ML20079G892
| ML20079G892 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 08/27/1991 |
| From: | Spencer J CAROLINA POWER & LIGHT CO. |
| To: | Ebneter S NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| REF-PT21-91 BO9-13520, NUDOCS 9110100010 | |
| Download: ML20079G892 (1) | |
Text
D-CD&L Carolina Power & Light Company Brunswick Nuclear Project P. O. Box 10429 Southport, NC 284810429 August 27,1991 FILE: B09-13520 10CFR21 Mr. S. D. Ebneter, Regional Administrater U.S. Nuclear Hegulatory Commission 101 Marietta St. NW Sulte 2900 Atlanta GA 30323 BRUNSWICK STEAM ELECTRIC PLANT UNITS 1 AND 2 DOCKET NO. 50-326 AND 50-324 UCENSE NO. DPR 71 AND DPR-62 NOTIFICAT!ON OF A 10CFR21 REPORTABLE OCCURRENCE
Dear Mr. Ebneter:
This confirms the telephone conversation at 1342 hours0.0155 days <br />0.373 hours <br />0.00222 weeks <br />5.10631e-4 months <br /> on August 26,1991 between Mr. H. Christenson (of your staff) and Me, G. Theerling (of my staff) which satisfied the requirements of 10CFR21 reporting criteria.
On July 30,1991 Carolina Power and Ught Company submitted LER 2-91005 titled. ESF Actuation Caused By Voltage Regulator Transient With Failure Of Primary Containment isolatbn Solenoid Operated Valves.
At that time an evaluation was in progress to determine if this failure was reportable under the requirements of 10CFR21. This evaluation Idertified the failure of the normally energized ASCO model L206-832 solenoid valves due to gelling of the lubricant (Dow Coming 550) as reportable per 10CFR21. This evaluatlon was presented to the Plant Nuclear Safety Committee on August 22,1991. The Plant General Manager, and the Vice President Brunswick -Nuclear Project were notified on August 23, 1991. The 10CFR21 Evaluation / Notification review completed August 22,1991, found the original LER 2 91005, as submitted, supplied the information required for 10CFR21 reporting.
Very truly yours, 7
V. Spencer, Ge r ! Manager Brunswick Nuclear Project Enclosure cc:
Mr. N. B. Le Mr. H. C. Christenson Mr. R. L Prevatte
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28461 0429 July 30, 1991 FILE:
B09-13510C 10CFR50.73 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Vashington, D. C. 20555 BRUNSVICK STEAM ELECTRIC PLANT UNIT 2 DOCKET NO. 50-324 LICENSE NO. DRP-62 LICENSEE EVENT REPORT 2 91-005 Centlemen:
In accordance with Title 10 of the Code of Federal Regulations, the enclosed Licensee Event Report is submitted. This report fulfills the requirement for a written report within thirty (30) days of a reportable occurrenca and is submitted in accordance with the format set forth in NUREG-1022, September 1983.
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Mr. S. D. Ebneter Mr. N. B. Le BSEP NRC Resident Office
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A surveillance to check the operation of the Manual sud Auro Main Generator Voltage Regulators was in progress. Following a step of the procedure which required the voltage regulator Mode Selector switch to be.placed in the Manual position, the Transfer voltmeter deflected significantly. Emergency Bus E4 was lost and the Reactor Protection System Motor-generator set 2B tripped. Emergency Diesel Generator #4 auto-started and a half SCRAM signal vse received along with Primary Containment System Isolation sigaals: Croup 3 (Reactor Vater cloanup), Group 6 (Containment Atmospheric Control), half Group 1 (Main Steam Line) Group 2-Division II (Transverse Incore Probe and Dryvell Floor / Equipment Drains). Main Generator output voltage was raised using the Manual voltage regulator and the voltage regulator was trcnsferred to the Automatic mode. ESF actuations occurred except for the outboard Dryvell Floor Drain Isolation valve which f ailed to close on the Group 2-Division II signal. The Inboard Floor Drain Isolation valve was closed after four attempts and the line was isolated. The cause of this event is still under investigation. Due to the plant being at full power, the decision was made to allow the voltage regulator to remain in the Automatic mode until troubleshooting takes place during the September, 1991 scheduled shutdown for a refueling outage. Initial investigations indicate that the valve failures were due to a lubricant which gelled inside the ASCO solenoids causing the core to adhere to the top casing in its energized position. Scratches on the outboard valve solenoid internals may have contributed to the failure. As corrective action the solenoids on the two valves that failed were replaced. Valves with similar solenoids were tested and surveillance frequency increased. A task force has been established to investigate the ASCO solenoid issue. Under tecsonable and credible alternative conditions this event would not have been more severe.
