Document: NUREG-0800
Document ID: b07c8dd1-23f6-41f1-a3ba-aa378f9ea59a
Document Type: srp
Title: RISK-INFORMED INSERVICE INSPECTION
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0325/ML032510135.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.9.8
CFR Part: 
CFR Title: 

Content:
opriately addressed. Parameter uncertainty, model uncertainty, and completeness uncertainty should be addressed in accordance with the guidelines of Regulatory Guide 1.174. The programs and procedures regarding the long-term maintenance, update, and use of the PRA should be sufficient to ensure that any anticipated changes in the ISI program that do not require 3.9.8-9 NRC notification or approval will always be based on an appropriately generated set of risk insights. II.2.2.1 Scope of Piping Systems The piping systems included in the RI-ISI program for the purpose of evaluating the impact of the proposed changes in the ISI program on total plant risk and for the purpose of screening to classify the safety significance of piping systems should be such that any proposed increases in CDF and risk are small and are consistent with the intent of the Commission’s Safety Goal Policy Statement. II.2.2.2 Piping Segments An acceptable method for modeling a run of a pipe in a PRA or to define its ISI requirements is to divide the pipe run into segments. Portions of piping within the piping systems that have the same consequences of failure should be systematically identified. Consequences of failure include an initiating event, loss of a particular train, loss of a system, or a combination thereof. The location of the piping in the plant, and whether inside or outside the containment, should be taken into account in defining piping segments. Piping sections subjected to the same degradation mechanism should be systematically identified. Most of the degradation mechanisms present in nuclear power plant piping are dependent on a combination of design characteristics, fabrication processes and practices, operating conditions, and service experience. The degradation mechanisms to be considered include, but may not be limited to, vibration fatigue, thermal fatigue, corrosion cracking, primary water stress corrosion cracking (PWSCC), IGSCC, microbiologically induced corrosion