ML20101G803

Informs That Test Rept Re Overvoltage Effects on Motor Control Ctr Contactor Coils Anticipated in Feb 1985.Results Will Be Submitted in Mar 1985.Life of Contactor Coils Exceeds 10 Yrs.Some Size 1 Coil Replacement Anticipated

ML20101G803
Person / Time
Site:	North Anna
Issue date:	12/21/1984
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Harold Denton, John Miller Office of Nuclear Reactor Regulation
References
696, NUDOCS 8412280020
Download: ML20101G803 (2)

Text

e VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 20261 W.L.Srawaar Vaca Passionwr December 21, 1984 NectaAm OramArrown Serial No. 696 EC:BSD:baj:2003N Docket Nos. 50-338 50-339 License Nos. NPF-4 NPF-7 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation Attention: Mr. James R. Miller, Chief Operating Reactors Branch No. 3 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA UNIT NOS. 1 AND 2 GENERAL DESIGN CRITERIA 17 ANALYSIS Your letter of November 13, 1984, provided a revised and updated Safety Evaluation for North Anna Units 1 and 2 with relation to GDC-17. In that letter, it was requested that the NRC be kept appraised of the status of the motor control center contactor coils until such time that the final report regarding this matter is submitted for NRC review.

In our letter of July 7,1983 (Serial No. 326), Vepco stated that tests would be performed on motor control center contactor coils to determine the effects of overvoltage. Based on our presently available information we anticipate the test report will be available to Vepco in February,1985. Based on the receipt of the report in February, Vepco will submit the results to you in March, 1985.

Based on the aging which has been completed, the life of the contactor coils exceeds 10 years. We do anticipate that the replacement of some size 1 coils may be required at some future date. Since most loads fed from size 1 starters operate intermittently and operate less than 20 percent of the time, most size 1 coils will not require replacement. A review of the duty cycle of size 1 contactors is in progress.

In our letter of May 15, 1984, we stated that, "The continuing work which extends into 1986, as indicated in the Detailed Five - Year Summary Report B412280020 841221 pk PDR ADOCK 05000338

i VamoswtA Ex.zcTate Axn Powra CouPAwy To dated January 1,1984 and revised on April 1,1984 is to install new torque switch limiter plates on the MOVs." Therefore, we have not installed the new limiter plates during the 1984 refueling outages as you stated in your letter of November 13, 1984. As we have previously stated the motor operated valves have been reviewed and analyzed, and the results of the analysis indicate these valves will operate at reduced voltages predicted by our GDC-17 analysis. We will therefore continue to consider this item closed unless otherwise informed.

We will continue to provide you with updates on the motor control center

contactor coil test results per your request.

Ve trul y o s, W. . St wart [

, BSD/WLS/baj cc: Mr. James P. O'Reilly Regional Administer Region II

Mr. M. W. Branch NRC Resident Inspector North Anna Power Station E

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UNITED STATES *g gg NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 r, g

~s.,...../ NOV 131984 N0iG NOV 201964 wee Docket Nos. 50-338 and 50-339 Mr. W. L. Stewart Vice President - Nuclear Operations Virginia Electric and Power Company Post Office Box 26666 Richmond Virginia 23261

SUBJECT:

ADEQUACY OF STATION ELECTRIC DISTRIBUTION VOLTAGES (B-48),

UPDATED SAFETY EVALUATION: NORTH ANNA POWER STATION, UNIT NOS 1 AND 2 (NA-182)

Enclosed is our updated subject Safety Evaluation (SE) which was previously transmitted to you on January 11, 1983. The changes made to our original SE are highlighted by vertical lines in the right hand margin for ease of Our January 1983 SE was complete except for your deter-identification.

mination through the valve and motor operator manufacturers if Safety injection (SI) or Containment Depressurization Actuation (CDA) activated MOV originally specified to start at 90% of rated voltage could be rerated t start at 80% of rated voltage.

starter manufacturer the effect of overvoltage on the contactor coils.

