Mitigation PWSCC by Ultrasonic Nanocrystal Surface Modification (UNSM) technology International Light Water Reactor Materials Reliability Conference and Exhibition 2016 Hong-Seok Cho 1 , Young-Sik Kim 2 , Auezhan Amanov 3 , Young-Sik Pyun 3 , Hong-Seok Cho 4 , Vijay K. Vasudeva n 5 , Seetha R. Mannava 5 and Abhishek Telang 5 1 Technology Research and Development Institute, KEPCO KPS, Naju 58217, South Korea 2 Materials Research Center for Energy and Green Technology, Andong National University, Andong 36729, South Korea 3 Department of Mechanical Engineering, Sun Moon University, Asan, 31460, South Korea 4 School of Materials Science and Engineering, Pusan National University, Pusan, 46241, South Korea 5 Department of Mechanical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221-0072, United States Corresponding author: [email protected]
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Mitigation PWSCC by Ultrasonic Nanocrystal Surface Modification (UNSM) technology
International Light Water Reactor Materials Reliability Conference and Exhibition 2016
1Technology Research and Development Institute, KEPCO KPS, Naju 58217, South Korea2Materials Research Center for Energy and Green Technology, Andong National University, Andong 36729, South Korea
3Department of Mechanical Engineering, Sun Moon University, Asan, 31460, South Korea4School of Materials Science and Engineering, Pusan National University, Pusan, 46241, South Korea
5Department of Mechanical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221-0072, United States
Primary Water Stress Corrosion (PWSCC) Cracking Mitigation by Surface Stress Improvement (SSI) (MRP-335 Revision 3, 3002007392 Final Report, February 2016)
▪ Surface stress improvement (SSI)mitigates PWSCC by inducing compressiveresidual stress at the surface exposed to reactor coolant
– Initiation of PWSCC flaws requires tensile stress at the surface
– Any existing flaws that are fully within the surface compressive stress zone cannot grow via PWSCC
▪ SSI provides an option to mitigate reactor vessel closure head penetration nozzles instead of replacing the entire head
▪ SSI provides an option to mitigate components that are not easily replaced or mitigated from outer surface using weld overlay or mechanical stress improvement (e.g., reactor vessel inlet/outlet nozzles)
SSI (Surface stress improvement) on DWMs (Dissimilar metal but welds)
ASME Code, Case N-766 ( N-516-3, N-770 )
J-Groove Head Vent Nozzles RPVHPNs
Output increased while decreasing operation cost of N-Power plant by “Acceptance of Inspection Relief ”
Asset Management
(10 CFR 50.59 Process)
Licensees may make changes to the facility, procedures and conduct tests and experiments without prior NRC approval
If change requires no license or technical specifications modifications
If change does not meet one or more of the eight criteria specified in 10 CFR 50.59(c)(2)
No license amendment request required
This process does not grant inspection relief
Optimized Inspection Intervals
(10 CFR 50.55a Process)
For NRC (the Nuclear Regulatory Commission) approved and regulation-mandated programs (e.g. in-service inspection programs) separate from the license
Licensees may submit “relief requests” to the NRC
NRC reviews and approves relief requests by Safety Evaluations (SE)
10 CFR 50.55a specifies the processes for requesting alternatives to, or relief from, the in-service inspection and testing requirements of the ASME Code
Code of Federal Regulations
Process for Acceptance of Inspection Relief
Development of ASME Code Requirements and U.S. NRC(the Nuclear Regulatory Commission) Review of Topical Report
Revised ASME Section XI Code Cases include performance criteria and inspection intervals for components mitigated by peening:– Alloy 82/182 DMWs per Code Case N-770-4, approved by ASME May 7, 2014– RPVHPNs per a revised version of Code Case N-729, expected to be approved soon by ASME
These revised code cases have not yet been approved by U.S. NRC and incorporated by reference in 10 CFR 50.55a
U.S. NRC approved the industry’s topical report supporting appropriate inspection relief with peening
– MRP-335 Revision 3 “Topical Report for Primary Water Stress Corrosion CrackingMitigation by Surface Stress Improvement (3002007392 Final Report, February 2016)
Materials Reliability Program
A novel SSI “UNSM” integration with Inlay Welding in Korea
KURIS : KPS Underwater Repair & Inspection System
UNSM: Compressive residual stress and improving Surface roughness