1. ADSR Design Concept Development (Parade of the Straw-men) Steven J Steer, sjs218@cam.ac.uk 12 th July 2010, sjs218@cam.ac.uk

2. Contents Aim: Define an ADSR “Straw-man” design concept Group Exercise Goals and Design Elements Example: The Most Sustainable ADSR Summary of the ADSRs Designed for a Single Goal Conclusion from the Design Exercise Summary of Contextualised ADSRs Step 3: Contextualised ADSR Scenarios Summary (1) (2) (3) (4) (5) (6) (7) (8)

3. 12 th July 2010, sjs218@cam.ac.uk Group Exercise (Step 1) Information Gathering: bring design issues to the forefront of our minds, share understanding on aspects of the system. 3-Step exercise: 2 ½ hours long, 6 ThorEA members in attendance (the Cambridge Nuclear Engineering Group) (Step 2) Design Simplified ADSRs: scenarios with a single goal (Step 3) Design Contextualised ADSRs: scenarios with multiple goals, consideration given to different market and policy demands

4. 12 th July 2010, sjs218@cam.ac.uk Goals and Design Elements (Identifying Goals) Because timescales for development are comparable the ADSRs were designed to Gen-IV forum goals. We condensed these into 4 groups: Sustainability, Economics, Safety, and Proliferation Resistance. We added a 5 th category: “The Fastest Deployable ADSR” Summary of the Gen ‑ IV goals as given by the Gen ‑ IV Forum: http://www.gen-4.org/PDFs/GIF_Overview.pdf Sustainability-1 Generation IV nuclear energy systems will provide sustainable energy generation that meets clean air objectives and provides long-term availability of systems and effective fuel utilization for worldwide energy production. Sustainability-2 Generation IV nuclear energy systems will minimize and manage their nuclear waste and notably reduce the long-term stewardship burden, thereby improving protection for the public health and the environment. Economics-1 Generation IV nuclear energy systems will have a clear life-cycle cost advantage over other energy sources. Economics-2 Generation IV nuclear energy systems will have a level of financial risk comparable to other energy projects. Safety and Reliability-1 Generation IV nuclear energy systems operations will excel in safety and reliability. Safety and Reliability-2 Generation IV nuclear systems will have a very low likelihood and degree of reactor core damage. Safety and Reliability-3 Generation IV nuclear energy systems will eliminate the need for offsite emergency response. Proliferation resistance and Physical Protection Generation IV nuclear energy systems will increase the assurance that they are very unattractive and the least desirable route for diversion or theft of weapons-usable materials, and provide increased physical protection against acts of terrorism. (Design Elements and Design Options) Prior to the exercise 9 elements were identified to be important to defining the ADSR concept, these usually have 2 associated design options Fast or thermalised reactor k eff value ~0.995 (~2 MW beam) or ~0.985 (~10 MW beam) LINAC or compact accelerator Single or multiple targets Window or windowless target Fuel composition (multiple options) Open or closed fuel cycle Modular cores or a single large one Coolant choice (multiple options) Design Elements and Options

5. 12 th July 2010, sjs218@cam.ac.uk Example: The Most Sustainable ADSR (One of the five Step 2 Designs) Fast or thermalised reactor k eff value ~0.995 (~2 MW beam) or ~0.985 (~10 MW beam) LINAC or compact accelerator Single or multiple targets Window or windowless target Fuel composition (multiple options) Open or closed fuel cycle Modular cores or a single large one Coolant choice (multiple options) Design Elements Implies closed cycle k eff ~ 0.995 is more sustainable, but a feasible MA enriched core requires 0.985 Fast is more fuel efficient and necessary for MA to be feasible Large cores are selected on their own merits – lower enrichment required, greater fuel sustainability Fast Closed Cycle keff ~ 0.985 (~10 MW beam) Single Large Core CO 2 or He Gas Coolant was deemed less critical than neutron spectrum. the fast spectrum limited coolant choices, gas was selected for its reduced decommissioning issues (For Gen-IV “Sustainability” means fuel usage and waste disposal) Pure Th U Enriched Th Pu Enriched Th MA Enriched Th Fuel Options Pu-MA Enriched Th

