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Accelerator Driven Subcritical Reactors

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  1. Accelerator Driven Subcritical Reactors or How Accelerators can save the planet Roger Barlow Institute of Physics Meeting Imperial College April 12th 2010 Roger Barlow: ADSRs 1

  2. We have to stop burning fossil fuels • They cause climate change • They are increasingly concentrated in countries with dodgy politics • They are going to run out Roger Barlow: ADSRs 2

  3. Renewables can’t fill the gap Even major (country-scale) developments will not be enough Turbine typically delivers 1.5 MW peak Alternatives (windmills,tidal power, solar power, improved insulation, retreat to the middle ages) can’t supply the deficit Roger Barlow: ADSRs 3

  4. Nuclear Power Fossil fuels will need to be replaced by a basket of alternatives It is hard (impossible?) to put such a basket together without nuclear power Big issues (real or in the eyes of the public?) with: • Safety: Chernobyl and 3 Mile Island • Waste disposal. Storage for millenia - NIMBY • Proliferation. Rogue states and terrorist organisations Roger Barlow: ADSRs 4

  5. Safe Subcritical Reactors Each fission absorbs 1 neutron and produces ~2.5 Some neutrons lost, leaving k neutrons to produce k fissions Sub Critical Run with k<1 Use accelerator to supply extra neutrons Hence: Accelerator Driven Subcritical Reactor (ADSR) Conventional: Run with k=1 exactly k<1 stops k>1 explosion Roger Barlow: ADSRs 5

  6. ADSRs Spallation Target OFF Accelerator “Manifestly Safe” Switch off accelerator and reaction stops Energy balance is OK: need 5-10% of power to run accelerator Core Roger Barlow: ADSRs 6

  7. Thorium When do we run out Uranium? In about 100 years, unless we move to a fast breeder system. Uranium is not the only possibility… Thorium: Fertile, not fissile 232Th +n233Th233Pa233U • Abundant. (Like lead) and spread around • Much smaller waste problems (no long-lived minor actinides) • Proliferation resistant Roger Barlow: ADSRs 7

  8. Thorium Reactors Thorium mixed with U or Pu • MSR (1964) • Winfrith (Dragon) • Fort St Vrain (1976) • Shippingport (1977) • Germany Julich (1967), THTR (1983) • Kurchatov Institute/Thorium Power • India But Thorium and ADSRs go together Roger Barlow: ADSRs 8

  9. Energy Amplifier (Rubbia) Thorium ADSR fast reactor Idea has been around for years Lead/Bismuth Eutectic acts as target and coolant and moderator. Nobody’s built one yet! Feeling is that the accelerator is the weak point. Roger Barlow: ADSRs 9

  10. Waste from ADSR Needs storing – but not forever Minor Actinides (Np, Cm, Cf) are not produced Roger Barlow: ADSRs 10

  11. Transmutation • Fast neutron flux can burn actinides produced by conventional reactors. MYRRHA project. • Also destroy most-problematic fission products (e.g. 99Tc: soluble, T½=211,000 Y) by ‘Adiabatic Resonance Crossing’. Lead moderator to ensure neutrons hit the resonance for absorption Roger Barlow: ADSRs 11

  12. Fuel lifetime Typical Uranium/Plutonium PWR needs refuelling in months, limited by fission product neutron poisoning Typical Thorium fuel lasts for years as fission product effects counterbalanced by increasing amounts of 233U Do we need reprocessing? Yes. Not for recycling of fuel but because 233U storage is problematic Roger Barlow: ADSRs 12

  13. Proliferation Thorium fuel system does not produce weapons • Explains why nuclear power went the U/Pu route back in the 1950’s • Solves today’s dilemma of states like Iran Specifically • There is no equivalent to a 235U device • Constructing the equivalent of a Pu device, using 233U, is made very difficult due to contamination with 232U Roger Barlow: ADSRs 13

  14. Summary so far ADSRs: Nuclear Power that avoids the real and perceived problems of criticality accidents Thorium as fuel removes problems of • Long-lived waste • Proliferation Worth a closer look… Lots to do in understanding The reactor. Thorium cross sections The Target and spallation Fuel reprocessing Accelerators Let's look at this Roger Barlow: ADSRs 14

  15. Accelerator requirements Proton Energy ~ 1 GeV gives ~20 spallation neutrons per proton. For 1GW thermal power: • Need 3 1019 fissions/sec (200 MeV/fission) • 6 1017 spallation neutron induced fissions/sec (k=0.98 gives 50 fissions/neutron) • 15 1017 spallation neutrons/sec • 7.5 1016 protons/sec Current ~10 mA. Power ~ 10 MW Compare: PSI cyclotron: 590 MeV, 2mA, 1MW ISIS synchrotron: 800 MeV, 0.2mA, 0.1 MW Roger Barlow: ADSRs 15

  16. Accelerators for ADSRs Synchrotron Current far too high. Complicated (ramping magnets) Cyclotron Energy too high for classical cyclotron. On the edge for other types FFAG Looks like the answer “Cyclotron currents at Synchrotron energies” Simplicity = reliability Linac Can do the job. But VERY expensive Roger Barlow: ADSRs 16

  17. Reliability: the 3rd Frontier Target runs hot. If beam stops, target cools & stresses & cracks: Require not more than 3 trips per year (or similar numbers) In the real world: Accelerators often trip for seconds/hours/days. They are complicated systems operating in real world environments But there are complex real world pieces of apparatus that trip rarely. Planes, computers, radio sets… Roger Barlow: ADSRs 17

  18. Straw man scheme: AESIR Accelerator Energy System with Inbuilt Reliability Design and build a Thorium ADSR, hopefully with an nsFFAG providing the accelerator (Other accelerator solutions are acceptable.) 1 GeV 10 mA protons with high reliability and low losses (don't want contamination problems) Roger Barlow - UK ADSR programme 18

  19. Stage I: LOKI The Low-key demonstrator 35 MeV H- system -or H+ or H2+ High current. (1 mA? 10 mA?) • Commercial source • RF Quadrupole • Standard Linac Study reliability and build it in from the start. Looks like the Front End Test Stand?? Copy? Move? Daresbury is the obvious place to do this as - Space available People available Friendly RDA Cockcroft, Universities, etc... Roger Barlow - UK ADSR programme 19

  20. Stage 2: FREA FFAG Research for the Energy Amplifier • Add a 2nd stage ring: boost energy to 390 MeV • Why 390? Pion production. But ~300 would still be interesting • Produces spallation. Not as much as 1 GeV, but enough to be interesting. • Continue to emphasise reliability. Increase current to 10 mA • Use a proton nsFFAG – with a cyclotron as fallback. Or Linac • Gives useful proton machine (c.f. TRIUMF, PSI). 99mTc production? • Links to proton therapy Roger Barlow - UK ADSR programme 20

  21. Stage 3: Thor Add a second ring to give 1 GeV nsFFAG, with RCS and Linac as backup options Use with a real target and nuclear core for production Need private funding Roger Barlow - UK ADSR programme 21

  22. Conclusions Things are moving • More people • More ideas • Possibility of funding at some level • Way ahead for Daresbury Roger Barlow - UK ADSR programme 22