ML20064G725
| ML20064G725 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 12/07/1978 |
| From: | Ferris M, Gahm J, Warembourg D PUBLIC SERVICE CO. OF COLORADO |
| To: | |
| Shared Package | |
| ML20064G723 | List: |
| References | |
| NUDOCS 7812130179 | |
| Download: ML20064G725 (6) | |
Text
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REPO'RT DATE:
Dectabar 7, 1978 REPORTABLE OCCURRENCE 78-05 ISSUE 1 OCCURRENCE DATE:
November 7,1978 Page 1 of 6 FURT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 60651 REPORT No. 50-267/78-05/03-I-1 Supplemental Report: Additional Information IDENTIFICATION OF OCCURRENCE:
l A malfunction of one of the three speed modifiers for 1A circulator caused a loss of Plant Protective System function to one channel of the high speed trips.
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A malfunction of one of the three speed modifiers and a signal cable connector resistance change to a second of the three speed modifiers caused a loss of l
Plant Protective System function in two channels of the high speed trips for 1C circulator. On January 11, 1978, the conditions were analyzed and determined to not be reportable. Subsequent re-evaluation on March 13, 1978, has determined thct this resulted in operation under a degraded mode permitted by LCO 4.4.1 and is reportable per Fort St. Vrain Technical Specification AC 7.5.2(b)2.
On seven occassions between April 25, 1978, and November 18, 1978, additional problems similiar to those described were experienced with the circulator speed j
modifiers or signal cable connectors. This report is submitted as a supplement to Reportable Occurrence Report No. 50-267/78-05/03-L-0, Preliminary, to provide '
additional information on the problems experienced since three of the seven mal-functions occurred between November 7,1978, and November 18, 1978.
EVENT DESCRIPTION:
g While operating the reactor at 13% thermal power and zero electrical power, l
operations personnel observed that one of the three channels for the lA circulator speed indication was at zero while the other two channels indicated approximately i
2300 RPM. They also observed that two of the three channels for 1C circulator speed were at 200 RPM while the other channel indicated approximately 2300 RPM.
The problems included in this supplemental report are:
1)
On April 25, 1978, while operating at 55% thermal power and 170 W electrical power, operations personnel observed that one of the three channels for the 1C circulator tripped on low speed while the other two channels indicated approximately 6300 RPM.
2)
On May 7,1978, while operating at 33% thermal power and 25 W electrical l
power, operations personnel observed that one of the three channels for l
the 1C circulator speed indication went to zero while the other two channels indicated approximately 4000 RPM.
I 7812130lh
REPORTABLE OCCURRENCE 78-05 ISSUE 1 Page 2 of 6 EVENT DESCRIPTION (continued):
3)
On July 8,1978, while operating at 50% thermal power and 148 W electrical power, operations personnel observed that one of the three enannels for the 1D circulator speed indication was at approximately 5200 RPM while the other two channels indicated approximately 6000 RPM. They also observed that two of the three channels for the 1C circulator speed indication were at approx-imately 5000 RPM while the third channel indicated approximately 6100 RPM.
4)
On October 14, 1978, while operating at 37% thermal power and 110 W elect-rical power, operations personnel observed that one of the three channels for the ID circulator speed indication was at approximately 2100 RPM while the other two channels indicated approximately 4300 RPM.
5)
On November 7,1978, while operating at 55% thermal power and 170 W elect--
(')
rical power, operations personnel observed that one of the three channels for the 1A circulator speed indication went to zero while the other two channels indicated approximately 4300 RPM.
6)
On November 12, 1978, while operating at 60% thermal power and 180 W elect-i rical power, operations personnel observed that one of the three channels for the 1C circulator speed indication tripped on low speed while the other two channels indicated approximately 5600 ' RPM.
7)
On November 18, 1978, while operating at 60% thermal power and 195 W electrical power, operations personnel observed that one of the three channels for the 1C circulator speed indication went to zero while the other j
two channels indicated approximately 5600 RPM.
I i
See Figure 1.
The speed measuring system (SM), ;
is designed to measure the 3
rotational speed and alignment wobble of the hel um circulator shaf t.
This is accomplished by the use of a re'luctsace type detector probe (SE), (2j, connected
,(
to a phase sensitive carrier type electronics system.
Precision machined slots in the rotating shaf t of tLe helium circulator provide timing pulses whose frequency is proportional to shatt rotational speed.
t l
The electronic system which produces this signal operates on the principle of a balanced bridge connected to probes consisting of two identical coils.
