Kayla J. Sax MPhil Candidate in Engineering Department of Engineering, University of Cambridge Supervised by Dr. Geoff T. Parks Investigating the Scope for the Reduction of ADSR Accelerator Requirements Through Fuel Cycle Choice Universities Nuclear Technology Forum University of Huddersfield, 12 April 2011

Rapidly Increasing Global Energy Demand Climate Change Threats Renewed Focus on Nuclear Power Solutions Motivation

Promotion of ADSR High Relative Cost Safety Concerns Proliferation Concerns Problem of Waste Management Motivation (Continued)

Thorium is sustainable and cost-effective. High Relative Costs Operating subcritically. Shut down reactor by shutting down accelerator. Safety Concerns Thorium fuel cycle generates less plutonium than conventional cycles. Proliferation Concerns Low waste. Can burn legacy waste from conventional systems. Problem of Waste Management Proponents of ADSR highlight:

Thorium is sustainable and cost-effective. High Relative Costs Operating subcritically. Shut down reactor by shutting down accelerator. Safety Concerns Thorium fuel cycle generates less plutonium than conventional cycles.. Proliferation Concerns Low waste. Can burn legacy waste from conventional systems. Problem of Waste Management Proponents of ADSR highlight:

Basic ADSR Schematic ThorEA, “Towards an Alternative Nuclear Future,” 2009

Economics of ADSRs Upfront capital cost of accelerator is significant. – CERN group’s Energy Amplifier accelerator costs€160M. A larger accelerator will require a larger fraction of electricity produced by reactor. Reducing accelerator requirements and therefore cost makes ADSRs more competitive with: – Conventional reactor designs. – Other energy generation technologies.

Reducing Accelerator Requirements Fuel cycle choice can affect accelerator requirements. What does a good fuel cycle choice look like? k eff time 1

ADSR Beam Current To meet the constraints of a 10 MW proton accelerator, we need k > P th = 1.55 GW k = 0.95 i = 33.7 mA k = 0.99 i = 6.5 mA

Approach Initial Analysis: – Produce transient criticality profiles of various fuel compositions. – Identify fuel compositions that would minimize accelerator requirements. Further Analysis: – Analyze fuel compositions for response to various reactor perturbations to establish safety margin. End goal: – Identify which fuel compositions have the potential to be economically competitive and safe enough for commercial operation.

Initial Analysis Effective multiplication factor (k eff ): – Neutrons produced/neutrons absorbed. Modification of an existing “lumped” model developed by David Coates: – Account for neutron absorption by fission products.

Lumped Model 49 nuclide model. Simple “lumped” homogenous reactor model assuming uniform neutron flux, using average neutron cross-sections, and ignoring spatial effects. Boundary Conditions: – The effects of the decay and capture mechanisms from nuclides outside of the model are not accounted for.

Actinide Evolution Pathways The rate of change of a nuclide population within a reactor is a function of natural decay and neutron reactions (i.e. fission, capture and (n,2n))

Modeled with Differential Equation General form: – 49 equations are created for each of the 49 isotopes accounted for in the model. – Fourth order Runge-Kutta numerical integration applied. Development of the 33 nuclide fast model described in: – Actinide Evolution and Equilibrium in Fast Thorium Reactors David J Coates and Geoffrey T Parks Annals of Nuclear Energy, Vol. 37, pp. 1076–1088 (2010)

Accounting for Fission Product Poisoning Incorporates the effects of 27 fission products important to fast reactors. – Accounts for about 80% of macroscopic capture reactions by all fission products in the equilibrium core of a large, fast reactor. Similar to modeling of actinides: – Uses average neutron cross-sections. Accounts for some decay mechanisms outside the actinide and fission product isotope set: – “Adjusted” fission product yields.

Next Steps in Initial Analysis Account for other parasitic effects: – Absorption by non-fuel elements. – Leakage. Conduct comparative analysis of fuel compositions.

Further Analysis May require a non-traditional approach to criticality analysis. Subcritical multiplication factor (k s ): – Ratio of fission neutrons to the total neutrons in the system by fission and source. Calculated with variables corresponding to the number of fission neutrons and delayed neutron precursors. Coefficients are the multiplication rates of prompt fission neutrons, delayed neutrons, and source neutrons. – Variables correspond to actual values with real physical meaning regardless of the proximity to criticality. – Related work uses MCNPX.

Kayla J. Sax MPhil Candidate in Engineering Department of Engineering, University of Cambridge Supervised by Dr. Geoff T. Parks Investigating the Scope for the Reduction of ADSR Accelerator Requirements Through Fuel Cycle Choice Universities Nuclear Technology Forum University of Huddersfield, 12 April 2011