DEMO divertor maintenance

This paper presents a DEMO divertor segmentation and maintenance scheme together with maintenance time estimations. As far as it is known, it is the first such study for DEMO, and the work was coordinated by EFDA. The approach of the study was that DEMO divertor and its handling shall be very similar to that of ITER, therefore ITER divertor segmentation and maintenance schemes were used as starting point. The maintenance scheme for both ITER and DEMO is the following: the divertor is segmented into cassettes. For maintenance 3 divertor ports are used through which all equipment and cassettes are inserted and removed. A toroidal rail based machine transports the element toroidally in front of the port, from where a radial tractor is used that move it between cask and VV. The main difference between DEMO and ITER is the increase in major radius from 6.2 to 7.5 m, and the cassette segmentation changed from 6.66° to 11.25°. These two factors increase the cassette weight from 12 to 25 tons. Therefore the cantilevered radial transportation of ITER cassettes was not adapted, but instead, the first design of a new, bottom supported radial machine is proposed. For the entire blanket maintenance 70 days were calculated instead of the 179 days in ITER. It was also concluded, that if in-vessel toroidal machine is used for blanket maintenance, there are no real possibilities for parallel blanket/divertor replacement.