Waste streams, radionuclides removal

Chemical treatment is a weU-proven technique and is less expensive. Generally, specific chemical precipitation is carried out in situ in big tanks holding the radioactive waste stream to remove radionuclides while permitting nonradioactive ions to be released in the effluent from the process. The radionuchdes present in the waste are precipitated, co-precipitated, carrier precipitated, or adsorbed by insoluble compounds. A clariflocculator is used for flocculation and clarification. This technique is used as a batch or a semibatch process for large volumes of effluents containing only low concentrations of activity. It provides lower DF values (10-100) than evaporation. 

ADTECHS Corporation (ADTECHS) has developed the radionuclides separation (RASEP) process for the removal and stabilization of radionuclides from liquid waste streams. The process uses filtration, selective adsorption, and electrodeposition fixation followed by cement sohdifi-cation. According to the vendor, the technology is commercially available. 

Although META-LOCK removes radionuclides from contaminated media, it produces a secondary waste stream. The product sludge is radioactive and must be handled and disposed of accordingly. Other additives may be required to process certain contaminants. META-LOCK does not destroy microorganisms. 

This technology can treat both acidic and basic solutions. It has the ability to remove organics, inorganics, radionuclides, and heavy metals from contaminated aqueous streams and is capable of treating process wastes and mixed wastes as well. 

Scientists at PNNL have developed an automated radiochemical sample preparation-separation-detection system for the determination of total "Tc in nuclear-waste process streams.46 85 86 144145 This analyzer was designed to support a technetium removal process planned as part of the development of a nuclear-waste processing plant. The process stream composition is both complex and variable, with a high pH, high salt matrix. Depending on the source of the feed, the total base content, the concentration of organics, and complexant concentrations will vary, as will the aluminum, nitrate, nitrite, dichromate, and radionuclide composition. 

Since 1966 the basin has been operated as a closed system. The basin water is continuously recycled through a diatomaceous earth filter, and no contaminated water is released to ground. Makeup water is added to the basin by spraying casks as a part of the cask decontamination procedure. The water level is controlled by adding additional water to the basin if needed, or by purging a small stream from the basin to the plant waste evaporator. An increase in the concentration of radionuclides and dissolved solids in the water has occurred as a result of the recycle process. Consequently, a plant-scale ion-exchange unit was installed in July 1973, based on the results of laboratory studies, to remove radionuclides from the basin water. The fuel storage basin water at that time had the approximate chemical and radiochemical composition shown in Table I. 

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