ARIES-AT Maintenance System Definition and Analysis

A fusion power plant must have a high availability to be competitive in the electrical generation market. Attaining high plant availability is difficult because the fusion power core has a limited service lifetime. Moreover, the core components are radioactive and very large. To assess these issues, the maintainability of the ARIES fusion power core was analyzed and integrated into the early power core design process, which resulted in a maintainability approach capable of attaining a relatively short refurbishment time. The developed timelines are presented for the scheduled maintenance of the power core. The short core refurbishment time coupled with evolutionary improvements in the maintainability of the reactor plant equipment and the balanceof-plant equipment infer an attractive plant availability in the range of 90%. Power Core Maintenance Philosophy Several of the guiding principles or goals for the overall fusion power plant will continue to significantly influence the design and operation of its maintenance system — the plant must be safe and economical. The plant must be safe both to the general population and to the plant workers, including the maintenance workers. A fusion power plant is a nuclear device that emits high-energy neutrons during operation. During shutdown periods, secondary reactions from the highly irradiated power core materials continue to produce beta and gamma radiation inside the power core at a much lower rate as compared to the dose rate during operation. The power core materials were chosen to minimize these secondary radiation levels and long-lived radioactive waste products. After a 24-hour cooling off period, the radiation level within the power core will decrease to a level suitable for access with radiation-hardened maintenance equipment. It is anticipated that the regulations for allowable radiation levels for nuclear plant workers will continue to be upgraded to assure no hazardous exposure. This assumption would effectively mandate that all maintenance and refurbishment of power core replaceable components would be accomplished entirely by robotic equipment. No hands-on maintenance of the power core components is assumed. To be economical, the maintenance actions must be efficient and expedient to keep the maintenance downtimes as short as possible. It is assumed that aggressive maintenance research and development programs will be implemented to accomplish a robotic maintenance system that can quickly and efficiently inspect, diagnose, repair, remove, replace, and inspect all components of the power core. This includes both the life-limited and the life-of-plant components. Fully automated, autonomous maintenance machines will efficiently accomplish the remote operations. The use of expert systems will be expanded to help develop experience