Atomic and Nuclear Structure We will denote any isotope by using the notation A X Z where X is the element’s chemical symbol (e.g. H for Hydrogen, He for Helium etc.), Z is the atomic number (the number of protons in the nucleus) and A is the mass number (the number of neutrons and protons in the nucleus). If we denote the number of neutrons in the nucleus by N, then we have ; A= Z + N For example 235 U 92 is the isotope Uranium-235 with a nucleus consisting of 92 protons and 235 – 92 = 143 neutrons. 1 H Is a proton, the nucleus of the isotope Hydrogen-1, whereas Hydrogen-2 is the nucleus of the isotope Deuterium (heavy hydrogen) which consists of a proton and a neutron bound together.
The Mass Defect and Nuclear Binding Energy The sum of the masses of the individual masses of the protons, neutrons and electrons, gives the total constituent mass of an atom. The rest masses of these three fundamental particles are: Rest mass of electron me = 0.0005486 u Rest mass of proton mp = 1.007276 u Rest mass of neutron mn = 1.008665 u where u is the atomic mass unit = 1.660539x10-27 kg If one compares this with the total mass of the actual atom (with the bound nucleus) one discovers that the latter is smaller, and the difference is the so-called nuclear mass defect mdefect. Einstein (1905) made the celebrated proposal (since substantiated by experiment) that this mass defect is equivalent to energy, namely the binding energy of the nucleus, so that EB = mdefectc2 where c is the speed of light (3x108 ms-1). Because energy conversions are required in this sort of topic, we can express c2 in energy/mass units namely 931 MeV/u, where 1 eV = 1.602 x10-19 J.
What is fusion ? First fusion reactions discovered… D2 + T3 He4 + n1 + 17.6 MeV energy gain ~ 450:1 by an Australian, Sir Mark Oliphant (and Lord Rutherford), 1932 Why D-T? It has the lowest energy barrier of all fusion reactions Basis of Fusion Energy Science : Can we exploit this reaction (and other low activation barrier reactions), to produce base-load energy ?
Nuclear Processes in the Sun 1 4 0 0 0 4 H He + 2 e +3 +2 Q = 24.8 MeV 1 2 1 0 0 which is actually made up of the following steps; 1 1 2 0 0 Step 1: H + H H + e + Q = 0.4 MeV 1 1 1 1 0 2 1 3 0 Step 2: H + H He + Q = 5.5 MeV 1 1 2 0 Note that step 2 must occur twice before step 3 can take place 3 3 4 1 0 Step 3: He + He He + 2H + Q = 13.0 Me V 2 2 2 1 0 For the overall balance, steps 1 and 2 occur twice giving the energy release of 2x(0.4 + 5.5) + 13 MeV = 24.8 MeV. Actually there is an alternative step 3 but the information above gives an indication
Each reaction is characterised by its energy release and its rate. Fusion Reactions 1/2 Each reaction is characterised by its energy release and its rate. Total energy release (MeV) 2D + 2D 3He(0.82) + 1n(2.45) 50% 3.27 2D + 2D 3T(1.00) + 1p(3.03) 50% 4.03 2D + 3T 4He(3.52) + 1n(14.08) 17.6* 2D + 3He 1p(14.7) + 4He(3.7) 18.4 3T + 3T 4He(1.24) + 1n(5.03) + 1n(5.03) 11.3 * This was the first fusion reaction performed in the laboratory. Work carried out by Oliphant et al. (1934) One gram of deuterium undergoing the first 2 (D-D) reactions releases about 1011 J i.e. roughly 25,000 kWh per gramme mass of the reacting nuclei (a similar yield to that for the fission of Uranium). Side reactions (3 and 4) increase this energy yield by about a factor 5.
