05000352/LER-1997-003, :on 970204,degraded Back Pressure Dampers Needed for Pipe Rupture Mitigation Resulted in Operation Being Outside Design Basis.Caused by Failure to Include Periodic Cycling & Cleaning of Bdps.Addl Failures,Corrected
| ML20141C517 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 05/12/1997 |
| From: | Kantner J PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | |
| Shared Package | |
| ML20141C515 | List: |
| References | |
| LER-97-003, LER-97-3, NUDOCS 9705190083 | |
| Download: ML20141C517 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3521997003R00 - NRC Website | |
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FACILITY NAME (1)
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Limerick generatine Leation. Unit 1 05000 352 1 OF 6 ilILE (4) Degraded Back Pressure Dampers Needed lor F1pe kupture Mitigation ResuiLs in Operation Outside Design Basis.
EVENT DAIE (5)
LER HUMBER (6)
REPORT DATE (/)
OTHER FACILITIES INVOLVED (8)
SEQUENTIAL REVISION FACILIIf MME DOCKET NUMBER MONTH DAY YEAR YEAR MONTH DAY YEAR NUMBER NUMBER Limerick, Unit 2 05000253 02 04 97 97 003 __
FACILIIy NAME DOCKET NUMBER 1
5 12 97 05000 OPERATING 1HIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5: (Check one or more) (11)
MODE (9) 1 20.402(D) 20 405(c) 50./3(a)(2)(iv) 13./1(D)
POWER 20.405(a)(1)(i) 50.36(c>(1) 50./3(a)(2)(v) 73.11(c)
LEVEL (10) 100 to.405(a)(1)(iij 50.36(c)(2)
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OTHER 20.405(a)(1)(iii) 50./3(a)(2)(i)
SU./3(a)(2)(v111)(A)
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X 50.73(a)(2)(ii) 50.73(a)(2)(viii)(b)
[e to.405(o)(1)(v) 50./3(a)(2)(iii) 50.73(a)(2)(x)LICENSEE CONTACT FOR THIS LER (12) hAMi TELEPHONE NUMBER (include Area Code)
J. L.
Kantner, Manager - Expereince Assessment, LCS (610) 718-3400 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)
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CAUSE
SYSTEM COMPONENT MANUFACTURER
CAUSE
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ABSTRAci (Limit to 14vu spaces
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During the February 1997 refueling outage for Unit 2, a total of eight (8) Unit 2 pairs, one (1) Unit 1 pair, and several single Back Pressure Dampers (BPDs) failed to actuate following a test signal.
The BPDs are required to mitigate the consequences of a postulated pipe rupture.
On 02/06/97 it was determined that this condition may have resulted in a failure to meet the design basis for a high energy line break (HELB) event.
All Unit 2, common Control Enclosure (CE) and all accessible Unit 1 BPDs were tested and additional failures were immediately corrected.
All of this testing was completed prior to the restart er Unit 2.
The six (6) inaccessible Unit 1 BPDs were tested during a power reduction on 04/12/97.
Four (4) of the six (6) Unit 1 inaccessible dampers and one (1) Unit 2 damper in a subsequent test sample failed to actuate.
These five (5) failures were immediately corrected.
Excessive friction in the bushing located between the solenoid and the BPD linkage caused all of the damper failures.
Periodic cycling of the BPDs was not included in the original preventive maintenance (PM) program.
An engineering analysis concluded that the additional components potentially impacted by the HELB event would still be capable of performing their safety function, but were not fully qualified.
The appropriate PM activities for each BPD have been developed.
9705190083 970512 PDR ADOCK 05000352 S
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PAGE (3) yg SEQUENTIAL REVISION NUMBER mR Limerick Cencrating Station, Unit 1 05000 352 2 0F 6 97
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Unit Conditions Prior to the Event Unit 1 was in Operational Condition (OPCON) 1 (Power Operation) at 100% power when this event was initially discovered.
Unit 2 was in OPCON 5 (Refueling) when this event was initially discovered.
There were no structures, systems or components out of service that contributed to this event.
On April 12, 1997, Unit 1 was in OPCON 1 at 24% power and Unit 2 was in OPCON 1 at 100% power when the additional degraded dampers were discovered.
Description of the Event f
Following maintenance activities conducted during the February 1997 Unit 2 refueling outage, Instrumentation and Controls (I&C) technicians were performing post maintenance testing of several pressure differential switches (PDS, EIIS:PDS) associated with back pressure dampers (BPD, EIIS:UDMP).
