NSTX Response to theLessons Learned Report

NSTX TF Coil Repair Review

September 3-4, 2003

Al von Halle

A PPPL/PAO review committee was identified to review the cause of the TF coil failure and recommend remedial actions:

John Schmidt, Chairman

Wayne Reiersen

Larry Dudek

Al von Halle

Jim Graham

Greg Pitonak (DOE/PAO)

Cause of the Failure

“The root cause of the failure has been identified as inadequate design margin in the bolted joint connecting the flag and TF conductor, which resulted from a lack of complete, documented, understanding of how the joint would function under operating loads.”

Contributing causes included inadequately reviewed design changes following the final design review, lack of strict adherence to Laboratory change control procedures and quality control issues related to the original coil manufacture.

“Redesign the centerstack to address design deficiencies based on a valid understanding of the mechanical behavior of the joint/hub assembly.”

• The centerstack has been redesigned with oversight and review from independent external and PPPL experts.

• Detailed three-dimensional models have been developed for analysis of the joint/hub assembly.

• The critical issues of maintaining adequate contact pressure across the joint to provide low contact resistance and reacting the EM loads on the flags without overstressing the joint have been adequately addressed.

“Analyze and, where necessary, test critical components to the level of detail required to provide confidence that the design is adequate.”

• Three three-dimensional models have been developed and utilized to optimize the design and identify components where additional testing is necessary.

• R&D has been performed on the following components:– Collar epoxy: shear tests

– Copper threads and TapLok [tm] inserts: cyclic and pullout tests

– Flag joint: resistance and friction

• Additional testing is being performed:– Mechanical prototype

– Electrical prototype

“Specify the quality requirements necessary for the design to work and verify that those requirements are met.”

• The fabrication of new components for the centerstack assembly has incorporated written quality control requirements including inspection requirements and “hold-points”.

• Non-conformances are documented by QC and dispositioned by the cognizant engineer, approved by the Responsible Line Manager and concurred with by Engineering Department Head.

• Critical quality requirements will be incorporated into operating and/or maintenance procedures as required.

“Complete the documentation of the design and design basis before conducting a [final] design review.”

• Completed and checked drawings and analyses were provided for the Final Design Review.

• Analyses addressed multiple, relevant operating points (e.g., start-of-flattop, end-of-flattop, end-of-pulse)

• Subsequent changes (primarily the collar design) will be internally reviewed and also reviewed by FDR panel members.

“Adherence to the Work Planning Procedure (ENG-032) and the Control of Nonconormances Procedure (QA-005), which are relied on for configuration management on NSTX.”“Document non-conformances and failures.”

• The NSTX coil repair activity is covered by Work Planning Form #1032.

• Non-conformances are documented by QC and dispositioned by the cognizant engineer, approved by the Responsible Line Manager and concurred with by Engineering Department Head.

• An on-line trouble reporting system exists to document failures. Additional oversight and follow-up by NSTX management will be required.

“Organize well-balanced engineering design teams to address important mechanical design issues.”“Organize well-balanced design review teams.”

• The redesign of the TF centerstack has incorporated engineering expertise and participation from the Mechanical Design, Engineering Analysis, Electrical Design, Power Systems, Construction and Experimental Branches of the Engineering organization.

• The Final Design Review included panel members and participants from ORNL, MIT, GA, Culham and DOE as well as PPPL.