ML20154M767

Safety Evaluation Supporting Response to Items 4.2.1 & 4.2.2 of Generic Ltr 83-28 Re Reactor Trip Sys Reliability Provided Licensee Confirms Conditions as Stated

ML20154M767
Person / Time
Site:	Millstone
Issue date:	03/07/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20154M758	List: ML20154M755 ML20154M767
References
GL-83-28, TAC-53133, NUDOCS 8603140468
Download: ML20154M767 (4)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION NORTHEAST NUCLEAR ENERGY COMPANY, EL AL.

MILL 5IONE NUCLEAR POWER STATION, UNIT 2 DOCKET NO. 50-336 REACTOR TRIP SYSTEM RELIABILITY ITEMS 4.2.1. AND 4.2.2 of GENERIC LETIER 83-28

1.0 INTRODUCTION

On July (GL) 83-28.8,1983, Letter This letterthe Nuclear Regulatory addressed Commission intermediate-term actions (NRC) issued Ge to be 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 reactor 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.

Northeast Utilities, the licensee for Mill tone Nuclear Power Station Unit 2, submitted responses to the Generic Letter on November 8, 1983, and June 25, 1985. This report presents an evaluation of the adequacy of those responses and of the licensee's preventive maintenance and surveillance programs for RTBs.

2.0. EVALUATION CRITERIA 2.1 Pcriodie Maintenance Program The primary criteria for an acceptable periodic maintenance program are contained in Maintenance Instruction GEI-50299EI, " Power Circuit Breakers, Types AK-2/2A-15, AK-2/3/2A/3A-25, AKU-2/3/2A/3A/-25," and Service Advice 175-9.35 and 175-9.20, by General Electric, and NRC IE Information Notice No. 85-58. The NRC staff has reviewed these items and endorsed the mainte-nance program they describe. The criteria include those items in the General Electric instructions and advisories that relate to the safety function of the breaker, supplemented by those measurefrents which must be taken to accumulate data for trending. Those items identified for mainte-nance at 6 month intervals that should be included in the licensee's RTB maintenance program are:

8603140468 840307 PDR ADOCM 05000336 P PDR

, a. Verification of breaker cleanliness and insulation structure; all foreign materials, such as paint, dust, or oil should be removed to prevent electrical breakdown between points of different potential;

b. Verification of breaker physical condition, including wiring insulation and termination, all retaining rings, pole bases, arc quencher, stationary and movable contacts, and tightness of nuts and bolts;

c. Verification of proper manual operation of the breaker, including checks for excessive friction, trip bar freedom, latch engagement, operating) mechanism trip (UVT device armaturealignment freedom; and freedom, and undervoltage

d. Verification of the optimum freedom of the armature;

e. Verification of proper trip lutch engagement as specified in Service Advice 175-9.35, Item #52.

f. Verification of undervoltage pick-up setting, as specified in Service Advice 175-9.35, Item #S3, and dropout voltage;

g. Verification that the trip torque required on the trip shaft is less than 1.5 pound-inches, as specified in Service Advice 175-9.35, Item #S4; "Before" and "Af ter" maintenance torque values should be recorded;

h. Verification of positive tripping by checking the adjustment between the UVT device and trip paddle as specified in Service Advice 175-9.35, Item #55;

i. Verification of proper trip response time as specified in Service Advice 175-9.35, Item #56;

j. Shunt Trip Attachment (STA) operation verification;

k. Examination and cleaning of breaker enclosure;

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

2.2 Trending of Parameters Generic letter Item 4.2.2 specifies that the licensee's preventative maintenance and surveillance program is to includa trending of parameters to forecast degradation of operation. The parameters to be measured during the maintenance program described above which are applicable for trending are undervoltage trip attachment dropout voltage, trip torque, and breaker response time for undervoltage trip. The staff position is that the above

three parameters, in addition to the breaker ;nsulation resistance, are acceptable in forecasting breaker operation degradation. If subsequent experience indicates that any of these parameters are not useful as a tool toanticipatefailuresordegradation,thelicenseemay,withjustification and NRC approval, elect to remove that parameter from those to be tracked.

3.0 EVALUATION 3.1 Evaluation of the Licensee Position on Item 4.2.1 The licensee's response of June 25, 1985 indicates that his maintenance program includes or will include all of the maintenance items delineated in Paragraph 2.1 of this report to the extent described in Attachment 2 of the licensee response.

The licensee takes exception to the 6-month maintenance frequency of Items a,b,c,d,e,f,h,andk(Paragraph during 2.1ofthisreport)Ingcycleatperforming each refueling outage instead. The average operat them Millstone 2 is approximately 13 months. Items g, i, j, and I will be per-formed on the recommended 6-month basis. The licensee states that there have been no failures of the Millstone 2 reactor trip breakers. The service duty of the reactor trip breakers is stated to be significantly less than their design capability. The reactor trip breakers are located in a clean and dry environment. The licensee has replaced all trip shaft and latch roller bearings with Mobil 28 lubricated bearings.

The staff finds that the licensee's extended maintenance interval is acceptable. This acceptance is based on GE's recommendation that main-tenance on RTBs located in mild environments should be performed annually.

The vendor recommendation that RTBs located in harsh environments or experiencing severe load conditions be maintained more frequently is not applicable to these RTBs because of their location in a mild environment and reduced service duty at Millstone 2 (less than 200 RTB cycles annually).

The staff finds that the licensee's maintenance procedures meet the criteria defined in Paragraph 2.1 of this report, provided the licensee confirms that:

a) The UVT device roller rivet-armature clearance is measured with the UVT armature down in the energized position, as recommended in IE Notice No. 85-58; and b) Checkandadjustmentofthetriplatchengagementisperformed as specified la Item 52 of the Servie Advice 175-9.35. That is, the check and adjustment can only be performed by the method described in the applicable GE instruction manual; visual estima-tion of the latch engagement is not adequate.

3.2 Evaluation of the Licensee's Position on Item 4.2.2 The licensee will trend undervoltage trip attachment dro out voltage i-trip force and breaker response time but does not trend reaker insuIa- j tion resistance. The licensee states that the insulation resistance is verified by procedure to be greater than 5 megohns and is normally greater than 100 megohms. Anydiscernibledropinthlsvaluewould '

normally be corrected prior to returning the breaker to service. The licensee will perform any appropriate preventive or corrective maintenance if the analysis of the trend data indicates need for such action. The i staff finds the Ilconsee position on Item 4.2.2 acceptable. l 4.0. CONCLUSIONS ,

Based on a review of the licensee response, the staff finds the licensee position on Item 4.2.1 acceptable, provided the licensee confirms those items discussed in Paragraph 3.1 of this report. The Itcensee positinn on Item 4.2.2 is acceptable to the staff. ,

l Date: March 7, 1986 i Principal Contributor:  !

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