ITER TOKAMAK COOLING WATER SYSTEM: MANAGEMENT OF POWDERED RESINS AS RADWASTE IN FRANCE

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1 ITER TOKAMAK COOLING WATER SYSTEM: MANAGEMENT OF POWDERED RESINS AS RADWASTE IN FRANCE G. Genard 1, C. Angulo 1, A. Petrov 2, S. Vanderperre 1 1 Tractebel Engineering, Avenue Ariane 7, B-1200 Brussels, Belgium 2 Oak Ridge National Laboratory, Oak Ridge 37831, USA gilles.genard@gdfsuez.com INTRODUCTION The ITER project [1] is a scientific experiment aiming to prove that fusion is a viable energy source for the future. It is currently under construction in Cadarache (Southern France). A global collaboration has been formed to test the feasibility of ITER. The seven major members of the ITER Organization (China, European Union, India, Japan, South Korea, Russia and the United States) have all created Domestic Agencies. Among other duties, US-ITER [2], the American Domestic Agency, is in charge of designing, procuring, and delivering the Tokamak Cooling Water System (TCWS) components to France for installation in the ITER facility. Major subsystems of the TCWS are the Chemical and Volume Control System (CVCS) units, dedicated to particular Primary Heat Transfer Systems (PHTS) [3]. Some of the functions of the CVCS are: To remove soluble and insoluble species from PHTS water; To purify draining and refilling tanks and loops. To cope with these two functions, several mechanical filters and ion exchangers are necessary. The precoat filter/demineralizer technique has been one of the potential methods considered to treat the contaminated water. By using this technique, radioactive powdered resins would be produced during operation of ITER and should be handled properly as radwaste in agreement with local regulations. In this paper, we will first provide details about the precoat filter/demineralizer technique and the properties of the powdered resins. We will also present in a general way the procedure to be followed to obtain the agreement of the French authorities and the possible treatments of the radioactive resins in order to allow their final disposal in France. THE PRECOAT FILTER/DEMINERALIZER TECHNIQUE PRINCIPLE The filtration and demineralization of the contaminated water of the ITER TCWS circuits can be performed in different ways and with different techniques. The precoat filter/demineralizer technique is based on a system consisting of filter elements whose septum is coated with a thin layer of powdered resins (cationic and anionic) and inert fibers mixture [4]. Fig. 1 illustrates such a system. In addition of a smaller space required, this technique provides a better filtration and a kinetically superior ion exchange than deep bed polishers but, on the other hand, a lower capacity for the removal of ionic impurities. Fig. 1 Principle of a (bottom) precoat filter/demineralizer system Source: Graver Water Systems Inc, Cranford, NJ USA In functional conditions, strainers can be foreseen at the end of the condensate polishing vessel in order to avoid precoat media ingress into the system. Combination designs can also be met, e.g. a precoat filter/demineralizer placed before a mixed bed exchanger to protect it from crud. The tubular septa elements of the filter in the vessel are usually wound yarn or plastic or metal wire. The layer of powdered resin on the septa ranges from 3 to 10 mm thick. As the filter/demineralizer technique is less effective in its demineralizing function than more conventional ion exchangers, it is necessary to frequently change the demineralization elements. This is performed by applying a new coating, after having removed the spent resins, in order to ensure long service life for the septa elements. For the removal, air and water are passed through the filter elements, in the reverse direction than the functional one. In this manner, the only waste that is produced is coming from

2 the used powdered resins within the backwash water. A separation can possibly be applied afterwards. As a result, the powdered resins within the backwash water constitute a radwaste to be treated. POWDERED RESINS In case of use of powdered resin for the ITER TCWS, the Powdex resin, which is a Graver Technologies product, would probably be chosen. Different types of products are available: Cationic resins: H +, NH4 +, Na +, Morpholinium; Anionic resins: OH -, Cl -. One can also find the Powdex Premix which consists in a mixture of both types with several possible anionic to cationic resin ratios. The matrix of all these resins is a styrene- or an acrylic-divinylbenzene gel, which is an organic material. No fibers are added. The other properties are, depending of a particular product: The average particle size: about µm (according to [4]); The ionic conversion: 95-99%; The moisture percentage: 40-75%; The total capacity: meq/dry g and meq/dry g (milliequivalents per dry gram) for the Powdex and Powdex Premix, respectively. Some advantages of powdered resin, compared to more conventional bead resins are: Less space required; Lower pressure drop; Lower capital cost; Faster unit start-up time; Better removal of organics; The fact that the resin composition can be varied to meet changing conditions. WASTE ACCEPTANCE CRITERIA As stated above, the powdered resins are radwaste products that must be handled properly and conducted to disposal in their final state (after needed transformation or treatment). Due to the properties of the type of radwaste taken into account in this context, the final repository should be the Disposal facility for short-lived low and intermediate level radioactive waste (CSFMA) at Soulaines (Aube, France Fig. 2). As a new radioactive waste Operator, the future ITER Operator should thus implement a qualified process and, thereafter, obtain an agreement from ANDRA, the French Radioactive Waste Management Agency. This means that some performance tests should be carried out and some documents provided. Based on the current return of experience, such a qualification procedure may take four to five years. Fig. 2 The Disposal facility for short-lived low and intermediate level radioactive waste of Soulaines Source: ANDRA GENERAL REQUIREMENTS Some common requirements related to the qualification procedure of the Powdex resin should also be complied with and are outlined in the following in a very general way. Regulatory requirements French decree of 16 April 2008 provides a legal basis for the disposal of radioactive waste and includes, among others, a scheme for waste classification as applied in France. For each nuclear activity, the French Autorité de Sûreté Nucléaire (ASN) has issued fundamental safety rules. The fundamental safety rules applicable for solid waste to be disposed of in a surface repository are developed in Conditions relatives à l agrément des colis de déchets radioactifs solides destinés à être stockés en surface (rule III.2.e). Regulations are in constant evolution, due to increasing knowledge about and experience with radioactive waste and disposal facilities. The implementation of the process must comply with the latest regulations in force. Documentation requirements Acceptance is required for each waste treatment process. Documentation requirements are needed in the process implementation and in the production phase as well. In the process implementation phase and in order to provide a structured file, a step by step approach, which requires regular interaction between the Operator and ANDRA, is necessary: Preliminary exchanges between ANDRA and Operator; Kick-off meeting; Identification of the relevant parameters and the necessary studies; Characterization program, consisting of the necessary tests, calculations and studies, with a follow-up of the execution of the tests by ANDRA;