15, 1984, you stated that recent studies and voltage By letter dated Mayanalyses show that SI or CDA activated YourMOVs letter originally 90% of rated voltage will also start at 80% of rated voltage.

further stated that various MOV enhancements, including installations of new torque switch limiter plates, would be implemented during the 1984 refueling outages for NA-182.

The installation of the new limiter plates further i

ensures operation of the SI and CDA MOVs at minimum analyzed voltage, In addition, you stated in your May 1984 letter that additional testing would j

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be required to determine the effect of overvoltage on the contactor coils and indicated the your However, testmonthly resultsstatus would not be updates for available for our B-48 now indicate review slippage in u 1984.

completing the contactor coil tests until February 1985 and 21,with 1984submittal

- o your final report until March 1985 (VEPC0 letter dated September Serial No. 2530).

l With the issuance of the enclosed updated SE, we are closing out the NA-182 However, completion of these NA-1&2 action multi-plant action items B-48.

items does not mitigate our concerns stated in our April 15, 1984 letter that l

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_2-all aspects of B-48 be completed in a timely manner. Plant Specific Action Items are being assigned to NA-182 for our review of the contactor coil tests and final report. As stated in our April 15, 1984 letter, we request that you continue to provide us with a monthly update on the status of the contactor coil test until such time that your final report regarding this matter is submitted for our review.

Sincerely, fA/ ~

James R. Mil r, C e Operating Reactors anch #3 Division of Licensi g

Enclosure:

Safety Evaluation cc w/ enclosure:

See next page l

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Virginia Electric and Power Company cc: Mr. J. H. Ferguson Richard M. Foster, Esquire Executive Vice President - Power Musick, Williamson, Schwartz, Virginia Electric and Power Co.

Leavenworth & Cope P.C.

Post Office Box 26666 P. O. Box 4579 Richmond, Virginia 23261 Boulder, Colorado 80306 Mrs. Margaret Dietrich Michael W. Maupin, Esquire Route 2, Box 568 Hunton, Williams, Gay and Gibson Gordonsville, Virginia 22042 P. O. Box 1535 Richmond, Virginia 23212 Mr. W. T. Lough Virginia Corporation Comission Mr. Paul W. Purdom Division of Energy Regulation Environmental Studies Institute P. O. Box 1197 Drexel University Richmond, Virginia 23209 32nd and Chestnut Streets Philadelphia, Pennsylvania 19104 .

U.S. Environmental Protection Agency Region III Office Atomic Safety and Licensing Appeal ATTH: Regional Radiation Board Panel Representative '

U.S. Nuclear Regulatory Comission Curtis Building Washington, DC 20555 6th and Walnut Streets Philadelphia, Pennsylvania 19106 Ellyn R. Weiss, Esquire Sheldon, Haman, Roisman and Weiss Regional Administrator 1725 1 Street,'N.W., Suite 506 Nuclear Regulatory Commission Washington, DC 20006 Region !!

Office of Executive Ofrector Mr. E. W. Harrell for Operations P. O. Box 402 101 Marietta Street N.W.. Suite ?c00 Mineral, Virginia 23117 Atlanta, Georgia 30373 Mr. Anthony Gambardella Old Dnminion Electric Cooperative Office of the Attorney General c/o Executive Vice President 11 South 12th Street - Room 308 Innsbrook Corporate Center Richmond, Virginia 23219 4222 Cox Road, Suite 102 Glen Allen, Virginia 23060 Resident inspector / North Anna c/o U.S. NRC Mr. Richard C. Klepper Senior Resident Inspector

• Board of Supervisors Route 2, Box 78 Louisa County Courthouse Mineral, Virginia 23117 P. O. Box 27 Louisa, Virginia 23093 m- _ _ _ _ . _ _ _ _ _ _

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UNITED STATES

! o NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555

$ . ,I SAFETY EVALUATION NORTH ANNA POWER STATION, UNITS 1 AND 2 DOCKET N05. 50-338 AND 50-339 ADEOUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGE 5 INTRODUCTION AND

SUMMARY

Virginia Electric and Power Company (VEPCO) was requested by NRC letter dated August 8,1979 to review the electric power system at North Anna, Units 1 and

2. The review was to consist of:

a) Determining analytically the capacity and capability of the offsite power system and onsite distribution system to automatically start as well as operate all required loads within their required voltage ratings in the event of 1) an anticipated transient, or 2) an accident (such as LOCA) without manual shedding of any electric loads.

b) Determining if there are any events or conditions which could result in the simultaneous or consequential loss of both required circuits from the offsite network to the onsite electric distribution system and thus violating the requirements of GDC 17.

