Accelerator-Driven Subcritical Reactors: How Accelerators Can Save the Planet

1. Accelerator Driven Subcritical Reactors or How Accelerators can save the planet Roger Barlow Institute of Physics Meeting Liverpool February 25th 2010 Roger Barlow: ADSRs

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

3. Renewables can’t fill the gap Even major (country-scale) developments will not be enough Turbine typically delivers 1.5 MW peak “Up to“ 5% of UK electricity Alternatives (windmills,tidal power, solar power, improved insulation, retreat to the middle ages) can’t supply the deficit Roger Barlow: ADSRs

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

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

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

7. 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 neutrons/sec (k=0.98 gives 50 fissions/neutron) • 3 1016 protons/sec Current 5 mA. Power = 5 MW Reliable! Spallation target runs hot. If beam stops, target cools and stresses and cracks: no more than 3 trips per year Compare: PSI cyclotron: 590 MeV, 2mA, 1MW ISIS synchrotron: 800 MeV, 0.2mA, 0.1 MW Several trips per day Roger Barlow: ADSRs

8. Reliability: the 3rd Frontier 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

9. 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

10. 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

11. 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

12. 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

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

14. 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

15. 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

16. Proliferation: Issues and Questions “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 Is it true? • ‘Dirty bomb’ • ‘Little boy’ type device • ‘Fat man’ type device Roger Barlow: ADSRs

17. “Dirty Bomb” (Spent) fuel rods will contain fission products Dispersal over civilian areas would cause panic, expense, and few fatalities It is thought that during the 1960s the UK Ministry of Defence evaluated RDD*s, deciding that a far better effect was achievable by simply using more high explosive in place of the radioactive material. Wikipedia So possible – but not to be considered a major threat * RDD: Radiological Dispersion Device Roger Barlow: ADSRs

18. Enriched Thorium Can you build a bomb from Thorium, the counterpart of the 235U device? No Roger Barlow: ADSRs

19. 233U device Analogue of Plutonium In principle possible – Critical mass ~15kg No spontaneous fission problems: simple gun-type device Extract 233U chemically from Thorium and fission products in old fuel. Use for new fuel – or bombs? Roger Barlow: ADSRs

20. 232U : so bad it’s good 232U decays with a half life of 69 y, producing 228Th which decays producing a 2.8 MeV  ray. Really nasty stuff 50 ppm 232U in 233U gives ~2 rem/hr for a worker 0.5m from a 5kg sphere. Health and safety limit 5 rem/y. Lethal doses 200-1000 rem It also destroys electronics Roger Barlow: ADSRs

21. And it comes along with 233U 232Th(n,2n)231Th 231Pa then 231Pa(n,) 232U 14 mb for neutron energies above threshold ~6 MeV 233U(n,2n)232U 4 mb for neutron energies above threshold ~6 MeV Fast 6+ MeV neutrons from tail of fission spectrum – or spallation Roger Barlow: ADSRs

22. Possible loophole Ionium to the rescue! Ionium is 230Th • Does not occur in Thorium, which is pure 232 • Does occur in Uranium, part of the 238U decay chain • ‘spike’ Thorium with Ionium: chemical separation gets 231Pa and 232Pa along with the 233Pa, and thus 232U • You can’t separate U isotopes chemically • But you can chemically isolate the intermediate 233Pa. • Wait (27 d half life) for it to decay to pure 233U Roger Barlow: ADSRs

23. Proliferation: Conclusions • It may be impossible to convert for weapons purposes, and certainly extremely hard • Technology beyond the reach of back street terrorists, detectable by WMD inspectors • Advantage to have all fuel exposed to fast neutrons to ensure 232U concentration • Ionium may be used to make it pointless to separate the Pa Roger Barlow: ADSRs

24. Summary ADSRs provide a form of Nuclear Power that avoids the real and perceived problems of criticality accidents It also makes possible the use of Thorium as fuel, removing problems of • Long-lived waste • Proliferation • Running out of Uranium Worth a closer look… Roger Barlow: ADSRs

25. A way forward Formation of the Thorium Energy Amplifier Association: Universities and labs and industry A research consortium aimed at • Networking (website, workshops) • Sharing knowledge, within and outside UK • Arousing interest in Research Councils, Whitehall, etc. • Collaborative response to funding opportunities • Design of a Thorium ADSR, aimed at power generation with transmutation as bonus. FFAG is baseline accelerator If you’re interested, see www.thorea.org Next Meeting: Oxford April 13th Roger Barlow: ADSRs