NUCLEAR FUSION PERSPECTIVES

Transcription

1 7 th National Conference on Renewable Energy Source of The Institute of Solar Technology Conference & Cultural Centre of the University of Patras 6 8 November 2002, Patras, Greece. NUCLEAR FUSION PERSPECTIVES P.Rocco, M.Zucchetti Dipartimento di Energetica, Politecnico di Torino, Corso Duca degli Abruzzi 24, I Torino, Italy. Physical conditions for D-T fusion reactions in hot plasmas are reviewed, showing the difference between inertial and magnetic confinement. The principles of muon-catalized fusion are given as an example of alternative approach. The main features of the tokamak, i.e. the magnetically-confined plasma configuration which is most investigated in reactor studies are described. ITER, a 500 MW th tokamak reactor design, is an international project and represents the single step toward a DEMO, a demonstration electricity-generating fusion power station. Safety and environmental aspects of tokamak reactors, in particular their inherent safety, were investigated in the E.C. Safety and Environmental Assessment of Fusion Power-Phase 2 (SEAFP-2). Management options for tritiated - activated fusion waste are described, either with disposal in fission waste repositories, or according to other concepts. Data on fusion cost and time schedule are given. INTRODUCTION Various energy-producing fusion reactions occur in the stars. Reactions involving hydrogen isotopes, namely d-t and d-d reactions are those which can occur on the earth with the present physical and technological possibilities, or with reasonable future extrapolations. As shown in the equivalence of table 1, nuclear fusion offers the possibility to produce energy from small amounts of deuterium and tritium, which are abundant in nature or easily producible. Table1. Equivalence of different energy sources [sto] To fuel a 1000 MW E power plant we need, per year: Coal: Oil: Fission: Fusion: 2.5 million tons, or 250 trains with 100 cars each. 11 million barrels, or 11 super tankers. (1 barrel = 164 litres) 20 tons of enriched UO 2, from 140 tons of uranium ore, or 1.5 railcars. 45 kg of deuterium and 68 kg of tritium (produced on site from 154 kg of lithium-6), or one pickup truck. A concise information is given in the following sections on the physical and technical aspects of fusion as future energy source. 1. FUSION REACTIONS IN THERMONUCLEAR CONDITIONS [eng], [car] Under certain conditions nuclei fuse together producing a heavier nucleus, other particles and energy. The simplest fusion reactions in a terrestrial environment involve deuterium (D) and tritium (T), the hydrogen isotopes of mass two and three: 1

2 and: D + T (He MeV) + (n MeV) (1) D + D (He MeV) + (n + 3 MeV), or: (T MeV) + (p MeV) The energy is produced as kinetic energies, redistributed among the end products inversely proportional to their masses, e.g in eq. (1) the energy of the alpha particle ( He 4 ) is one fourth of that of the neutron (n). D-T fusion, is more easily achievable that D-D fusion, eq. (2) as the cross-section of the reaction in the relevant range of energy (10 to 100 kev) is larger by about one order of magnitude, so that next fusion reactors will run on D-T reactions. Tritium however is very scarce in nature and must produced continuously within the same fusion reactor, as explained in section 3, whereas a hypothetical reactor based on D D reaction should not require self- breeding. There are two physical conditions under which D-T fusion reactions occur in plasma with a probability of practical interest: 1) The kinetic energy of the nuclei is high enough to overcome the repulsive electrostatic forces between them. This energy, for singly charged nuclei, is of the order of the Coulomb potential energy, i.e., : ε kin = ε Coul = 150 kev corresponding to a temperature of : Θ = 100 kev or 10 9 o K Under these conditions, matter is present as fully ionised gas, or plasma. However, the reaction cross-section of D-T fusion at a temperature of 10 kev is not appreciably lower than that for Θ = 100 kev due to the tunnel effect and because of the presence of suprathermal particles in a Maxwellian distribution. Thus, a temperature of 10 kev is actually sufficient for D - T fusion. 2) The fusion energy production is of interest only if it is, at least, larger than the thermal energy content of the plasma where the fusion reactions take place. It can be taken: a) the reaction rate <σv r > at 10 kev, i.e cm 3 /s (σ = reaction cross section; v r = relative speed of particles); b) the energy produced by a d-t fusion reaction, 17.6 MeV ; c) the equal particle density of D and T components, i.e. n D =n T = n/2. Previous assumptions lead to the Lawson criterion: nτ E > s/cm 3 (3) where τ E is the energy confinement time, which measures the time over which the plasma, once heated to thermonuclear temperatures, cools down by thermal losses such as convection, conduction, radiation. Condition shown in eq. (3) however is not sufficient. The confined D - T plasma must be kept at thermonuclear temperatures by self-heating, (2a) (2b) 2

