ML20128M678

Responds to RAI Re Breaker Coordination

ML20128M678
Person / Time
Site:	Catawba
Issue date:	10/07/1996
From:	Mccollum W DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TAC-M86367, TAC-M86368, NUDOCS 9610160148
Download: ML20128M678 (14)

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• DukeIbwer Company WlUJMIR. AlcCount, k V Catarrba Nuclear Generation Department lice hesident

. . :4800ConcordRoad (SM}UIDX) Dffice

• York, SC29745 ' (BMJUh1I26Far DUKEPOWER October 7, 1996 U.S. Nuclear Regulatory Commission Attention: Document Control Desk )

Washington, D.C. 20555 l

Subject:

Catawba Nuclear Station Docket Nos. 50-413 and 50-414 Response To Request For Additional Information Regarding Breaker Coordination (TAC Nos. M86367 and M86368) l l

In .a letter. dated August 21, 1996, the NRC requested I additional information .on the coordination of certain electrical circuit breakers at the Catawba Nuclear Station.

.In this letter the NRC asked, "Please search'your records and. determine at what point in time did DPC realize.that the 1 as-built conditions ... were not accurately represented by i the UFSAR. Specifically, was the realization a result of the staff's EDSFI- finding, or the result of DPC efforts

.before the EDSFI?"

Duke Power -has conducted . a records search on the plant systems affected by this- NRC. ' request for additional information. These systems are EPL (125-volt DC . Vital Instrumentation and Control Power)- and- EPE -(600-volt 'AC Essential Auxiljary Power).

The NRC requested Duke provide a response within 30 days of the August 21 letter. However, during a September 13, 1996, telephone' call to ONRR, Duke requested an approximate two weeks extension on the response.

Based' on the records search and interviews with Duke personnel cognizant of this subject, Duke has determined that Catawba did not recognize the discrepancy'between.t.he UFSAR r ad the as-built condition of the plant until being 1.\'

k informe of the NRC's '. interpreta' tion of the UFSAR content.

Attachment.I provides a chronological summary of the history of- this issue at Catawba. Attachment II- provides descriptive'information of the EPL and EPE systems. Duke 9610160148 961007 F PDR:.;ADOCK 05000413 P PDR anarwawarraw

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' Document Control Desk Page 2

' October 7, 1996 l

l believes this information shows a reasonable consistency between the applicable UFSAR sections and the actual design of the EPL and EPE systems.

'As discussed in the attachments, prior to the September 6, 1987 McGuire event and the related NRC Information Notice 88-45, Catawba had no reason to question the adequacy of the ci,7cuit breaker coordination in the plant. In accordance i wir.h Generic Letter 88-15, Catawba reviewed circuit breaker coordination and concluded that for the as-built system designs, the level of breaker coordination was adequate.

In late 1991, a consultant made a comprehensive review of Catawba's electrical power systems: in preparation for the upcoming NRC Electrical Distribution System Functional Inspection (EDSFI) . It was only after this consultant's review that Catawba became aware of an alternative interpretation of the UFSAR language for the breakers in the EPE system. No question was raised by the consultant regarding the consistency between the UFSAR and the as-built plant for coordination of the EPL system.

Before Catawba could determine the. accuracy of the consultant's alternative reading of the UFSAR, the NRC informed Catawba - during the EDSFI inspection in January r 1992, that it interpreted the UFSAR to require greater circuit breaker coordination than had been provided for-both the EPE and EPL systems. Duke had not previously understood the subject UFSAR sections as evoking a commitment to breaker coordination. The NRC subsequently issued EDSFI Deviation 50 413, 414/92-01-06 in connection with this issue. Recently, this discrepancy was resolved by the NRC's issuance of a license amendment tnat accepted the plant's as-built condition.

In light of this history, Catawba has conc.luded that it definitely learned about the discrepancy between the language in the UFSAR and the as-built condition of the plant only when the discrepancy was fully described by the NRC.

