ADSR Workshop, May ‘08 ADSR Systems for Power Generation: some practical considerations Bob Cywinski 7 May 2008, Daresbury

ADSR Workshop, May ‘08 Conventional Nuclear Reactors

ADSR Workshop, May ‘08 ADSR for power generation

ADSR Workshop, May ‘08 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

ADSR Workshop, May ‘08 Proton energy: Number of neutrons produced per proton (as a function of proton energy and spallation target radius)

ADSR Workshop, May ‘08 Proton energy: Variation with proton energy of: (i) the neutron multiplicity np (ii) neutron yield per unit energy of incident proton (np/E p ) (Calculated using using MCNPX) The energy gain of an ADSR is directly proportional to np/E p. Clearly there is little need for proton energies greater than 1GeV

ADSR Workshop, May ‘08 Proton energy: 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

ADSR Workshop, May ‘08 Proton current ? 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

ADSR Workshop, May ‘08 Proton current ? k eff =0.95, i=33.7mA k eff =0.98, i=13.1mA k eff =0.99, i=6.5mA To meet the constraint of a 10MW proton accelerator we need k eff =0.985

ADSR Workshop, May ‘08 Safety margins? k=0.985

ADSR Workshop, May ‘08 Time evolution of k eff H.M. Broeders, I. Broeders : Nuclear Engineering and Design 202 (2000) 209–218 Evolution of the criticality value, k eff, over 6 years for lead-cooled Th/U 233 ADSRs 1. Initial loss due to build-up of absorbing Pa 233 and decrease of U 233 enrichment by neutron absorption and fission Increase due to increasing U 233 enrichment from subsequent β- decay of Pa Long term decrease due to build up of neutron absorbing fission products

ADSR Workshop, May ‘08 Flux distribution in core 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

ADSR Workshop, May ‘08 Flux distribution in core: triple source H.M. Broeders, I. Broeders : Nuclear Engineering and Design 202 (2000) 209–218 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 each. The colour scale varies from 20 W:cm 3 (blue) to 320 W:cm 3 (red). The power densities are maximum near the beam buffer zones. The over-all power distribution is satisfactory.

ADSR Workshop, May ‘08 ns-FFAG ADSR Design? 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

ADSR Workshop, May ‘08 Alternative particles? The Euroschool Lectures on Physics with Exotic Beams, Vol. II - J. Benlliure

ADSR Workshop, May ‘08 Electron-driven ADSRs Yaxi Liu PhD Thesis, North Carolina State University, May, 2006

ADSR Workshop, May ‘08 Electron-driven ADSRs Yaxi Liu, PhD Thesis, North Carolina State University, May, 2006

ADSR Workshop, May ‘08 Electron-driven ADSRs Yaxi Liu, PhD Thesis, North Carolina State University, May, 2006

ADSR Workshop, May ‘08 Electron-driven ADSRs: multiple source Yaxi Liu, PhD Thesis, North Carolina State University, May, 2006 For P th = 1.55GW, and using Pb as coolant and target, a 0.67Amp 1GeV electron beam - or perhaps 5 x 130mA 1GeV electron beams –is required cf ESRF, Grenoble: 200mA at 6 Gev

ADSR Workshop, May ‘08 Summary and conclusions Proton energies >1GeV are not cost effective For a credible ADSR power station generating 600MW th at least 10MW of accelerator power is required (ie 10mA at 1 GeV). To improve neutron flux distribution, to relieve constraints on the accelerator, and to overcome issues of accelerator stability, three 3.3mA 1GeV accelerators feeding three spallation targets within the core are desirable ns-FFAGs may make multiple beam ADSR configurations affordable Multiple electron/deuterium beam driven ADSRs may also be possible MCNP simulations of these accelerator/target/core configurations are needed urgently!