ML16141A795

Forwards Request for Addl Info Re TS Changes for Plant Hydro Underground Path Breaker Control Mod

ML16141A795
Person / Time
Site:	Oconee
Issue date:	03/30/1994
From:	Wiens L Office of Nuclear Reactor Regulation
To:	Hampton J DUKE POWER CO.
References
TAC-M88556, TAC-M88557, TAC-M88558, NUDOCS 9404060051
Download: ML16141A795 (6)

Text

UNITED STATES 0 8NUCLEAR REGULATORY COMMISSION I

4WASHINGTON, D.C. 20555-0001 March 30, 1994 Docket Nos. 50-269, 50-270 and 50-287.

Mr. J. W. Hampton Vice President, Oconee Site Duke Power Company P. 0. Box 1439 Seneca, South Carolina 29679

SUBJECT:

OCONEE UNITS 1, 2, AND 3 -

REQUEST FOR ADDITIONAL INFORMATION RE.

TECHNICAL SPECIFICATION CHANGES FOR KEOWEE HYDRO UNDERGROUND PATH BREAKER CONTROL MODIFICATION - (TAC NOS. M88556/M88557/M88558)

By letter dated February 24, 1994, Duke Power Company (DPC) proposed a change to the plants' Technical Specifications to require surveillance testing-of at proposed modification to the control circuitry for the Keowee hydro station's output breakers. The modification is intended to eliminate a single failure, vulnerability previously identified by DPC. This vulnerability has been precluded by administrative controls which require an alignment which prevents simultaneous generation to the system grid with both Keowee hydro units. As noted in the modification package submitted with the amendment request, one purpose of the modification is to make both Keowee hydro units again available for simultaneous generation of electrical power to the offsite grid.

In order to complete our review, we require additional information. The specific questions are enclosed. The NRC is concerned about the use of emergency onsite sources as a source of commercial power for the offsite system. This concern is based on the potential interaction between the onsite and offsite sources, with the resultant increased potential for common mode failures. This concern is increased when not just one of the hydro units, but both hydro units are connected together to the grid. As a result of our concern, the encrosed questions are not just related to the requested Technical Specification. change but also are intended to obtain information that will address.our concerns relating to this mode of operation.

940 40605 903002 PDR ADOCK:05000269 P

PDR

Mr. J. W. Hampton

- 2 This requirement affects fewer than ten respondents and, therefore, it is not subject to Office of Management and Budget review under P.L.96-511. If you have questions regarding this matter, contact me at (301) 504-1495.

Sincerely, Original signed by:

L. A. Wiens, Project Manager Project Directorate 11-3 Division of Reactor Projects -

I/II Office of Nuclear Reactor Regulation

Enclosure:

Request for Additional Information cc w/enclosure:

See next page DISTRIBUTION Docket File>

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PM:PD2 RP D:P RPE EELB/B NAME LBerry LWienh DMa ews C.BERLINGER DATE

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Mr. J. W. Hampton Duke Power Company Oconee Nuclear Station cc:

A. V. Carr, Esquire Mr. Steve Benesole Duke Power Company Compiance 422 South Church Street Duke Power Company Charlotte, North Carolina 28242-0001 Oconee Nuclear Site P. 0. Box 1439 J. Michael McGarry, III, Esquire Seneca, South Carolina 29679 Winston and Strawn 1400 L Street, NW.

Mr. Mark Lesser, Section Chief Washington, DC 20005 Project Branch #3 U. S. Nuclear Regulatory Commission Mr. Robert B. Borsum 101 Marietta Street, NW. Suite 2900 Babcock & Wilcox Atlanta, Georgia 30323 Nuclear Power Division Suite 525 Ms. Karen E. Long 1700 Rockville Pike Assistant Attorney General Rockville, Maryland 20852 North Carolina Department of Justice Manager, LIS P. 0. Box 629 NUS Corporation Raleigh, North Carolina 27602 2650 McCormick Drive, 3rd Floor Clearwater, Florida 34619-1035 Mr. G. A. Copp Licensing -

ECO50 Senior Resident Inspector Duke Power Company U. S. Nuclear Regulatory Commission 526 South Church Street Route 2, Box 610 Charlotte, North Carolina 28242-0001 Seneca, South Carolina 29678 Dayne H. Brown, Director Regional Administrator, Region II Division of Radiation Protection U. S. Nuclear Regulatory Commission North Carolina Department of 101 Marietta Street, NW. Suite 2900 Environment, Health and Atlanta, Georgia 30323 Natural Resources P. 0. Box 27687 Max Batavia, Chief Raleigh, North Carolina 27611-7687 Bureau of Radiological Health South Carolina Department of Health and Environmental Control 2600 Bull Street Columbia, South Carolina 29201 County Supervisor of Oconee County Walhalla, South Carolina 29621

ENCLOSURE EELB QUESTIONS OCONEE NUCLEAR STATION - UNITS 1, 2 and 3 KEOWEE UNDERGROUND PATH BREAKER CONTROL MODIFICATION TAC NOS. M88556/M88557/M88558

1. Oconee design modification package NSM # ON-52966 discusses a modification to the control circuitry for the Keowee air circuit breakers (ACB-3 and ACB-4) for the underground emergency electrical path which should eliminate a single failure vulnerability relative to the differential protective relaying at Keowee hydro units.