The PDSs are designed to sense an increase in differential pressure from a postulated pipe rupture and actuate a solenoid release mechanism that actuates the BPD through a linkage.
The BPDs are installed in ventilation ductwork where isolation is needed for compartments that enclose high energy lines.
These BPDs are installed in pairs with independent actuation mechanisms for single failure considerations.
Four (4) pairs of BPDs are located in ventilation ductwork connected to the Unit 2 Outboard Main Steam Isolation Valve (MSIV, EIIS:ISV) room.
On February 4, 1997, it was discovered that three (3) pairs of BPDs associated with this room failed to close following a test signal.
On February 6, 1997, at 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> it was determined that this condition may have existed while Unit 2 was at power that may have resulted in a. failure to meet the design basis for a high energy line break (HELB) event in this room.
On February 6, 1997, at 1339 hours0.0155 days <br />0.372 hours <br />0.00221 weeks <br />5.094895e-4 months <br />, a four (4) hour notification to the NRC was made per the requirements of 10CFR50.72 (b) (2) (1) since this condition may have resulted in a seriously degraded condition while Unit 2 was at power.
5 The Limerick Generating Station (LGS) Updated Final Safety Analysis Report (UFSAR) Section 3.6 describes the design basis for protection against a HELB event.
This analysis assumes that essential systems and components are either located in areas not affected by pipe ruptures or are qualified for operation under the maximum environmental conditions that they may be subject to as a result of pipe ruptures.
This analysis also assumes that a single active component failure occurs which could include a failure of a single BPD to close.
In the outboard MSIV room, a rupture of a main steam line i
I NRC W 366A U.S. NUCLEAR REGULAIORY C0f9tl5510N' APPROVED Br OMB NO. 3150 0104 (5 92)
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YEM SEQUENT)AL REVISION Limerick Generating Station, Unit 1 05000 352 3 0F 6 97 003 --
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i or a.high pressure feedwater line would result in a large amount of i
high energy steam to be discharged into the room.
During this event,
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one of the two BPDs in each pair is required to close to prevent steam from entering adjoining rooms and impacting essential systems or 1
components located in these rooms.
An initial engineering analysis of l
a' postulated HELB in this room with the failure of all six (6) BPDs i
was performed on February 7, 1997.
This analysis concluded that the resulting environmental conditions in the adjoining rooms would have exceeded the environmental qualification limits for certain components required to mitigate the consequences of the HELB event.
On February 5 and 6, 1997, fourteen (14) additional BPDs were tested to address the potential generic implications of the failures.
Four (4) additional pairs and two (2) single BPDs failed to actuate during the testing.
Based on these results, all Unit 2 BPDs (36 pairs), all i
L common Control Enclosure BPDs (33 pairs) and all accessible Unit 1 BPDs (33 of 36 pairs) were tested.
The testing identified twenty-six (26) failures (8 pairs and 10 singles) on Unit 2, two (2) failures (2 singles) on the Control Enclosure, and seven (7) failures (1 pair and 5 singles) on Unit 1.
At that time, the inaccessible Unit 1 BPDs were determined to be operable based on the following:
i e All six (6) were last inspected and tested in February 1996 during l
the 1R06 outage.
i I
e A review of the maintenance records for all six (6) dampers had shown a history of successful testing.
78% of the dampers testing satisfactorily as-found had not been j
tested for at least seven (7) years.
Only one (1) of the thirty-five (35) as-found Unit 1, Unit 2, and Common failures occurred less than three (3) years since the last satisfactory test.
The single damper failure rate was 17.2%.
The failure rate for damper pairs was 8.82%.
To gather additional data, testing of the inaccessible Unit 1 BPDs was planned for the next load reduction of sufficient magnitude to allow I
acceptable radiation levels for access.
The six (6) inaccessible Unit 1 dampers were tested during a power l
NRC FORM 365A (5 92)
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reduction on April 12, 1997.
Four (4) of the six (6) dampers failed to actuate.
An additional 30 dampers were tested following these failures to assess potential generic implications.
One (1) Unit 2 damper failed to actuate during this additional testing.
This Unit 2 damper had been tested satisfactorily on February 6, 1997 and was part cf a population of fourteen (14) BPDs which were originally tested in February but were only cleaned upon discovery of a failure.
