Steven J Steer, sjs218@cam.ac.uk

1. The Economics of Accelerator-Driven Subcritical Reactors and the Impact of Accelerator Reliability Uncertainty Steven J Steer, sjs218@cam.ac.uk

2. Contents Aim: Assess the impact of accelerator performance on Accelerator-Driven Subcritical Reactor (ADSR) technology Accelerator-Driven Subcritical Reactors A Multiple Reactor Park with Redundancy (1) (5) Performance of Contemporary Accelerators Flexible and phased construction of a 1st-of-a-kind reactor park (6) (2) Sensitivity of ADSR Economic Value to LINAC Performance The Economics of Different Accelerator-Reactor Configurations (3) (7) Accelerator Redundancy Summary and Conclusions (4) (8)

3. Accelerator-Driven Subcritical Reactors Key principals: Main Benefits: • Accelerator supplies spallation neutrons to the core (~0.5% of total) • Fission reactions reduce to nominal levels ~1 second after • accelerator ceases to provide neutrons • Energy from the reactor provides electricity to the accelerator • “Kick start” the accelerator, then the whole system is self-sustaining • Acceptable safety margin in fast spectrum • - sustainability (fuel efficiency) • Thorium fuel instead of uranium • - sustainability (more resources) • - proliferation resistance (probably) • Accelerator system increases control • - safety • - load following • Can burn minor actinides • - environment • - proliferation • particularly good for closed fuel cycle • - sustainability (fuel efficiency) • - proliferation resistance • - environment Significant Challenges: • Accelerator Performance • - achievable beam power • - reliability and required maintenance • Economics • - affordable electricity for all • Target station performance • Heavy liquid metal corrosion Session - Current and Future Reactor Design D. Coates “Actinide Evolution and Equilibrium in Fast Thorium Reactors” Fri 9.45 A. Ahmad “Study on the Neutronic Characteristics of Subcritical Reactors Driven by an Accelerated Pulsed Proton Beam” Fri 10.15 L. Goncalves “A Comparison of ADSR Concepts for Power Generation” Poster

4. Performance of Contemporary Accelerators Relative trip duration frequency per 24 hour trip linear accelerator Contemporary High-power accelerators: • Max power of ~1 MW • - ADSRs expect to need 5-10 MW • Scheduled to operate for ~70% of the time • - more is better, ADSRs will likely need ≥85% • Experience ~7500 trips per year • - Technically: ADSRs can tolerate (5 – few hundred) /year • - Financially: less is better, ~200 is the upper limit • All accelerator types have similar reliability profiles • - Which will be better: One powerful accelerator (LINAC) • or many low power ones (FFAG, SC cyclotron) ns-FFAG accelerator Vertical bars are a 50% uniform uncertainty, not a standard deviation A trip is defined as an unplanned shutdown of an accelerator that lasts >1 second

5. Sensitivity of LINAC-ADSRs Economic Value to Accelerator Performance Consequences of unplanned accelerator shutdowns • Within ~1 second of the accelerator shutting down the fission • reactions in the core reduce to nominal levels • - a thermal shock occurs, this causes fatigue in components • Electricity is no longer generated, the company is in breech of • its contracts until the ADSR is restarted • - a financial loss is made during the shutdown • Regulators will have to give the go ahead before it’s restarted • - the minimum shutdown duration will be ~24 hours • - even a 2-3 second trip will shutdown the reactor for a day A LINAC-ADSR is the ‘benchmark’ for ADSR designs Details of the Economic Model are available on request Effective Availability: Fraction of the year that an accelerator can effectively operate for after accounting for maintenance time and costs associated with unplanned failures. The reactor has been assumed to be 100% reliable and available for 85% of the year (310 days) To return a total net profit the levelised cost of electricity must be less than the wholesale price of electricity. Ten 24 hour shutdowns reduce the annual effective operational availability by ~4%points Costs quoted in 2006 money

