ML20086D442
| ML20086D442 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 02/02/1976 |
| From: | Utley E CAROLINA POWER & LIGHT CO. |
| To: | Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| Shared Package | |
| ML20086D433 | List: |
| References | |
| AO-50-261-76-2, NG-76-151, NUDOCS 8312010483 | |
| Download: ML20086D442 (8) | |
Text
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i File: NG-3513 (R)
Serial: NG-76-151 5b1 261 Mr. Norman C. Moseley, Director U. S. Nuclear Regulatory Commission Region II, Suite 818 230 Peachtree Street, N.W.
Atlanta, Georgia 30303
Dear Mr. Moseley:
H. B. ROBINSON UNIT NO. 2 LICENSE NO. DPR-23 FAILURE OF ONE AND DELAYED OPERATIO?i 0F TWO REACTOR TRIP RELAYS In accordance with 6.6.2.a of the Technical Specifications for
!!. B. Robinson Unit No. 2, the attached Abnormal Occurrence Report is submitted for your information. This report fulfille the requirement for a written report within ten days of an Abnormal Occurrence and is in accordance with the format set forth in Regulatory Guideline 1.16, devision 1.
Yours very truly,
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E. E. Utley Vice-President Bulk Power Supply DBW:nvp px Attachment e.,
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Mr. D. C. Knuth
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Mr. W. G. Mcdonald 11d.
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V ABNORMAL OCCURRENCE RT. PORT 1.
Report No.
50-261/76-2 2a.
Report Date:
January 29, 1976 2b.
Occurrence Date:
January 21, 1976, January 22, 1976 3.
Facility:
H. B. Robinson Unit No. 2 Hartsville, South Carolina 29550 4.
Identification of Occurrence Failure of one and delayed operation of two reactor trip relays which constitutes an abnormal occurrence as defined by Plant Technical Specification 1.8.d.
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5.
Conditions Prior to Occurrence The plant was operating at 100% of rated power with normal full power plant parameters during the period involved. A monthly periodic test CP&L-PT-19 A/B, which verifles proper operation of reactor protection logic components, was in progress on train "A" of the Reactor Protection System. An equalizing charge had just been completed on Unit No. 2 "A" station battery (90 minutes prior to first malfunction) and an extended equilizer was in progress on "B" battery.
The extended equalizer was terminated on January 22, 1976, approxinately 135 minutes prior to the identification of the third malfunction.
6.
Description of Occurrence At approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, on January 21, 1976, reactor trip relay RT-3 was observed.as sluggish to open. As in other. logic circuits two relays in parallel are required to open in order te generate the reactor trip condition. Relay RT-3 was exercised and found to open on delays of up to 20 seconds.
"A" Reactor Trip Breaker was-tested in conjuction with RT-3 (train "A") and its opening resulted in' similar delays.
The relay was replaced with a new unit from stock at 1615 hours0.0187 days <br />0.449 hours <br />0.00267 weeks <br />6.145075e-4 months <br /> on January 21, 1976.
At approximately 0845 hours0.00978 days <br />0.235 hours <br />0.0014 weeks <br />3.215225e-4 months <br />, on Ji nary 22, 1976, reactor trip relay RT-4 on train "B" of the Reactor Protection System was found to be-failed.
The discovery was made as a result of a visual inspection prior to the performance of part "B" of periodic test PT-19 A/B.
The failed relay was replaced with a new component and the circuit was returned to normal-service at 0920 hours0.0106 days <br />0.256 hours <br />0.00152 weeks <br />3.5006e-4 months <br /> on January 22, 1976.
On January 22, 1976, at approximately 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br />, reactor trip relay RT-8 on train "B" was observed to operate in a sluggish manner.
The.
extended equalizing charge (48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />) had been completed on Unit No. 2 "B" station battery at.approximately 0830 that day.
The questionab'e relay was replaced with a new component.from stock at 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br /> on'
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7.
Designation of Apparent Cause of Occurrence The cause of the relay f ailure (RT-4, train "B") was identified as an open coil winding.
The coil holds the relay trip contacts in the closed position, therefore, failure of the coil causes the relay contacts to open Vith spring tension resulting in a fail-safe disposition.
The cause of the delay malfunction has not been determined to date..However, suspicion is directed to high voltage conditions which exist during the monthly station battery charge.
Disassembly of the relays revealed discolored and brittle nylon sleeves which are used as coil liners in which the operating plungers travel. It is believed that this deterioration, noted on all three relays in question, is a thermal effect which resulted from increased voltage during abattery charge. The relays are rated for continuous service at 125/130 volts dc.
During an equalizing charge on a battery, that train of relays is subjected to 140 volts dc.
In addition, the frequency of charging "B" station battery had been increased in the past four months in order to reduce a sulfate buildup. This increased voltage is suspected to be the cause of the apparent thernal degradation.
