Thorium, ADSRs…… and ns-FFAGs Bob Cywinski School of Applied Sciences

1. Thorium, ADSRs…… and ns-FFAGs Bob Cywinski School of Applied Sciences

2. The Carbon Problem source: Government Energy Support Unit (confirmed by OECD)

3. Meeting the Energy Challenge (2008)

4. Fission....... and breeding U-Pu Th-U

5. Thorium as a fuel.... Advantages 233U has superior fissile properties Robust fuel and waste form Generates no Pu and fewer higher actinides Proliferation resistant g 232Th 233Th n b Disadvantages Requires introduction of fissile seed (235U or Pu) 233U is weapon grade unless denatured Parasitic 232U production results in high gamma activity. Thorex processing of waste needs substantial development 22 mins 233U 233Pa b 27 days

6. Annual energy resources Thorium equivalent ~5x109 tonnes of coal 27x109 barrels of oil 2.5x1012 m3 of natural gas 65x103 tonnes of uranium 5x103 tonnes of thorium After Sorenson

7. Estimated global Th resources

8. IAEA, status report May 2005 ….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……. I A E A

9. Past experiences

10. Current Power Strategy: India 3-stage closed cycle 500 MW prototype FBR is under construction in Kalpakkam is designed to breed 233U-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

11. 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

12. An alternative approach: The Energy Amplifier or Accelerator Driven Subcritical Reactor Concept

13. MYRRHA: an ADSR transmutation proposal 350 Mev, 5mA proton beam 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 U-Pu MOX core and blanket Can an ADSR operate on thorium only?

14. η~40% η~50% The Energy Amplifier/ADSR energy balance electrical energy converter output MWe 1550MWth 600MWe 20MWe MWth 10MW Energy gain: 155 accelerator sub critical reactor 232Th + n →233Th →233Pa (27d)→ 233U

15. Target size Proton energy

16. Neutron energies 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

17. Given that a 1 Gev proton produces 24 neutrons (in lead) this corresponds to a proton current of Proton beam requirements for EA/ADSR The (thermal) power output of an ADSR is given by with N = number of spallation neutrons/sec Ef = energy released/fission (~200MeV) ν = meannumber of neutrons released per fission (~2) keff= criticality factor (<1 for ADSR) So, for a thermal power of 1550MW we require

18. keff=0.95, i=33.7mA keff=0.98, i=13.1mA keff=0.99, i=6.5mA Proton beam requirements To meet a constraint of a 10MW proton accelerator we need keff=0.985

19. k=0.985 Safety margins

20. ...but why has no ADSR ever been built ? ...because existing accelerators are not sufficiently stable and reliable

21. ADSR geometry (a) single target GEANT4 232Th core

22. Flux distribution in ADSR core Power density distribution improves with keff 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 H.M. Broeders, I. Broeders : Nuclear Engineering and Design 202 (2000) 209–218

23. Triple target ADSR Power density distribution (W:cm3) in a lead-cooled ADSR with Th:U233 fuel. The three beams with buffer zones are described by seven lead-filled fuel element positions. The over-all power distribution is satisfactory.

24. Triple target ADSR Power density distribution (W:cm3) in a lead-cooled ADSR with Th:U233 fuel. The three beams with buffer zones are described by seven lead-filled fuel element positions. The over-all power distribution is satisfactory. Trefoil of 3 ns-FFAGs each providing 3.5mA at 1 GeV Three ns-FFAG drivers should be no more expensive than a singe conventional driver.... Pb-cooled Th/U233 subcritical core with: keff=0.985 Pth=1550MWth Molten lead is both core coolant and spallation target .....and will provide the required reliability margin

25. ADSR geometry (b) triple target GEANT4 232Th core

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

27. ThorEA – the thorium energy amplifier association

28. The way forward ? The AESIR project: (Accelerator Energy System with Inbuilt Reliability) Time 2-3 years + 4-5 years + 7-8 years Cost £17M £50 M £1-2B 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) 2nd 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 “.. dream the unthinkable because we desperately need new ideas” Carlo Rubbia (ThorEA meeting, Huddersfield, April 2009)

29. 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!!

30. (1941) FERMI’slogbookcontainingthedesign of PILE-1

31. Acknowledgements Professor Roger Barlow (Manchester) Dr Cristian Bungau (Manchester/Cockcroft) Dr Adrian Bungau (Huddersfield/Cockcroft) Dr Bill Nuttall and Geoff Parks (Cambridge) RCUK, EPSRC, STFC