3 Production of the summary documents; Follow-up of the first production campaign by ANDRA; Acceptance by ANDRA. In the production phase, the waste package file and the record keeping of waste package characteristics are needed. Here, the main objective is to ensure the traceability of the waste package. The Operator can reach this aim by declaring its physical, chemical and radiological characteristics. In view of demonstrating that the critical parameters do not exceed the acceptance levels, performance tests are executed during the production phase and the results of these performance tests are recorded in the waste package file. They can be mandatory for each produced waste package or performed only on a sample part. The Operator has to implement technical tools (hardware and software) to perform these performance tests. Additionally, to establish the waste package file, the Operator has to develop organizational tools (process sheets, template of the file). Finally, in case of use of a mobile waste treatment system directly on the site, a specific responsibility structure has to be applied. On the one hand, the Operator is responsible for the overall process: i) taking care of the compliance of the non conditioned waste with the requirements (limits) of the waste treatment system, ii) the set-up of the waste package file, and iii) the further handling and follow-up. On the other hand, the service provider (owner and operator of the mobile waste treatment system) is responsible for providing the documentation for the acceptance of the waste treatment process and for the measurement and the recording of the process parameters needed for the set-up of the waste package file. REQUIREMENTS FOR WASTE AND WASTE PACKAGES In addition, it is mandatory to comply with the different technical specifications issued by ANDRA. These specifications are directly related to the waste or waste package for which the agreement is asked. They are dealing with: General requirements; Radiological requirements; Specific requirements with criteria on e.g. mechanical characteristics or water content; Specific requirements for waste packages that need additional treatment at the CSFMA; Requirements for labeling of waste. WASTE TREATMENT AND CONDITIONING PROCESSES In France, the waste conditioning is usually necessary. In the case of radioactive powdered resins, this implies to confine the radioactivity by embedding. This technique consists in casting a matrix inside a container (concrete cask, metallic drum ) with the waste mixed as homogeneously as possible (depending on the type of waste). Different matrixes can be considered. After considering the possible pretreatments, the opportunity to use each of these matrixes with powdered resins is evaluated. PRETREATMENT Prior to the embedding, a pretreatment consisting in the separation of the resins from the backwash water may be needed, depending on the kind of final treatment. According to a note about radioactive waste management at nuclear power plants from the IAEA [5], four main technical processes are available for treatment of liquid waste, among which the chemical precipitation/flocculation and the ion exchange that cannot be applied in this specific case. A third process is the evaporation technique that enables to remove the water in the vapor phase, leaving behind the non-volatile components such as the salts or the dry part of the resins in the form of pellets that have to be treated thereafter. The last possible technique is the solid-phase separation technique that consists in a direct separation of the resin from the liquid and then obtaining a wet waste. The draining can be based on the centrifugation principle that allows the segregation of the powdered resins in function of their diameter, which is appreciable for some conditioning techniques. If one wants to use strainers (or filters), one has to bear in mind the size of the powdered resin. Indeed, the filter mesh ought to be very small to ensure a perfect separation. Up to now, some filter cartridges present a performance scale down to 1 µm or even 0.1 µm thanks to nanofiber filter media, as visible in Fig. 3. In addition, due to the small size of the resins and of the mesh, the flow of the water can rapidly be blocked. In the ITER TWCS context, two types of radioactive waste to be processed would then be arising: the spent powdered resin in the backwash water and the spent powdered resin separated as a solid waste (dry or wet).

