ML20129H787

Safety Evaluation Supporting Licensee Response to Generic Ltr 83-28,Items 4.2.1 & 4.2.2 Re Reactor Trip Sys Reliability,Provided Corrective Action Taken If Higher than Normal Valves Observed in Trip Force & Response Time Values

ML20129H787
Person / Time
Site:	Point Beach
Issue date:	05/16/1985
From:	NRC
To:
Shared Package
ML20129H761	List: ML20129H756 ML20129H787
References
GL-83-28, TAC-53140, TAC-53141, NUDOCS 8506070659
Download: ML20129H787 (5)

Text

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SAFETY EVALUATION WISCONSIN ELECTRIC POWER COMPANY POINT BEACH NUCLEAR PLANT UNITS 1 AND 2 DOCKET N05. 50-266 AND 50-301 REACTOR TRIP SYSTEM RELIABILITY ITEMS 4.2.1 AND 4.2.2 0F GENERIC LtIIER 83-28

1. INTRODUCTION I On July Letter GL(8,)1983, 83-28. Thistheletter Nuclear Regulatory addressed Comission (NRC) intermediate-term issued actions to beGeneric taken by licensees and applicants aimed at assuring that a comprehensive program of preventive maintenance and surveillance testing is implemented for the reactor trip breakers (RTBs) in pressurized water reactors. In particular, Item 4.2 of the letter required the licensees and applicants to submit a description of their preventive maintenance and surveillance program to ensure reliable rea,ctor trip breaker operation. The description of the submitted program was to include the following:

GL, Item 4.2.1 A planned program of periodic maintenance, including lubrication, housekeeping, and other items recommended by the equipment supplier.

GL, Item 4.2.2 Trending of parameters affecting operation and measured during testing to forecast degradation of operation.

Wisconsin Electric Power Company, the licensee for Point Beach Nuclear Plant, Unit Nos. I and 2, submitted responses to the Generic Letter on November 7, 1983 and December 28, 1984 This report presents an evaluation of the adequacy of those responses and of the licensee's preventive maintenance and surveillance programs for RTBs.

2. EVALUATION CRITERIA 2.1 Periodic Maintenance Program The primary source for periodic maintenance program criteria is Westing-house Maintenance Program for DB-50 Reactor Trip Switchgear, Rev. O. This document is the breaker manufacturer's recommended maintenance program for the DB-50 breaker and provides specific direction with regard to schedule, inspection and testing, cleaning, lubrication, corrective maintenance and record keeping. The document was reviewed to identify those items that contribute to breaker trip reliability consistent with the generic letter.

Those items identified for maintenance at six month intervals that should be included in the licensee's RTB maintenance program are:

1. Verification of trip bar freedom

2. Verification of operating mechanism alignment and freedom

3. Retaining ring verification DR 6

4. Verification of nut and bolt tightness

5. Verification of pole bases physical condition -

6. Verification of arcing and main contacts physical condition

7. Verification of insulating link's physical condition

8. Verification of wiring insulation and tennination physical condition

9. Verification of arc chute physical condition

10. Verification of breaker cleanliness

11. Undervoltage Trip Attachment (UVTA) dropout voltage test and lubrication

12. Shunt Trip Attachment (STA) operation verification

13. Verification of operation of auxiliary switches

14. Inspection of positioning lever condition

15. Functional test of the breaker prior to returning it to service.

The licensee's RTB periodic maintenance should also include, on a refueling interval basis:

16. Verification of cell interlock operation

17. Examination and cleaning of breaker enclosure

18. Measurement of trip force required

19. Functional test of the breaker prior to returning it to service

20. Breaker response time for undervoltage trip.

. All of the items listed above are reconenended by the manufacturer except Item 20. This is the breaker trip response time measurement which is implied by the IEEE Standard 279-1971.

2.2 Trending of Parameters Generic Letter Item 4.2.2 specifies that the licensee's preventative maintenance and surveillance program is to include trending of parameters affecting operation and measured during testing to forecast degradation of operation. The parameters measured during the maintenance program described

. - -above which are applicable for trending are undervoltage trip attachment

. dropout voltage, trip force, and breaker response time for undervoltage trip. The staff position is that the above three parameters in addition i . to the breaker insulation resistance are acceptable and reconsnended trending parameters to forecast breaker operation degradation or failure. If sub-

- sequent experience indicates that any of these parameters is not useful

- as a tool to anticipate failures or degradation, the licensee may, with justification and NRC approval, elect to remove that parameter from those to be tracked.