The August 8,1979 letter included staff guidelines for performing the required voltage analysis and the licensee was further required to perform a test in order to verify the validity of the analytical results. VEPC0 responded by letters dated August 7, 1979, August 16, 1979, October 29, 1979, January 20, 1982, February 26, 1982 May 20, 1982, June 4, 1982, July 1, 1982, October 26, 1982, June 7, 1983, October 14, 1983, January 20, 1984 and May 15, 1984.

A detailed review and technical evaluation of the submittals was performed by EG&G under contract to the NRC, with general supervision by NRC staff. This work is reported by EG&G in Technical Evaluation Report (TER), " Adequacy of Station Electric Distribution System Voltages, North Anna Power Station, Units 1 and 2 " dated July 1982 (attached). We have reviewed this report and concur i

in the conclusions that the offsite power system and the onsite distribution system, except for startup voltage for some MOVs and operating voltage for some contactor coils, are capable of providing acceptable voltages for worst case station electric load and grid voltages.

By letter dated May 15, 1984, VEPCO stated that recent studies and voltage analyses show that SI or CDA activated POVs originally specified to start at 90% of rated voltage will start satisfactorily at 80% of rated voltage. With regard to contactor coils, the licensee states that additional testing is reouired to determine the effect of overvoltage on these coils. VEPC0 stated that these test results would not be available for NRC review until October 1984. The NRC staff will review the contactor coils test results under Plant Specific OR Action Items when this information becomes available.

T-- o C 6pf-

EVALUATION CRITERIA The criteria used by EG8G in this technical evaluation of the analysis includes GDC 5 (" Sharing of Structures, Systems, and Components"), GDC 13

(" Instrumentation and Control"), and GDC 17 (" Electric Fower Systems") of Appendix A to 10 CFR 50; IEEE Standard 308-1974 (" Class IE Power Systems for Nuclear Power Generating Stations"), ANSI C84.1-1977 (" Voltage Ratings for Electric Power Systems and Eouipment - 60 Hz"), and the staff positions and guidelines in NRC letter to VEPC0 dated August 8, 1979.

ANALYSIS AND TEST FEATURES VEPCO analyzed each offsite power source to the onsite distribution system under maximum grid voltage (535 Ky) and minimum load and minimum grid voltage (505 Kv) and maximum load conditions. To insure that the worst case conditions were analyzed, various conservative assumptions and scenarios were postulated. The following is a list of the major assumptions used for the analysis:

1) All Unit 2 loads, Unit 1 accident shutdown loads, and intake structure loads were assumed to be supplied by Reserve Station Service Transformers (RSSTs). Shutdown loads for Unit I can be supplied via Unit Station Service Transformers (USSTs) through backfeeding from the switchyard.

2) No delay in transfer of non-safety buses from USSTs to RSSTs was assumed under reactor trip condition. A delay of 30 seconds is experienced under actual condition.

3) All motors required to start on a safety injection (SI) or containment depressurization actuation (CDA) signal were started at t = 0. None were assumed to be running prior to the analysis.

4) No manual load shedding or reduction in motor current due to decreased pump load was assumed.

5) All anticipated modifications were incorporated into that analysis.

The worst case Class IE equipment terminal voltages occur under the following conditions:

! 1) The minimum steady-state voltage occurs at 4160V eouirment when the offsite grid voltage is at its anticipated minimum (505 Kv), containment depressurization actuation (CDA) in Unit 2, and Unit 1 generating at 21.5 Kv.

! 2) The minimum steady-state voltage occurs at 480V equipment when the offsite grid voltage is at its minimum (505 Kv), CDA in Unit 2, and Unit I trips.