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' Document Control Desk Page 3 October 7, 1996 If there are any questions regarding this response please contact Mike Kitlan at (803) 831-3205 W.R. McCollum, J .

t Attachments xc: S.D. Ebneter, Regional Administrator, Region II U.S. Nuclear Regulatory Commission Atlanta, Ga 30323 R.J. Freudenberger, Senior Resident Inspector Catawba Nuclear Station P.S. Tam Senior Project Manager, ONRR i

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. ATTACHMENT I CHRONOLOGY Catawba Nuclear Station, Units 1 and 2 EPE: 600VAC Essential Auxiliary Power System EPL: 125VDC Vital Instrumentation and Control Power System

System Design

EPE System Molded case incoming breakers were incorporated into the original Catawba design in 1978 per feedback from the Operations Group that a local main disconnect at the motor control center was needed. Since it was recognized that there would be an impact on system protective devices, breakers wita the highest magnetic-only trip rating were selected.

EPL System The EPL system consists of molded case circuit breakers throughout. Although formal fault current calculations were not done during original design, breaker sizes were selected and settings were chosen to limit the potential degradation of the system from faults.

Chronology of Events Sept 1987 On September 6, 1987 McGuire Unit 2 tripped as a result of lack of breaker coordination in a nonsafety power system. A May 4, 1988 NRR report on this event recommended that McGuire evaluate problems with breaker coordination. A June 3, 1988 internal DPC letter from J.E. Thomas to N.A.

Rutherford addressed how the Duke Power Desj gn Engineering Department would conduct the recommended evaluation. The letter stated that the McGuire coordination calculations would be reviewed against the more updated criteria used for Catawba breaker coordination calculations. The letter also stated that the breaker ccordination was not a safety issue and that there were no licensing commitments regarding breaker coordination.

July 1988 I

NRC issued Information Notice No. 88-45, " Problems In Protective Relay and Circuit Breaker Coordination". This notice described problems with breaker coordination at three ,

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} .plsnts. One-of the three examples discussed in this notice

}. was the September 6, 1987 McGuire Unit 2 trip. The

! discussion section of Information Notice No. 88-45 included j the following statement: "The staff relies on the exercise j

4 of good engineering practice by the designers of electrical power systems at nuclear . power plants to provide for the proper functioning of protective devices."

! Sept. 1988 On September 12, 1988 NRC Generic Letter 88-15, " Electric

Power Systems - Inadequate Control Over Design Processes",

I was issued. One section in this letter addressed how lack of breaker coordination can create the potential for an

unacceptable ' level of equipment loss during fault

] conditions.

J March 1989 The March.30, 1989 McGuire NRC Inspection Report Nos. 50-369/89-01 and 50-370/89-01 included close-out of Inspector Followup Item 369, 370/88-20-01. This item concerned review of electrical breaker coordination that resulted in the.

September 6, 1987 McGuire Unit 2 trip. The ongoing periodic review 'of the breaker coordination calculations was the primary factor cited for closing the item. The same section. 1 of the inspection . report also notes that Desi'gn personnel indicated that breaker coordination was not assured in all cases because of the type breakers used in some systems.

There were many similarities between the McGuire and Catawba power systems designs, including the types of breakers used.

1 December 1989 i A December 21, 1989 internal DPC letter from R.G. Kurilla to R.C. Futrell documented how Catawba was reviewing breaker  ;

coordination in light of Information Notice No. 88-45. This letter discussed the periodic reviews of electrical calculations and how the breaker coordination calculations would be reviewed in accordance with established schedules. l This review would include consideration of the questions posed by the NRC about the methodology used for McGuire i

- break.er coordination design prior to the September 6, 1987 McGuire Unit-2 trip. -This Catawba review focused on the adequacy of existing calculations and there- was no  ;

additional review of the portions of the EPE and EPL systems '

that'did not have coordination calculations.

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.Apr. 1990 A joint position paper for all three Duke nuclear plants on Generic Letter 88-15 was issued internally. Catawba's l position was that breaker coordination provided in existing l -designs was adequate. This was based on the fact that the

. existing breaker coordination -calculations on file had no l coordination issues identified. This was also based on

studies that showed. adequate breaker coordination to support I the Fire Protection Plan.

i Nov. 1991 l

Catawba hired a consultant to do a wide ranging audit of

electrical power systems in preparation for an announced NRC EDSFI inspection. The consultant's report identified the need to perform coordination studies for EPE and EPL systems. This report indicated there was no UFSAR commitment for EPL system breaker coordination but the consultant interpreted an UFSAR paragraph on the EPE system as a requirement for coordination.

l l Feb. 1992 In the EDSFI Inspection Report, Catawba was cited for a l

DEVIATION from written commitments in the UFSAR that protective devices shall limit the. degradation of Class lE power systems (EPL) and that a selective tripping scheme is provided (EPE).

i UFSAR Sections Cited in EDSFI Inspection Report EPL System: The UFSAR says the system complies with the requirements of IEEE 308-74. The IEEE Standard says:

" Protective devices shall be provided to limit the degradation of the Class 1E power systems".

