Progress in Nuclear Energy. Vol. 1, pp. 665 to 666. Pergamon Press 1977. Printed in Great Britain.

AN ON-LINE COMPUTERIZED REACTOR NOISE, VIBRATION AND LOOSE PARTS MONITORING SYSTEM

P. J. Pekrul

P~oject Manager Vibration and Loose Parts Monitoring'

Atomics International Rockwell International

Canoga Park, California 91304

The on-line Reactor Noise, Vibration and Loose Parts Monitor (V&LPM) described here wi l l continuously monitor a plant for anomalous behavior, become part of the plant instrumentation, and require no operator action unless a preset signal level is exceeded. This unit consists of piezoelectric sensors, preamplifiers, signal processor units, computers and other peripheral equipment, and provides on-line measurement without interference to normal plant operation.

An automatic scanning system* (Spectra-Scan) device places al l of the channels under computer control. The computer selects the channels sequentially for analysis on the spectrum analyzer. The output of the analyzer is compared with the spectra stored in the memory of the computer, and any significant deviations are annunciated. These deviations may be either in amplitude or in the'characteristic fre- quency of a mechanical resonance. The graphical results are displayed on the screen of a storage-type cathode ray tube, showing both the reference and the newly obtained spectra. I f no problems are found, the system continues to scan al l of the channels in sequence. A status tabulation is maintained on the display, giving identif ication on each of the channels being monitored.

Alert conditions are indicated for the threshold of worsening events and alarm conditions are indicated when action has to be taken rapidly. In the event of an alert or alarm condition, the operator is called and the component or location of the malfunction is indicated. The computer also prints out the appropriate action to be taken by the operator.

A magnetic data storage unit is included in the system to permit storage of spectra from the various channels under the different operating conditions of the plant. An interactive operating system for the computer wi l l permit the operator to call in the desired reference spectra by simple keyboard commands. This system wi l l also fac i l i ta te the generation of new reference spectra.

The Spectra-Scan device operates in two modes. The normal operating mode is in the continuous scan and monitor mode. A variety of condition and action statements can be programmed into the computer and displayed on a CRT. The other Spectra-Scan operating mode would be to present a sequence of PSD's. (A PSD is a characterization of a noise signal which is prepared by analyzing the frequency composition of the noise signal. The PSD plot is presented as amplitude squared vs frequency.) The presentation is psuedo-3-dimensional and presents the change in a single channel PSD vs time, or all PSD channels simultaneously.

The Spectra-Scan feature can be supplied with a cross-product capability which wi l l generate cross-spectra, cross-correlations in the time domain, and transfer functions. The transfer functions have gain, phase, and coherence for any two designated channels, selected manually.

Nuclear reactor core internals motion is an example of computerized

*Patent applied for.

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h~,r~ P.J. Pekrul

signature analysis handled by this system. This motion is monitored by the neutron noise method. This method uses the core-motion-induced reactivity changes as indicated by power range neutron detectors to indicate core vibration. Spectrum analysis is again used to separate the core dynamic characteristics from the ion chamber white noise, thus enhancing the signal-to-noise ratio. Correlation between two opposing detectors is then used to determine phase relationships of the various resonances observed.

Internal vibration, noise, and oscillatory anomalies in the plant may also be detected by analyzing the signal from typical plant instrumen- tation such as acceleration, displacement pressure, flow, or temperature. The existence of an oscillatory signal from a plant instrumentation channel can indicate previously unperceived motion in the plant. Flow or pressure pulsations can be the driving force for other anomalous behavior in the plant. Temperature fluctuations can be analyzed to determine whether thermal hydraulic anomalies are occurring in the heat transfer system but are sometimes bandwidth limited.

Loose parts in the flow lines power stations can be detected by a loose parts channel. The detection is performed by sensing those sounds which are associated with metal impact from parts moving in or along a f luid channel or pipe. The sensors can detect sounds that emanate at a considerable distance from the sensor because of the good acoustic wave transmission in welded pipe.

Actually, the loose parts monitor might be called an unusual events monitor. Besides loose parts, any intermittent contact, such as loose support structure, equipment rat t l ing, and high frequency metal rubbing (squeaks) can be detected. In addition to these, the sounds associated with pounding, sawing, and cutting can also be heard.

Applied to rotating equipment, this computer system requires only minor specification changes to ensure that: (1) new, small motors meet balance requirements, (2) medium and large rotating components have balancing capability provisions, and (3) large rotating equipment is adequately monitored.

In the case of production fac i l i t ies where the product value is in the range of $100 mill ion per year, a one-day fac i l i t y outage can cost as much as $300,000. Even in small fac i l i t ies , a day lost in production can cost a significant amount. Increased avai labi l i ty via vibration monitoring then can result in higher profits due to lower costs or increased production. These advantages can be achieved through signature analysis methods and equipment.

This paper describes one type of computerized equipment and gives some related experience.

REFERENCES

I ) Pekrul, P. J.,."Vibration Monitoring Increases Equipment Avai labi l i ty," Chemical Engineering, August 18, 1975

2) Morrow, R. S., "Why Use Minicomputer Systems for Vibration Monitoring," Hydrocarbon Processing Magazine, October 1975

3) O'Dea, D. M., "Computerized Machinery Vibration Analysis Improves Rel iabi l i ty," The Oil and Gas Journal, December 1975

4) Jackson, C., "Techniques of Alignment of Rotating Equipment," Hydrocarbon Processing Magazine, January 1976

5) Pekrul, P. J., "What Does Reactor Diagnostics Offer," Power Magazine, March 1976

6) James, R., et al, "Predictive Maintainance System," The Oil and Gas Journal, February 1976