Progress on the ITER TBM port plug design

•ITER TBM PP design progress with two Dummy TBMs was outlined.•Attachment of Dummy TBMs in TBM Frame was assessed to investigate mechanical and sealing performance.•Implementation of cover plates was described and the preliminary maintenance sequence was developed.•Clearance between TBM Frame and Dummy TBMs were reduced to have better shielding performance.•Cooling layout and castellation design were updated to minimize thermal induced stress. In three of the ITER equatorial ports, tritium breeding blanket concepts will be validated and tested using mock-up breeding blankets called test blanket modules (TBM). In these ports, two TBM-Sets are mechanically attached in a TBM Frame to form a TBM port plug (TBM PP). The ITER Organization is responsible for the design and manufacture of both this TBM Frame and the Dummy TBMs which will fill them. As a part of this development, in 2013, a conceptual design review (CDR) of TBM PP with two dummy TBMs revealed the need for improvement of design performance, interfaces and maintainability. This paper presents the main design improvements after the CDR as well as associated feasibility analysis of the improved design focusing on the attachment. Finally the work plan for the Preliminary Design phase is summarized.