Radioactive Waste Management For The Ignitor Nuclear Fusion Experiment

Transcription

1 Radioactive Waste Management For The Ignitor Nuclear Fusion Experiment M. Zucchetti, A. Ciampichetti DENER, Politecnico di Torino Corso Duca degli Abruzzi, Torino (Italy) Abstract - Ignitor is a nuclear fusion reactor aimed at studying Deuterium-Tritium plasmas. We have applied the Italian waste management regulations to the IGNITOR experiment radioactive materials: none of them should be classified in the High Level Waste category and most materials are classified as LLW (Low Level Waste). If European proposed waste management strategies were applied, all Ignitor radioactive materials could be recycled. INTRODUCTION In the frame of the IEA Co-operative Program on the Environmental, Safety and Economic Aspects of Fusion Power, a collaborative study of fusion radioactive waste has been set up [1]. The main goal of this activity is the definition of waste management strategies for fusion experiments and reactors. In this paper, we have applied the Italian waste management regulations to the IGNITOR experiment radioactive materials, and compared the results to those obtained applying instead a waste management strategy proposed by the European Union in the frame of the abovequoted collaborative study. FUSION RADIOACTIVE WASTE MANAGEMENT Most radioactive waste generated from fusion reactors will be activated solid metallic material from the main machine components. Some component will also have surface contamination including tritium. The dominating waste stream is generated in the decommissioning stage, while - for fission spent fuel is the main issue. A great deal of the decommissioning waste has a very low activity concentration, especially when a long period of intermediate decay is anticipated. Radioactive nuclides in fusion waste are mainly metallic activation products and tritium. Therefore, fusion waste is quite different from fission waste, both in type of material and isotopic composition: fusion waste does not include plutonium, fission products, transuranics and normally no alpha-emitting nuclides, and it is generally shorter-lived than fission waste. In most countries with a nuclear program, the waste management strategies are based on deep geological disposal of High_level Waste (HLW), while a less sophisticated disposal method, mostly a near-surface type repository, is used for Low-Level or Intermediate-Level Waste (LLW/ILW) [2]. An example of application of a national fissionoriented regulation to fusion is given in the following: it concerns the siting of the IGNITOR fusion experimental reactor in Italy.. THE IGNITOR REACTOR AND ITS SITING Ignitor is a proposed compact high-magnetic field tokamak aimed at studying plasma burning conditions in Deuterium-Tritium plasmas [3]. Ignitor has a major radius of 1.3 m, minor radii of 0.47 m and 0.87 m, a peak plasma temperature of 12 kev, a peak plasma density of ions/m 3, at a maximum fusion power of 90 MW. Pulses at different power levels are planned, with either DD or DT operation, distributed over a global operation time of 10 calendar years. The tokamak main components are: a graphite first wall (volume: 2 m 3 ), an INCONEL625 vacuum vessel (4.4 m 3 ), the Cu-based toroidal magnets (12.2 m 3 ), and the AISI316 machine structure (named "C-Clamp, 24 m 3 ).The IGNITOR experimental reactor operation lifetime will be divided into two phases: in the second one, tritium and neutron activated materials will be present, however quite moderately.

2 Safety assessments and siting evaluations were performed for this site, which excellent results in terms of extremely low environmental impact [4-6]. Recently, due to several technical reasons, it was identified a new site, the ENEL TERNA plant in Rondissone (Italy). The two sites are only a few kilometers distant each other. Figure 1 Core of the IGNITOR Tokamak Localisation of this experimental reactor in Italy has seen growing attention during the last years. The determination to carry out this project in Italy has driven to taking into account several candidate sites. In the nineties, a proposed site concerned the EUREX plant in Saluggia (Italy), a place that fully fitted all requirements for a nuclear installation. Preliminary Safety Report preparation activities for the siting of Ignitor in Rondissone are currently under way [7]. Ignitor main safety requirements are the following: The Ignitor experiment must protect the health and safety of the facility personnel and of the public, by mantaining an effective defense against hazards, IGNITOR must maintain an operation that is environmentally acceptable to present and future generations, and to satisfy the two basic requirements for environmental feasibility of fusion: 1. No need of public evacuation in case of the worst accident 2. No production of waste that could be a burden for future generations, i.e., minimisation of the production of longlived radwaste Finally the experiment must be such to be easily sited in Italy, according both to international and to that country s regulations The question concerning radioactive waste production and classification will be addressed in this paper for IGNITOR, according to Italian regulations. WASTE MANAGEMENT FOR IGNITOR Figure 2 Proposed IGNITOR site in Italy We will briefly report here the result of the application of Italian waste management regulations to Ignitor. Italian regulations deal with National Laws on radioactive materials [8], and with Technical Guides from the Italian nuclear regulatory committee ( Guida Tecnica 26 and others [9]). Wastes are classified into three categories ( I Categoria = First category = Very Low Level Waste, II Categoria = Second Category = Low Level Waste, III Categoria = Third Category = High Level