In normal operation the bridge is nulled for minimum zero phase shif t output with the ro-
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tating shaft centered in the bearing.
t Three seperate channels monitor the speed of each helium circulator. The pulse signals are transmitted by the SM's, d, to the speed transmitter (ST's),
- 3),
which produces a 0 to 10 volt output signal proportional to shaf t RPM for use in the summer modifiers and process trip modules. The process trip _, modules are the speed switches low (SSL), 14
, and speed switches high (SSH), 15).
If the circulator speed reaches either the h,igh or low trip settin,g, the SSL's or SSH's initiate trip signals to the two of three solid state logic, L,6_, which produces a circulator shutdown via the special control relays (XCR's). Q).
REPORTABI.E OCCURRENCE 78-05 ISSUE 1 Page 3 of 6 EVENT 4
i DESCRIPTION (continued):
l The circulator 1A speed modifier problem resulted in loss of the speed signal j
and trip capability in one of three associated high speed trip channels. Two redundant channels were available and operable.
l 1
The circulator 1C problem in one of the three speed modifiers, and a signal cable connector resistance change in a second of the three speed modifiers, re-l sulted in loss of the speed signals and trip capability for two of three high speed trip channels.
1)
The circulator 1C speed modifier problem resulted in loss of the speed signal and trip capability in one of three associated high speed trip channels. Two redundant channels were available and operable.
O' 2)
The circulator 1C signal cable connector resistance change resulted in 3
loss of the speed signal and trip capability in one of three associated high speed channels. Two redundant chennels were available and operable.
3)
The circulator 1D speed modifier problem resulted in a decrease of the speed signal in one of three associated high speed trip channels. Two redundant channels were available and operable. The circulator 1C speed modifier problems resulted in decrease of the speed signal in two of three associated high speed trip channels.
1 4)
The circulator ID speed modifier problem resulted in loss of the speed signal and -t' rip capability in one of three associated high speed trip channels. -Two redundant channels were svailable and operable.
l l
5)
The circulator 1A signal cable connector resistance change resulted in loss of the speed signal and trip capability in one of three associated high l
speed trip channels. Two redundant channels were available and operable.
( a, 6)
The circulator 1C speed modifier problem resulted in loss of the speed signal and trip capability in one of three associated high speed trip channels. -Two redundant channels were available and operable.
7)
The circulator 1C signal cable connector ruheance change resulted in loss l
of the speed signal and trip capability L a of three associated high speed trip channels. Two redundant channels were available and operable.
CAUSE DESCRIPTION:
Instrument calibration drift due to bridge unbalance.
The balancing problem is caused by a change in resistance between the two leads of the speed element and ground at the circulator connection end. The difference in resistance occurs over a period of time in the cable connectors as a result of the temperature and humidity of the ambient air.
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REPORIABLE OCCURRENCE 78-05 ISSUE 1 Page 4 of 6 CORRECTIVE ACTION:
l Adjusting the 1A circulatur speed modifier restored overspeed protection to the affected channel.
i Adjusting the 1C circulator speed modifier and replacing the input cable 4
restored overspeed protection to one of the channels. Adjusting the speed j
modifier of the other channel restored overspeed protection to the remaining channel.
- 1) and 6)
Adjusting the 1C circulator speed modifier restored overspeed protection to the affected channel.
- 2) and 7)
Replacing the input cable with an installed spara and adjusting the'lC circulator speed modifier restored overspeed protection
()
to the sffected channel.
3)
Adjusting the ID circulator speed modifier corrected the dis-crepancy in speed indication and fully restored overspeed pro-taction to the affected channel. Adjusting the 1C circulator speed modifier corrected the discrepancy in speed indication i
and fully restored overspeed protection to the affected enannels.
i 4)
Adjusting the 1D circulator speed modifier restored overspeed I
protection to the affected channel.
5)
Replicing the input cable with an installed spare and adjusting the 1A circulator speed modifier restored overspeed protection to the affected channel.
As an interim measure, the adjustment of the speed modifiers is being checked r
and documented on' a weekly basis.
(_is The problem is under investigation to determine what can be done to correct this situation. The results will be reported in a future supplemental report.
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REPORTABLE OCCURRILNCE 78-05 ISSUE 1 Page 6 of 6 Prepared by:
Le / ht_u MicAael J. Ferr sj Technical Servi (irs Engineer c
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Reviewed by:
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J.~W.
Gahm Technical Services Supervisor Reviewed by:
Frank M. Mathie Operations Manager Approved by:
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Don Warembourg g
Manager, Nuclear Production
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