ML18051A792

Reactor Internals Noise Monitoring Tests, 1983

ML18051A792
Person / Time
Site:	Palisades
Issue date:	12/31/1983
From:	CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
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ML18051A791	List: ML18051A790 ML18051A792
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NUDOCS 8402150301
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.. :-8402150301 840206 \ PDR ADOCK R "CONSUMERS POWER COMPANY PALISADES NUCLEAR PLANT REACTOR INTERNALS NOISE MONITORING TESTS January 1983 -December 1983 35 Page*s I ' I CONTENTS I Introduction II Description of Noise Analysis Method III General Core Arrangement and Signal Conditioning IV Summary of Noise Analysis Results V Conclusion References Figure 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

• LIST OF FIGURES Title Instrumentation Locations for Noise Tests Schematic of Signal Conditioning Equipment IAPD NI-05 7/11/83 IAPD NI-06 7/11/83 IAPD NI-07 7/11/83 IAPD NI-08 7/11/83 NPSD NI-05 2/3/82 NPSD NI-06 2/3/82 NPSD NI-07 2/3/82 NPSD NI-08 2/3/82 NPSD NI-05 1/10/83 NPSD NI-06 1/10/83 NPSD NI-07 1/10/83 NPSD NI-08 1/10/83 NPSD NI-05 7/11/83 NPSD NI-06 7/11/83 NPSD NI-07 7/11/83 NPSD NI-08 7/11/83 Coherence and Phase Diagrams February, 1982 Coherence and Phase Diagrams January , 1983 Coherence and Phase Diagrams July, 1983

,. I Introduction This report entitled Reactor Internals Noise Monitoring Tests covers the period January 1983 through December 1983. This reporting period encompasses the second half of core five. Contained in this report is a summary of results obtained from Technical Specification tests, Reference 1, which require data to be taken on reactor internals noise on a weekly and monthly basis. The data collected on a weekly basis, Phase One measurements, consists of the integral probability distribution function, standard deviation, and % RMS in selected frequency bands of reactor internals noise. The data collected on a monthly basis, Phase Two measurements, consists of a power spectral density, phase of transfer function, and coherence for each excore detector combination.

II Description of Noise Analysis Method As required by Reference 1, reactor internals noise monitoring is taken on a weekly and monthly basis. The weekly surveillance consists of the acquisition of the standard deviation,%

integral probability distribution (IAPD) of excore detector combinations in the frequency bands (l-3)Hz, (10-16)Hz and (16-20)Hz.

The monthly surveillance consists of the acquisition of the phase of transfer function, normalized power spectral density (NPSD) and coherence of excore detector combinations in the frequency band (0-25)Hz.

Presented below is a general discussion of each of the surveillance methods. % RMS Alert. and action limits, M sigma and N sigma have been assigned to the % RMS values per Reference 2 which are given below. (l-3)Hz (10-16)Hz (16-20)Hz M sigma .16% .11% .11% N sigma .24% .16% .16% These limits were analytically determined based on information in References 3 and 4 and Palisades core geometry. (f,. description of the mathematical technique of obtaining sigma and % RMS values from the cross power spectral density is given in Reference 5.) Integral of Amplitude Probability Distribution (IAPD) The Integral of the Amplitude Probability Distribution (IAPD) is determined for each excore detector in the frequency bands (l-3)Hz, (10-16)Hz and (16-20) Hz. The IAPD is formed in the following manner: 1) Data in the time domain is received by the fourier analyzer, 2) The fourier analyzer transforms the data to the frequency domain where the frequency band of interest is isolated, 3) This frequency band is then transformed to the time domain. Steps 1, 2 and 3 are performed for 50 entries into the fourier analyzer and the results are added to form histogram.

The histogram is area normal-ized and integrated to give the IAPD. The ordinate scale of an IAPD ranges between 0 and 1. Verification that the IAPD for ea.ch frequency band passes through the point (0+/-0.8)mv, (.5+/-.05) provides tne ::;urveillance criteria to determine if vibration of the core support barrel. or other reactor internals is being impeded in peak to peak S'..ring.

Such

• termi.nat ion of peak to :i:ieak swini:;; was seen in 1972 and was the result of the core support barrel contacting the snubbers.

The IAPD is a backup to % RMS. Phase of Function A transfer function between two excore detectors is formed by taking the fourier transform of the time domain data from one detector, dividing it by the fourier transformof the time domain data from the second detector and converting the results to polar coordinates.

Coherence The coherence function between two detectors describes the "common causality" between the two detectors.

Its value ranges between 0 and 1 and it is formed through the following expression:

where: square of the magnitude of cross spectrum c 11 -auto spectrum of detector 1 c 22 -auto spectrum of detector 2

.. . .

• Together with the phase, the coherence forms a qualitative diagnostic tool in which quantification is achieved through the % RMS. The coherence displays those frequencies that are common to two excore detectors and. the phase indicates whether the frequency is associated with vibration.

Coherence and phase diagrams can be formulated with data from all combinations of excore detectors and shifts of signature values in phase or coherence are readily observed.