3. EVALUATION l

3.1 Evaluation of the Licensee Position on Item 4.2.1  ;

l In the licensee's December 28, 1984 response to the staff's request for

. additional information (RAI), the licensee states that his existing ,

periodic maintenance program includes all the maintenance items at the '

l l

specified intervals listed, except the cell interlock operation.  !

Revision 2 of the licensee's Routine Maintenance Procedure (RMP26) , l l will include this item. The licensee also states that the performance i of all items of RMP 26 is on a refueling interval basis and that his experience with the reactor trip and bypass breakers has demonstrated that these devices are very reliable. Moreover, the number of breaker cycles is not expected to exceed 40 during the interval of operation between refueling outages.

1 L The Westinghouse Maintenance Program for DB-50 Reactor Trip Switchgear, l l Revision 0, states that "the semi-annual activities might be extended to

! 9 to 12 months if experience shows this to be sufficient provided that 200 breaker cycles are not exceeded during this interval."

Based on the above statements, the staff finds that the licensee's position on the scope and frequency of RTB maintenance is acceptable provided that the interval does not exceed 12 months.

3.2 Evaluation of the Licensee Position on Item 4.2.2 The licensee indicates that the undervoltage trip attachment dropout voltage is trended as recommended by Westinghouse. However, trip force, breaker response time for undervoltage trip, and breaker insulation resis-tance are not trended. Trip force and breaker response time for under-voltage trip are recorded and compared by the licensee to the maximum

, acceptable values of 31 ounces and 10 cycles, respectively.

The licensee justifies not trending the trip force and breaker response d

time for undervoltage trip by stating that he records these values and compares them to the maximum acceptable values of 31 ounces and 10 cycles,

! respectively. If the recorded values are significantly in excess of those

norrelly experienced and recorded, the licensee's procedures call for corrective action. The values for breaker trip force and breaker response time at which the licensee has indicated corrective action would be per-formed are well below the maximum acceptable values and provide assurance i that these values would not be exceeded. In addition, the licensee justifies not trending the breaker insulation resistance by stating that the breakers are cleaned, inspected for insulation cracks, and operated at less than one-half of rated voltage.

i The staff position is that trending the four parameters with respect to time can provide useful information to forecast the degradation of opera-bility of the breaker, t

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l The licensee does not trend the trip force and the response time. How-ever, the licensee does measure and record these parameters, .which is acceptable to the staff. Although it would be better if these parameters were trended, the licensee's program is acceptable, and provides assurance that corrective action will be taken when the measured values approach the manufacturer's recomended maximum values.

With regard to trending the breaker insulation resistance, the licensee's l position of neither measuring nor trending is acceptable because the breakers are operated at less than one-half of the rated voltage and are routinely inspected for insulation cracks and other signs of insulation deterioration.

4. CONCLUSIONS Based on the review of the licensee responses, the staff accepts the  ;

licensee position on Items 4.2.1 and 4.2.2 of the generic letter, provided: '

1. The licensee continues to record the trip force and the response time values, comparing them with the manufacturer's recommendations and taking corrective action if unusually higher than normal values are observed; and

2. The maintenance interval does not exceed 12 months.

Date: May 16, 1985 Principal Contributor:

N. Romney, DE T. Colburn 4

~

Mr. C. W. Fay Point Beach Nuclear Plant Wisconsin Electric Power Company Mr. Bruce Churchill, Esq.

Shaw, Pittman, Potts and Trowbridge 1800 M Street, N.W.

Washington, DC 20036 Mr. James J. Zach, Manager Point Beach Nuclear Plant Wisconsin Electric Power Company 6610 Nuclear Road Two Rivers, Wisconsin 54241 Mr. Gordon Blaha Town Chairman Town of Two Creeks Route 3 Two Rivers, Wisconsin 54241 Cho1rnan Public Service Commission of Wisconsin Hills Farms State Office Building Madison, Wisconsin 53702 Regional Administrator Nuclear Regulatory Commission, Region III Office of Executive Director for Operations 799 Roosevelt Road Glen Ellyn, Illinois 60137 U.S. NRC Resident Inspector's Office 6612 Nuclear Road Two Rivers, Wisconsin 54241

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