ITER prototype divertor cassette fabrication, integration and final assembly

Abstract

This paper reviews fabrication and assembly of the prototype ITER divertor cassette.It discusses component manufacturing, integration management, and final assembly operations on this large, 7.5-ton part. Produciblity and modularity were key design drivers for the ITER divertor hardware since it must be affordable yet satisfy demanding performance and remote maintenance requirements. Critical fabrication and integration issues that were addressed in producing the prototype hardware are discussed. INTRODUCTIONThe US Home Team coordinated the fabrication and assembly of a full-scale, 7.5 t, inner section, prototype of the ITER divertor cassette shown in Figure 1. The prototype cassette integrates actively-cooled Plasma Facing Components (PFCs) on to a cast 316LN stainless steel body structure fabricated by the US. The prototype PFCs include an inner vertical target, short dump and wing fabricated by the JA team and a central dome assembly fabricated by the US. The Russian gas-box liner was not included in the final integration due to fabrication difficulties that caused leaks in the final part; however, most of the liner fabrication steps were successfully demonstrated. The finished assembly has now been delivered to Sandia National Laboratories for flow testing. This will determine whether internal flow distribution and heat removal design criteria were met and evaluate dimensional stability at the 150°C operating temperature. Figure I . Completed Prototype ITER Divertor Cassette Assembly.The prototype cassette represents the inner section of one half of a full cassette in the original ITER design. Sixty such cassettes are mounted on toroidal rails at the bottom of the vacuum vessel to form the divertor. Each 6" cassette assembly was 5 m long, 2 m high, 0.5-1.0 m wide and weighed about 25 t. The prototype includes four replaceable PFCs (vertical target, short dump target, inner wing, and central dome). The PFCs attach to the body using structural keys that lock into slots machined in the body and the PFC rear surface. Expanded hollow pins inserted through a series of dove-tailed lugs were also considered for attachment of the dome assembly shown in Figure 1. The keys and pins were designed to accommodate both electromagnetic loads and differential thermal expansion. PFC interfaces were also consistent with single side access for remote removal and replacement of the components in a hot cell. Coolant is supplied to each PFC through two pipe-stub interfaces with the body that are designed to be remotely cut and re-welded using standard techniques. Most of these features have been retained in the ITER-Reduced Cost design concept, so the prototype cassette fabrication experience and lessons-learned are still relevant. CASSETTE BODYThe cassette body is a rigid, stainless-steel structure that was designed to be a full-life component, accommodating several sets of PFCs over the life of ITER. The body supports and accurately positions the PFCs, distributes cooling water to the PFCs, provides shielding for the vacuum vesse...