An Expanded View of RAMI Issues

1. An Expanded View of RAMI Issues 02 March 2009 RAMI Panel Members: Mohamed Abdou (UCLA), Tom Burgess (ORNL), Lee Cadwallader (INL), Wayne Reiersen (PPPL), John Sheffield (UT), John Smith (GA), Les Waganer (Boeing – retired)

2. RAMI Panel Objective • The Greenwald Panel was charged with identifying the broad scientific and technical questions that must be answered before we are ready to proceed to Demo • The Panel identified a set of scientific and technical questions organized into three broad themes. • Theme A. Creating predictable high-performance steady-state plasmas: The state of knowledge must be sufficient for the construction, with high confidence, of a device that permits the creation of sustained plasmas that meet simultaneously, all the conditions required for practical production of fusion energy. • Theme B. Taming the Plasma Material Interface: The state of knowledge must be sufficient to design and build, with high confidence, robust material components that interface the hot plasma in the presence of very high neutron fluences. • Theme C. Harnessing fusion power: The state of knowledge must be sufficient to design and build, with high confidence, robust and reliable systems that can convert fusion products to useful forms of energy in a reactor environment, including a self-sufficient supply of tritium fuel. • Within the HFP Theme, RAMI (Reliability, Availability, Maintainability, and Inspectability) was identified as a key requirement: Demonstrate the productive capacity of fusion power and validate economic assumptions about plant operations by rivaling other electrical energy production technologies.

3. RAMI Issues and Gaps • The Greenwald Panel identified the following issues related to RAMI • Reliability of fusion-specific components is not known with accuracy • Availability of a Demo plant is not known and little effort has been given to this area • Maintainability of a Demo plant is not well defined • … and the following gaps • Component failure rate data • Maintenance data • Inspection techniques • The gap that would likely remain after all the current and planned programs were complete was… • The knowledge base for efficient maintainability of in-vessel components to guarantee the availability goals of Demo are achievable (G15) • The RAMI Panel considered this list of issues incomplete and expanded them

4. It is difficult (or impossible) to extrapolate the reliability of some fusion core components to next generation devices • Where there is ample operating data and in which component designs are incrementally improved from generation to generation, there is a reasonable basis for extrapolating the reliability to next generation devices • For other components, relevant operating data may be limited and key technologies and component designs may undergo radical changes from generation to generation, e.g. first wall, blankets, TF coils, and neutral beams • Reliability may not have been a main driver in the design of those components on present machines, but rather performance and cost - demonstrated reliability may not be representative of what could be achieved • Prospects for extrapolating the reliability of plant systems are better than for the tokamak core, but the reliability of the tokamak core is what is critical and will be difficult or impossible to project for DEMO for some components with high confidence based solely on ITER and present-day machines.

5. The expected availability of DEMO is modest • It took fission decades and extensive operating experience for the technology and practices to mature to the point where plant availabilities are now typically above 90% • The complexity of a fusion plant compared to a fission plant is sobering • Elaborate systems for plasma heating and current drive • Extensive tritium breeding for tritium self-sufficiency • Superconducting coils • Plasma facing components with high heat loads in a high fluence of 14 MeV neutrons • Remote maintenance of tokamak core components • Just based on complexity (parts count) alone, fission should enjoy a distinct advantage in availability over fusion

6. The availability of DEMO will need to be high enough to make the economics of fusion attractive • The cost of electricity scales inversely with availability for technologies that are capital intensive such as fusion • In order for fusion to be attractive to utilities, the capital cost of DEMO and risk of a critical failure will have to be low enough and the availability high enough to make fusion attractive compared with alternate technologies • It is not reasonable to expect that if DEMO demonstrates an availability of less than 50%, that utilities would see an availability of 90% as readily achievable if fusion was commercialized • The availability gap – the difference between a reasonable expectation and the economic need – is large and needs to be addressed

7. High reliability and availability are the products of purposeful design • The pathway to high reliability and availability is to • provide an environment in which components can operate reliably • make design choices that promote reliability and maintainability • qualify components by operating DEMO-relevant components under representative conditions and make continual improvements to correct observed deficiencies. • Providing an environment in which components can operate reliably is often overlooked in discussions about reliability and availability • Without provisions for robust disruption and ELM avoidance, there is little hope for reliable tokamak operation on DEMO • We need to understand the underlying reasons for good and poor past performance and build on past experience • Design choices that promote reliability and maintainability have to be made which may be out of the mainstream and have far reaching consequences • Liquid metal divertors, radiative tiles, advanced fuel cycles (a catalyzed DD fuel cycle with tritium sequestration), external transform, moving away from “ship in a bottle” configurations, etc. • Improved reliability and availability (but not necessarily sufficient) can be achieved by operating DEMO-relevant components under representative operating conditions and making continuous, incremental improvements • Time-honored way, e.g. in automobiles, airplanes, and fission reactors, to achieve the impossible

8. Achieving high availability on DEMO requires a readily maintainable configuration for the tokamak core which must be developed as part of an integrated design • Maintainability of tokamak core components must be a driver in developing the configuration, but maintainability is not the only consideration • Concepts for promoting maintainability in the configuration include modularization, standardization, and inspectability to detect incipient failures • A hot cell facility efficient at refurbishing all radioactive power core components will also be required • But the devil is in the details… a fully integrated design addressing ALL design requirements is needed when developing a workable configuration

9. Conclusion Developing a tokamak reactor that can generate electricity with a high enough availability to be economically attractive will require development of reliable, long-lived components and order of magnitude improvement in the outage times to accomplish maintenance of in-vessel components – a huge step beyond ITER