Maintenance of a commercial fusion power station and its implications for safety

A recent study was undertaken (D.V. Sherwood et al., Fusion Eng. Des. 22 (1993) 367-378) to identify a maintenance scheme which would lead to an acceptable level of availability for a future commercial fusion power station. It was thought that a scheme involving the servicing of the divertor through dedicated maintenance ports provided in each sector of the torus, and the sub-division of the blanket in both the radial and poloidal directions to allow it to be handled through two opposite dedicated radial access ports, could lead to a plant availability in the order of 80% (including 7% unplanned shutdown), i.e. comparable with that expected from APWRs. The method of blanket replacement proposed is substantially different from that of the ITER CDA. Although still conceptual, the maintenance scheme has now been developed sufficiently (NNC Rep. FR/E/004399A, 1993) to allow the main potential hazards requiring control during maintenance and the main feasibility issues to be identified. Taking these into account, a more accurate assessment of the plant availability has been possible which confirms that 80% should be possible. The scheme is considered to present little risk to the maintenance staff and with proper safeguards there would be little potential for the spread of contamination.