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Asset Integrity Management of Critical Infrastructure
Editor
Mamdouh M. Salama
Mamdouh M. Salama
MMS4Aim LLC, USA
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Dragan Komljenovic
Dragan Komljenovic
Hydro-Québec, Canada
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Jovica R. Riznic
Jovica R. Riznic
Canadian Nuclear Safety Commission, Canada
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ISBN:
9780791887738
No. of Pages:
180
Publisher:
ASME
Publication date:
2024

The feedwater level in steam generators of a nuclear reactor is controlled by air-operated level control valves (LCVs). In the air operated valves, aging related degradation of diaphragm causing the air leak is a dominant mode of malfunction of the valve actuator. The paper summarizes the operating experience of a group of 32 large LCVs (10” size), which includes occurrences of various types of malfunctions, repair actions, and valve overhauls over a period of 20 years. The operating history of each valve is translated into complete and right-censored lifetime data. This paper presents the statistical analysis of the valve lifetime data and estimates the Weibull reliability curve for various failure modes of the valve. The three major groups of components, actuator, control, and packing have an adequate reliability. The mean lifetime of the actuator, control, and packing system are estimated as 21, 15, and 37 years, respectively. Further, these components do not exhibit any statistical aging effect, i.e., increase in failure rate with valve age. A simulation analysis was performed to confirm that the absence of aging effect is not an artefact of data. In other words, there is a high probability (over 0.8) of detecting the aging effect from the current dataset, if the aging were indeed present in the valve components.

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