Radioactive wastes membrane processes

Cell harvesters were developed to capture multiple samples of cells on membrane filters, wash away unincorporated isotopes, and prepare samples for liquid scintillation counting on special equipment developed to process and count multiple samples. Despite miniaturization and improvements in efficiency of this technique, the disadvantages of multiple liquid handling steps and increasing costs for disposal of radioactive waste materials severely limit its usefulness. Although specific applications require measuring DNA synthesis as a marker for cell proliferation, much better choices are available for detecting viable cell number for HTS. 

Gumming, I.W., and A.D. Turner, 1989, Optimization of an UF pilot plant for the treatment of radioactive waste, in Future Industrial Prospects of Membrane Processes (L. Cecille and J.C. Toussaint, Eds.), Elsevier Applied Sci., London, U.K., p. 163. 

Calcinm glectrowinning in piutniiium production. A potential application of inorganic membranes in radioactive waste treatment is in the industrially practiced direct oxide reduction process. In this process plutonium oxide is calciothermit y reduced to plutonium in the presence of calcium chloride according to the following reaction ... 

Mishra, B., D.L. Olson and P.D. Ferro, 1994, Application of ceramic membranes in molten salt processing of radioactive wastes, in Proc. 123rd Ann. Meeting of Minerals, Metals, and Mater. Soc., San Francisco, USA, p. 233. 

It has been demonstrated that membrane separation processes can be successfully used in the removal of radioactive substances, with some distinct advantages over conventional processes. Following the development of suitable membrane materials and their long-term verification in conventional water purification, membrane processes have been adopted by the nuclear industry as a viable alternative for the treatment of radioactive liquid wastes [1]. In most applications, membrane processes are used as one or more of the treatment steps in complex waste treatment systems, which combine both conventional and membrane treatment technologies. These combined systems have proved more efficient and effective for similar tasks than conventional methods alone. 

This section aims to explain the unique features of membrane separation methods, their superior performance in contaminant removal, and their operational sensitivities and limitations. We focus particularly on the factors that need to be carefully assessed when the membrane technology to be used in the treatment of liquid radioactive waste is being considered. These include membrane configuration and arrangement, process application, operational experience, data related to key performance parameters, and plant and organizational impacts. 

IAEA Technical Reports Series No. 431. 2005. Application of Membrane Technologies for Liquid Radioactive Waste Processing, pp. 1-145. Consultants Pabby A.K., Kohout R. (Canada), and TapseU G. (AustraUa) [http /www.iaea.org/Publications/index.html]. 

Among the disadvantages, the fouling and degradation of membrane surfaces of the polymeric membrane systems under adverse chemical and thermal conditions are often cited. However, these problems may be partly overcome by proper pretreatment of the effluents, optimizing the process variables and selecting suitable membrane materials. The radioactive wastes most suited for membrane separation are characterized by chemically insignificant amounts of radionuclides and small amounts (few hundred parts per rnilhon) of inactive ionic species. 

For radioactive effluent treatment, the relevant membrane processes are microfiltration, ulfrafiltration (UF), reverse osmosis, electrodialysis, diffusion, and Donnan dialysis and liquid membrane processes and they can be used either alone or in conjunction with any of the conventional processes. The actual process selected would depend on the physical, physicochemical, and radiochemical nature of the effluents. The basic factors which help in the design of an appropriate system are permeate quality, decontamination, and VRFs, disposal methods available for secondary wastes generated, and the permeate. 

Radioactive waste treatment applications have been reported [3-9] for the laundry wastes from nuclear power plants and mixed laboratory wastes. Another interesting application of reverse osmosis process is in decontamination of boric acid wastes from pressurized heavy water reactors (PHWRs), which allows for the recovery of boric acid, by using the fact that the latter is relatively undissociated and hence wdl pass with water through the membrane while most of the radioactivity is retained [10]. Reverse osmosis was evaluated for treating fuel storage pool water, and for low-level liquid effluents from reprocessing plants. 

Membrane Processes Employed for Liquid Radioactive Waste Treatment.850... 

Liquid Radioactive Waste Processing by Membrane Processes Advantages and Limitations.872... 

Radiation resistance of the material used as well as commercial availability of the membrane units and auxiliary equipment, process competitiveness in comparison with conventional methods, its economics and feasibdity are important criteria for application of the membranes for radioactive waste processing. 

Two systems for radiological control are required in case of membrane plant for radioactive waste processing first, for process control and the second, for securing the staff and for avoiding the spread of contamination. The latter usually exists if the... 

For the treatment of conventional, nonradioactive liquid waste the predicted lifetime of membranes is 4—5 years. The effective lifetime depends on the conditions in which the membrane is used the characteristics of solutions treated, pressure, and temperature. While selecting the membrane for radioactive waste processing, one has to remember about its resistance and... 

Spent membranes and membrane cartridges do not undergo regeneration they are treated as a solid radioactive waste. They can be stored for decay or processed as other solid waste material. 

MEMBRANE PROCESSES EMPLOYED FOR LIQUID RADIOACTIVE WASTE TREATMENT... 