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The minimum transient voltage occurs on Class IE equipment when offsite i f 3)

' grid voltage is at its minimum (505 Kv), CDA in Unit 1 and concurrent transfer of Unit 2 non-safety load to the reserve transfomers.

j The maximum steady-state voltage occurs at 4160V and 480V load center

4) buses when gru voltage is at its maximum (535 Ky), Unit 1 in refueling I

mode and Unit 2 is at 100% power; all safety buses are fed via preferred offsite feeder through the RSSTs. All non-safety buses are fed from l their respective USSTs.

The voltage analysis showed that, under the worst case minimum grid v'oltage i and maximum load condition, the voltage to Class IE motor operated valves ,

(MOVs) did not meet the minimum starting voltage (90% of 460V) requirement.  ;

The licensee is presently in the process of determining through the valve and i 1

' motor operator manufacturers if the SI or CDA activated MOVs originally specified rated voltage.

to operate at 90% rated voltage can be rerated to ope cannot be rerated below 90% with motor operators that are rated for 80%

starting voltage. .In addition, VEPC0 is comitted to determine through the valve manufacturer the compatibility between the 80% starting voltage and the l

valve's torque requirement. It is possible that, under the worst condition j anal ~yzed, when starting large motors, these MOVs could become subjec "

i voltage transient as low as 68.1% at T=0.

i MOVs that are rated for 80% starting voltage will start within a 4 second time

period. Starting within this time frame ensures MOVs operation and would not cause any equipment damage.

j By letter dated May 15, 1984 VEPC0 stated that completed studies and voltage analyses show that the SI or CDA activated MOVs originally specified to start l

at 90% of rated voltage will start satisfactorily at 80% of rated voltage.

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' The licensee also stated that various MOV enhancements including installation of new torque switch limiter plates are planned for implementation in the near t l

future. Installation of new limiter plates further ensures operation of the above MOVs at the minimum analyzed voltage, l

Under the maximuen grid voltage and light load condition, the voltage analysis i

i showed ratings. that all 4 XV and 480V buses are within 10% of 4000 i

the 110% maximum rating by 7%.

The impact of this overvoltage on the service life of those contactors which supply power to MOVs would be minimal due to

! the short time (a few minutes for the MOV to change state) exposure of these coils to overvoltage. This short time exposure to overvoltage minimizes the i

Also, a number of i probability of contactor coil or motor insulation damage.MCCs ar I

temperature below 40'C, thereby further reducing the possibility of coil

, As an added precaut'on, the licensee conducts l, damace caused due to heat.

resistance and insulation tests during each refueling period to monitor coil I failure.

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The licensee, through the starter manufacturer, is continuing to investigate the effects of overvoltage on contactor coils. By letter dated May 15, 1984, VEPCO stated that additional tests are reouired to determine the effect of overvoltage on contactor coils and stated that the test results would not be available to NRC for review until October 1984. The NRC staff will review the above test results under Plant Specific OR Actions when this information becomes available.

In view of the above and the licensee's established procedures to maintain the 500 Kv grid voltages below 535 Kv (max. voltage used for the analysis), the staff concludes that, even under the rare instances that overvoltage could be present, the damage to the Class IE equipment would be minimal. Therefore, we find the present overvoltage surveillance program to be acceptable subject to the submittal of the licensee's finding of overvoltage impact on the contactor coils from starter manufacturer or through testing and/or analysis.

DESIGN CHANGES As a result of voltage analysis VEPC0 has proposed to implement the following design changes:

1) Rerate or replace if necessary motor operators of valves that are activated by an SI or CDA signal to assure their starting within acceptable time frame at minimum voltage conditions. VEPCO's investigations into the operating characteristics of these MOVs indicate that 68 units may be rerated for starting at 80% voltage, two may be rerated for 84% - 86%, one cannot be rerated below 90%, and 57 units are still under investigation. Prior to any rerating, VEPC0 must determine the compatibility between the motor operator rerating and valve torque requirement through the valve and motor operator manufacturers. VEPCO's analysis indicates that 80% rated motor operators will start within 4 seconds after the initial accidenc. Starting within this time frame will preclude any equiperent damage. VEPCO has completed the above investigation and concludes that the above MOVs will start satisfactorily at 80% of rated voltage. The licensee also stated that they plan to install in the near future new torque switch limiter plates on the MOVs.

