Accelerator Driven Subcritical Reactors or How Accelerators can save the planet Roger Barlow Institute of Physics Meeting Liverpool February 25 th /25/2015Roger Barlow: ADSRs1

We have to stop burning fossil fuels 6/25/2015Roger 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 6/25/2015Roger 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 “Up to“ 5% of UK electricity 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 6/25/20154Roger 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 6/25/20155Roger 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 6/25/20156Roger Barlow: ADSRs OFF

Accelerator requirements Proton Energy ~ 1 GeV gives ~20 spallation neutrons per proton. For 1GW thermal power: Need fissions/sec (200 MeV/fission) spallation neutrons/sec (k=0.98 gives 50 fissions/neutron) 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 6/25/20157Roger 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… 6/25/20158Roger 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) 6/25/20159Roger Barlow: ADSRs

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 6/25/201510Roger 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: ADSRs11

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. 6/25/201512Roger Barlow: ADSRs

Waste from ADSR Needs storing – but not forever Minor Actinides (Np, Cm, Cf) are not produced 6/25/201513Roger 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 6/25/201514Roger 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 6/25/2015Roger Barlow: ADSRs15

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? 1.‘Dirty bomb’ 2.‘Little boy’ type device 3.‘Fat man’ type device 6/25/201516Roger Barlow: ADSRs

“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.UK Ministry of Defence Wikipedia So possible – but not to be considered a major threat * RDD: Radiological Dispersion Device 6/25/201517Roger Barlow: ADSRs

Enriched Thorium Can you build a bomb from Thorium, the counterpart of the 235 U device? No 6/25/201518Roger Barlow: ADSRs

233 U device Analogue of Plutonium In principle possible – Critical mass ~15kg No spontaneous fission problems: simple gun- type device Extract 233 U chemically from Thorium and fission products in old fuel. Use for new fuel – or bombs? 6/25/201519Roger Barlow: ADSRs

232 U : so bad it’s good 232 U decays with a half life of 69 y, producing 228 Th which decays producing a 2.8 MeV  ray. Really nasty stuff 50 ppm 232 U in 233 U gives ~2 rem/hr for a worker 0.5m from a 5kg sphere. Health and safety limit 5 rem/y. Lethal doses rem It also destroys electronics 6/25/201520Roger Barlow: ADSRs

And it comes along with 233 U 232 Th(n,2n)  231 Th  231 Pa then 231 Pa(n,  )  232 U 14 mb for neutron energies above threshold ~6 MeV 233 U(n,2n)  232 U 4 mb for neutron energies above threshold ~6 MeV Fast 6+ MeV neutrons from tail of fission spectrum – or spallation 6/25/201521Roger Barlow: ADSRs

Possible loophole Ionium to the rescue! Ionium is 230 Th Does not occur in Thorium, which is pure 232 Does occur in Uranium, part of the 238 U decay chain ‘spike’ Thorium with Ionium: chemical separation gets 231 Pa and 232 Pa along with the 233 Pa, and thus 232 U 6/25/201522Roger Barlow: ADSRs You can’t separate U isotopes chemically But you can chemically isolate the intermediate 233 Pa. Wait (27 d half life) for it to decay to pure 233 U

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 232 U concentration Ionium may be used to make it pointless to separate the Pa 6/25/201523Roger Barlow: ADSRs

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… 6/25/201524Roger Barlow: ADSRs

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 Next Meeting: Oxford April 13th A way forward 6/25/201525Roger Barlow: ADSRs