3 Waste) according to concentration limits for radionuclides. Without going into detail, the boundary between second and third category, for activated metallic materials, is a concentration of 3700 Bq/g for long-lived nuclides (T ½ > 100 y), Bq/g for medium-lived nuclides (5 y < T ½ < 100 y) and Bq/g for short-lived nuclides. This limit deals with waste that has been conditioned and treated for disposal. Second category may be defined Low Level Waste since it may be disposed of in surface or near-surface disposal sites, in a similar way to Low Level Waste eligible for Shallow Land Burial according to the United States Waste Regulation 10CFR61 [10]. First category waste may be defined Very Low Level Waste since it decays down to radioactive concentration levels comparable to natural substances in a maximum decay period of some years. Concerning clearance (immediate declassification to non-radioactive material ), a recent regulation has been issued in Italy [11], concerning the Allontanamento (Italian word for clearance ) of solid radioactive spent materials. This regulation is necessary for the ongoing decommissioning activities of the four shut down Italian fission reactors. Concentration limits are issued for each relevant nuclide, however they may be partially summarised as follows: a non-alpha-emitter metallic material may be cleared, if its specific activity is less than 1 Bq/g. For other materials than metallic ones and concrete, the limit is 0.1 Bq/g, while for concrete the limit is almost half-way, depending on the type of nuclides [11]. Recycling in Italy is permitted for cleared material only. We have applied this set of regulations to IGNITOR. Activation data were taken from [4-6]. The main results of the study are the following: if Italian regulations were applied as-they-are to this experiment, no radioactive material should be classified in the Italian High Level Waste category ( III Categoria ). Most of the material can be classified as LLW ( II Categoria ), with a total volume of about 40 m 3. The only remarkable point is the decay time necessary for the Vessel material (INCONEL625 alloy) to decay within the LLW limit, i.e., 100 years. The low volume of this component (about 4 m 3 ) shows the small safety relevance of this problem. Results are shown in Table 1. We have always supposed that adequate detritiation of material is carried out before disposal. Concerning Tritium inventory and tritiated waste, total inventory is limited to a few grams, and Tritium Handling System has been recently re-designed and positively safety assessed [7]. Italian regulation on declassification to nonradioactive waste ( Allontanamento ) is so restrictive that, in principle, none of the considered material is eligible for this classification, however first wall and cryostat are VLLW, i.e., it takes a relatively short time before they decay to radioactive concentrations similar to those of some natural materials. CONCLUSIONS AND PROPOSALS We have applied the Italian waste management regulations to the IGNITOR experiment radioactive materials. The main results of the study are the following: if Italian regulations were applied as-they-are to this experiment, no radioactive material should be classified in the Italian High Level Waste category ( III Categoria ). Most of the material can be classified as LLW ( II Categoria ), with a total volume of about 40 m 3. The rest is VLLW, that is, decays to radioactive concentrations similar to those of some natural materials after a short while. This confirms that IGNITOR fulfils the requirement of no production of waste that could be a burden for future generations, i.e., minimisation of the production of long-lived radioactive waste. In addition, we have identified in recycling within the nuclear industry for LLW activated materials - a possible solution to avoid their disposal into the environment. Concerning recycling, it is a question dealing not only with radiation protection, but also with metallurgy, materials science, shielding and remote handling techniques. A wide experience in these fields is available from fission research: a study of the application of existing techniques

