Accelerator Driven Subcritical Reactors or How Accelerators can save the planet Roger Barlow Institute of Physics Meeting Imperial College April 12 th 2010 Roger Barlow: ADSRs1

We have to stop burning fossil fuels Roger Barlow: ADSRs 1.They cause climate change 2.They are increasingly concentrated in countries with dodgy politics 3.They are going to run out 2

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

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 4Roger Barlow: ADSRs

Safe Subcritical Reactors 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) Each fission absorbs 1 neutron and produces ~2.5 Some neutrons lost, leaving k neutrons to produce k fissions 5Roger Barlow: ADSRs

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

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 232 Th +n  233 Th  233 Pa  233 U Abundant. (Like lead) and spread around Much smaller waste problems (no long-lived minor actinides) Proliferation resistant 7Roger Barlow: ADSRs

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: ADSRs8

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. 9Roger Barlow: ADSRs

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

Transmutation Fast neutron flux can burn actinides produced by conventional reactors. MYRRHA project. Also destroy most-problematic fission products (e.g. 99 Tc: soluble, T ½ =211,000 Y) by ‘Adiabatic Resonance Crossing’. Lead moderator to ensure neutrons hit the resonance for absorption 11Roger Barlow: ADSRs

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 233 U Do we need reprocessing? Yes. Not for recycling of fuel but because 233 U storage is problematic Roger Barlow: ADSRs12

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 1.There is no equivalent to a 235 U device 2.Constructing the equivalent of a Pu device, using 233 U, is made very difficult due to contamination with 232 U 13Roger Barlow: ADSRs

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 14Roger Barlow: ADSRs Let's look at this

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

Accelerators for ADSRs 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 Synchrotron Current far too high. Complicated (ramping magnets) 16Roger Barlow: ADSRs

Reliability: the 3 rd 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… 17Roger Barlow: ADSRs Target runs hot. If beam stops, target cools & stresses & cracks: Require not more than 3 trips per year (or similar numbers)

Straw man scheme: AESIR Accelerator Energy System with Inbuilt Reliability 18Roger Barlow - UK ADSR programme 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)

Stage I: LOKI The Low-key demonstrator 35 MeV H - system -or H + or H 2 + 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... 19Roger Barlow - UK ADSR programme

Stage 2: FREA FFAG Research for the Energy Amplifier Add a 2 nd 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). 99m Tc production? Links to proton therapy 20Roger Barlow - UK ADSR programme

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 21Roger Barlow - UK ADSR programme

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