The remaining dampers in this population were tested satisfactorily following the April event and were left in a clean, lubricated, fully functional condition.
l The initially discovered f ailed BPD pair on Unit 1 was located in the Safeguard Valve Room and contains High Pressure Coolant Injection (HPCI, EIIS:BJ) system steam supply piping. An engineering evaluation has concluded that the environmental conditions resulting from a postulated HELB in this room with the failure of the BPD pair would exceed the tested environmental qualification limits for components in the adjoining rooms; however, the equipment was determined analytically to remain capable of performing its design function.
It was concluded that the degraded BPD conditions existed while Units 3 and 2 were at power.
An analysis of the consequences of each of the failed BPDs (single dampers and pairs) on Unit 1, Unit 2 and the l common Control Enclosure was performed.
This analysis concluded that a HELB event with these failures along with an assumed single active failure of a redundant BPD may have resulted in environmental conditions in the adjoining rooms exceeding the environmental qualification limits for certain components required to mitigate the consequences of the HELB event.
Therefore, this report is submitted in accordance with the requirements of 10CER50.73 (a) (2) (ii) (B) as operation outside the design basis of the plant.
In all cases (i.e.,
initial and subsequent failures), the failure of each BPD to actuate was the result of excessive friction in the bushing located between the solenoid and the BPD linkage.
Each failed BPD was immediately repaired by cleaning and lightly lubricating the bushing and solenoid stem. The BPD was then retested satisfactorily prior to testing the next BPD.
All of the testing of Unit 2, common Control Enclosure, and accessible Unit 1 BPDs was completed by February 21, 1997, prior to the restart of Unit 2 from the refueling outage.
The initial operability determination for the six (6) inaccessible Unit 1 dampers was based upon a review of the maintenance history of,
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the dampers and engineering judgment.
Examination of these dampers following test failure revealed that, although the six (6) dampers had been stroked and maintained during the February 1996 Unit i refuel outage, they had not been maintained to the degree required to ensure that the damper mechanism was clean and free to move.
All four (4) of the failed dampers were immediately repaired and all six (6) dampers were restored to a cleaned, lubricated and fully functional condition.
Analysis of the Event
The actual consequences for this condition are minimal since an event requiring the actuation of the BPDs has not occurred at LGS.
An engineering analysis was conducted to determine the effects of a postulated HELB event in a compartment associated with a failed BPD.
HELB analysis sensitivity evaluations concluded that the affected equipment in the adjoining room (s) could have been exposed to temperature, pressure and humidity levels above the current 4
environmental qualifications of the equipment located in adjoining rooms.
The specific equipment was further analyzed, and the equipment was determined to be capable of performing the functions necessary to mitigate the HELB event, but not fully qualified.
This conclusion is based on the short duration of the elevated environmental conditions and environmental qualification analysis of the same equipment currently approved for Peach Bottom Atomic Power Station.
The degraded BPDs would not impact the termination of the pipe rupture because the isolation valves are located in HELB compartments and are 3
qualified for harsh environments.
The maximum amount of radioactive material released as a result of the event would not increase, since the pipe rupture release is terminated and essential equipment.is capable of performing its safety function.
Therefore, it is concluded that the ability to shut the reactor down safely would have been i
maintained, the Primary Containment integrity would have been maintained, and the resultant offsite doses would have been below analyzed limits.
Cause of the Event
The cause of the degraded BPD actuation mechanisms was the failure to include periodic cycling, cleaning, or 1,ubricating of the BPD's as part of the original preventive maintenance program. As a result, increased friction in the actuation mechanism occurred preventing the mechanism from releasing the linkage and damper.
Damper cycling is not sufficient to ensure that the mechanism is fully functional.
. Periodic cleaning and lubricating must be incorporated into a NRC FCRM 366A (5 92)
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Corrective Actions
All Unit 2, common Control Enclosure (CE) and all accessible Unit 1 BPDs were tested, additional failures were immediately corrected, and all BPDs were left in an operable condition. All of the testing was completed by February 21, 1997, prior to the restart of Unit 2. The inaccessible Unit 1 BPDs were tested on April 12, 1997.
All failures were immediately corrected.
The appropriate PM activities for each BPD, including the appropriate i
frequency for BPD actuation and scope of PM to be performed were developed by April 4, 1997. The frequency and scope of PM activities to be performed will be further evaluated based on the results of future testing of BPDs.
The appropriate responsible personnel were advised of the potential generic concern associated with the need to adequately test safety related components with active functions.
A review of the adequacy of PMs for Q-active components which are i
redundant and normally not in service such that a failure would not be self-revealing is in progress.
Previous Similar Occurrences f
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