Masters Theses

Aidong Wei

Date of Award

5-1991

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

Belle R. Upadhyaya

Committee Members

L. F. Miller, J. Landes, R. E. Uhrig

Abstract

Air-Operated Valves (AOVs) are used in almost all fluid systems in a Nuclear Power Plant. Their failures have resulted in increased plant maintenance. More importantly, the operational readiness of nuclear plant safety-related systems has often been affected by AOV degradation and failure. Thus, in recent years AOVs have received considerable attention by the U. S. Nuclear Regulatory Commission and the nuclear power industry. A comprehensive study of AOV operations was performed and the results of this study are presented in this thesis. The primary objective of this research is to identify valve related variables that are sensitive to valve anomalies. This was accomplished through experimental and theoretical analysis of AOV dynamics. The AOV related events in nuclear power plants were studied and typical AOV anomalies are summarized. A test loop has been constructed to develop AOV condition monitoring techniques. The operations of the test AOV were monitored by measuring air supply line pressure, stem position, and pressure drop across the valve. These three sensors were interfaced with a data acquisition system. The acquired data were studied both in the time domain and in the frequency domain. An extensive experimental study of the valve operations and both transient and steady-state signal analysis were performed. An analytical model of a typical AOV was developed. Simulations of the model responses for normal operations and with anomalies were performed and compared with experimental data. Two important signals, stem motion as measured by a linear variable differential transformer and the valve differential pressure, reflect the changes in the valve behavior and can be monitored using these two measurements. Both transient valve stroking signatures and normal fluctuations may be processed for establishing valve operating characteristics. The results of valve dynamic modeling confirm experimental observation. A set of guidelines for implementing this monitoring technique in power plants is outlined.

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