CONFORM Open Day, 11 May 2008 Thorium, ADSRs…… and ns-FFAGs Bob Cywinski School of Applied Sciences Thorium, ADSRs…… and ns-FFAGs Bob Cywinski School of Applied Sciences

CONFORM Open Day, 11 May 2008 The Carbon Problem Energy source Grammes of carbon per KWh of electricity Nuclear 4 Wind 8 Hydro electric power 8 Energy crops 17 Geothermal 79 Solar 133 Gas 430 Diesel 772 Oil 828 Coal 955 source: Government Energy Support Unit (confirmed by OECD)

CONFORM Open Day, 11 May 2008 Meeting the Energy Challenge (2008)

CONFORM Open Day, 11 May 2008 Fission Th-U U-Pu and breeding

CONFORM Open Day, 11 May 2008 Disadvantages Requires introduction of fissile seed ( 235 U or Pu) 233 U is weapon grade unless denatured Parasitic 232 U production results in high gamma activity. Thorex processing of waste needs substantial development Thorium as a fuel.... Advantages 233 U has superior fissile properties Robust fuel and waste form Generates no Pu and fewer higher actinides Proliferation resistant

CONFORM Open Day, 11 May 2008 Annual energy resources ~5x10 9 tonnes of coal 27x10 9 barrels of oil 65x10 3 tonnes of uranium 2.5x10 12 m 3 of natural gas Thorium equivalent 5x10 3 tonnes of thorium After Sorenson

CONFORM Open Day, 11 May 2008 Estimated global Th resources

CONFORM Open Day, 11 May 2008 ….in recent times, the need for proliferation-resistance, longer fuel cycles, higher burn up, improved waste form characteristics, reduction of plutonium inventories and in situ use of bred-in fissile material has led to renewed interest in thorium-based fuels and fuel cycles in several developed countries……. IAEA, status report May 2005 I A E A

CONFORM Open Day, 11 May 2008 Past experiences

CONFORM Open Day, 11 May 2008 Current Power Strategy: India 3-stage closed cycle 500 MW prototype FBR is under construction in Kalpakkam is designed to breed 233 U-from Th The FBR is expected to be operating in 2011, fuelled with uranium-plutonium oxide It will have a blanket of thorium and uranium to breed fissile U-233 and plutonium respectively

CONFORM Open Day, 11 May 2008 Spallation “A high-energy nuclear reaction in which a target nucleus struck by an incident particle of energy greater than about 50 MeV ejects numerous lighter particles and becomes a product nucleus correspondingly lighter than the original nucleus. The light ejected particles may be neutrons, protons, or various composite particles…” Encyclopaedia Brittanica

CONFORM Open Day, 11 May 2008 An alternative approach: The Energy Amplifier or Accelerator Driven Subcritical Reactor Concept

CONFORM Open Day, 11 May 2008 MYRRHA: an ADSR transmutation proposal The MYRRHA design proposes a windowless Pb-Bi target: The target surface results from the vertical co-axial confluent Pb-Bi liquid metal flow The beam impacts the target vertically from above MYRRHA is being designed to transmute Pu waste 350 Mev, 5mA proton beam U-Pu MOX core and blanket Can an ADSR operate on thorium only?

CONFORM Open Day, 11 May 2008 The Energy Amplifier/ADSR energy balance accelerator sub critical reactor electrical energy converter output MW e MW th η~50% η~40% 600MW e 10MW 20MW e 1550MW th Energy gain: Th + n → 233 Th → 233 Pa (27d)→ 233 U

CONFORM Open Day, 11 May 2008 Target size Proton energy

CONFORM Open Day, 11 May 2008 The energy spectrum of the spallation neutrons at different incident proton energies. The target is a lead cylinder of diameter 20 cm At 1 Gev, approximately 24 neutrons per proton are produced Neutron energies

CONFORM Open Day, 11 May 2008 Proton beam requirements for EA/ADSR The (thermal) power output of an ADSR is given by withN = number of spallation neutrons/sec E f = energy released/fission (~200MeV) ν = mean number of neutrons released per fission (~2) k eff = criticality factor (<1 for ADSR) So, for a thermal power of 1550MW we require Given that a 1 Gev proton produces 24 neutrons (in lead) this corresponds to a proton current of

CONFORM Open Day, 11 May 2008 Proton beam requirements k eff =0.95, i=33.7mA k eff =0.98, i=13.1mA k eff =0.99, i=6.5mA To meet a constraint of a 10MW proton accelerator we need k eff =0.985

CONFORM Open Day, 11 May 2008 Safety margins k=0.985

CONFORM Open Day, 11 May because existing accelerators are not sufficiently stable and reliable...but why has no ADSR ever been built ?