6. Accelerator Redundancy Economic implications of redundancy • The additional LINAC will increase the construction cost ~20% • - this increases the exposure to risks due to construction delays • When one accelerator experiences a fault the other must be able to compensate within 1 second of the fault occurring • - different modes of how this can be achieved are being considered • The engineering challenge of achieving very high accelerator • performance is exchanged for requiring a robust switching • mechanism to change which accelerator is driving the core • - which of the two engineering challenges is easier to achieve? • - how does the economic case for each design compare? Assuming reactor is available for 85% of the year (310 days)

7. A Multiple Reactor Park with Redundancy Unique potential benefit to ADSRs of a reactor park • Constructing reactors at the same location saves on costs • - the construction process is more efficient • - the reactors can share site facilities requiring less to be built • - savings can be as large as 20% of the total construction cost • An integrated network of accelerators • - Any accelerator can have its protons diverted to any reactor • The redundancy cost can now be shared between three reactors • - the demands on accelerator performance remain low • - the switching mechanism is only marginally more complex

8. Flexible and Phased Construction of the 1st-of-a-Kind Reactor Park If R&D projections suggest that the challenges of re-directing proton beams are significantly smaller than the challenges of developing accelerators that trip only a few times per year… … it is recommended that the most economically efficient way of demonstrating LINAC-ADSRs is to demonstrate the 1st-of-a-kind plant with a conservative design that incorporates redundancy. It the technology is successful, forward planning allows for maximising the value of that initial investment by following it up with two phases of construction leading to a 3-reactor park. The design of the park is flexible and therefore responsive to the exact success of the engineering Phases 2 and 3 should be planned for, but there is no obligation to pursue them

9. The Economics of Different Accelerator-Reactor Configurations Construction cost savings for building multiple reactors on the same site have not been accounted for. This is a comparison between constructing independent ADSRs and ADSRs with an integrated accelerator network Integrated Reactor Park Single Accelerator 3/3 Benchmark Dual Accelerator

10. Summary and Conclusions Aim: Assess the impact of accelerator performance on Accelerator-Driven Subcritical Reactor (ADSR) technology Low CO2, controllable fast reactor, greatly extends consumption of natural resources and can consume radioactive waste The capital cost of redundancy is reduced by sharing a single redundant accelerator between multiple reactors (1) (5) Accelerators are a major challenge. Contemporary accelerators are less powerful, less available and less reliable than required Forward planning and flexibility enable the design to be responsive to technology outcomes, minimising the capital at risk (6) (2) If R&D shows that rapidly re-directing proton beams is practical then the economic and technical risks associated with beam trips cn be greatly reduced The cost of generating electricity will escalate rapidly if accelerators perform poorly (3) (7) Redundancy changes the engineering challenge from accelerator performance to beam re-direction A research avenue for minimising the risks posed by poor accelerator performance has been identified. Although only LINACs have been considered in this analysis the principal lends itselfto other types of accelerators that might be used to drive ADSRs (4)

11. Appendix A (Using the example of 4 LINACs and 3 Reactors) (A) All accelerators are on and are each supplying protons to all of the reactors, but they are operating at ¾ of full power. In the event that one accelerator trips, the power is increased in the remaining three to compensate. +ve: Because the reactors are still receiving some external protons the time window for increasing the power output of the remaining accelerators will be increased (will this time be significantly long?) –ve: The beam dynamics between the two different operating powers will be different (B) Three accelerators are on at full power, one has all systems on except the ion source. The Ion source high voltage is switched on only when another accelerator trips. +ve: The beam is only ever transmitted at a single power, the beam dynamics do not change –ve: Potential to misdirect the beam due to it changes in components while the system is off (C) All accelerators are on, but the beam of one is directed into a beam dump (possibly with a low duty cycle) until it is required. +ve: No issues with varying beam dynamics and only a limited chance of misdirecting the beam . Can utilise the ‘spare’ beam. –ve: Potentially significant irradiation of the beam dump (Suggest calculations comparing it to a fuel rod)

12. Appendix B The number of occasions per year two out of four accelerators experience unplanned shutdowns per year assuming they operate for 85% (310 days) of the year