JET and Fusion Energy for the Next Millennia

Transcription

1 JET and Fusion Energy for the Next Millennia JET Joint Undertaking Abingdon, Oxfordshire OX14 3EA JG99.294/1

2 Talk Outline What is Nuclear Fusion? How can Fusion help our Energy needs? Progress with Magnetic Confinement Fusion Advantages and Disadvantages of Fusion Energy Developing Fusion in the future JG99.294/2

3 What is Nuclear Fusion? Nuclear Fusion is the energy-producing process taking place in the core of the Sun and stars The core temperature of the Sun is about 15 million C. At these temperatures hydrogen nuclei fuse to give Helium and Energy. The energy sustains life on Earth via sunlight JG99.294/3

4 Energy Released by Nuclear Reactions Light nuclei (hydrogen, helium) release energy when they fuse (Nuclear Fusion) The product nuclei weigh less than the parent nuclei Heavy nuclei (Uranium) release energy when they split (Nuclear Fission) The product nuclei weigh less than the original nucleus JG99.294/4

5 Energy Released by Nuclear Fusion and Fission Fusion reactions release much higher energies than Fission reactions Nuclear binding energy released Fusion D 3He T Li 4 He Energy released in Fusion D Deuterium 3 He Helium 3 T Tritium Li Lithium 4He Helium 4 U Uranium Fission Energy released in fission U JG97.362/4c D Atomic mass n u T 4He FUSION FISSION JG99.294/5

6 Fusion Reactions Deuterium Tritium from water (0.02% of all hydrogen is heavy hydrogen or deuterium) from lithium (a light metal common in the Earth s crust) D+T 4 He + n Tritium production 6 Li + n 4 He + T 7 Li + n 4 He + T + n Deuterium + Lithium Helium + Energy This fusion cycle (which has the fastest reaction rate) is of JG97.362/3c interest for Energy Production JG99.294/6

7 How can Fusion help our Energy needs? Growth in world population and growth in energy demand from increased industrialisation/affluence will lead to an Energy Gap which will be increasingly difficult to fill with fossil fuels Growth in population and energy demand POPULATION INDUSTRIALISED COUNTRIES DEVELOPING COUNTRIES ENERGY 2020 POPULATION INDUSTRIALISED COUNTRIES DEVELOPING COUNTRIES ENERGY JG97.362/1c Without improvements in efficiency we will need 80% more energy by 2020 Even with efficiency improvements at the limit of technology we would still need 40% more energy JG99.294/7

8 Fusion Energy Advantages Fusion fuels have very large energy density: 1 gram of fully reacted Deuterium-Tritium fuel gives around about kw hr of electricity, enough for about 5000 households for 1 day. 1 gram of fully burnt Coal gives only about 3W.hr of electricity (ie 10 million times less) Fusion fuels are abundant and geographically widespread: Deuterium (extracted from sea water), enough for 300 thousand million years Tritium is made from Lithium using a fusion reaction. Lithium (abundant on land and in the oceans), enough for about 2000 years JG99.294/8

9 Fusion Energy Advantages (continued) Fusion fuels are clean : - Fusion does not give rise to Greenhouse gases (CO 2 ) or Acid rain gases (SO 2, NO 2 ) Fusion reactors are inherently safe: - A very small quantity of fuel is kept in the reactor region (only enough for a few tens of seconds operation) - Critical or meltdown situations associated with Nuclear Fission are physically impossible - Accidents are self limiting and Public evacuation would not be necessary JG99.294/9

10 Fusion Energy Advantages (continued) Fusion fuels are not involved in nuclear proliferation problems: - No plutonium - Tritium remains on site in the fuel cycle Fusion reactors leave no long lived highly radioactive waste: - No long-lived radioactive waste from the fuel cycle - After around 100 years the Fusion reactor using selected materials would only leave low level radio-active structural components JG99.294/10