CONFORM Open Day, 11 May 2008 ADSR geometry (a) single target GEANT4 232 Th core

CONFORM Open Day, 11 May 2008 H.M. Broeders, I. Broeders : Nuclear Engineering and Design 202 (2000) 209–218 Power density distribution improves with k eff but remains non-optimal Solution is generally to increase fissile enrichment in several core zones (eg see step at zone boundary on left) A better solution might be to use several proton beams and spallation targets Multiple beams/targets should also alleviate accelerator stability problems Flux distribution in ADSR core

CONFORM Open Day, 11 May 2008 Power density distribution (W:cm 3 ) in a lead-cooled ADSR with Th:U 233 fuel. The three beams with buffer zones are described by seven lead-filled fuel element positions. The over-all power distribution is satisfactory. Triple target ADSR

CONFORM Open Day, 11 May 2008 Power density distribution (W:cm 3 ) in a lead-cooled ADSR with Th:U 233 fuel. The three beams with buffer zones are described by seven lead-filled fuel element positions. The over-all power distribution is satisfactory. Triple target ADSR Pb-cooled Th/U 233 subcritical core with: k eff =0.985 P th =1550MW th Trefoil of 3 ns- FFAGs each providing 3.5mA at 1 GeV Molten lead is both core coolant and spallation target Three ns-FFAG drivers should be no more expensive than a singe conventional driver and will provide the required reliability margin

CONFORM Open Day, 11 May 2008 ADSR geometry (b) triple target GEANT4 232 Th core

CONFORM Open Day, 11 May 2008 Miniature spallation target in central bore of fuel element assembly High power (MW) proton beam Spallation charging of Th fuel rods 232 Th to 233 U conversion can be better optimised, with mitigation against detrimental neutron absorption by 233 Th and 233 Pa Modifications to existing reactors are not necessary Wider global exploitation of nuclear technology is possible Fuel preparation and burn cycles are decoupled Can thorium fuel be used in conventional reactors?

CONFORM Open Day, 11 May 2008 ThorEA – the thorium energy amplifier association

CONFORM Open Day, 11 May 2008 The way forward ? ( The AESIR project: (Accelerator Energy System with Inbuilt Reliability ) Stage 1: LOKI ( The Low-key demonstrator) 35 MeV H - system ; High current. (10 mA?) Commercial source, standard Linac Stage 2: FREA ( FFAG Research for the Energy Amplifier) 2 nd stage ns-FFAG ring to boost energy to 390 MeV emphasis on reliability Gives useful proton machine (c.f. TRIUMF, PSI). Stage 3: THOR Add a second ns-FFAG ring to give 1 GeV Use with a real target and nuclear core for First operational ADSR system Time 2-3 years years years Cost £17M £50 M £1-2B “.. dream the unthinkable because we desperately need new ideas” Carlo Rubbia (ThorEA meeting, Huddersfield, April 2009)

CONFORM Open Day, 11 May 2008 Summary Thorium is an underexploited fuel resource that could meet all our power generation requirements for many centuries Thorium fuel is proliferation resistant and produces relatively low level radiotoxic waste Although thorium is fertile, not fissile, it may be possible to construct safe and reliable EA/ADSR power systems, using spallation neutrons to drive the transmutation/fission process Similar processes could provide thorium fuel elements for conventional power reactors The key to both technologies is the development of compact, cheap and reliable accelerators: We believe ns-FFAGs may fit the bill Thorium might just save the planet!!

CONFORM Open Day, 11 May 2008 (1941) FERMI’s logbook containing the design of PILE-1

CONFORM Open Day, 11 May 2008 Acknowledgements Professor Roger Barlow (Manchester) Dr Cristian Bungau (Manchester/Cockcroft) Dr Adrian Bungau (Huddersfield/Cockcroft) RCUK, EPSRC, STFC Dr Bill Nuttall and Geoff Parks (Cambridge)