Liquid radioactive waste treatment, membrane

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

MEMBRANE PROCESSES EMPLOYED FOR LIQUID RADIOACTIVE WASTE TREATMENT... 

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. 

Chmielewski, A.G., Harasimowicz, M., and Zakrzewska-Trznadel, G., Membrane technologies for liquid radioactive waste treatment, Czech. J. Phys., 49, 979, 1999. 

G.Zakrzewska-Trznadel,M.Harasimowicz,A.G.Chmielewski, Membrane processes in nuclear technology-application for liquid radioactive waste treatment, Sep. Purif. Technol. 2(23), 2001, 617-625. 

Direct contact membrane distillation (DCMD) is an effective process applied for the concentration of dissolved matter in water solutions. The process can be considered a feasible method for liquid radioactive waste treatment and, in some cases, it can effectively serve in reducing the hazard connected with its toxicity. 

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. 

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 Methods for the Treatment of Liquid Radioactive Waste.666... 

MEMBRANE METHODS FOR THE TREATMENT OF LIQUID RADIOACTIVE WASTE... 

FIGURE 25.12 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 J. Membr. Sci., 225, Zakrzewska-Trznadel, G., Radioactive solutions treatment by hybrid complexation—UF/NF process, 25-39, Copyright 2003, with permission from Elsevier.)... 

There are many methods used for liquid radioactive waste (LRW) treatment, including chemical precipitation, sedimentation, ion exchange, evaporation, biological methods [7,8], and membrane permeation. The relative costs of all separation processes are an important criterion in the selection of a treatment process. For example, Figure 26.1 shows the relative costs of some desalination technologies as a... 

G. Zakrzewska-Tiznadel, Advances in membrane technologies for the treatment of liquid radioactive waste. Desalination 321, 2013,119-130. 

G. Zakrzewska-Trznadel, M. Harasimowicz, A. Miskiewicz, A. Jaworska-Sobczak, Liquid low-level radioactive waste treatment by membrane processes. Mater. Res. Soc. Symp. Proc. 1475, 2012, 623-628. 

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. 

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. 

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... 

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. 

Some research groups worldwide are currently working on the application of membrane technology to the treatment of radioactive liquid wastes with different levels of activity, from low to high activity waste. Research is mainly focused on wastes from the nuclear industry. However, the nuclear industry is not the only source of radioactive wastes medical and research applications of radioisotopes also generate radioactive wastes. 

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. 

Amal JM, Sancho M, Campayo JM, Villaescusa JI, and Verdii G. Cs-137 Radioactive Liquid Wastes Treatment using Membrane Techniques. 10th International Congress of the International Radiation Protection Association, Hiroshima, May 14—19, 2000. 

Vicens and coworkers (Chapter 26) report the use of novel calix-fcw-crown ether compounds as carriers in a supported liquid membrane system for the removal of cesium from nuclear waste water. Decontamination factors of greater than 20 are obtained in the treatment of synthetic acidic radioactive wastes. Very good stability (over 50 days) and high decontamination yields are achieved. 

Calix[4]-W5-crowns 1-7 are used as selective cesium-carriers in supported liquid membranes (SLMs). Application of the D esi diffusional model allows the transport isotherms of trace level Cs through SLMs (containing calix[4]-6/5-crowns) to be determined as a function of the ionic concentration of the aqueous feed solutions. Compound 5 appears to be much more efficient than mixtures of crown ethers and acidic exchangers, especially in very acidic media. Decontamination factors greater than 20 are obtained in the treatment of synthetic acidic radioactive wastes. Permeability coefficient measurements are conducted for repetitive transport experiments in order to determine the SMLs stability with time. Very good results (over 50 days of stability) and high decontamination yields are observed with l,3-calfac[4]-Aw-crowns 5 and 6. 

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