11 No Long-lived Radioactivity after Shutdown Comparison of Relative Radiotoxicity 10 8 from various power sources EFR A 10 7 EFR B PWR 10 6 Relative radiotoxicity Coal Fusion Model 2 Fusion Model Time after shutdown (years) JG97.362/11c Fusion Model 1 : Fusion Model 2 : advanced materials (Vanadium alloys) requires development Low activation Stainless Steel/ water cooled Near-term technology JG99.294/11

12 Fusion Energy Disadvantages Fusion reaction is difficult to start! High temperatures (Millions of degrees) in a pure High Vacuum environment are required Technically complex and high capital cost reactors are necessary More Research and Development is needed to bring concept to fruition The physics is well advanced but requires sustained development on a long time scale (20 to 40 years) JG99.294/12

13 Fusion Power Station Schematic Reactor containment Lithium blanket Deuterium Primary fuels Vacuum vessel Plasma DT n Li T + He DT DT, He Helium 4He 4He Lithium Generator JG95.113/55c Steam generator Turbine JG99.294/13

14 Plasmas Contemporary Physics Education Project (CPEP) A Plasma is an ionised gas. A mixture of positive ions and negative electrons with overall charge neutrality Plasmas constitute the 4th state of matter obtained at temperatures in excess of 100,000 degrees Plasmas conduct electricity and heat JG99.294/14

15 Self-Sustaining or Ignited Plasmas Deuterium tritium fusion reaction: D + T 4He + n + Energy The 4He nuclei ( α particles) carry about 20% of the energy and stay in the plasma. The other 80% is carried away by the neutrons and can be used to generate steam. Plasmas become Self-sustaining or Ignited when there is enough α power to balance losses from the plasma In stars plasma particles (including α s) are confined mainly by gravity and high plasma densities achieved On Earth; hot dense plasmas can be confined in Magnetic fields (Magnetic Confinement Fusion) superdense plasmas can be obtained by imploding solid deuterium-tritium pellets JG99.294/15

16 Inertial Confinement Laser implosion of small (3mm diameter) solid deuterium tritium pellets produces fusion conditions Pressure generation 100 million atmosphere plasma envelope formed Compression Fuel is compressed by rocket-like blow off 200,000 million atmospheres in core Ignition and burn Fuel Shell Wm 2 Laser or particle beams 50M o C / 10 4 tonne per m 3 in core JG97.367/2c τ E ~R/4c s Peak compression fuel reaches times liquid density for extremely short time (10 11 seconds) Core is heated and spark ignition occurs JG99.294/16

17 Plasma Confinement Magnetic fields cause charged particles to spiral around field lines. Plasma particles are lost to the vessel walls only by relatively slow diffusion across the field lines JG95.113/33c Toroidal (ring shaped) system avoids plasma hitting the end of the container The most successful Magnetic Confinement device is the TOKAMAK (Russian for Toroidal Magnetic Chamber ) JG99.294/17

18 How Large a Device? For fusion power to ignite a plasma: There has to be sufficient density of deuterium and tritium ions (n i ); The reacting ions have to be hot enough (T i ); The energy from the fusion α s must be confined for long enough (τ E ). τ E increases with the square of the device size a large machine is needed. The fusion triple product (n i T i τ E ) and the ion temperature (T i ) must both be large enough (below a certain temperature the fusion reaction probability is too small) pressure (n i T i ) 2 atmospheres confinement time > 5 seconds plasma ion temperature Million C JG99.294/18

19 JET (Joint European Torus) The Joint European Torus ( JET ) is the largest magnetic fusion test device in the world. Situated at Culham, Oxfordshire, JET: constructed between ; has operated present; is the largest Project in the European Union s Fusion programme The participating countries are the 15 EU nations + Switzerland The Project has a capital investment of over 500 Million and an Annual Budget of around 53 Million JG99.294/19

