Maintenance duration estimate for a DEMO fusion power plant, based on the EFDA WP12 pre-conceptual studies

• Time to replace the blankets and divertor cassettes for a single sector is estimated to be approaching 1000 h.
• Time to replace just the blankets is the same as for the blankets and divertor because the divertor must be removed first.
• Four remote handling systems would be required to operate in parallel to meet the PPCS 75% availability target.
• Rapid remote maintenance is essential for an economically viable fusion reactor.

The erosion and high neutron flux in a fusion power plant results in the need for frequent remote replacement of the plasma facing components. This is a complex and time consuming remote handling operation and its duration directly affects the availability and therefore the commercial viability of the power plant.A tool is needed to allow the maintenance duration to be determined so that developments in component design can be assessed in terms of their effect on the maintenance duration. This allows the correct balance to be drawn between component cost and performance on the one hand and the remote handling cost and plant availability on the other.The work to develop this tool has begun with an estimate of the maintenance duration for a fusion power plant based on the EFDA DEMO WP12 pre-conceptual design studies [1]. The estimate can be readily adjusted for changes to the remote maintenance process resulting from design changes. The estimate uses data extrapolated from recorded times and operational experience from remote maintenance activities on the JET tokamak and other nuclear facilities.The Power Plant Conceptual Study from 2005 [2] proposes that commercial viability of a power plant would require an availability of 75% or above. Results from the maintenance estimate described in this paper suggest that this level of availability could be achieved for the planned maintenance using a highly developed and tested remote maintenance system, with a large element of parallel working and challenging but feasible operation times.