3 that is by the deposition of the energy of the fusion α-particles as the energy linked to fusion neutrons is deposited out from the plasma. This ignition condition leads to a nτ E value which is 5 times larger than the Lawson limit of eq. (3): nτ E s/cm 3 (4) The confinement of hot plasmas may be achieved in two ways. If one relies on inertia of particles that, at 10 kev, have a typical speed of 10 8 cm/s, the confinement is limited in time and the reactor operation should be pulsed. It may be shown that the fulfilment of the ignition condition, eq. (4), requires plasma densities above cm -3, almost 100 times the density of solid D - T. In inertial confinement fusion, or ICF, frozen D-T pellets are bombarded with lasers or particle beams to reach fusion temperatures at high densities but during extremely short periods. Fig.1 shows the scheme of a reaction cell where ignition is indirectly driven, namely the laser beams impinge on the inner surface of the chamber generating x- rays that produce ignition. If, on the other hand, the plasma is confined magnetically, a continuous operation of the reactor should in principle be possible. Depending on technical reasons limiting the magnetic field, plasma densities would be limited to somewhat above cm 3, leading to the requirement of energy confinement times of some seconds at least. Magnetic confinement machines consist of linear or toroidal solenoids, which confine the particles radially. A toroidal configuration, the tokamak, see fig 2, is the most widely investigated and its extrapolation to reactor conditions, namely with a net energy gain, is the main goal of the European Fusion Programme. The plasma is produced in a toroidal vacuum chamber, the plasma chamber. A poloidal magnetic field is produced by a toroidal current flowing through the plasma. The current is induced by a transformer, the secondary winding of which is the plasma itself; the primary being wound on an iron core is the central solenoid. A coil system placed around the vacuum chamber perpendicularly to the plasma ring generates a toroidal magnetic field. The resultant of the toroidal and poloidal fields is a helical field confining the plasma particles. The plasma ring is however unstable and tends to expand; control coils must be added to create a vertical magnetic field to compensate the hoop forces on plasma. 2. AN ALTERNATIVE WAY: THE MUON - CATALYSED FUSION [maj] It has been shown as nuclear fusion in plasmas of heavy hydrogen isotopes mixtures depends on the energy content and dimensions of the plasma, and on the particles density. Other methods to produce energy by fusion can be envisaged and one among them, based on interactions among nuclei in muon-atoms, is described here. The muon (or meson µ - ), is an elemental particle produced by decay of a pion - (or meson π): π - µ - + ν, where ν is a neutrino The muon may be considered an heavy electron (m µ = 207 m e ) and decays to eνν with a lifetime τ µ =2.2µs. Energetic muons entering a compressed hydrogen gas (e.g. hydrogen liquid density defined by n o = 4.25 x atoms/cm 3 ) are slowed down and µ-atoms are formed, dµ and tµ, where the muon substitutes the peripheral electron. Then a mesomolecular ion dtµ is produced where the two nuclei oscillate around an equilibrium distance R = cm. In such conditions, see 3

