1. 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

2. 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

3. 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%

4. 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= conversions/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

5. 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

6. 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

7. 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

8. 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