4 . TABLE 1 Application of Italian Radwaste Regulations to IGNITOR Radioactive materials Component Material Classification Necessary Decay Time Vessel INCONEL625 alloy LLW (II Categoria) 100 years First Wall Graphite VLLW (I Categoria) One week Magnet Copper LLW (II Categoria) Less than 10 years C-Clamp Structure AISI 316 steel LLW (II Categoria) Less than 5 years Cryostat Composite material VLLW (I Categoria) (See Note) Less than 5 years. Note: For Cryostat, Declassification to non-radioactive waste ( Allontanamento ) could be immediately possible if C14 was chemically extracted and separated, however this appears not to be a justified procedure, since - after a few years - Cryostat decays to radioactivity concentrations similar to those of some natural substances. to fusion radioactive materials is quite useful, to assess whether and when recycling of such materials is feasible or convenient; radiological, technical, economic and strategic questions have to be considered. An example of this may be found in [12]. For the moment, no recycling of radioactive material is admitted or foreseen in Italy, mainly since this country does not have any Nuclear Program. However, European Union has recently studied a waste management strategy for fusion radioactive materials [13]. Since most of fusion waste comes from relatively low activated material, in shielded position from the plasma, it is appropriate to explore the possibility of ùfinding alternative pathways for the management of such waste, in order to minimise the use of final repositories, based upon two main concepts: Recycling of moderately radioactive materials within the nuclear industry. Declassification of the lowest activated materials to non-active material (Clearance), based upon an extension to fusion [14] of two documents [15-16] issued by IAEA and ICRP. If this strategy could be applied to IGNITOR, Vacuum Vessel (INCONEL625) and Magnets (Copper) could be easily recycled within the nuclear industry, while all the other materials (First Wall, C-Clamp and Cryostat) could be cleared, that is, declassified to non-active material. No waste disposal of any kind should be necessary. This shows how conservative Italian waste management regulations are, and also that they could need some revision in order to take into account the peculiar characteristics of fusion activated materials (lower radiotoxicity than fission waste). An international common strategy for fusion radioactive materials should be proposed, focusing especially on materials recycling: this might integrate the national regulations for the fusion case. REFERENCES [1] W. Gulden, Minutes of the June 14, 2000 meeting of the Executive Committee on the International Energy Agency (IEA) Cooperative Program on the Environmental, Safety and Economic (ESE) Aspects of Fusion Power, Cannes, France, June [2] K. Brodén and G. Olsson, Review of earlier studies of waste management options for fusion in Europe, USA and Japan, Report RW-00/26, Studsvik, Sweden, April 2000 [3] B. Coppi, A. Airoldi, F. Bombarda, et al., The Ignitor Experiment, Nuclear Fusion, vol 41, pp , [4] A. Carpignano, S.Francabandiera, R.Vella, M. Zucchetti, Environmental impact analysis for the main accidental sequences of Ignitor,

5 Fusion Technology, vol. 30, pp , [5] M. Zucchetti, R. Bisesi, A. Carpignano, Dose assessment for the Ignitor experiment, Fusion Engineering and Design, vol. 42, pp , [6] G. Mura, S. Rollet, M. Zucchetti, R. Forrest, Positive safety impact of Ignitor design modifications, Fusion Engineering and Design, vol , pp , [7] M. Zucchetti, A. Ciampichetti, F. Subba, Tritium Inventory Evaluations for the Ignitor Experimental Reactor, in Proceedings of 30th EPS Conference on Contr. Fusion and Plasma Phys., St. Petersburg, 7-11 July 2003 ECA Vol. 27A, P [8] Italian Legislation: Decreto Legislativo n.230, Suppl. Ord. GU n Serie Generale (in italian), Decreto Legislativo n.241, Suppl. Ord. GU n Serie Generale (in Italian). [9] ENEA, Guida Tecnica n.26: Gestione dei rifiuti radioattivi, ENEA (Roma), 1990 (in Italian) [10] US Nuclear Regulatory Commission, Licensing Requirements for Land Disposal of Radioactive Waste, 10CFR part 61, US Federal Register, 47, 1982, p [11] Italian Legislation: Ordinanza 11 aprile 2003 n. 5, GU n Serie Generale (in italian). [12] V.Massaut, L.Ooms, Decommissioning, Decontamination and Waste Management Strategies fur future Fusion Reactors (based on current fission reactor experience), D&D SCK-CEN, Mol, Belgium, R-3768, 276/03-02, [13] P.Rocco, M.Zucchetti, Waste Management for Different Fusion Reactor Designs, Journal of Nuclear. Materials, vol , pp , [14] N.Taylor, E.T.Cheng, D.Petti, M.Zucchetti, Overview of International Waste Management Activities in Fusion, Fusion Technol., vol. 39, pp , [15] Clearance Levels for Radionuclides in Solid Materials: Application of the Exemption Principles, Interim Report for Comment, IAEA TECDOC- 855, Vienna, January [16] Radiation Protection 89, Recommended Radiological Protection Criteria for the Recycling of Metals from the Dismantling of Metals of Nuclear Installations, European Commission, Directorate General Environment, Nuclear Safety and Civil Protection, 1998.