ML20206T251

Forwards Util Position on Current First Level Undervoltage Protection Testing.No Mod to Tech Specs Necessary to Continue High Reliability of Program

ML20206T251
Person / Time
Site:	Yankee Rowe
Issue date:	06/30/1986
From:	Papanic G YANKEE ATOMIC ELECTRIC CO.
To:	Mckenna E Office of Nuclear Reactor Regulation
References
DCC-86-080, DCC-86-80, FYR-86-060, FYR-86-60, NUDOCS 8607080059
Download: ML20206T251 (4)

Text

6 lANKEE ATOMIC ELECTRIC COMPANY ig",*,(o.Qo*,'e , '

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• 1671 Worcester Road Framingham, Massachusetts 01701 DCC 86-080

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-. . s June 30, 1986 FYR 86-060 United States Nuclear Regulatory Conunission Washington, DC 20555 Attention: Ms. Eileen M. McKenna Project Manager, Project Directorate No.1 Division of PWR Licensing - A

References:

(a) License No.' DPR-3 (Docket No. 50-29)

(b) USNRC Letter to YAEC, dated June 3, 1977 (c) USNRC Letter to YAEC, dated November 30, 1985 (d) YAEC Letter to USNRC, dated December 26, 1985

Subject:

First Level Undervoltage Protection

Dear Ms. McKenna:

In Reference (d), Yankee committed to respond by June 30, 1986 to a USNRC r

request, Reference (c), that Yankee address the first level (loss of voltage) undervoltage protection testing at Yankee Nuclear Power Station.

Attachment 1 presents the Yankee position on why our present testing program is sufficient and that no modification to the Technical Specifications is necessary to continue the high reliability of Yankee's first level undervoltage protection circuitry and testing program.

If you have any questions, or require further information, please contact us.

Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY i

• G. Papa , Jr. V Senior Project' Engineer Licensing i

i olS e i 1 8607080059 860630 9 PDR ADOCK 0500 P

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ATTACHMENT 1 f

The Staff position on degraded grid voltage protection was transmitted to YAEC 3

by an NRC Generic Letter, Reference (b). This letter required the addition of

. a second level (degraded voltage) undervoltage protection as well as Technical Specification changes to include a monthly test to demonstrate the operability l of both first level (loss of voltage) and second level (degraded voltage) undervoltage protection. '

5 Presently, at Yankee there are two levels of voltage protection: the first level which provides loss of voltage protection and the second level which provides degraded voltage protection.

l The first level (loss of voltage) undervoltage protection was installed

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approximately 15 years ago and, on loss of voltage, initiates the following

. actions: (a) isolates the 480 volt emergency busses from the nonemergency l busses; (b) starts the emergency diesel generators; and (c) closes the diesel

. generator breakers, energizing the emergency busses.

i

) The system consists of a Westinghouse Type CV-7 electromagnetic induction disc relay on each of the three 480 volt emergency busses. These relays, mounted in the Main Control Room (NCR) on the Safety Injection Panel (SIP), are set to 4

actuate in 1.8 seconds on a complete loss of power or 3.0 seconds at 277 volts

, (58%) or 7.0 seconds at 370 volts (77%). These circuits are tested once per 18 months by Operating Procedure OP-5762.

j The second level (degraded voltage) undervoltage protection was installed j during tne 1984 refueling outage. This system actuates an alarm in the Control Room if a degraded voltage of 421 1 4.5 volts or 429 i 4.5 volts j exists on emergency busses or nonemergency busses, respectively, for l 1011 seconds. In this situation, the operator takes specific actions as

} required by plant Operating Procedures OP-3838, 3844 and 3845.

i l The time delay of ten seconds is provided to prevent actuation of the alarm A

during transients caused by motor starting or short-term grid disturbances.

l If an accident condition exists coincident with the degraded voltage, then {

i actions such as those described for the first level (loss of voltage) l undervoltage protection will be automatically initiated along with the i starting of the safety injection HPSI and LPSI pumps. These circuits are

tested once per month in accordance with Technical Specification 4.3.2.1.