Normalized Power Spectral Density (NPSD) The Normalized Power Spectral Density is formed through the following equation:

NPSD N where: F -Fourier transfcrmof data from a detector 1 F 1* Complex conjugate of fourier transfur_m N -Normalization constant which .includes a power and frequency normalization.

The usefulness of the NPSD is to monitor signature frequencies.

III General Core Arrangement and Signal Conditioning Figure 1 shows the relationship of excore detectors to significant primary system items. The excore detectors NI-05, NI-06, NI-07 and NI-08 are 0 . located approximately 45 from the hot legs. The cold legs of the reactor vessel are approximately at the same angular location as the excore detectors.

A rough outline of the core is also shown in the figure. Current from the excore detectors is brought through a current to voltage amplifier and then as shown in Figure 2, through a voltage amplifier, a filter and then to the fourier analyzer.

The voltage amplifier is AC coupled so that only the fluctuating (noise) component of the signal is amplified.

The filters are used to bandpass the signal in range .025Hz to 25Hz. The fourier analyzer, HP5451B, is used to perform all statistical analysis on the noise component.

Steam B J>----------

CORE *---;). pressurizer prossurn * {Jteam generator A ..,.. -------------'

FIGURE 1 Instrumenlallon locutions for noise tests .. r_ .. -.

Input to Fourier Analyzer Low Pass Filter 24db/oct High Pass Filter 24db/oct 1---------------*0

+ ------*------()

Operational Amplifier Nominal Gain of 50 FIGURE 2 SCHEMATIC OF SIGNAL CONDITIONING EQUIPMENT Buffered Excore Detector Test Signal -----------------------------

1/10/83 3/21/83 5/3i/83 7/11/83 IV Summary of Noise Analysis Results Presented below is a summary of the surveillance results for the reporting period. These results are organized by surveillance

% RMS Table 1 lists % RMS values for the frequency bands (l-3)Hz, (10-16)Hz and (16-20)Hz for all detector combinations.

Representative results are listed from tests throughout the reporting period. It is seen that the alert limits of .16% RMS for the frequency band of (l-3)Hz and .11% RMS for the frequency bands (10-16)Hz and (l6-20)Hz have not been exceeded.

TABLE 1 % RMS FOR DETECTOR COMBINATIONS FOR FREQUENCY BAND (l-3)Hz, (10-16)Hz, (16-20)Hz

.. 05-06 05-07 05-08 06-07 06-08 07-08 i 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 .o4o .005 0 .026 .007 .001 .050 .006 .001 .063 .005 0 .024 .006 .002 033 .006 .059 .004 0 .049 .006 .001 .059 .004 0 .070 .003 0 .045 .005 .002 .062 .006 *--

---** .089 .005 0 .069 .007 .002 .070 .006 0 .091 .005 0 .070 .005 0 077 .005 -*

.097 .oo4 0 .090 .006 0 .070 .005 0 .095 .083 .006 .002 091 .006 1 = l-3Hz 2 = 10-16Hz 3 = 16-20Hz 3 .002 .002 __ ., _____ 0 0 IAPD Figures 3, 4, 5 and 6 show the integral of the amplitude probability for July 11, 1983; this was one month before the plant was shutdown for refueling.

As stated before, the ordinates of the IAPDS are from 0 to 1. The abscissa is expressed in terms of millivolts.

At 100% power the excore detector is 8 volts averaged.

On top of the 8 volts a millivolt noise component.

This is what is measured by the fourier analyzer and why it appears in the IAPD. As can be seen from the figures, when the IAPD has a value of .5 on the ordinate scale, the abscissa is at 0 millivolts.

This signifies that vibration is of small enough magnitude that peak to peak motion is not being hindered.

Normalized Power Spectral Denisty (NPSD) Figures 7 through 18 show a NPSD for each detector at three different times during core 5, i.e. February 3, 1982, January 10, 1983 and July 11, 1983. These three dates correspond to 5%, 49% and 93% of core life respectively.

Through an observation of the NPSD (and the coherence discussed in the next section) the following and their postulated sources display a resonance.

1. .5 Hz Thermal hydraulic oscillation

2. 2.3 Hz Fuel bundle vibration

3. 11.25 Hz Unknown 4. 12. 5 Hz Core support barrel vibration

5. 14.75 Hz Primary coolant pump blad_e frequency

6. 15.5 Hz Shell mode vibration of reactor vessel 7. 18 Hz Core support barrel vibration

8. 20.5 Hz Unknown 9. 23 Hz Unknown The signature of frequencies has remained relatively constant throughout the reporting period with the exception of the peak at 20.5 Hz. Previously, the peak amplitude for thisfrequency was approximately

-105db. The increase in amplitude suggests that some anomally occurred during the reporting period. Table II lists the peak amplitude of each of the above frequencies.