Please provide copies of the elementary electrical schematic diagrams for the design modification. The diagrams should show the differential relaying circuitry current transformers for the Keowee hydro generating units and the Keowee main stepup transformer, the differential relays, and attendant downstream relay circuitry. Also provide detailed electrical schematics for the additional relay logic installed by this modification including the final open and close electrical actuation circuitry for ACB-3 and ACB-4. In addition, please provide a copy of the surveillance procedure to be used for the annual testing of the installed modification encompassed by proposed Technical Specification 4.6.2 c.

2. On Page 5 of Calculation No. OSC-5556 under Section 11, it is stated that the new modification provides separate and redundant logic for the closing circuits of ACB-3 and ACB-4 except for the contacts of common device LOR 86T. If a failure modes and effects analysis has been performed for this device, please submit a copy for review. Also discuss how this common device affects the required independence of the two hydro units.

3. Oconee Calculation/Analysis No. OSC-5096, Section H, "Fault/Failure Analysis For Oconee Nuclear Station Emergency Power System When Two Keowee Hydro Units Are Generating To The Grid," Item 12, indicates that both ACB-1 and ACB-2 could close automatically and tie the units together without synchronization check protection. A modification to the control circuit for the overhead ACB's has been made to eliminate this potential problem. In view of this, please provide elementary electrical schematic diagrams for-this modification.

4. Item 2 in Section H of OSC-5096 discusses a scenario where both hydro units could. be lost due to the protective actions of overspeed devices, auxiliary shutdown relays, and breaker anti-pump devices. The analysis concludes, for that scenario, that the Keowee Power System does not meet the required single failure criterion. Please discuss this scenario in detail along with any planned corrective action to prevent this from occurring. Provide elementary electrical schematics for any modifications. Also discuss the status of the 66MW restriction on both Keowee hydro units.

5. Section H considers electrical faults and the fault clearing time of protective relaying. On Page 1 of OSC-5096, the following statement is made:

When considering electrical faults, it is necessary to consider if the fault will be cleared fast enough to ensure that the Keowee units remain stable. Instability could cause a common-mode loss of both units, due to damage from a large current pulse that would occur if synchronism with the rest of the system is lost. If damaged, the units would be unavailable to provide emergency power.

Section H concludes that the Keowee units are protected from instability induced damage because of the clearing time of various relays.

Please provide a discussion of the classification (Class 1E, non-Class 1E, commercial grade, etc.) of these relays. Also, discuss their surveillance and maintenance.

6. On Page 19 of Section H it is stated that if the KLF-1 relay in both Keowee hydro units should operate during a worst case transient, a common mode event would exist that could lockout both units if they are being used for peaking power. Section H documents an analysis that shows these relays will not operate during worst case fault and post-fault recovery_

periods. Please discuss the classification, surveillance and maintenance of these loss of field relays. Also, discuss the historical operation of a KLF-1 relay due to a miss-set regulator (although found to be correctly set) described on Page 1 of Attachment 4 to OSC-5096.

7. While the Keowee units are being used in parallel to the grid, discuss the common vulnerability of the offsite and onsite electrical sources to a lightning strike.

8. In paragraph 4 of Section 3.2.4.1 of NRC Inspection Report No. 50-269/93 02, 50-270/93-02, and 50-287/93-02 the failure of a Keowee voltage regulator was discussed. The report quotes an internal licensee memorandum as stating that "smart failures" within control systems are not considered in failure analyses. Please discuss this philosophy in light of our concerns related to the vulnerability of both hydro units and the offsite sources when they are tied together. Without analyses which encompass all component failures, discuss what assurance is available that operating both hydro units in parallel to the grid at the same time is not a safety concern.

9. In Technical Specification 3.7.1 (b) two independent onsite emergency power paths each containing a Keowee hydro unit are required to be operable. Discuss how this Technical Specification is met when both Keowee,hydro units are connected together and to the grid.

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10. On Page 8.3-13 of the plants' FSAR, the following statement is made:

The emergency power sources are independent of each other...

Paralleling of emergency power sources is prevented by redundancy in transfer logic equipment and interlocking.

Discuss how this FSAR statement remains valid during periods when both Keowee hydro units are connected together.

11.

The licensee's letter dated February 24, 1994, responded to a Notice of Violation described in NRC Inspection Report No. 50-269/93-31, 50-270/93 31, and 50-287/93-31. In that letter the following statements were made:

As detailed in our response, following implementation of this modification, two separate and independent power paths will continue to be available. Existing interlocks installed to ensure independence were not changed by this modification. This modification will allow additional generation to the electrical grid without compromising the separate, independent power paths... The paths will remain separate and independent of each other at all times... As required by the FSAR, both paths remain independent throughout the scenario.

Explain this statement in light of the fact that both hydro units will be electrically tied together when they are both used together to power the grid (the start of the scenario).

12.

NRC General Design Criterion 39 (old), "Emergency Power for Engineered Safety Features," required as a minimum that the.onsite and offsite electrical power systems shall each, independently, provide the capacity to permit the functioning of the engineered safety features assuming a failure of a single active component in each power system. On Page 3-20 of the plants' FSAR, it is stated that the Oconee electrical systems meet the intent of this criterion. Discuss the application of this criterion when the onsite and offsite sources are tied together. Provide a discussion of analyses which exist that provide assurance that the Oconee electrical systems meet the intent of the criterion when both Keowee hydro units are generating power to the grid.

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