ML20082N797
| ML20082N797 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 04/12/1995 |
| From: | Boyce R PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9504250381 | |
| Download: ML20082N797 (5) | |
Text
-1 i
Robert C. Boyca Plant Meager
<3.2~
1 Limerick Generating Station
- t PECO ENERGY
= 5"-a ~ "v Umerick Generating Station PO Box 2300 Sanatoga - PA 19464-0920 215 327.1200 Ext. 2000 -
April 12, 1995 Docket'Nos. 50-352 50-353
. License Nos. NPF-39 NPF-85 U. S. Nuclear-Regulatory Commission Attn: Document Control Desk Washington, DC 20555
Subject:
Limerick Generating Station, Units 11and 2
'Information Regarding Malfunction or Degradation aof Agastat Relays on the Onsite 4kV AC Safeguard-Power System - Additional'Information Addressing Reportability By letter dated March 31, 1995, we provided'information regarding the malfunction or degradation of several Agastat relays on the onsite 4kV AC Safeguard Power System.
Subsequent to this submittal, informal comments were received implying a desire'for additional details concerning
.the reportability determination made withLrespect to these failures. to this letter provides more-detailed information concerning our reportability determination.
For-reference purposes, Attachment 2 provides the' original information regarding the results of the investigation into the cause and the' corrective actions for these conditions.
t If you have any questions or require any additional information, please contact us.
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GHS/DBN:cah Attachments r
cc:
T. T. Martin, Administrator, USNRC, Region I j
N. S. Perry, USNRC Senior Resident Inspector, LGS j
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DQcket Nos. 50-352 and 50-353 April 12, 1995 Page 1 of 2 LIMERICK GENERATING STATION, UNITS 1 & 2 Information Regarding the Reportability of the Malfunction or Degradation of Agastat Relays on the Onsite 4kV AC Safeguard Power Distribution System The reportability determination for the events involving the malfunction or degradation of Agastat relays on the onsite 4kV AC safeguard power distribution system is based on two (2) positions.
These positions are the Emergency Diesel Generator system boundary and the Technical Specification 3.8.1.2 applicability.
Each of these positions is discussed in detail below.
Emercency Diesel Generator System Boundary The specific relay involved in these events is the 4kV dead bus relay (127).
A contact from this relay energizes an auxiliary relay (127x) which in turn energizes a relay (162) in the Emergency Diesel Generator (EDG) start circuit.
The System Design Baseline Document for.the EDG System at Limerick Generating Station (LGS), Units 1 and 2, " Diesel Generator and Auxiliary Systems," Section 2.1.3.2, regarding the boundary between the EDG System and the 4kV System, indicates that the boundary for the EDG System is at the contacts of the 162 relay which causes the automatic starting of the EDG in a Loss of Offsite Power (LOOP) condition.
Therefore, components beyond this boundary, including the 127 and 127x relays, are in the 4kV System and not the EDG System.
This configuration is confirmed by Regulatory Guide 1.9,
" Selection, Design, Qualification, and Testing of Emergency Diesel Generator Units Used As Class 1E Onsite Electric Power Systems At Nuclear Power Plants," Rev.
3, dated July 1993.
Figure 1 of Regulatory Guide 1.9, for a typical EDG System design, shows the boundary between the EDG System and Support Systems, including the Class 1E AC Distribution System, and confirms that the 4kV dead bus relay (127) is outside the EDG system boundary.
i Docket Nos. 50-352 and 50-353 April 12, 1995 Page 2 of 2 Regulatory Guide 1.108, " Periodic Testing of Diesel Generator Units Used As Onsite Electric Power Systems At Nuclear Power Plants," Rev. 1, dated August 1977, Section C.2.e(2) states that
" Unsuccessful start and load attempts that can definitely be attributed to malfunction of equipment that is not part of the defined diesel generator unit design should not be considered valid tests or failures."
Therefore, an unsuccessful start attempt due to malfunction of the 127 relay is not considered a valid test or failure, and is not required to be reported in accordance with Section 3 of Regulatory Guide 1.108.
Furthermore, the accelerated testing required by Technical Specifications (TS) Section 4.8.1.1.2.a due to valid failures (per the Regulatory Guide 1.108) does not include operation of the relays in question.