Fusion Reactions 2/2 Total energy release (MeV) 3T + 3He 1p(5.38) + 4He(4.76) + 1n(5.38) 51% 12.1 3T + 3He 2D(9.54) + 4He(4.76) 43% 14.3 3T + 3He 5He(11.9) + 1p(2.4) 6% 14.3 3He + 3He 1p(5.73) + 1p(5.73) + 4He(1.44) 12.9 1p + 6Li 3He(2.3) + 4He(1.72) 4.02 3He + 6Li 1p(12.4) + 4He(2.89) + 4He(2.89) 16.09 1p + 11B 4He(2.89) + 4He(2.89) + 4He(2.89) 8.67
The plasma state : the fourth state of matter plasma is an ionized gas 99.9% of the visible universe is in a plasma state Inner region of the M100 Galaxy in the Virgo Cluster, imaged with the Hubble Space Telescope Planetary Camera at full resolution. A Galaxy of Fusion Reactors. Fusion is the process that powers the sun and the stars
How of fusion reactions Aim : Overcome electrostatic repulsion between like charges Particle acceleration (eg. Linear accelerator, pyroelectric crystal, beam-target [laser-block], beam-beam ) Inertial compression (confinement) (eg. laser target fusion) Catalytic process (eg. Muon catalysis) Confinement (plasma near thermal equil) (gravitational, electric, magnetic) nuclear accelerator + -
The Conditions for Net Fusion Energy Production 1/2 For a steady-state fusion reactor the input power equals the output power. For net energy production, the electrical output (after conversion of the reactor thermal output (Eo) to electricity with efficiency e) must be more than sufficient to feedback energy (which is converted at efficiency i) to provide the input energy (Ein) to sustain the reactor. This condition is ei Eo > Ein (5.4-1) Now, let Ec = fusion energy from charged-particle products En = fusion energy from neutrons Er = fusion fuel radiation loss Eth = fusion thermal energy (3nkBTV, where V is the volume of plasma) El = fusion fuel energy loss (Eth + Er) For a steady state of the fusion fuel, the heating input must balance the losses i.e. Ein + Ec = El (5.4-2) Assuming that all (the losses and fusion neutron) energy can be recovered, then El + En = Eo (5.4-3)
Conditions for Net Fusion Energy Production 2/2 Combining these three equations (5.4-1) to (5.4-3) to eliminate El, we have Ec + En > Eing() (5.4-4) where g() = 1/(ei) – 1. Now Ec + En is the total energy released by fusion reactions Ef. Using this result (Ef/g() > Ein) and the definition of El we have Ef/g() + Ec - Er > Eth (5.4-4) Now a fusion reactor is characterized by an energy confinement time (i.e. representative of the time it takes for the energy in the plasma to be lost by processes other than radiation, if there is no power input). Let this time be represented by . The plasma power loss (independent of radiation losses) are then Eth/. In terms of the corresponding powers (E/(V)= P), then (5.4-4) can be expressed as n > (3kBT)/Pf/(g()n2) + Pc/(n2) – Pr/(n2) (5.4-5)
Conditions for fusion power in confined systems - - + + + + D T Achieve sufficiently high ion temperature Ti exceed Coulomb barrier density nD energy yield energy confinement time E 100 million °C “Lawson” ignition criteria : Fusion power & heat loss = f(Ti,nD,E) Fusion power > heat loss nD ETi>3 1021 m-3 keV s At these extreme conditions matter exists in the plasma state
Progress in magnetically confined fusion “Ignition” regime, Q∞ : Power Plant. Q=: Ignition Q = Pout /Pheat ~1 “Breakeven” regime : Eg. Joint European Tokamak : 1983 - 1997 : Q=0.7, 16.1MW fusion 1997- : steady-state, adv. confinement geometries Q=1: Breakeven D2 + T3 He4 (3.5 MeV) + n1 (14.1 MeV) “Burning” regime : ITER ≥ Pheat Q>5 ITER Pout Q=5: Burning
D-T fusion fuels are very abundant NB: 99.9885% of all matter is H Deuterium Tritium Lithium Relative Abundance 1D : 6000H 1T : 1017 H. Manufactured: Li+n→ He + T 1Li:106 H (earth) 1Li:1000H (solar system) According to the DOE (2001), world energy usage = 13.5 TW Estimated Earth reserves are : 6 x 108 TW years of D-T, 2 x 1011 TW years of D-D T. J. Dolan, Fus. Res., 2000
Low level waste, compared to fission Comparison of fission and fusion radioactivity after decommissioning Present ferritic technology allows a reduction of >3,000 over 100 years 100% recycling is possible after 100 years Using future Vanadium alloy structures, fusion is 1,000,000x less radioactive after 30 years than fission. http://fi.neep.wisc.edu http://www.ofes.fusion.doe.gov
Why exploit fusion-power on Earth? Fossil Fission Fusion Renew. Base-load energy generation ? High energy density Power grid stability Low greenhouse emitter Universal accessibility of fuel Large scale availability ~50 yrs Terrorist Potential Low High Nuclear non proliferation - Radioactive waste 104 yrs 100 yrs
What are Australia’s energy needs? Australia is a hot, dry, sparsely-populated, resource-rich nation Our population is 20 million - 1.2% growth rate (2006), >10 million live in Sydney, Melbourne, and Brisbane Our cities and industry are powered by large-scale base load supply Erraring power station : 2.64GW – Australia’s largest power plant Nearby Tomago Aluminium smelter (Hunter Valley)