20 JET JET is a Tokamak with: Torus radius 3.1m Vacuum vessel 3.96m high x 2.4m wide Plasma volume 80m3 Plasma current up to 5MA Main confining field up to 4 Tesla (recently upgraded from 3.4 Tesla) JG99.294/20

21 JET is Unique 1/3rd Scale Model of ITER JET is the nearest in scale and operating conditions to the International Thermonuclear Experimental Reactor (ITER). JET has the plasma and divertor configuration of ITER. Tritium Compatibility JET is the only experiment world-wide able to study fusion power production and physics (DTE1) in the deuterium-tritium fuel mixture of a future fusion power station. Remote Handling Capability JET has developed a unique capability for remote installation and repair, which was used successfully to exchange the divertor without manned in-vessel intervention in the activated environment following DTE1. JG99.294/21

22 Progress with Magnetic Confinement Fusion JET and the similar large Tokamaks in: USA Tokamak Fusion Test Reactor (TFTR) Doublet IIID Tokamak (DIIID) Japan Japanese Tokamak 60U (JT-60U) Have made significant progress in: Technology of fusion Approaching the conditions of an Ignited plasma; Predicting the behaviour of a reactor plasma; Controlling impurities which enter the plasma Operating with Tritium fuel JG99.294/22

23 Progress towards Ignition The Fusion Triple Product (P i τ E = n i T i τ E ) required to reach ignition can be compared with leading edge performance of the devices year-on-year. 100 Inaccessible region Reactor conditions Ignition Q DT =1 Year Fusion product, n i τ E. T i (x10 20 m 3 s.kev) JT-60U JET JET TFTR DIII-D JET JET JT 60U TFTR JET JET TFTR TFTR DIII-D TFTR Q DT =0.1 ALC-C JT-60 DIII-D FT TFTR Reactor relevant conditions DIII-D TEXTOR ALC-A ASDEX Limit of Bremsstrahlung PLT T10 TFR TFR PLT T3 D T Exp JG98.208/13c Central Ion temperature T i (kev) The best plasmas now need an improvement of only 6 in performance. This requires a new larger device. JG99.294/23

24 Controlling Impurities Fuel Impurities are a major threat to reactor success Two primary sources of impurities exist: Helium ash from the fusion reaction Material impurities from plasma-wall interactions Impurities must be controlled since they: Radiate energy, and reduce the plasma temperature Dilute the fuel, thereby preventing ignition The Magnetic Divertor is a device for controlling impurities. This has been tested successfully in JET. Three different concepts have been compared. Results agree with code predictions. JG99.294/24

25 Progress with Magnetic Confinement Fusion Pumped Divertor in JET Slow drift across fields Plasma Impurities Cryopump JG97.367c Impurities (C, Be) are produced by ion impact on target and are ionised in the plasma and returned to target JG99.294/25

26 Mark I 1994/95 Mark I "open", very flexible JG93.552/3c Mark IIa Horizontal target JG93.552/1c 1996/97 Mark IIA more "closed", higher static power handling capability ITER - type Divertor Mark II "Gas Box" 1998 Mark IIGB ITER "Gas-box" type JG93.552/4c JG99.294/26

27 Fusion Production at JET 1991 World s first production of controlled fusion, about 2MW for one second Used a weak fuel, 90% deuterium and 10% tritium :50 deuterium / tritium fuel used Three world records established: Fusion Power 16MW Fusion Energy 22MJ Ratio of Fusion 0.64 Power to Input Power JG99.294/27

28 Fusion Power Development 15 JET (1997) I Fusion power (MW) 10 5 TFTR (1994) II III JET (1997) JET (1991) Time (s) The diagram encompasses : Two pulses with 10% T in D in JET in 1991; A result from the D-T studies on TFTR (1993 to 1997); High fusion power and quasi steady-state fusion power from the >200 pulses with >40% T in D in the JET D-T experiments of JG97.565/3c JG99.294/28