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5 It is also to be noted that for this technique, the resins must be stored underwater, which means that no separation should be performed. EMBEDDING WITH GÉOPOLYMÈRE Another matrix is the Géopolymère. This process uses the geopolymerization which is an alternative technical solution for the effective stabilization and immobilization of toxic and radioactive materials. Geopolymerization is a reaction that chemically integrates minerals and that involves silico-aluminates [7]. An example of the structure of such a compound is shown in Fig. 6. Though not tested to condition resins, this matrix has proven its structural stability and the safe chemical encapsulation for sludge containing radionuclides. Fig. 6 Example of structural framework of the Géopolymère [7] Although it seems that the size of the resins should not be a concern, a dedicated feasibility study is also necessary for ANDRA to accept this type of conditioning matrix. The spent powdered resins could be provided in water and the type of Géopolymère should be adapted to this specificity. INCINERATION In this technique, the radioactive waste is incinerated and, thereafter, the remaining material must be conditioned. This provides eventually a very interesting volume reduction factor (10 to 20). In France, the CENTRACO unit, owned by SOCODEI (Fig. 7), is designed to process shortlived low-level radioactive combustible solid and liquid waste, including ion exchangers and filters. The resulting waste (incineration ashes and clinker) is sent back to the customer after conditioning with a hydraulic binder in 400 liter shielded metallic drums. The accepted waste is of low level activity with the limits of 2.0x10 4 Bq/g, 3.7x10 2 Bq/g and 5.0x10 1 Bq/g for βγ emitters, α emitters in solid form and in liquid form, respectively. In the near future, an additional specific limit of 2.0x10 4 Bq/g for tritium will appear, whereas, currently, it is included in the βγ emitters (limits will then be less stringent). Fig. 7 The melting furnace of CENTRACO Source: SOCODEI Liquids are an acceptable waste form but the incineration is absolutely not applicable to backwash water (not a combustible liquid) and the separation is then mandatory. DISCUSSION Each of these treatment techniques presents pros and cons but none of them could be declared as totally applicable without any preliminary experimental investigations. The embedding with hydraulic binder seems to be achievable without any further study than the performance tests to get the agreement. Indeed, the THOR process is already mastered with types of waste that could possibly be compared to the powdered resins and even with larger resins. Anyway, a feasibility study is still mandatory. The existing treatment unit based at about 100 km from the ITER site could be used for the feasibility tests and the treatment during operation. If the Mercure unit is taken as a reference, the embedding with polymer requires that the waste be sent in water. A feasibility study should be envisaged due to the size of the resins. With this technique, no separation from the backwash water should be foreseen. The use of the geopolymer technology in order to embed the spent powdered resins is very challenging. Indeed, this constitutes a new technology which, nevertheless, has already proven its quality and efficiency in the solidification of different (radioactive) waste. The feasibility of applying it to Powdex should be the scope of a particular study in the R&D program of the Geopolymer Institute. The separation of the resins from the backwash water is not compulsory and hence no filtration system should be foreseen. Incineration could be a good alternative. After having carried out the separation of the resins and the backwash water, the waste could be

6 handled up to the conditioning (embedded with hydraulic binder in 400-liter drums) by CENTRACO, although the radiological criteria to accept the waste for incineration are very stringent. Moreover, it is interesting to note that, both in the USA and in Sweden, no embedding is carried out before the storage of the powdered resins in tanks. Finally, according to US experts of Powdex treatment, the polymer encapsulation and cementation may not work. For the future, it could be worth investigating on which experience or facts this important conclusion is based. CONCLUSION So far in France, powdered resins have been neither used nor treated. Thus, if the precoat filter/demineralizer technique was chosen to purify the ITER TCWS, in addition of the necessary actions to perform in order to receive the acceptance by ANDRA for the treatment and disposal of such a waste, the future ITER Operator would first have to perform feasibility studies to determine the more suitable conditioning process to apply to the spent powdered resins. Based on the used powdered resins characteristics, the advantages and drawbacks of each potential process should be evaluated by the US-ITER team in function of more functional parameters. REFERENCES [1] [2] [3] Nuclear Chemistry of Water-Cooled Fusion Reactors: Issues and Solutions, A. Petrov and J. Flanagan, Proceedings of the Nuclear Plant Chemistry Conference 2010, October 3-8, 2010, Quebec City, Canada, CNS, [4] Condensate Polishing Guidelines for Fossil Plants, EPRI Technical Report, March [5] Radioactive waste management at nuclear power plants, An overview of the types of low- and intermediate-level wastes and how they are handled, V.M. Efremenkov, IAEA Bulletin, 4/1989, 37. [6] N. Moriyama, S. Dojiri, T. Honda, Solidification of powdered ion exchange resins with polyethylene, Nuclear and Chemical Waste Management, 3 (1982) [7] E. Hermann, C. Kunze, R. Gatzweiler, G. Kiessig, J. Davidovits, Solidification of various radioactive residues by Géopolymère with special emphasis on long-term stability, Géopolymère '99 Proceedings.