2) Install overvoltage monitors and alarms en all 4 Kv and 480V Class IE buses.

3) Modifytheloadtapchangers(LTCs)ontheRSSTstoeliminateresponse delays in the LTCs for the first three minutes following either an SI or a CDA in either unit or on transfer of the Unit ? non-safety loads to the reserve transformers.

4) Install a generator breaker on Unit 1 to provide an additional inanediately available source of offsite power through the Unit station transformers. This has been completed.

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5) Modify the existing control logic for Unit I and Unit 2 nonnal to emergency bus ties to eliminate the automatic transfer feature of the '

emergency buses from the reserve station service (RSS) feeders to the normal bus feeders supplied by the USSTs for Unit 1 and delete the i proposed automatic transfer of Unit 2 emergency buses from the RSS a feeders to the normal bus feeders.

6) Remove automatic switchina between offsite power sources in order to provide direct transfer from offsite power to the respective diesel generators under loss of voltage / degraded voltage conditions. All transfers between normal and alternate offsite power sources will be manual.

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7) Install throwover switches in the secondary leads of 34.5 Kv switchyard transformers to provide redundancy of power source in case of loss of one transformer. This has been completed. l

8) Provide automatic tripping of 34.5 Kv current limiting reactors following an SI or CDA on either unit when a unit's normal buses are fed by Reserve

Station Service Transformers.

9) Install disconnect switches in all secondary leads of 34.5 Kv switchyard service transformers and remove the secondary leads of one transformer

.! from the common trough and install it in a conduit to prevent the possibility of sinultaneous loss of both offsite power sources. This has l been completed.

10) Provide automatic load shedding capabilities when all of Unit 2 loading is on the Reserve Station Service Transfonners and SI or CDA occurs on Unit 1.

11) To prevent overloading the RSST B or C due to loss of one or the other '

when the tie breakers on the secondary sides of these transfonners are l

closed, all circulating water pumps of the unit experiencing the accident i are automatically shed when an SI or CDA occurs. I i 12) Block the auto starting of large non-IE motors, when the station service bus feeding the motors is supplied from the same source as the emergency bus of a unit experiencing an SI or CDA.

4 CONCLUSION i

We have reviewed the EG&G Technical Evaluation Report and concur in the findines that: .

1. The proposed modifications will insure North Anna 1 & 2 compliance with GDC 17 requirements.

2. The test used to verify the analysis was valid and showed that analysis to be conservative.

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3. All SI or CDA activated motor operated valves motor operators need to be rerated or replaced to ensure proper valve operation under some In addition, worst case condition analyzed. This has been completed.

contactor coils may be subjected to overvoltage of approximately 7%

beyond the maximum 110% design rating under the above worst case condition. Other than the above, all Class IE equipment will be supplied with acceptable voltages under all projected combinations of plant load and normal offsite power grid conditions, including an accident in one unit and the safe shutdown of the other unit.

Due to the voltage problems associated with the above mentioned HOVs and contactor coils the licensee has connitted:

A)

To determine through the valve and motor operator manufacturers the possibility of rerating or replacing if necessary those motor operators which may not be provided with sufficient starting voltage in order to l ensure proper valve actuation. This has been completed.

B)

To determine through the starter manufacturer the effect of overvoltage on the contactor coils. The licensee will be conducting tests to determine the effect of 20% overvoltage on the contactor coils, and the results will be submitted for staff review in the near future.

We require that the licensee provide the results of the completed studies or findings to NRC for review. In addition, if these studies show that replacement is required for any motor operator, we require that an Licensee implementation schedule for these replacements also be provided.

studies and analyses show that the MOVs discussed under item 3A above are Therefore, motor operator capable of starting at 80% rated voltage.We, therefore, find the North Anna 1 & 2 replacement was not necessary.

' design to be acceptable with respect to adequacy of station electric distribution system voltages sub,iect to completion and resolution of Item 38 discussed above, i

Principal Contributor:

H. Emami, DSI

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