EPE System: The UFSAR says: " Protective devices on the 600VAC Essential Auxiliary Power System are selected and set-to achieve a selective tripping scheme so that a minimal amount of equipment is isolated from the system for adverse l

conditions such as a fault."

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[ In Catawba's April 16, 1992 response to the Notice Of 4 Deviation Catawba committed to study the scope of potential  ;

hardware changes that would improve coordination and to

weigh the benefits of such changes. The response stated j that Catawba would either proceed with plant changes if 1

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justified or update the UFSAR to justify the deviation. A

, commitment was made to complete this study by 10/30/92, j Oct. 1992  !

i Catawba completed the study committed to in the April 16, )

1992 response and concluded that the existing systems were adequately designed and hardware changes were not justified.

Nov. 1992 I

Catawba engineers met with engineers from Oconee and McGuire j- Nuclear Stations to jointly review disposition of EDSFI issues. Catawba presented the study committed to in the April 16, 1992 response and the working group endorsed Catawba's position of not making hardware changes.

April 1993 An EDSFI Follow-up Inspection was conducted at Catawba.

Engineering personnel explained to the Inspector the scope and conclusions of Catawba's study on the EDSFI Deviation.

Jan. 1994 After several telephone confet aes in the preceding months with NRR, Catawba agreed to make a trip to White Flint to answer four questions from NRR staff: 1) Where are the faults? 2) What breakers are coordinated and not coordinated? 3) What is the impact of-the upstream breaker clearing? 4) What is the safety significance of taking out a train?

In January 1994 the calculations were put together that answered the four questions above and documented the level of breaker coordination provided in the EPE and EPL syster.s.

Prior to this, there was no coordination study of the EPL system, or the portion of the EPE system that included the motor control center incoming breakers.

Feb. 1994 Four engineers from Catawba met with three NRR staff l personnel at NRR White Flint Office. The NRR primary reviewer was one of the three NRR representatives in this meeting. Fault current calculations were explained and coordination curves were reviewed. NRR requested that Duke I provide a formal response documenting the meeting discussion and data reviewed.

March 1994

! ' Catawba sent NRR a detailed documentation package with copies of data and curves reviewed in the February 1994

meeting.

Sometime between March and Sept. 1994 NRR requested a duplicate copy of the documentation package j and coordination curves, which Catawba then immediately sent j to NRR.

l Sept. 1994 On September 14, 1994 Catawba received from NRR a request for additional information. This letter stated that the staff could not accept the proposal to change the UFSAR

rather than the breakers based solely on the information 4 submitted to date. Among the additional information

] requested was a 10CFR50.59 evaluation to accompany the UFSAR change proposal.

Dec. 1994

1. Catawba completed the 10CFR50.59 evaluation that showed i UFSAR changes without hardware changes represented no unreviewed safety question. The 50.59 evaluation package i included PRA analysis. The 50.59 results were presented to i the Catawba Plant Operating Review Committee which approved 4

maintaining the position of not making hardware changes.

The 10CFR50.59 package was transmitted to NRR on December l 29, 1994.

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Feb. 1995 Catawba received a list of questions posed by the new NRR reviewer. These questions primarily involved PRA l methodology and the use of NPRDS data.  !

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A conference call was held between Catawba Engineering, c General Office PRA engineers, the NRR Catawba Project Manager, and the NRR reviewer to discuss the questions Catawba received in February 1995. Some of the reviewer's questions were discussed at length but no agreement was reached.

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l May 1995

!- The Catawba NRR Project Manager went on a plant walkdown i with Catawba plant engineer to look at the scope of

! modifications that would be required to install larger l breakers in the EPL system or remove incoming breakers from l the EPE system. )

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l June 1995 l 1 The Catawba plant engineer involved with the 10CFR50.59 l

{ package answered questions regar. ding the package over the

{ . phone with the NRR Catawba Project Manager. l

Nov. 1995 i The NRR Catawba Project Manager telephoned the Catawba plant

! engineer to discuss details of the EPL system design.