Other similar ASCO events were LER 2-88-001 and Plant Incident Report 90-036; Voltage Regulator events LER 2-81-01, 1-86-024, 2 90-015.
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FAOUTY NAME (1) oOceTT NUM8ER (2)
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PAGE (3)
Brunswick Steam Electric Plant 05000324 vtAR SEo REV 2
Unit 2 91 005 0
TEXT pf mere space is rested. use acomonal NAC Porm 3%A's) (1D INITIAL CONDITIONS On June 30, 1991 at approximately 05:15 (EDT), the unit was operating at approximately 954 power after a power reduction to perform Main Turbine valve testing.
1 ECCS systems and EL.ergency Diesel Generators (EDG) were operable and in standby.
EVENT NARRATIVE A Control Operator was performing a weekly surveillance using an operating procedure to check tho operation of the Manual (DC) and Auto (AC) Main Generator Voltage Regulator. After completing a step of the procedure which places the Voltage Regulator Mode Selector switch in ths Manual position, the Control Operator obs e rved a significant deflection of the Trcnsfer voltmeter (TVM). The TVM monitors the output of the Manual (DC) and Auto (AC) voltage regulators and is used to match the outputs of the two re5ulators so that generator voltage does not change when the regulator is transferred. The observed deflection of the TVM indicated that generator excitation had decreased u on transferring from Auto to the Manual toda. The Control Operator asked the Senior Contro Operator (SCO) if he had seen the TVM d:flection and the SCO replied that he had. The Control Operator looked again at the TVM and clsa observed that the generator megavars had decreased from 80 to 10. An alarm came in for a 250 volt battery B ground followed by an alarm for a 250 volt battery A ground. The Control Optrator began to receive alarms indicating a loss of Reactor Protection System Bus B and Em3rgency Bus 4 (E4 bus). At approximately 05:19 the Bus 2C to Emergency Bus E4 master and slave breakers tripped due to actuation of the E4 Bus undervoltage relays. This initiated an cuto-start of the M Emergency Diesel Generator. One undervoltage relay associated with the cuto-start logic for the a3 EDG actuated.
Recults of the loss of the E4 Bus included;
- 1. Auto-start of the associated Emergency Diesel Generator which re-energized the E4 Bus.
- 2. Trip of the 2B Reactor Protection System (RPS) Motor Generator (MC) set resulted in the following; 1/2 SCRAM-Division II Primary Containment Isolation System; GROUP 2 ISOLATION-Division II (Transverse Incore Probe and Drywell Floor and Equipment Drain Valves) (2-G16-F004 failed to close)
CROUP 3 ISOIATION (Reactor Water Cleanup)
GROUP 6 IS0lATION (Containment Atmospheric Control)
At approximately 05:29, the control Operator manually raised the main generator output voltage using the Manual voltage regulator. The voltage reguWor was transferred to the Automatic mode at approximately 05:33. Expected actuations resulting from a loss of the E4 Bus occurred as required except for the Drywell Floor Drain Outboard Isolation valve (2-C16-F004) which failed to close on a GROUP 2 isolation signal. After verification of actuations, tha 2B MG SET vas restarted. The 230 KV Voltage Recorder trace indicated a reduction from cpproximately 234 KV to approximately 227 KV over an approximately 1-2 minute period. The 230 l
KV bus volta 6e remained at this degraded level approximately 6-7 minutes.