Subsequent fragmenting or deformation of the sleeve could have created a restriction to free movement of the plunger and resulted in the delayed actuating times.
The open coil (RT-4), although not a direct result of high temperature, cannot be discounted as an ultimate result of this condition.
Inspection, in all cases, revealed only the thermal effects described above. No definitive cause of the sluggish results has yet been found.
8.
Analysis of Occurrence Relay RT-4 train "B",
a normally energized device failed such that it resulted in one of the two deenergized relays necessary to initiate a reactor trip. This particular malfunction, therefore, resulted in a fail-safe condition.
Immediately upon identification of the delaying of RT-3 train "A" and RT-8 train "B", each defective relay was expeditiously replaced.
The delayed reaction times were in excess of assumptions made in safety analyses reports. However, the delays only affected one parallel circuit in one logic train of the particular protective systems.
Therefore, adequate redundancy was available.
RT-3 and RT-4 are in logic trains actuated by Overtemperature and overpower.AT and Low Low Steam Generator Level. RT-8 serves Safety Injection Actuation and Pressurizer High iressure. As a result of the occurrence plant safety was not' jeopardized, nor were any limiting conditions of operation violated.
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9.
Corrective Act_ ton Immediate corrective action was replacement of the three defective relays. Design specifications require that the subject relay's drop out time be within 12 to 25 milliseconds. Obvious concern and considerable attention has been directed towards positively identifying the cause of these malfunctions, since the delayed behavior.directly affects reactor trip time. An investigation is in progress by both utility and vendor to identify this cause.
As an evaluation of the performance of the remaining reactor trip relays, each was tested to verify it's " drop-out" time as compared to design specifications. With the exception of one, all relays tested were found to be withia the prescribed limits with the average drop-out time to be approximately 17 milliseconds. The one relay not conforming to vendor's design was found to have a drop-out time of approximately 28 milliseconds. This relay has been replaced and will be inspected as part of the continuing investigation.
To mitigate the potential for thermal degradation, the decision has been made to replace all d.c. relays of the type and application involved in the occurrence. The replacement relays will be rated for the higher voltages encountered during a battery charge. Until some time that these relays are replaced, battery charges will be practiced only at the frequency required by Technical Specifications.
10.
Failure Data No previous relay failure of this nature has occurred.
Name plate data (relay):
4 Westinghouse Cat. No. BFD-31 Style 46E7352 Coil - 125/130 volt d.c.
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February 2, 1976 File: NG-3513 (R)
Serial: NG-76-151
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Mr. Norman C. Moseley, Director M[
U. S. Nuclear Regulatory Commission
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Region II, Suite 818 T4
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230 Peachtree Street, N.W.
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Atlanta, Georgia 30303 IEFILE COPY
Dear Mr. Moseley:
H. B. ROBINSON UNIT NO. 2 LICENSE NO. DPR-23 FAILURE OF ONE AND DELAYED OPFMTION OF TWO REACTOR TRIP RELAYS In accordance with 6.6.2.a of the Technical Specifications for
- 11. B. Robinson Unit No. 2, the attached Abnormal Occurrence Report is submitted for your information. This report fulfills the requirement for a written report within ten days of an Abnormal Occurrence and is in accordance with the format set forth in Regulatory Guideline 1.16, Revision 1.
Yours very'truly,
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. l8 M d. /.6 E. E. Utley k
Vice-President Bulk Power Supply DBW:mvp Attachment cc:
Mr. D. C. Knuth Mr. W. G. Mcdonald I
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o ABNORMAL OCCURRENCE REPORT f
1.
Report No.
50-261/76-2 2a.
Report Date:
January 29, 1976 4
f 2b. Occurrence Date:
' January 21, 1976 January 22, 1976 e
3.
Facility:
H. B. Robinson Unit No. 2 l
Hartsville, South Carolina 29550 l
4.
Identification of Occurrence I
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Failure of one and delayed operation of two reactor trip relays which
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constitutes sa abnormal occurrence as defined by Plant Technical
. )
Specification 1.8.d.
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5.
Conditions Prior to Occurrence
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.The plant' was operating at 100% of rated power with normal full power plant parameters during the period involved. A monthly periodic test CP&L-PT-19 A/B, which verifies proper operation of reactor protection logic components, was in progress on train "A" of the Reactor Protection System. An equalizing charge had just been completed on Unit No. 2 "A"-
station battery (90 minutes prior to first malfunction) _ and an extended equilizer was in progress on "B" battery.. The extended equalizsr was terminated on January 22, 1976, approximately 135 minutes prior to the identification of the third malfunction.
l, 6.
Description of occurrence f.
At approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, on January 21, 1976, reactor trip; relay
~
RT-3 was observed as sluggish to open. As in other logic circuits two il relays in parallel are required to open in order te generate the reactor trip condition. Relay RT-3 was exercised and found_to open on delays of up to 20 seconds.