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! Mar. 1996 i

l The NRR Catawba Project Manager telephoned Catawba to

discuss the PRA calculation associated with the 10CFR50.59

package. He indicated that NRR planned to submit additional questions on Catawba's December 1994 submittal and that an

( .NRR team would like to meet at Catawba in April 1996.

Apr. 1996 A two day review meeting was held at Catawba with four NRR reviewers to answer questions associated with the December 1994 10CFR50.59 package. These reviewers also went on a plant ~ walkdown to view the subject breakers and to review plant backup protection capabilities.

Catawba received a letter from R.E. Martin requesting i I

documented responses to the questions discussed in the April 1996 meeting at Catawba.

May 1996 On May 17, 1996 Catawba transmitted the response to the RAI ,

from R.E. Martin. l Aug. 1996-

$ .On August 21, 1996 Catawba received the RAI from NRR which is the subject of this letter.

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Sept. 1996 i

A September 17, 1996 letter from H.N. Berkow to W.M.

i McCollum' requested that UFSAR changes be submitted per the

! license amendmant process.

! On' September 21, 1996 Duke Power Company submitted a license 1

amendment request for-Catawba to make UFSAR changes.

a l On September 28, 1996 the NRC approved the license amendment i submitted September 21, 1996. The September 28, 1996 NRR j' Safety Evaluation Report, related to the license amendment, concluded that the licensee had documented adequate technical justification for the lack of breaker coordination

in the EPE and EPL systems. In referencing five submittals from the licensee the SER recognized the licensee's efforts to work with the NRC staff to resolve this issue.

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'AT'TACHMENT II SYSTEM DESIGNS I A. 600 VAC Essential Auxiliary Power System (EPE) :

i UFSAR section 8.3.1.1.2.2, fifth paragraph (text at i

time of EDSFI):

" Protection devices on the 600VAC Essential Auxiliary Power System are selected and set to achieve a selective tripping scheme so that a minimal amount of' equipment is isolated from the system for adverse

conditions such as a fault. The load center breakers are set to protect the cable feeding the essential motor control centers and coordinate with essential motor control center feeder breakers. The relays on the essential load center transformer feeders are set to protect the transformers and coordinate with the load center breakers."

Although the motor control center incoming breakers were in the original design of the 600 VAC Essential Auxiliary Power System (EPE), they are not addressed in the above UFSAR paragraph or anywhere in Chapter 8 of the UFSAR. The only discussion of the motor control center incoming breakers in the UFSAR is Section 14.4.37, " Electrical Load Capacity Test." The above quoted UFSAR paragraph from section 8.3.1.1.2.2 describes the selective tripping scheme of specifically identified breakers, but does not address the motor control center incoming breakers.

The motor control center incoming breakers were incorporated into the original system design in 1978 for a specific purpose and the breakers were judged to function acceptably in this system's protection scheme. All commercially available breakers and switches of the appropriate ratings were considered for this application. Breakers were selected that provided the best compromise between equipment / personnel protection and reduced the potential of undesired tripping. Upon original installation, the breakers were set at the highest achievable trip setting to minimize undesired tripping. This design was considered compatible with the selective tripping scheme of the EPE system.

The Duke Power Company Design Engineering Department  !

considered the application of protective devices in the EPE system design to be consistent with recommendations in )

Information Notice 88-45, " Problems In Protective Relay And  :

Circuit Breaker Coordination." The discussion section of Information Notice 88-45 includes the following, "The staff l

a re' lies on the exercise of good engineering practice by the designers of electrical power systems at nuclear power plants to provide for the proper functioning or protective devices."

1 A Self Initiated Technical Audit (SITA) of Catawba's l

electrical distribution system by an outside consultant was l completed on November 1, 1991. This audit report noted that l there was no coordination study to satisfy UFSAR section l 8.3.1.1.2.2 for a portion of the 600 VAC Essential Auxiliary '

Power System at the motor control center level and below.