6. 12 th July 2010, sjs218@cam.ac.uk Summary of ADSRs Designed for a Single Goal (Most Sustainable) Driver: Pu-MA fuel reprocess actinide closed cycle; low k eff value in order to be feasible; fast spectrum increase fuel efficiency and MA burn; large core for low enrichment; gas coolant is subject to only low radioactivation (Safest) Driver: thermal Thermal reduces rate of change of power during transients; water is a well understood thermal coolant; low k eff value for larger external n source; U enriched Th as U has large delayed n fraction; many low power accelerators preferred, but type does not matter; therefore multiple targets and windows appropriate; and for target placement practicality a large core is desirable (Most Prolif. Res.) Driver: Pure Th fuel Fresh fuel is no risk spent is difficult for ~1000 years (short-term prolif. res. was preferred over long-term); open cycle avoids separating nuclides; fast reactor to ensure high 232 U abundance; LHM or Na coolant to suit fast spectrum and provide physical protection to reactor; “black box” small cores (Most Economic) Driver: choices mainly independent Pu-Th fuel hedges against U price escalation; no Th reprocessing, as it is plentiful; thermal technology poses less risk to capital; this enabled water to be the coolant, again no development risks; a high k eff allows for low accelerator power and therefore more reliability; compact accelerators likely to be cheaper (technology risk was recognised); and large cores have a lower cost per kW. (Fastest Deployable) Driver: thermal Using well characterised U fuel minimises neurotic uncertainties; thermal enables a low k eff – less regulatory problems and minimises risks from power transients; water cooled; multiple ~600kW LINACs minimise accelerator reliability risks; window target; open cycle eliminates need for reprocessing industry; and large cores reduce enrichment requirements

7. 12 th July 2010, sjs218@cam.ac.uk Step 3 Contextualised ADSR Scenarios Three scenarios were used to define the context in which ADSRs might be expected to be developed (“An ADSR for Britain”) Connotations: made by Britain to be built and operated in Britain,; comparatively limited R&D budget; Pu stockpile available; needs to be profitable in a developed large electricity grid; the existing reprocessing industry means reprocessing will be an option. (“An ADSR for Europe”) Connotations: Wide skills base and research expertise, countries can specialise on narrow aspects of the design; the large combined R&D budget allows for R&D capital intensive technologies with beneficial payoffs to be pursued; varying national opinions on nuclear energy (some positive some negative); strong conscience for waste management, sustainability and proliferation resistance. (“An ADSR for the World”) Connotations: Must feel safe allowing any country to purchase and operate the reactor; not all countries have a skilled workforce; must be able to perform on remote and undeveloped electricity grids; widespread uptake implies high demand on resources.

8. 12 th July 2010, sjs218@cam.ac.uk Summary of Contextualised ADSRs (Consensus) Equal weight given to the five Step 2 designs A thermal reactor (3 of 5); use an enriched fuel (4 of 5); open cycle (3 of 4); be a single large core (4 of 5); water cooled (3 of 5); multiple targets (2 of 2); with a window (3 of 3). No consensus for k eff value or accelerator type. (For Britain) The UK Pu stockpile would be utilised, the fuel would therefore be Pu-Th; to minimise risk and R&D investment costs the accelerator system would be similar to the nearest-term deployable ADSR (multiple 600kW linear accelerators); this also implies multiple targets and windows; a large reactor core would aid the economics through economies of scale; possible reprocessing was left as an open question; nor was it decided if the reactor should be fast or thermal, but it was clear that that decision would then dictate the coolant choice (For the World) Proliferation resistance was the key factor, avoid individual nations processing fuel – central facilities that enrich the Th and ship it to reactors, spent fuel returned; open cycle, never need to separate nuclides; thermal reactors, high k eff value and window – minimise technology demands and hence the need for local expertise; water cooled; small modular cores for remote grids; therefore single targets; compact accelerators as they will eventually be easier to operate than linear accelerators (For Europe) Fast reactor technology in a closed fuel cycle would be developed to manage waste inventories and aid sustainability; an “enriched but not U” fuel would be selected for economic reasons; a windowless target design was considered feasible and beneficial; this implies a single target; large reactor for economies of scale; lead coolant for sustainability and safety; large k eff value to reduce fears over accelerator performance; compact accelerators the goal, linear a back up plan.

9. 12 th July 2010, sjs218@cam.ac.uk Conclusion from the Design Exercise The preferred design of an ADSR varies considerably depending on (1) which design goals are most emphasised and (2) the context in which it will be deployed. ThorEA should clearly define if, how, when and where ADSRs will fit into society to ensure time and money is spent more efficiently on R&D during the academic and commercial design process.

10. 12 th July 2010, sjs218@cam.ac.uk Summary Aim: Define an ADSR “Straw-man” design concept Group Exercise Goals and Design Elements Example: The Most Sustainable ADSR Summary of the ADSRs Designed for a Single Goal Conclusion from the Design Exercise Step 3: Contextualised ADSR Scenarios (1) (2) (3) (4) (5) (6) (7) Summary of Contextualised ADSRs 9 Straw-man ADSR designs created in a 2½ hour group exercise. The goals of Commercial ADSRs need to be clearly defined