Consequently, considering the relay malfunctions as a valid EDG start failure would not provide for increased testing of the suspect components and would provide no verification of relay reliability.
Therefore, these relays are not considered to be part of the EDG system.
Technical Specifications 3.8.1.2 Apolicability LGS Unit 2 was shutdown for refueling at the time of the D22 and D24 4kV bus relay failures described by this letter.
In this operational condition, LGS TS Limiting Condition for Operation (LCO) 3.8.1.2 only requires that two (2) diesel generators be operable.
At the time, the D21 and D23 EDGs were operable and satisfied this TS requirement.
Therefore, the D22 and D24 EDGs were not required to be in surveillance in accordance with TS Survoillance Requirement (SR) 4.8.1.2.
This TS SR requires that the two EDGs which satisfy TS LCO 3.8.1.2 be demonstrated operable in accordance with TS SRs 4.8.1.1.1, 4.8.1.1.2, and 4.8.1.1.3.
TS SR 4.8.1.1.3 requires that all EDG failures, valid or non-valid, be reported.
However, this TS SR was not applicable to the D22 and D24 EDGs since they were not required to be operable and in surveillance at the time.
Therefore, the D22 and D24 4kV bus relay failures are not reportable.
g:
' Attachment 2 Docket Nos. 50-352 and 50-353 April 12, 1995 Page 1 of 2 LIMERICK GENERATING STATION, UNITS 1 & 2 Information Regarding Malfunction or Degradation of Agestat Relays on The Onsite 4 kV AC Safeguard Power System (Note: this attachment supercedes the version issued on 3/31/95)
During the third refueling outage for Limerick Generating Station (LGS) Unit 2, conducted during February, 1995, surveillance l
testing was performed on the four (4) Unit 2 onsite 4 kV AC safeguard power divisions.
These tests are required by the Technical Specifications and include a simulated Loss of Offsite Power (LOOP) condition on each individual safeguard bus to. test the dead bus relays and associated circuits.
The dead bus relays monitor the 4 kV bus voltage and de-energize on a loss of power, closing contacts to energize DC powered auxiliary relays.
The auxiliary relays start the associated Emergency Diesel Generator.
(EDG) and initiate a load shed.
During the outage testing, two (2) of the four (4) dead bus relays failed to properly function and.the associated EDG did not start on a simulated LOOP condition.
Also, a third relay was found to be degraded during a preventive maintenance inspection that was performed prior to the LOOP tests.
These relays are manufactured by Agastat, model number EGPI.
The three (3) relays were immediately replaced and the tests were then performed satisfactorily.
The failure analysis of the first two (2) relays identified that the relays malfunctioned due to oxidation of the relay contacts causing high contact resistance when the relay de-energized.
These relays are normally energized and the contacts associated with the auxiliary relays are maintained open.
These contacts i
are seldom closed and as a result, oxidation was able to develop, even though the relay has a cover and is located in a switchgear enclosure in a mild environment.
The only previous similar failure at LGS occurred on the Unit 2 D22 EDG in March of 1993.
The failure analysis of the third relay identified a degraded relay coil that is unrelated to the contact oxidation failure mode.
This relay was replaced as a conservative measure.
There j
have been no previous similar relay coil concerns identified at
+
LGS.
l To ensure that the four (4) Unit 1 dead bus relays were functional, the relays were replaced with new relays on March 9, 1995.
Each of the removed relays was then tested in a laboratory simulating field conditions and each relay functioned properly.
...o
.c Dgcket Nos. 50-352 and 50-353 April 12, 1995 Page 2 of 2 To ensure that the eight (8) dead bus relays installed in the Unit 1 and Unit 2 4 kV Safeguard Power Control Circuits continue to be capable of functioning, each relay will be tested on an accelerated schedule (currently once every six (6) weeks) to avoid the build up of oxidation on the contacts.
Additional information gathered during the investigation identified that the three (3) relays were manufactured in 1987, in three (3) different weeks over a fifteen (15) week span.
A review of the seventy eight (78) related industry events reported on the Nuclear Network identified ten (10) relay failures related to normally energized Agastat relays.
None of the industry failures were associated with the identical application as LGS.
These relay conditions have been added to the LGS relay performance monitoring program.
An analysis is being performed to determine the appropriate testing frequency of the dead bus relays and if any additional corrective actions are warranted.
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