Based on the following, YAEC believes that: 1) the current 18-month testing

) interval for the first level (loss of voltage) undervoltage protection relays-j is appropriate and' justifiable, and 2) that a change to monthly testing and an i added Technical Specification requirement is not necessary. Our' justification is based on the demonstrated high reliability of the first level (loss of voltage) Relay System, the unique and highly reliable Plant Auxiliary System arrangement, and the simplicity of the existing system design as described l below.

1

. s. b Page 2 of 3 ATTACHMENT 1 (Continued)

1. Relays Reliability Westinghouse Type CV-7 undervoltage relays were installed in 1972 and have been tested every 18 months. The testing consists of the determination of the tripping time following a loss of voltage.

The available maintenance history since 1975 indicates the following:

(a) The tripping time in 13 out of 15 relays tested has not deviated more than +0.06 seconds over 18 months of operation. In two relays, a deviation of +0.16 and +0.15 seconds, respectively, was found.

Corrective actions were taken to reset the tripping time of the two affected relays to the initial value and make them consistent with the other relays.

The impact of a 0.16 seconds increase in the relay's tripping time would not have affected the assumptions used in accident analysis.

(b) Since 1972 there has not been a single case in which the undervoltage relays have been challenged and failed to actuate.

(c) The undervoltage relay on 480 volt Emergency Bus 2 (normally fed by the main generator) is automatically challenged on any-reactor scram due to the generator trip. After many years of use, the relay has never failed to initiate the safeguard loads sequence starting.

2. Plant Auxiliary Electrical System Arranaement The plant's Auxiliary Electrical System features three electrical divisions: two outer divisions (2,400 volt Busses 2 and 3) are permanently connected to two 115KV incoming lines, and the center division (2,400 volt Bus 1) is normally powered by the main generator.

Both incoming 115 KV lines are: (a) available without the need for transfer following a loss of the main generator, and (b) required to be in service for normal operation. Each 2,400 volt electrical division feeds a 480 volt normal bus which in turn is tied to its associated 480 volt emergency bus. Each emergency bus is powered from the normal 480-volt bus or, upon a loss of off-site power, from its independent emergency diesel generator. The engineered safety feature' loads are equally divided between the 480 volt emergency busses, forming a three redundant safety bus system. If one of the emergency busses is lost, then limited plant operation is still allowed within the action statement of the Technical Specifications.

The center bus is connected to the main generator and is without power immediately following a generator trip. Power is restored by manually closing a tie breaker to either 2,400 volt Bus 2 or 3, unless the trip is caused by a fault in the generator at Which time the center bus is automatically tied to 2,400 volt Bus 3.

s e Page 3 of 3 ATTACHMENT 1 (Continued) i When the main generator is connected to the grid, the voltage at the switchyard is essentially controlled by the generator. When the main generator is disconnected from the grid, the voltage at the switchyard is controlled by the grid.

The plant Auxiliary Electrical System is supplied by off-site power when the main generator is not connected to the grid. From the time of initial startup in 1960, the plant auxiliaries have been supplied by off-site power for approximately 22% of the time.

3. Simplicity of System Desian 1 The simple basic design of the existing first level undervoltage

protection has demonstrated a high reliability over 15 years of operation. The modifications required by NRC to permit on-line testing of the first level undervoltage protection are complex. Consequently, this modification will complicate the existing circuitry and could reduce circuit reliability. YAEC's record of over 25 years of safe and reliable operation demonstrates the consistency of our design philosophy to keep systems simple and, therefore, reliable, which has been the case for I

undervoltage protection.

Based on the above discussion, Yankee believes that its present testing program for first level (loss of voltage) undervoltage protection is adequate and justifiable.

The 18-month period surveillance, combined with appropriate administrative controls, provides a high degree of confidence that the first level (loss of voltage) undervoltage protection system will be operated and maintained within applicable limits and tolerances. We believe that a modification of the i

existing first level (loss of voltage) undervoltage protection to permit monthly surveillance is not necessary and that the addition of this test program to the Technical Specifications is also not necessary.

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