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NuVision Engineering and Westinghouse Apply MSIP at Watts Bar Unit 1


Westinghouse Electric Company and NuVision Engineering have successfully implemented the Mechanical Stress Inprovement Process (MSIP®) to the pressurizer nozzles at Tennessee Valley Authority (TVA) Nuclear Power Division's Watts Bar Unit 1 in Spring City, Tenn. The application was completed in substantially less time than comparable alternative techniques.

MSIP®, developed and owned by NuVision, is a mechanical process that prevents or mitigates stress corrosion cracking at Alloy 600 locations in piping and welds by generating a compressive stress pattern from the pipe inside surface to more than halfway through the wall thickness. Westinghouse and NuVision are exclusively teamed to offer this technology to utilities with pressurized water reactors.

TVA chose MSIP® as its preferred mitigation technique due to its simplicity of application, obvious schedule and dose benefits, and regulatory acceptance of the technology to mitigate stress corrosion cracking of pipe systems. TVA Project Manager Marie Gillman and her team worked closely with Westinghouse and NuVision to prepare for and implement this project.

MSIP® was applied to mitigate stress corrosion cracking of the nozzle to safe-end welds on all six pressuruizer nozzles. The implementation schedule was a total of four days: from completion of pre-mitigation Performance Demonstration Initiative (PDI) Ultrasonic Testing (UT) to compleetion of post-mitiagation PDI UT on the last nozzle. The work was completed ahead of schedule with no injuries.

MSIP® was applied to one nozzle at a time. Total project dose was well below initial projections due to careful planning, 3-D modeling, an extensive shielding program by TVA and the use of an experienced project team. The schedule and dose performance are substantially less than what has been achieved on weld overlay projects of similar scope.

"The success of this project can be attributed to the teamwork and collaboration of Westinghouse, NuVision and TVA," said Greg Turley, manager for Westinghouse Alloy 600 materials evaluation and repair.

With the success at Unit 1, MSIP® is being considered for application on the pressurizer nozzles at Watts Bar Unit 2.

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