Catawba agreed with the prudence of doing the coordination study but was not prepared to agree with the corisultant's conclusion that breaker coordination was a licensing requirement. The consultant made no quantified assessment of the actual level of coordination existing within the system and, therefore, did not address the subject as an UFSAR deviation.

The October 1992 Catawba response to the EDSFI Deviation stated that there was a " design oversight" concerning the content of the subject UFSAR paragraph. This statement referred to the lack of clarification in the text that part of the EPE system design provided less selectivity than the breakers specifically described, but that the overall system design was considered adequate and in conformance with licensing requirements. Catawba's position on the design adequacy was based on a number of factors that have been documented in previous submittals on this subject.

The Catawba facility operating license amendment for the subject section of the UFSAR, which the NRC approved on September 28, 1996, involves supplementing the original wording to clarify the acceptability of the existing tripping scheme. This revision acknowledges that the motor control center incoming breakers may not fully coordinate with motor control center load breakers. The justifications for the UFSAR revision include aspects of the system design that make highly unlikely those catastrophic faults that would challenge the existing breaker coordination capabilities. The UFSAR change also notes that the resulting amount of potential equipment isolation is acceptable; there is no impact on the UFSAR Chapter 15 safety analyses and redundant equipment is not affected.

The plant's operational experience has included no challenges to the protection scheme for the EPE system and the system has never been considered to embody any design deficiency with respect to the motor control center incoming breakers.

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l After researching Catawba files and soliciting feedback from responsible personnel there is no evidence of Catawba being i aware, prior to EDSFI . discussions in January 1992, that UFSAR section 8.3.1.1.2.2 did not accurately represent the i as-built plant condition. This does not imply that Catawba

! considered all the breakers fully coordinated; but that the i system design was considered to provide adequate selective

tripping.

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j B. 125 VDC Vital Instrumentation And Control Power System (EPL) :

UFSAR Section 8.3.2.2.4 (text at time of EDSFI) :

l " Compliance with Begulatory Guide 1.32, IEEE Standard j 308-74, and IEEE Standard 450-1975 and IEEE 450-1980

- The design of Class 1E dc power systems complies j

with the requirements of IEEE 308-1974 as augmented by Regulatory Guide 1.32. The Class 1E batteries are given a service test at an interval not to exceed 18 months. Additionally, the Class 1E battery performance and acceptance tests comply with Section 5 of IEEE 450-1975 and/or section 6 of IEEE 450-1980."

Section 5.2.1.6 of IEEE 308-1974:

" Protective devices: Protective devices shall be provided to limit the degradation of the Class 1E power systems. Sufficient indication shall be provided to identify the actuation of a protective device."

Chapter 8 of the UFSAR includes no discussion of how or to what degree the protective devices in the 125 VDC Vital Instrumentation and Control Power System (EPL) limit degradation from faults. When this system was designed, the protective devices provided, and other features of the system design, were judged to adequately limit the degradation potentially created by fault conditions. This conclusion was based on consideration of a number of factors that have been documented in previous submittals on this subject.

The November 1, 1991 SITA audit report recommended that Catawba perform a coordination study for the EPL system.

The report also stated that the Catawba UFSAR contained no requirement for breaker coordination in the EPL system.

Catawba agreed with the prudence of performing this study

l bu't made no correlation with any licensing requirement concerning breaker coordination.

The Catawba facility operating license amendment for the subject section of the UFSAR, which the NRC approved on September 28, 1996, involves supplementing the original wording to clarify the acceptability of the existing protective devices to limit the degradation of the EPL system. This revision acknowledges that some DC distribution center breakers may not fully coordinate. The justifications for the UFSAR revision include aspects of the system design that make hiahly unlikely those catastrophic faults that would challenge the existing breaker coordination capabilities. The UFSAR revision also notes that the resulting amount of potential equipment isolation is acceptable; there is no impact on the UFSAR Chapter 15 safety analyses and redundant equipment is not affected.

After researching Catawba's files and soliciting feedback from responsible personnel there is no evidence of Catawba being aware, prior to EDSFI discussions in January 1992, that UFSAR section 8.3.2.2.4, concerning compliance with IEEE Standard 308-74, did not accurately represent the as-built plant condition. This does not imply that Catawba considered all the breakers fully coordinated but that the system design was considered to adequately limit degradation from faults.

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