Session: CS-15-01 Probabilistic and Risk-Informed Methods for Structural Integrity Assessment

Paper Number: 62560

Start Time: Wednesday, July 14, 2021, 08:00 PM

62560 - Technical Basis for Increased Inspection Interval of Cold Leg Pressurized Water Reactor Dissimilar Metal Welds Using xLPR 

Alloy 82/182 Dissimilar Metal Welds (DMWs) have been the subject of significant work due to their susceptibility to primary water stress corrosion cracking (PWSCC).  The current rules for inspection of DMWs are contained in ASME Code Case N-770 (latest revision).  These rules are based on crack growth rates that were originally published in MRP-115 in 2004.  Since that time significant work has been performed to better understand the crack growth behavior of Alloy 82/182 materials in pressurized water reactors (PWRs) and updated crack growth rates have recently been published in MRP-420 (Rev. 1).  These updated crack growth rates show a significant difference at lower temperatures which line up with the cold leg temperatures for PWRs (approx. 540-560°F).  Additionally, the US Nuclear Regulatory Commission (NRC) working along with the Electric Power Research Institute (EPRI) recently released the xLPR computer code which is a probabilistic fracture mechanics code for evaluating DMWs.  This paper evaluated various cold leg DMWs for PWRs using the xLPR probabilistic computer code to determine if the inspection durations for unmitigated DMWs could be increased from their current requirements in ASME Code Case N-770.  Failure probabilities were determined for the current technical basis using MRP-115 crack growth rates (with the current inspection duration) and compared to the probabilities using the new crack growth rates in MRP-420, Rev. 1 (with increased inspection durations).  Based on the change in probabilities determined between the two scenarios it was determined that it is justified to increase the inspection durations for unmitigated cold leg DMWs in N-770.

Presenting Author: Christopher Lohse Structural Integrity Associates

Authors:

Christopher Lohse Structural Integrity Associates
Do Jun Shim Structural Integrity Associates
Dilip Dedhia Structural Integrity Associates
Rohan Dutta Structural Integrity Associates
Nathan Glunt Electric Power Research Institute