"A" Reactor Trip Breaker was tested in conjuction with l ',
RT-3 (train "A") and its opening resulted in similar delays. The relay was replaced with 'a new unit from stock at 1615 hours0.0187 days <br />0.449 hours <br />0.00267 weeks <br />6.145075e-4 months <br /> _on January 21, 1976.
i At approximately 0845 hours0.00978 days <br />0.235 hours <br />0.0014 weeks <br />3.215225e-4 months <br />, on January 22, 1976, reactor trip relay-f RT-4 on' train "B" of the Reactor ~ Protection System was found to be failed. The discovery was made as a result of a. visual inspection prior to the performance of part "B" of periodic test PT-19 A/B.
The failed relay was replaced with a new component and the circuit was returned to normal service at 0920 hours0.0106 days <br />0.256 hours <br />0.00152 weeks <br />3.5006e-4 months <br /> on January 22, 1976.-
.On January 22, 1976 _ac approximately 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br />, reactor trip relay RT-8 'on train "B" was observed to operate in a sluggish manner. The extended equalizing charge. (48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />) had been completed on Unit No. 2
)
'"B" station battery ac2approximately.0830 that day..The questionable i
relay was, replaced with -a new component from stock ae 1140 -hours on I*
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3 7.
Designation of Apparent Cause of Occurrence 2
The cause of the relay failure (RT-4, train "B") was identified as an i
open coil winding. The coil holds the relay trip contacts in the closed 1
position, therefore, failure of the. coil causes the relay contacts to open with spring tension resulting in a fail-safe disposition. The cause of the delay malfunction has not been determined to date..However, suspicion is directed to high voltage conditions which exist during the monthly station battery charge.
I Disassembly of the relays revealed discolored and brittle nylon sleeves
'l which are used as coil liners in which the operating plungers travel.
It is believed that this deterioration, noted on all threit relays in question, is a thermal effect which resulted from increased voltage-during abattery
'l charge. The relays are rated for continuous service at 125/130 volts dc.
4
.During an equaliains charge on a battery, that train;of relays is subjected I
to 140 volts de. In' addition, the frequency of charging "B" station j
battery had been increased in the past four months in order to reduce a sulfate buildup.. This increased voltage is suspected to be the cause of the apparent thermal degradation. Subsequent fragmenting or deformation of the sleeve could have created a re?triction to free movement of the plunger and resulted in the delayed actuating times. The open coil j
(RT-4), although not a direct result of high temperature, cannot be i
discounted as an ultimate result of this condition.
Inspection, in l
all cases, revealed only the thermal effects described above.
No~
i definitive cause of the sluggish results has yet been found.
1 8.
Analysis of Occurrence Relaf RT-4 train "B",
a normally energized device -failed such that it resulted in one of the two deenergized relays neces'sary to initiate ~
a reactor trip. This particular malfunc' tion, therefore, resulted in j
a fail-safe condition.
Immediately upon identification of the delaying of RT-3 train "A" and RT-8 crain "B", each defective relay was expeditiously replaced. The
~
delayed reaction times were in excess of assumptions made in safety analyses reports. However, the delays only affected one perallel
'l circuit in one logic train of the particular protective systems.
i Therefore, adequate redundancy was available. RT-3 and RT-4 are in logic trains actuated by Overtemperature and overpower AT and Low Low Steam Generator Level. RT-8 serves Safety Injection Actuation and Pressurizac High 1ressure. As a result of the occurrence plant safety i
was not jeopardized, nor were any. limiting conditions of operation i
violated.
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9.
Corrective Action i
Immediate corrective action was replacement of the three defective relays. Design specifications require that the subject relay's drop out time be within 12 to 25 milliseconds. Obvious concern and considerable attention has been directed towards positively identifying the cause of these malfunctions, since the delayed behavior.directly i
affects reactor trip time. An investigation is in progress by both utility and vendor to identify this cause.
f As an evaluation of the performance of the remaining reactor trip relays, each was tested to verify it's " drop-out" time as compared i
to design specifications. With the exception of one, all relays j
tested were found to be within the prescribed limits with the average drop-out time to be approximately 17 milliseconds. The one relay i
not conforming to vendor's design was found to have a drop-out time of approximately 28 milliseconds. This relay has been replaced and will be inspected as part of the continuing investigation.
To mitigate the potential for thermal degradation, the decision has been made to replace all d.c. relays of the type and application involved in the occurrence. The replacement relays will be rated for the higher voltages encountered during a battery charge. Until some time that these relays are replaced, battery charges will be practiced only at the frequency required by Technical Specifications.
10.
Failure Data No previous relay failure of this nature has occurred.
Name plate data (relay):
Westinghouse Cat. No. BFD-31 Style 46E7352 j
Coil - 125/130 volt d.c.
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