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Title: Component unavailability versus inservice test (IST) interval: Evaluations of component aging effects with applications to check valves

Abstract

Methods are presented for calculating component unavailabilities when inservice test (IST) intervals are changed and when component aging is explicitly included. The methods extend usual approaches for calculating unavailability and risk effects of changing IST intervals which utilize Probabilistic Risk Assessment (PRA) methods that do not explicitly include component aging. Different IST characteristics are handled including ISTs which are followed by corrective maintenances which completely renew or partially renew the component. ISTs which are not followed by maintenance activities needed to renew the component are also handled. Any downtime associated with IST, including the test downtime and the following maintenance downtime, is included in the unavailability evaluations. A range of component aging behaviors is studied including both linear and nonlinear aging behaviors. Based upon evaluations completed to date, pooled failure data on check valves show relatively small aging (e.g., less than 7% per year). However, data from some plant systems could be evidence for larger aging rates occurring in time periods less than 5 years. The methods are utilized in this report to carry out a range of sensitivity evaluations to evaluate aging effects for different possible applications. Based on the sensitivity evaluations, summary tables are constructed showing how optimalmore » IST interval ranges for check valves can vary relative to different aging behaviors which might exist. The evaluations are also used to identify IST intervals for check valves which are robust to component aging effects. General insights on aging effects are also extracted. These sensitivity studies and extracted results provide useful information which can be supplemented or be updated with plant specific information. The models and results can also be input to PRAs to determine associated risk implications.« less

Authors:
 [1];  [2]
  1. Vesely, (W.E.), Dublin, OH (United States)
  2. Oak Ridge National Lab., TN (United States)
Publication Date:
Research Org.:
Nuclear Regulatory Commission, Washington, DC (United States). Div. of Engineering Technology; Oak Ridge National Lab., TN (United States)
Sponsoring Org.:
Nuclear Regulatory Commission, Washington, DC (United States)
OSTI Identifier:
505260
Report Number(s):
NUREG/CR-6508; ORNL-6909
ON: TI97007394; TRN: 97:013337
DOE Contract Number:  
AC05-96OR22464
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Jul 1997
Country of Publication:
United States
Language:
English
Subject:
22 NUCLEAR REACTOR TECHNOLOGY; NUCLEAR POWER PLANTS; IN-SERVICE INSPECTION; VALVES; AVAILABILITY; AGING; SERVICE LIFE; SENSITIVITY ANALYSIS; CALCULATION METHODS; RECOMMENDATIONS; THEORETICAL DATA

Citation Formats

Vesely, W E, and Poole, A B. Component unavailability versus inservice test (IST) interval: Evaluations of component aging effects with applications to check valves. United States: N. p., 1997. Web. doi:10.2172/505260.
Vesely, W E, & Poole, A B. Component unavailability versus inservice test (IST) interval: Evaluations of component aging effects with applications to check valves. United States. https://doi.org/10.2172/505260
Vesely, W E, and Poole, A B. Tue . "Component unavailability versus inservice test (IST) interval: Evaluations of component aging effects with applications to check valves". United States. https://doi.org/10.2172/505260. https://www.osti.gov/servlets/purl/505260.
@article{osti_505260,
title = {Component unavailability versus inservice test (IST) interval: Evaluations of component aging effects with applications to check valves},
author = {Vesely, W E and Poole, A B},
abstractNote = {Methods are presented for calculating component unavailabilities when inservice test (IST) intervals are changed and when component aging is explicitly included. The methods extend usual approaches for calculating unavailability and risk effects of changing IST intervals which utilize Probabilistic Risk Assessment (PRA) methods that do not explicitly include component aging. Different IST characteristics are handled including ISTs which are followed by corrective maintenances which completely renew or partially renew the component. ISTs which are not followed by maintenance activities needed to renew the component are also handled. Any downtime associated with IST, including the test downtime and the following maintenance downtime, is included in the unavailability evaluations. A range of component aging behaviors is studied including both linear and nonlinear aging behaviors. Based upon evaluations completed to date, pooled failure data on check valves show relatively small aging (e.g., less than 7% per year). However, data from some plant systems could be evidence for larger aging rates occurring in time periods less than 5 years. The methods are utilized in this report to carry out a range of sensitivity evaluations to evaluate aging effects for different possible applications. Based on the sensitivity evaluations, summary tables are constructed showing how optimal IST interval ranges for check valves can vary relative to different aging behaviors which might exist. The evaluations are also used to identify IST intervals for check valves which are robust to component aging effects. General insights on aging effects are also extracted. These sensitivity studies and extracted results provide useful information which can be supplemented or be updated with plant specific information. The models and results can also be input to PRAs to determine associated risk implications.},
doi = {10.2172/505260},
url = {https://www.osti.gov/biblio/505260}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1997},
month = {7}
}