such membranes show high chemical, temperature and radiation resistance. They have good stability with a contact of radioactive solutions and they can operate in full pH range. Easiness of washing with alkaline and acidic solutions allow long and stable membrane work. The hybrid UF/complexation process allows the purification of the waste, as well as selective separation of some specific compounds present in the solution.
	Thermal process, namely membrane distillation (MD) with use of resistant, porous membranes manufactured from PTFE was proposed and tested for radioactive waste concentration. The results collected in laboratory and in pilot plant experiments allowed to consider the process usable for small installations operated with utilization of cheap energy sources or waste heat. The method is characterized by high decontamination factors and big volume reduction; distillate produced in one-stage process has a purity sufficient for safe discharge to the environment.
	The paper refers to the study on these membrane methods, giving the comparison with commonly used conventional methods of liquid radioactive waste processing.