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Research Papers

Risk Assessment of Emergency Diesel Generator Subject to Design-Basis Earthquake Shaking

[+] Author and Article Information
Patxi Uriz

Exponent—Failure Analysis Associates,
149 Commonwealth Drive, Menlo Park, CA 94025
e-mail: puriz@exponent.com

Troy A. Morgan

Exponent—Failure Analysis Associates,
420 Lexington Avenue, Suite 1740, New York, NY 10170
e-mail: tmorgan@exponent.com

Manuscript received March 05, 2015; final manuscript received October 18, 2015; published online November 20, 2015. Assoc. Editor: Chimba Mkandawire.

ASME J. Risk Uncertainty Part B 2(1), 011007 (Nov 20, 2015) (7 pages) Paper No: RISK-15-1047; doi: 10.1115/1.4031843 History: Received March 05, 2015; Accepted October 18, 2015

A monitoring system intended to track vibrations associated with the operation of an emergency diesel generator (EDG) at a nuclear power plant was originally installed to trip generators during potential out-of-balance shaking. Years after original installation, plant engineers raised questions as to whether the monitoring system would have functioned properly in the event of excessive vibrations associated with earthquake ground shaking. As part of the plant’s examination of this issue, analytical models were developed for three vibration transducers via experimental characterization. A suite of ground motion records was selected and scaled such that their mean and dispersion were representative of the design-basis event (DBE) level of intensity at the plant site. The scaled suite of ground motions was used as an input for a three-dimensional (3D) analytical model representing the structure and soil-foundation interface, where the EDGs were installed. The voltage signal from the analytical transducer model provided input to the physical vibration alarm monitor. This monitor filters the vibration transducer signal and generates an output to a time-delay relay that will trip the EDG if the output from the vibration monitor is not reset within 5 s. The analysis and testing completed and described in this paper concluded that a DBE would not have caused the vibration monitoring circuit to spuriously trip the EDGs.

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Figures

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Fig. 1

Comparison of 5% damped site-specific horizontal and vertical design spectra with mean of scaled vertical ground motion suite

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Fig. 2

Stick-model used in the analysis

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Fig. 3

Comparisons of ratio of FF to EDG response spectra for soil–structure interaction (SSI) model and from individual plant examination for external events (IPEEE) report

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Fig. 4

Velocity transducer mounted to the EDG

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Fig. 5

Empirical transfer functions for transducer 3A based on the test data sheets and supplemental shake table testing

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Fig. 6

Transducer modeling results for input excitation of 10 Hz at 6 ips for types 2A, 3A, and 3B

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Fig. 7

Transducer model voltage output comparison for ground motion number 5

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Fig. 8

Truncated voltage time-history shown with original time-history for ground motion number 3. The three solid black lines represent (from left to right) power loss, search for alternate power, and the activation of the monitor

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Fig. 9

Block diagram of four monitor stages

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Fig. 10

Voltage time-history input into electronic module and duration of trigger

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