Using Thorium in conventional reactors: fertile to fissile conversion The final report Roger Barlow +Bob Cywinski, Cristian Bungau, David Cooke, Jake Smith, Paul Martin ThorEA meeting, 7th March 2012 Turn inert 232Th into fissile 233U using spallation neutrons Separate the A from the R in ADSR

Tool: GEANT4 Developed for HEP experiments: modern and flexible Already adapted to medicine, space probes… Need to establish new classes to describe changes in isotopic composition Careful validation of neutron production models Bug found in isotopic conversion reactions

How much 233U do we need? Find reactivity of typical reactor system with Thorium fuel rods + small % 233U Criticality reached at 1.8 % Use H20 and D20 moderator Use GEANT4 and MCNP Conclude: goal 2%

Irradiation Good news A 1 GeV proton on a large Thorium target produces ~ 27 conversions. (“1 GeV in, 5 GeV out”) 27 x 1mA x 3600=6.1 1020conversions/hour. 0.1% of a mole Bad news You need a large target (~8 tons). The neutron cascade is spread out Smaller target – higher concentration – lower rate Clever geometry? Neutron reflector? No success Separate target? Big hit in rate Rate scales with energy above 1 GeV. Below that it drops off fast

Some details Thorium or Thoria? Should we use the metal or the oxide? Conclusion: it makes little difference. Go with the oxide, ThO2 What about the 233Pa? Intermediate 27-day state can absorb neutrons. Problem? No. No significant absorption. No signs of saturation. Not a problem. Basically the concentration is so low

Fuel rod stability Lattice of Thorium and Oxygen ions. Interatomic potentials. Study thermal expansion, energy of lattice defects, specific heat etc. for various U concentrations. Basic conclusion: Thoria is boring and very stable Note: this conclusion involved serious CPU usage on the local cluster and on the grid. Note: this has led to other studies e.g. of molten salt reactors

Fission fragment measurements Need more data for reactor and waste studies Lohengrin Spectrometer at ILL 233U target for neutrons Fragments deflected electrically and magnetically (gives A/Q and E/Q) and dE/dx measured. Data taken: analysis in progress

Conclusions The process is possible – but only on a large industrial scale We have developed GEANT4 as a tool for reactor studies We have measurements of 233U fission products Computational chemists have got interested and involved in modelling reactor fuel