July-August 2018 NPJ

Laser Peening for Long-term Operation By William Sims, Entergy and Vince Elias, Westinghouse Electric Company LLC. William Sims As part of his role as director, chief engineer of Major Projects for Entergy Nuclear, William Sims oversees all of Entergy’s peening projects. During his 28-year career with Entergy, Mr. Sims has had many first- of-a-kind designs and projects. Notably in relation to peening, Mr. Sims served as chairman of the Electric Power Research Institute’s Materials Research Program (MRP) Assessment Committee. While chairman, he led the development of MRP-335 to allow the use of water jet and laser peening to mitigate degradation of Alloy 600, which was approved by the NRC during his tenure. Mr. Sims holds a Bachelor of Science degree in Mechanical Engineering from the University of Arkansas. Westinghouse is the first to bring laser peening to the U.S. nuclear environment, deploying this technology at Entergy’s Arkansas Nuclear One (ANO) Unit 1 to cost effectively extend the operating years of the reactor internals. Westinghouse is poised to implement laser peening again at ANO Unit 2. For decades, the primary water stress corrosion cracking degradation process has plagued high-strength nickel alloy components and welds in the nuclear in- dustry. Applying laser peening on reactor coolant systemAlloy 600 components pre- vents and mitigates primary water stress corrosion cracking. At ANO Unit 1, laser peening was performed on the bottom-mounted in- strumentation noz- zles, demonstrating the technology and achieving design production rates. For ANO Unit 2, laser peening will be ap- plied to the reactor vessel head nozzles to mitigate the dam- aging effects of pri- mary water stress corrosion cracking and extend the life of the reactor head. The technology can also be developed for the dissimilar metal butt – or groove-type – welds on the hot and cold leg piping adjacent to the reactor vessel. In support of the Nuclear Energy Institute’s Delivering the Nuclear Promise® initiative, the application of laser peening is intended to help utilities lower their operating costs by preventing the need for unplanned, expensive repairs associated with stress corrosion and by extending inspection intervals for components to which it has been applied. The patented approach concentrates short-pulse laser energy in targeted locations on a metal’s surface, generating controlled shock waves that compress the material for improved cracking resistance. The shock waves propagate into the material with a force exceeding the metal’s dynamic yield strength, producing plastic deformation that leaves the surface layer in a state of compressive residual stress. The result is a robust and uniform stress improvement that arrests existing shallow primary water stress corrosion cracking and precludes future such cracking from developing. Laser peening enhances all metals, and can be applied to complex geometries and within confined spaces. The quiet pulsing laser peening process bypasses the hazards associated with other primary stress corrosion cracking mitigation techniques. It does not cause secondary vibration-induced effects on the surrounding components or require ultra-high-pressure piping and hoses. It Multiple laser peening tools can be used simultaneously – saving valuable critical path outage time. (Continued on page 56) 54 NuclearPlantJournal.com Nuclear Plant Journal, July-August 2018 Pursuant to the work of the EPRI MRP Assessment Committee, the NRC has proposed rulemaking 10 CFR 50.55a, “Codes and Standards,” to allow peening in accordance with MRP- 335 Revision 3A, “Topical Report for PWSCC Mitigation by Peening Surface Stress Improvement.” The NRC stated in a public meeting on July 30, 2018, that the agency expects to approve 10 CFR 50.55a in 2019.