4 fig.3, fusion reaction occurs easily: D + T n + α, and the muon most likely is left as free and is able to start again, acting as a real catalyst. Note from fig. 3 that all rates of the various steps are much larger than the muon decay rate, so that a muon could catalyse several hundreds of reactions. Muon however may stick to the α-particle. The αµ system is positively charged and is repelled by other nuclei. This process breaks the chain of muon catalised fusions. In some cases the muon can be re-expelled. Some estimates are that a muon remains stuck to the α-particle once each 160 fusions, but the cycling rate depends on several parameters and the possibilities to increase it are not fully investigated. At present the yield to attain a positive energy output is supposed to be A positive energy output from muonic fusion depends also on the energy cost to produce muons, which is estimated at present to be a few GeV. This cost may however decrease with improvements to muon - generating devices. 3.FEATURES OF TOKAMAK REACTORS The large majority of reactor studies carried out within the European Fusion Technology Programme aims at developing tokamaks, hence details are given on systems of this type of reactors. Tritium breeding. The fusion reaction shown in eq. (1), needs to be fed with deuterium and tritium. Deuterium is abundant in nature as one over 3500 water molecule is HDO. Extraction of deuterium from water by distillation is not expected to be a major cost in D -T fusion. Conversely tritium, a radioactive hydrogen isotope with a half-life of 12.3 years, is extremely scarce. Its natural inventory on the earth, where it is formed from deuterium by action of cosmic rays is limited by its radioactive decay to about 20 kg. Tritium is also a product of fission reactors: a) triple fissions in the fission fuel by, b) neutron capture in heavy water used as moderator in some reactors, c) produced in dedicated fission reactors in the frame of nuclear weapon programmes. Tritium amounts existing at present can be used to fuel experimental fusion machines and to form the initial inventory in experimental fusion reactors. A D - T power reactor must have a tritium-producing zone, a breeding blanket where tritium is produced from lithium (or lithium compounds, due to the chemical reactivity of lithium). Natural lithium consists of Li 6 (7.5%) and Li 7 (92.5%). There are two tritium producing reactions: Li 7 + n He 4 + T+ n (E n > 2.8 MeV) (5) Li 6 + n He 4 + T (E n < 0.3 MeV) (6) It is evident that each fusion neutron interacting with lithium should produce more than a tritium atom, as other neutrons are lost for captures and streaming. Thus n, the neutron of lower energy produced in eq. (5) by the impinging fusion neutron must interact again with a reaction of the type indicated in eq. (6). In some case the blanket contains also a neutron multiplier. Beryllium and lead may be used, as they have n, 2n interactions with neutrons. Neutrons deliver their thermal energy in the blanket, whereas the alpha particles energy is deposited in the plasma that keeps the thermonuclear temperatures by self-heating. Heat and particle removal. Alpha particles energy is released from the plasma under form of radiation or of kinetic energy of escaping particles. Direct contact of this energy with the 4

5 first wall, the inner layer of the vacuum chamber, is avoided by a limiter, a clad and cooled piece protruding from the first wall to intercept the escaping particles. These particles can also be exhausted into a separate chamber to deliver their energy to a target plate by means of extra magnetic coils, forming the divertor. Superconducting magnets. In order to reduce ohmic losses, the magnetic systems of fusion reactors will be made by superconducting coils working at cryogenic temperatures. A cryostat insulates these coils from the environment. Pulsed and nearly-steady operation. As seen in section 1, the plasma current is generated by induction, whence the tokamak is a pulsed system. Alternative ways to generate the current with non-inductive current drive, are under development. They will allow a long-pulse or a quasi-steady tokamak operation. Plasma heating. The Ohmic heating power dissipated inside the plasma by the flowing current is not enough to produce ignition as the plasma resistance drops while the plasma becomes hotter. Two supplementary heating methods can be envisaged: a) Injection of neutral particles. Energetic charged particles cannot be injected in the plasma for the strong toroidal magnetic field. Thus, charged deuterons produced in a ion source are accelerated and neutralised before impinging on the plasma where they deliver energy by collisions. b) Wave heating. An electromagnetic generator produces plasma waves migrating to some plasma region where the electromagnetic energy is absorbed. Fuelling. The fuelling system will provide a flow of deuterium and tritium in the form of a gas or frozen pellets. In general, the gas puffers will provide fuelling during the initial start up and the pellets injectors will provide fuelling after the plasma has been established. 4. THE EXPERIMENTAL REACTOR ITER [iter] The subject of an international collaboration of Canada, Europe, Japan and Russia, ITER (which means the way in Latin) is a tokamak design of 500 MW th, see Figs. 4 & 5. Its linear dimensions will be twice that of the largest existing tokamak and the expected fusion performance will be many times greater. It will be the first major fusion device to produce thermal energy at the level of electricity generation, providing the single experimental step to reach the demonstration electricity-generating power plant (DEMO). Examples of the physics goals of ITER are: a) to achieve extended burn and demonstrate quasi-steady operation in inductive and non inductive current drive respectively, b) to provide satisfactory power and particle exhaust by a divertor-configuration and ensure acceptable levels of impurities in the plasma, c) to prevent damage to the plasma facing components by ensuring efficient transfer of the α-particles energy to the plasma. ITER will host blanket test modules investigating various technical options for DEMO European test modules [car] Six blanket test modules have been defined up to now. The two European modules will have the following characteristics: 5