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Dua to the f ailure of 2-G16-F004, an eight hour active Limiting Condition for Operation (LCO) in accordance with Technical Specifications (T.S.)
was initiated.
This Technical Sp cification requires that with only one operable valvs, the affected penetration line be
-isolated within eight hours by use of at least one deactivated automatic valve secured in the isolated position. This required the closure of the Drywell Floor Drain Inbr3ard Isolation
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FAC LffY MAME (1) 00CKET NUM8ER (2)
GR NUMBER (6)
PAGE (1) -
1 Brunswick Steam Electric Plant 05000324 vEAR SEo REV 3
Unit 2 91 005 0
TUT (tf more sosco to reawed, use poetsorw NRC Form 366A's) (17)
.Velve (2-G16-F003). At approximately 12:45, the Control Operator attempted to close 2 G16-F003 valve using the control switch At 12:55, after four attempts, the valve closed. Although the penetration line was already isolated, the : problems encountered in closing the valve required declaring the valve inoperable resulting in two primary containment isolation valves in series being inoperable.
With the two primary containment isolation valves in series being inoperable, the unit was unable to perform an Operational Leakage surveillance required per Technical Specifications.
After solenoid replacement on 2 G16-F004 and 2-G16-F003 the valves were declared operable and returned to service at approximately 22:10 and 23:00 respectively.
At approximately 23:20, the Operational Leakage surveillance was performed satisfactorily.
CAUSE OF EVENT VOLTAGE REGUTATOR Tha cause of this event is still under ir.vestigation. After the event a General Electric (GE)
Technical Representative was brought to the plant site to assist in investigating the voltage regulator transient. Due to the plant being at full power, the decision was made to allow the voltage regulator to remain in Automatic mode. No causal determination was made during this initial investigation with GE.
2.C16-F003 AND 2-G16-F004 FAILURES The cause of this event is still under investigation. The failed valves are Model L206832RVF ASCO solenoid valves which vent air pressure upon loss of power. The Instrument Air pressure at these valves is 90 psig.-The normal power supply is 115 VAC from the Emergency buses. The valves are both located outside of primary containment, in the same area and are supplied by the same-Instrument Air header. The valves have separate air pressure regulators and filters.
Besed upon these facts : Carolina Power and Light requested a root cause investigation of the two solenoid valves to be performed by Failure Prerention, Inc.
The report titled, ROOT CAUSE OF THE FAILURE OF TWO SOLENOID VALVES AT BRUNSUICK UNIT 2 dated July 6, 1991, revealed that lubricant had completely coated the top of the solenoid core in 2 G16-F003. A-few light scratches were found on the valve's upper and lower stems.
A patch of copper bearing material was found adhering to the upper stem in a e 'on that passes through a brass bushing.
of the solenoid for 2-G16-F004 was performed by CP&L personnel who found the Disassembly _ lightly bent.
lower stem s Failure Prevention, Inc. 's examination of the 2-G16-F004 solenoid found that lubricant coated about 50% of the top of the core as well as many scratches on the lower stem area. A long thread machining burr was found between the upper seat bushing and the main body and was still attached to the threaded region of the valve's ' pressure' port.
These preliminary investigations indicate that the cause of this event was due to the lubricant (:hr Corning 550) used by the vendor. Failure Preventions, Inc.'s report stated that the root cause of the sticking of the 2-G16-F003 was an abundance of lubricant that had galled causing the solenoid core to adhere to the top casing in its energized position.
The report also stated that the cause for 2-G16-F004 solenoid valve failure was likely a corbination of the lubricant gelling and foreign matter. The report stated that either one could be the cause, but a combination was the most likely reason.
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Unit 2 ao-91 005 0
rtxt of more we. i. e.w.o...umw Nac Pam 1 eta euin CORRECTIVE ACTIONS The weekly surveillance that was being performed on the Voltage Regulator during the initiation of this event has been deferred on both units until further investigation een be conducted.
The solenoids for 2 016 F003 and 2 016-F004 were replaced.