TABLE II PEAK AMPLITlJJ)E OF NPSD FOR DESIGNATED FREQUENCIES . NI-b5 DATE .5Hz 2.3Hz ll.25Hz. 12.5Hz 14.75Hz 15.5Hz 18Hz 20.5Hz 23Hz t2/3/82 74 96 103 ll/10/83 68 89 96 -101 rr111/83 62 93 88 89 NI-06 DA'T'E .5Hz 2 3Hz ll.25Hz 12.5Hz 14.75Hz 15.5Hz* 18Hz 20.5Hz 23Hz 12/3/82 73 89 97 -104 1/10/83 67 91 91 100 7/11/83 -57 .,.63 91 91 102 NI-07 '.J.. ,. 5Hz 2 3Hz 11 25Hz 12 5Hz 14 75Hz 15 5Hz 18Hz 20 5Hz 23Hz * . 2/3/82 74 85 1/10/83 68 88 97 -101 7/11/83 63 88 -90 I 89 -101 NI-08 DATE .5Hz 2.3Hz ll.25Hz 12.5Hz 14.75Hz 15.5Hz 18Hz 20.5Hz 23Hz 2/3/82 74 87 -89 1/10/83 69 91 92 7/11/83 64 89 -86 NOTE: All values in db; blanks signify no resonance

{_ ,. Coherence and Phase Figures 19, 20 and 21 present phase and cohere.nee diagrams for the months of February 1982, January 1983 and July 1983. The phase at a particular frequency and given detector combination is given by a straight line for 0° phase and a sinusoidal line for a 180° phase. A 90° phase is composed of half a straight line and half sinusoidal line. The coherence for the particular frequency and detector combination is written adjacent to the phase line. Significant points from the coherence and phase diagrams are listed below. 1. The .5Hz frequency displays for all detector combinations a o 0 phase until late in core life when a 90° phase is seen diagonally across the core. Coherence is low in the diagonals whereas high coherence is observed across the hot legs. 2. The 2.3Hz frequency displays for all detector combinations at beginning of core a o 0 phase. Later in core as can already be seen in Figure 20 vibration will occur at this frequency, in the direction of the hot legs. This frequency is believed to be fuel bundle vibration, Reference

6. 3, The 11.25Hz frequency displays for detector combinations and throughout core life a o 0 or 90° phase. 4. The 12.5Hz frequency which is also believed to be core support barrel vibration displays a measureable coherence throughout core life. 5, The 18Hz frequency displays throughout core life a vibration in the direction of the hot legs. .This frequency is believed to be core support barrel vibration.

6. The 20.5Hz frequency also displays throughout core life a vibration in the direction of the hot legs.

V Conclusion The results from the surveillance methods presented in Section rv* show no significant reactor internals vibration existed during the reporting period. The magnitude of the % RMS values in the various frequency bands did not exceed alert or action limits. This in conjunction with the other noise analysis data conclusively shows that the core barrel was tightly clamped during the reporting period.

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FIGURE 11 NPSD NI-05 1/10/83 70 -80 I 100 ,, Frequency (Hz)

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B B FIGURE 19 COHERENCE AND PHASE DIAGAAMS February 1982 B B 8 5 8 8 8 ,5 .

I 7 1 {'VJ .42 A .Zlo .3D A .'ii .Z4 / . .30 .35 A .iz. 6 7 '"7 6. 7 .

A A 11.25 Hz 12.5 Hz A A .5 Hz 2.3.Hz B B i. " .. . . ._ e:* Legend: A 14.75 Hz

.... /""-6 .OB 7 A 18 Hz 8 5 A 20.5 Hz 7 5,6,7,8 A,B oo Phase 900 Phase 180° Phase Excore Detectors Hot Legs Steam Generator A .5 Hz B A 14.75 Hz FIGURE 20 COHERENCE AND PHASE DIAGRAMS January 1983 B B .b/o A 2.3.Hz B B 7 A A 18 Hz 20.5 I!z 5 7 . ' B I e Legend: lJr-oo Phase 900 Phase -<./"\_A_.,)'

180° Phase 5,6,1,e Excore Detectors A,B Hot Legs Stearn Generator B B .10 .7 A 14.75 Hz FIGURE 21 COHERENCE AND PHASE DIAGRAMS B .22 A* 2.3.Hz B 7 July 1983 I -B JZ A 11.25 Hz -B . 8 .l2. 5 8 5 6 A 18 Hz 7 6* A 20.5 Hz 7 B A 12.5 Hi. 5,6,7,8 A,B Legend: oo Phase 900 Phase 180° Phase Excore Detectors Hot Legs Steam Generator i' ..

T--... .. -- REFERENCES

1. Palisades Plant Technical Specifications, Section 4.13. 2. Letter, DMKennedy to JAMeincke, "Palisades Plant -Reactor Internals Vibration Monitoring Mand N Sigma Limits", May 14, 1979. 3. "Calculation of the Scale Factor for Inference of Pressurized Water Reactor Core Barrel Motion from Neutron Noise Spectral Density", Nuclear Technol_ogy, Vol. 40, mid August 1978. 4. "Quantification of Core Barrel Motion Using an Analytically Derived Scale Factor and Statistical Reactor Noise Descriptors", Nuclear Technology, Vol.40, mid August 1978. 5. Reactor Noise by Joseph Thie; Rowman and Littlefield, Inc. 1963 6. XN-74-33, Summary of Mechanical Tests of Palisades Fuel Bundle and Component Parts, September 3, 1974.