6 1 st modulus Ceramic breeder: Li 2 TiO 3, or Li 4 SiO 4 Neutron multiplier: Be 2 nd modulus Liquid breeder: Pb 17Li (the eutectic Li 17 Pb 83 ) For both modules Structural material: Coolant: Eurofer (9 chromium ferritic/martensitic steel) Helium 5. INHERENT SAFETY OF FUSION REACTORS 5.1. General SEAFP-2 (Safety and Environmental Assessment of Fusion Power Phase 2) is the part of the European Fusion Programme dealing with safety and environmental impact of future fusion power plants. Three plant models investigated: PM-1, PM-2, PM-3 were tokamaks with a power of 3000 MW th. They were assumed to be identical for all ex-vessel components. The in-vessel structural material and breeder-coolant systems consist of: V-4Cr-4Ti and Li 2 O Helium (PM-1), low-activation martensitic steel (LAM) and Pb-17Li - water (PM-2), LAM and Li 4 SiO 4 with Be-multiplier helium (PM-3). Safety and environmental studies on these plant models, although limited to assessments on preliminary design features, have shown that the main conceivable accidents can be mastered. An important feature of tokamak reactors is their inherent safety. The thermal energy stored in the plasma is less than 1 GJ. Furthermore, burning plasma operates in such stringent conditions that any faulty condition will lead to plasma cooling and to quenching of the reactor. The SEAFP-2 analysis of the temperature evolution in a tokamak reactor after a coolant accident is another example of inherent safety. This assessment, based on very pessimistic assumptions, is reported in the following section Post accidental passive cooling capability [and] Table 2 shows the decay heat evolution in PM-1 and PM-2. The shut down values are 1.6% and 2.6% of the thermal power, which compare favourably with the 7% shut down-value of a fission reactor. Decrease of decay heat is however slower in fusion than in fission. The great advantage of a tokamak on fission plants is its low power density, which assures slow temperatures increases in the case of coolant accidents. Fig.6 shows the effects of a total LOCA (Loss-Of-Coolant-Accident) in the inboard zones of PM-1. Beside the failure of active cooling, it is assumed that cooling circuits are drained and act as radiating cavities only, without conduction and convection effects. It may be seen that the temperatures increase are very slow. The hottest zones are the first wall and the adjoining blanket layers that reach a peak temperature of 800 o C after about 11 days, well below the melting point of the V-alloy, and then there is a relatively slow decrease. 6

7 Table 2. Total decay heat power in SEAFP-2 reactors, MW Time PM-1 PM min min h h day days days month year MANAGEMENT OF FUSION RADIOACTIVE WASTE 6.1. General Radioactivity in d-t fusion will be due to tritium and to neutron - materials interaction (activation). Tritium will be present in liquid waste from the fuel system (tritium extraction from the breeder, fuel pellets preparation ) and will permeate easily through components around the plasma chamber About 10 times more neutrons will be produced in a d-t fusion system than in fission system of the same power and fusion neutrons will be more energetic also. Hence, neutron activation will be more important in fusion, constituting most part of fusion radioactivity. A great advantage of fusion is that there is not a radioactivity build up of long-lived actinides and fission products radioactivity. Liquid waste arising from the tritium cycle within the plant (e.g. fuel pellets preparation) will be managed with procedures derived from those adopted for tritiated waste from fission (heavy-water reactors) and from medical applications. Information is given here on possible options for the management of solid activated - tritiated waste arising from the periodical substitution of in-vessel components and by the plant decommissioning Detritiation of activated waste [zu1] Activated waste arising from zones near the plasma chamber will contain tritium and will require detritiation procedures, e.g., melting under vacuum. Tritium may be recovered or immobilized in ordinary or polymer-impregnated cement and disposed in steel drums Activated waste management based on recycling and clearance After detritiation, this management option envisages a decay of the activated waste at the reactor site, assumed to be 50 years. Then, three options are applied, depending on the residual radioactivity: 7

