Membrane processes in nuclear technology-application for liquid radioactive waste treatment

Abstract

Membrane methods can be considered as the most energy-saving separation techniques. Separation abilities of membranes allow the elimination of many non-effective and energy consuming methods and their replacement by new, modern technologies, friendly environment friendly. An application of membrane methods for liquid radioactive wastes treatment requires solving many problems connected with the proper selection of the membranes, membrane modules and other equipment according local conditions: chemical and radiochemical composition of the effluents treated, their activity and total salinity. The installations working in nuclear industry have to fulfil very strict requirements. They ought to be reliable, constructed from special materials defined by separate regulations. Only small number of manufacturers of membrane devices has for their products the certificates of International Atomic Energy Agency. Reverse osmosis (RO) as a method for liquid waste treatment has been examined at laboratory and pilot plant installations. The experience with the process led to design and construction of the industrial plant, 1 m3 capacity, composed of three RO stages. The plant will be included into the system for liquid radioactive wastes purification operating at Institute of Atomic Energy in Swierk near Warsaw, treating the liquid waste from all of Poland. Membrane distillation (MD) can be an alternative for liquid radioactive waste concentration. On the basis of previous laboratory tests a pilot plant for liquid radioactive wastes concentration employing direct contact MD was constructed. Pilot plant experiments showed MD is interesting solution for liquid low-level radioactive waste treatment. As MD is characterised by high retention, large decontamination factors were obtained in separation of radionuclides, which are present in liquid low-level radioactive wastes mainly in an ionic form. The RO and MD plants for liquid low level radioactive wastes treatment are presented in the paper and the evaluation of both methods, as well.