The frequency of stroking similar valves with this type ASCO solenoid has been increased to vackly.
'A Site-Incident Investigation Team (SIIT) was established to investigate the following;-
- 1. The cause of the voltage regulator malfunction.
- 2. The cause of the ASCO solenoid valve failures.
3.- Verification of the operation of the relays associated with the Emergency Mesel Cenerator auto-startin5 logic.
The voltage regulator is to remain in the Automatic mode until troubleshooting takes place-during the September,--1991 scheduled shutdown for'a refueling outage.
Failure Prevention,-Inc. recommended increasing the exercising frequency to weekly for Unit 1 and Unit 2 ACSO normally energized solenoids to prevent any galled lubricant from having-
-time to cause adherence.
An air quality study was done with no indications that this was a problem.
As a result of these valve failures. 10 valves with normally energized Automatic Swit:h Company'(ASCO) solenoids-on Units 1 and 2 were tested following the event.
Ons valve on Unit I was declared inoperable upon the subsequent testing due to a slow s roke time. Upon stroking the valvo four t b s, the stroke time improved and the valve was declared operable.
Tha SIIT team has-been disbanded. A task force is continuing investigation and troubleshooting-of the ASCO solenoids.
Undervoltage relays associated with the auto start logic for the Emergency Diesel Canerators were verified to have functioned as designed.
SAFETY ASSE?C'E.
Safety systems functioned as designed with tne exception af the Drywell Floor Drain Primary Containment Isolation valves. Considering this, the event would not have been more severe in
- thet: neither a: reasonable and credible alternative condition would have provided a source
. term within the Drywell. Without the source term, there is no increase in the quantity of material which would be released through the nonisoit,ted penetrations. Furthermore, the 2 016 F003 valve did go closed with the fourth attempt and did in fact isolate the path from ths Drywell. During the operators response to safety system actuations/isolations, a response verification is performed as it was in this case. In the event that a verification revealed that the required responses were not received under actual accident conditions, the operator would' attempt to effect the response to mitigate any consequences due to an unisolated primary containment penetration. This event was the result of a power failure and the appropriate Technical Specification was implemented.
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FAQUTY NAME (1)
DOCFrf NUMBER (2)
LER NUMBER (6)
PAGE (3)
Brunswick Steam Electric Plant 05000324 RYA 4 SEo REV 5
Unit 2 Na 91 005 0
tex 7 (n mw. no.c. i re w.o....assonu NRC aum maA si tir)
PREVIOUS SIMIIAR EVENTS VOLTAGE REGULATOR Brunswick has had at least two similar events that involved reactor SCRAMS due to Voltage Rogulator transients, 2-87-01 and 1-86-024. These events involved problems with the motor cperated potentiometers which establish the Voltage Regulator setpoint. Fotentiometer oxide buildup was determined to be the cause for of these events. After these events, the potentiometer was changed out to a sealed type to prevent recurrence. Another SCRAM occurred in September 1990, LER 2 90-015, which involved erratic operation of the Automatic Voltage Rogulator due to inproper adjustment of the various Auto Regulator settings.
DRWELL FLOOR AND EOUIPMENT DRAIN VALVES Brunswick has had at least two othat events involving the Dryvell Floor and Equipuent Drain Inboard and Outboard valves (1/2 G16-F003, 1/2-G16-}004, 1/2-G16-F019, 1/2-G16 F020) which oli have normally energized ASCO solenoids. One occurred in January of 1988, LER 2-88-001 on Unit 2 and one in May of 1990 Plant Incident Report 90 036 for Units 1 and 2.
EIIS COMPONENT IDENTIFICATION System /Comoonent EIIS Code RUCU CE RPS MG SET JC/MG EDG EK CENERATOR VOLTAGE REGULATOR TB/RG TRANSVERSE INCORE PROBE ISOLATION VALVE JM/IG/ISV DR WELL FLOOR DRAIN IS01ATION VALVE JM/ISV DR WELL EQUIPMENT DRAIN ISOLATION VALVE JM/ISV TVM EI f
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