8 Recycling in the nuclear industry: building new pieces for nuclear installations with the activated material. Either residual radioactivity can be kept within the pieces, or the most noxious radionuclides can be eliminated previously. In this last case however there is a stream of secondary waste. Clearance: the release of the activated material from regulatory control either for disposal as non-active waste, or for unconditional recycling (i.e. re-use in conventional industry). Permanent disposal of the waste that cannot be recycled in the nuclear industry or cleared. Table 3 shows a classification of fusion waste proposed by the authors [ro1], which is based on the radioactivity only. The limits are given by values of contact dose rate, decay heat per unit volume and clearance index (this index is defined in the table) after 50 years of cooling. Waste may be sorted into four classes: 1) to be disposed off, 2) recyclable with complex remote-handling procedures, 3) recyclable with simple RH procedure or by hands on operation, 4) may be declassified to non-active waste. A clearance index derived by the nuclidespecific clearance levels proposed in [iaea] is defined in the same table 3. Table 4 shows how this option is applied to the waste arising from the SEAFP-2 reactors PM-1 and PM-2 [zu1]. It may be stated that solid waste arising from fusion reactors may be either re-used in the nuclear industry (60% 72 %), or declassified to non-active waste (40% 28%). It is worth noting that the clearance may be substituted by recycling in non nuclear activities. The levels for this unconditional recycling are not too different from the clearance levels indicated previously. Table 3. Proposal of categories of fusion activated materials [ro1] Activated Materials Classification R D msv/h H W/m 3 PDW = Permanent Disposal Waste >20 >10 (not recyclable) CRM = Complex Recycle Material (complex RH procedures) SRM = Simple Recycle Material <2 <1 (simple RH procedures; HOR for D < 10µSv/h NAW = Non Active Waste (to be cleared) RH = Remote handling: HOR = hands on recycling. I c (D) >1 R D = contact dose rate at 50y ; H = decay heat per unit volume at 50y. I c (D) = clearance index for disposal at 50y. It is defined as follows: Z A i I c (D) = ; A i, L i = specific activity and clearance level of the i th nuclide. i= 1 L i Clearance level is the limit of specific activity of a given radionuclide that is the only contaminant in a non-active waste [iaea] 8

9 Table 4. Disposal, recycling and clearance options for waste arising from the SEAFP-2 reactors PM-1 and PM-2, [zu1] Management Option PM-1 PM-2 Weight % Weight % Permanent disposal waste , Recycling in the nuclear industry 40, , Clearance 26, , Total weight (1) 66,800 95,300 (2) weight of activated material, including periodical substitutions and decommissioning 6.4. An alternative to recycling: reprocessing and clearance [ro2] Recycling reduces the radioactive waste amount but has the disadvantage to use old and radioactive materials in new plants. An alternative to recycling in the case of V-alloy structures, consists in the reprocessing with elimination of the noxious radionuclides, followed by clearance. The V-alloy investigated was V-5Ti, adopted in PM-1 in a first phase of SEAFP. It was found that Nb 94, deriving from the activation of 60 ppm w of niobium impurity in the alloy, exceeded its clearance level by more than 2 x Clearance level values were exceeded, although by much lesser extents, in other radionuclides present in the activated alloy. Taking a 50% weight of Nb 94 as contributor to the total radioactivity, it was found that clearance could be possible if: (a) Nb 94 activity were reduced by a 2.5 x 10-5 factor, and (b) the activities of the other radionuclides were reduced in such a way that the sum of all factors A c /L c, be less than unity. Niobium impurity concentration in the alloy could be reduced to 0.1 ppm w, with a reduction of Nb 94 activity by a factor of 600. An additional reduction by a factor of 70 should be obtained by reprocessing. A process based on elemental dilution with stable niobium and zone melting with suppression of niobium impurity could be adopted. The activity of other noxious radionuclides as C 14, Ni 63 should also be reduced Disposal in fission waste repository [ro1] Aspects of fusion waste disposal in German and Swedish repositories for fission waste have been analysed. In Germany: Konrad, an old iron mine, and Gorleben, a deep geological repository in a salt formation, are sites investigated; the latter may store heat-generating waste (HGW), i.e. high-level waste Sites investigated in Sweden: SFR a shallow geological repository placed 50 m under sea bottom and SFL a 500 m deep geological repository expected to be operational around 2020, the latter can store hig-level waste. Waste was assumed to be conditioned into packagings according to practices adopted in the repositories Results of these analyses are shown in tables 5 and 6. 9