The RO process was implemented at the Institute of Atomic Energy, Swierk. The wastes collected there, from all users of nuclear materials in Poland, have to be processed before safe disposal. Until 1990 the wastes were treated by chemical methods that sometimes did not ensure sufficient decontamination. To reach the discharge standards the system of radioactive waste treatment was modernized. A new evaporator integrated with membrane installation replaced old technology based on chemical precipitation with sorption on inorganic sorbents. Two installations, EV and 3RO, can operate simultaneously or separately. The membrane plant is applied for initial concentration of the waste before the evaporator. It may be also used for final cleaning of the distillate, depending on actual needs. The need for additional distillate purification is necessitated due to entrainment of radionuclides with droplets or with the volatile radioactive compounds, which are carried over. 

FIGURE 30.12 Decontamination of the sample of liquid radioactive waste in UF/complexation process with a use of different complexing agents, CeRam Inside membrane, 15 kDa. (Reprinted from Zakrzewska-Trznadel, G., J. Membr. Sci., 225, 25, 2003. Copyright [2003] with permission from Elsevier.)... 

The process conducted in batch-type counter-flow apparatus (Figure 30.17) equipped with capillary PP Acccurel membranes showed good effectiveness of membrane distillation for purification of radioactive waste. Permeate obtained was pure water. All solutes together with radioactive compounds were rejected by the hydrophobic membrane. At tenfold volume reduction of the initial portion of waste, approximately tenfold concentration of radioactivity in the retentate stream was reached, while radioactivity of permeate retained on the level of namral background (Figure 30.18). As was observed in experiments small sorption in the system took place. However, permeate was free of radioactive substances and other dissolved compounds, the concentration and radioactivity factors sometimes slightly differed from volume reduction factors. 

In Table 30.15, decontamination factors for different processes for low- and medium-level radioactive waste treatment are shown. Membrane distillation with its high decontamination factors is a competitive method in this field. However, it has to be mentioned that these high-decontamination factors are achieved from low-volatile solute after adequate pretreatment. 

Membrane distillation modules are at present expensive in comparison with RO elements and their costs influence significantly the capital costs of the MD installations. The market of MD systems is limited in spite of the many advantages MD method is not widely accepted by the industry. Moderate interest of users influences the production capacities and in consequence reduces the wide implementation of the MD method in different branches of industry. It was proved that advantages of MD decreases with increase of the installation capacity big installations, of productivity comparable with RO, need large number of modules. Anyway, the comparison of two processes RO and MD proved technical and economic reasonability of the letter in some cases, such as radioactive waste concentration. The advantages of MD come from... 

Despite of some technical and process limitations, membrane techniques are very useful methods for the treatment of different types of effluents. They can be applied in nuclear centers processing low- and intermediate-level liquid radioactive wastes or in fuel reprocessing plants. All the methods reported in the chapter have many advantages and can be easily adapted for actual, specific needs. Some of them are good pretreatment methods the other can be used separately as final cleaning steps, or can be integrated with other processes. Membrane methods can supplement or replace techniques of distillation, extraction, adsorption, ion exchange, etc. Evaluation of membrane processes employed for liquid radioactive waste treatment is presented in Table 30.17. 

International Atomic Energy Agency, Application of Membrane Technologies for Liquid Radioactive Waste Processing, Technical Report Series No. 431, IAEA, Vienna, 2004. 

Zakrzewska-Trznadel, G., Harasimowicz, M., and Chmielewski, A.G., Membrane processes in nuclear technology—appUcation for fiquid radioactive waste treatment, Sep. Purif. Technol., 22-23, 617, 2001. 

Some areas of application are the nuclear industry and the treatment of radioactive liquid wastes, with two main purposes reduction in the waste volume for further disposal, and reuse of decontaminated water. Pressure-driven membrane processes (microfiltration, ultrafiltration, nanofiltration, and reverse osmosis [RO]) are widely used for the treatment of radioactive waste. 

Since 1995, the Chemical and Nuclear Engineering Department of the Polytechnic University of Valencia in Spain has been working on the application of membrane technology to the treatment of low and medium level radioactive liquid wastes. In this chapter, we describe two practical cases of radioactive liquid waste treatment using membrane processes the treatment of Cs-contaminated water generated after a radioactive incident in a stainless steel production factory, and the treatment of 1 liquid wastes from nuclear medicine services at hospitals. 

This section describes some case studies carried out by the authors, which are related to radioactive liquid waste treatment using membrane processes a study about the influence of radiation on reverse osmosis membranes, a practical case about concentration of I radioactive liquid wastes by ultrafiltration and reverse osmosis processes, and a practical experience about decontamination of Cs liquid waste by reverse osmosis, including a study of radiological protection during the treatment. 

Membrane technologies have a great potential in the treatment of radioactive liquid wastes, as it has been proved throughout this chapter. In this sense, it is expected a growing use of the membrane processes in the radioactive field, with different possibilities alone, combined between them (microfiltration or ultrafiltration and reverse osmosis) or combined with other conventional processes like evaporation or ion exchange. Furthermore, some special membrane processes, like membrane distillation or liquid membranes, could be applied for the specific treatment of radioactive wastes. 

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