29 Remote Handling at JET Operation of a fusion power machine will make it radioactive JET has developed a sophisticated Remote Handling technique This system is unique; it uses a man-machine interface so that the remote operator feels what he is doing with the hands of his robot This equipment was used in early 1998, entirely to reconstruct the divertor to an ITER-like configuration and, in 1999, to conduct the first remote handling welding operations. JG99.294/29

30 The MASCOT Servo-manipulator Modifying the Divertor Assembly JG99.294/30

31 Developing Fusion in the Future The Next Step is to demonstrate Fusion as an Energy Source Scientific Study the ignition domain and operating conditions of a power station. Aim to improve confinement and reduce reactor size. Develop continuous modes of operation. Develop exhaust and fuelling. Technical Develop technologies of first wall material, superconductors, and tritium production and processing. Safety and Environment to demonstrate the safety and environmental advantages of magnetic fusion. Economic to demonstrate a cost per GW comparable to other energy sources. JG99.294/31

32 The Next Step Experiments on JET, JT-60U and TFTR and smaller machines specify the parameters for a power producing reactor A Reactor with 1.5 Gigawatts power would need: Plasma Current 20MA (4 JET) Magnetic Field 5-6 Tesla ( JET) Torus Radius 6m (2 JET) Torus Height 8m (2 JET) Plasma Volume 1100m3 (14 JET) Plasma duration >1000s (20 JET) The International Thermonuclear Experimental Reactor (ITER) is a world-wide project to design a Next Step machine in the 0.5 to 1.5 Gigawatt range. The European Union and Canada, Japan, the Russian Federation and the USA have contributed to the Engineering Design Activities of ITER. Cost would be in the region of 3 6 Billion (1997) JG99.294/32

33 Developing Fusion in the Future ITER ITER would produce GW of fusion power for 1000s. With this pulse length, superconducting magnets are needed. Cryostat Super conducting magnets Central solenoid Plasma Shielding blanket modules Divertor JG95.113/59c Entire magnet assembly must be encased in a cryostat to maintain superconducting temperatures. JG99.294/33

34 A Cost - Effective Investment Although an ITER-like device sounds expensive, Fusion research represents only a small fraction of world research effort The global Fusion effort is about 1.25 Billion US$ per year. Europe (EU) accounts for about 40% of this. But the EU Fusion research budget is only 5% of the total EU total Science Research budget In addition, pooling of resources on a project such as ITER, minimises risks and maximises benefits to the medium-large sized economies of the EU nations In the end, one is left to conclude that, although tokamaks appear rather expensive, given the small cost of a tokamak development programme compared to world-wide expenditure on electricity production, the enormous potential benefits justify the expenditure JG99.294/34

35 Conclusions The D-T Fusion process holds out the promise of: Virtually unlimited energy source from cheap abundant fuels; No atmospheric pollution of greenhouse and acid rain gases; Low radioactive burden from waste for future generations. In addition our experiments show that a Reactor size fusion device is now realisable. JG99.294/35

36 The Tokamak: A Transformer Device Magnetic Circuit (iron transformer core) Primary Transformer Circuit (inner poloidal field coils) Toroidal Field Coils Plasma Positioning and Shaping Coils (outer poloidal field coils) I p Poloidal field JG98.245/1c Toroidal field Resultant Helical Magnetic Field (exaggerated) Secondary transformer circuit (plasma with plasma current, I p ) JG99.294/36

37 Exterior of an Octant being Inspected JG99.294/37

38 Toroidal Field Coils being assembled into Octants JG99.294/38

39 An Octant from the Inner Edge showing the Four Toroidal Field Coils, Vacuum Vessel and Exterior Structures JG99.294/39

40 Construction Showing the Eight Limbs of the Transformer Core JG99.294/40

41 The Final Octant of the JET Vessel being Emplaced (1983) JG99.294/41

42 Plasma inside the JET Vessel JG99.294/42