10 Table 5. Number, weight and volumes of packages with waste from SEAFP-2 PM-1, PM-2, PM-3 disposed in German repositories for fission waste [ro1] No. of packages * Weight /package ** tonnes Total volume *** m 3 15, ,000 70,000 60,000 * same value for PM-1, PM-2, PM-3 ** min.-max. weight of package *** values for PM-1, PM-2, PM-3 are indicated in sequence Table 6. Number, weight and volumes of packages with waste from SEAFP-2 PM-1, PM-2, PM-3 disposed in Swedish repositories for fission waste [ro1] No. of packages * Weight /package ** tonnes Total volume * m 3 30, ,000 * same value for PM-1, PM-2, PM-3 ** min.-max. weight of package LINES, COST AND SCHEDULE OF FUSION PROGRAMMES 7.1. The E.C. Controlled Thermonuclear Fusion Programme [fus] CTFP (duration: ) is a part of the Fifth framework programme of the European Community for research, technological development and demonstration activities ( ). CTFP main lines: - Next step activities: develop the capacity in fusionphysics and technology, aiming to the construction of an experimental reactor (ITER). - Concept improvements: activities in the field of physics, to improve the basic concepts of fusion devices. - Long-term technology: technological activities for a demonstration power reactor (DEMO). CTFP funds, EURO 788 million, i.e 197 M /y, are distributed as follows: - Financial contributions of 25% towards the current expenditures of associations (i.e., the national laboratories associated to the European effort on fusion) and towards contracts of limited duration. - Capital costs of specifically defined projects may be financed at 45%. - Specifically defined activities, as the use of experimental facilities may be financed up to a maximum rate of 75%. Table 7 shows the US fusion programme. It has to be noted that U.S. data concern the total budget whereas CTFP funds do not include fusion budgets of European association and industries. 10

11 Table 8 shows a comparison among the total Budgets of EC, Japan and USA. The value of the US budget shows a small difference from the FY 01, FY 02, FY 03 of table 7, probably it refers to a previous FY. It is shown that the E.C. expenditures are the largest. Table 7. US Fusion Energy Science Programme Budget (in millions $) Main lines Science Facility Operations FY 01 FY 02 FY 03 Sub-items Tokamak Exp. Research, Alternative Concept Exp. Research, Theory, General Plasma Science TFTR, DIII-D, Alcator C-MOD, NSTX, NCSX, GPP, GPE Enabling R&D Engineering Research, Materials Research Total Program Table 8. Comparison of Fusion Programs Budget, per year Budgets E.C. Japan USA National currency EURO 500M /y 500M /y 35 G /y 303 M /y 230 M$/y 234 M /y ( 1 Є = = 0.98 $) 7.2. ITER schedule and cost [iter] Fig.7 shows the ITER construction schedule. Purchase orders for the tokamak building and magnets should follow the construction agreement by about 20 months and the first plasma should be expected 96 months after. Construction agreement is envisaged at beginning Then first plasma could be on mid The decision on ITER site is however still pending so that a delay is likely. Figures on ITER cost are given in table 9. Table 9. ITER cost (in M $) (*) Direct construction : 2755 Staff cost for construction: 477 Manufacturing R&D: 70 Annual cost of operating ITER: 188 totalling 3760 M over 20 year of operation Decommissioning: 335 (*) Jan 1989 values. Direct construction and Annual cost are 49% and 54% of the 1998 values. [iter] 11

12 7.3. DEMO preliminary design DEMO reactor should take into account results of ITER operation. Power reactor relevant results will be obtained after 7-8 years of operation [iter]. Assuming the ITER milestones indicated in section 7.2, DEMO preliminary design could begin on CONCLUSIONS Physical and technological aspects of fusion were reviewed in the previous sections. Electromagnetic and inertial confinement of hot plasma were described, indicating the physical conditions allowing fusion reactions with a net energy gain. The principles of muon-catalised fusion were indicated, as an example of alternative way to obtain energy from fusion. It was stated that fusion reactor designs based on the tokamak electromagnetic confinement configuration are the most investigated at present. ITER, a 500 MW th experimental tokamak reactor is the subject of an international collaboration. It will be the first fusion reactor to produce energy and will be the one-step device before the construction of electricity-producing power stations. In Europe, the safety and environmental aspects of fusion are investigated in SEAFP-2. A SEAFP-2 analysis reported in this paper showed that tokamaks power reactors are inherently safe also in extreme conditions of loss-of-cooling-capability. Management options for fusion activated waste were described. They include fusion-specific solutions and disposal in repositories for fission waste. Fusion expenditures and expected schedules were reported. ACKNOWLEDGEMENTS Useful information was obtained from: - A.Cardella, E.Salpietro, EFDA CSU, Max-Planck- Institut für Plasmaphysik, Garching, Germany, - P. Fenici, E.C. Joint Research Centre, Ispra, Italy. REFERENCES [sto] E.Storm, LLNL, oral communication, [eng] F.Engelmann, Introduction into Fusion Plasma Physics, in: Plasma physics for thermonuclear fusion reactors, Harwood academic publisher, London&N. York, [car] First Carolus Magnus Summer School on Plasma Physics, Vaals, The Netherlands, September 6 17, 1993, Trans. Fus. Techn. March 1994 Vol 25, No 2T, Part 2 [maj] B.Brunelli and G.G. Leotta (Eds.), Muon-Catalised Fusion and Fusion with Polarized Nuclei, Ettore Majorana international science series, Physical sciences; v.33, Plenum Press, New York, [iter] [and] F.Andritsos, A.Angelini, H.W.Bartels, SEAFP Passive Removal of the Decay Heat, Joint Research Centre -Technical note No I , December [ro1] P.Rocco, K.Brodén, R.A.Forrest, C.B.A. Forty, M.Lindberg, M. Zucchetti, E.C. longterm studies on fusion waste management, Fus. Eng. and Des. 48 (2000) 443. [zu1] M.Zucchetti, R.Forrest, C.Forty, W.Gulden, P.Rocco, S.Rosanvallon, Clearance, recycling and disposal of fusion activated material, Fus. Eng. Des. 54 (2001)

13 [iaea] Clearance Levels for Radionuclides in Solid Materials: Application of Exemption Principles, IAEA TECDOC-855, Vienna [ro2] P. Rocco, M.Zucchetti, Management Strategy to Reduce the Radioactive Waste in Fusion, J. Fusion Energy, 16 (1 2), (1997), 141. [fus] Fig 1. Inertial fusion by indirect laser drive. Laser beams impinge on the chamber inner surface, producing x-rays which compress and ignite the plasma. Fig.2. The Tokamak scheme. Control coils (not indicated in the figure), must be added to create a vertical magnetic field to compensate the hoop forces on plasma. [car] 13

14 Phase Process Characteristic Order of Notes Quantity Magnitude a Slowing down and atomic capture Slowing time 10-6 µs Formation of µ-atomic systems (size cm) b Transfer Transfer rate 300C T µs - Depend on t-concentration c Formation of muonic molecular ion Formation rate 500µs -1 VERY HIGH for d-t mixures. Depends on temperature and density d Nuclear fusion Fusion rate 10-6 µs MeV neutron formed e Muon free for new catalysis OR 1 f Sticking Sticking probability ω in g Reactivation Reactivation probability R 0.9 1/4 Muon sticks to α particle Muon can be shaken off. Effective sticking is: ω eff = ω in (1-R) Fig. 3. Main steps of the muon- catalized fusion in deuterium-tritium mixtures. [maj] 14

15 Fig.4. ITER cross-section [iter] Fig.5. ITER cutaway [iter] 15

16 Fig 6. Temperature history in a power tokamak after a LOCA (Loss-Of-Coolant -Accident). [andr] Fig.7. ITER construction schedule 16