ML19332C005

LER 89-025-00:on 891012,Wyle Labs Notified Util of Anomaly in Test Results on Two Pressurizer Safety Valves.Caused by Improperly Machined Disc Insert.Disc Insert Replaced W/Flat Polished Mating surface.W/891113 Ltr

ML19332C005
Person / Time
Site:	Millstone
Issue date:	11/13/1989
From:	Hulme N, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-025, LER-89-25, MP-13727, NUDOCS 8911220187
Download: ML19332C005 (5)

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N .I. N feYo# d.'t$ Yde U c N e'n7 P.O. Box 270 tYn.*.ei$i.E Ii7c*oJuny HARTFORD. CONNECTioVT Ot414-0270 twrvenet e*e r tre pv co nnant (203)666-6000 lbvember 13, 1989 MP-13727 3

Re: 10CFR50.73(a)(2)(i)

'n U.S. Nuclear Regulatory Commission Document Control Dest Washington, D.C. 20555 1

Reference:

Facility Operating License No. NPF-49 Docket No. 50-423 Licensee Event Report 89-025-00 Gentlemen:

This letter forwards Licensee Event Report 89-025-00 required to be submitted within thirty (30) days pursuant to 10CFR50.73(a)(2)(i), any operation or condition prohibited by the Plant's Technical Specifications.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY cp W Steph n E. Scace Station Superintendent Millstone Nuclear Power Station l

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Attachment:

LER 89-025-00 i

. ec: W. T. Russe'!, Region 1 Administrator l W. J. Raymond, Senior Resident Insr>ector, Millstone Unit Nos 1, 2 and 3  ;

, D.' H. Jaffe, NRC Project Manager, Millstone Unit No. 3  ;

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l l l e es T AAcT sumn w 4 0c oun. . wo,mt.+ em n .mn..on, vo.em., on.., nei On October 12,1969 Wyle Laboratones notified Northeast Utihties of an anomaly in the test results on two previously installed Pressurizer Safety Valves. The subject valves are required by Technical Specifications to be operable with a setting of $00 psis al percent (0475-2525 psia) during Modes 1. 2, and 3. Bench testing at Wyle Laboratory revealed one valve (S/N N56964-07-0102) initiaPy lifted at 0534 psia and the other valve ($/N Nf 65r64-07-0059) initially lifted at 25$3 psia. As the valves were not installed in the plant at the time, no operator action was required in response to this event.

Th. root cause for Pressurizer Safety S/N 100 lifting higher than the one percent tolerance is unknown.

The root cause for Pressure Safety S/N $9 lifting higher than tolerance is believed to be an improperly i rnachined dist insert. An inspection of the S/N $9 revealed that a surface on the disc insert which mates to the disc holder was not flat. This allowed the disc to rock and possibly rescat in a different location after each lift. The different locations can affect spring tension and in turn the lift pressure. l The disc insert for S/N $9 was replaced with one specifically inspected to assure there was a flat. polished mating surface for the disc holder. Also, pr.rts conudered critical to the proper operation of safety S/N $9 were thoroughly inspected for proper fit and function.

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On October 10, 1989, Wyle Laboratones notihed Nonheast Utilities of an anomaly in the test resuhs on two previously installed pressanter Safety Yahes. The subject vahes are required by Technical Specifications to be operable with a setting of 2500 psia al percent (0175 - 252$ psia) i dunnp hlodes 1, 2, and 3. Bench tesung et Wyle Laboratory revealed one vahc (S/N l N5 69t,4-07-0102) initially lifted at 2534 psia and the other valve (S/N Nf 6964-07-00f 9) initiall) hhed at 2553 psia. Each vahe was tested three more times. The hrst valve (S/N 102) lifted within one percent of 2500 psia all three timr The second valve (S/N 59) hited within one percent one time, but was outside the tolera' .t one other two umes. Lift pressures of 2540 psia and 2309 psia respecthcly uere the recordeo values. As the vahes were not mstalled in the plant at the time, no immediate operatur action .;as required in response to this event.

Klillstone Unit 3 has six Pressunter Safety Valves available for use: three are installed safeties, and '

the other three are used as spares. Each refuehnp outape, it is the policy to replace the three installed safeues with the three available apares. The replaced vahes are sent to Wyle Laboratories for inservice testing (per ASN1E Section XI), refurbishment, and retesting to conbrm that each safety litts within one percent of 2500 psia. The successfully retested valves are then returned to hiillstone Unit 3 for installation during the followmg refuehng outape. The subject valves in this repon are two of the three safeties that were remosed dunng the last outare (which lasted from  ;

hiny 17,19b9 to July 9,1969). ,

11, Ne n! Event The root cause for S/N 102 lifting higher than the allowed one percent tolerence is unknown.

Aher the initial lift, vahe S/N 102 hfteci at pressures of 2507 psia, 2f11 psia, and 2509 psia. This indicates that the safety not only met the required one percent tolerance, but it also exhibited a consistency that is indicative of a good safety valve.

The root cause for S/N $9 hhing higher than the allowed one percent tolerance is behered to be an improperly machmed disc insert. An inspection revealed that a surface on the disc insert which mates to the dise holder was not flat. This allowed the disc to rock and possibly rescat in a i t

di!!erent location attrr each hit. The different locations can affect spring tension and in turn the lift pressure.

i 111. Annhs nf h ent This eve nt is reportable in accordance with the requirements of 10CFR50.73(a)(2)(i). Plant Technical Specibcation 3.4.2.2 requires all Pressunrer Safety Valves to be operable with a lift setting of 2500 psia 21 percent dunnp h1 odes 1, 2, and 3. The lift setting pressure corresponds to ambient conditions of the vahe at normal operating temperature and pressure.

The fact that safety S/N 102 hfted irutially at 1./ percent above its nominal setpoint is not  !

significant, especially smce it lifted within the one percent tolerance three tirnes immediately after the initial test. It is not unusual for a safety valve to initially hit somewhat outside the nominal setpoint tolerance, especiahy if the sabe has not lifted for a long period of timt in this case S/N 102 was refurbished and then verihed to lift withm one percent of 2500 psia in hiarch,1967. This .

represents a 2.5-year penod during which, the safety valve was neser challenged.

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Like vahe S/N' 100, vahe S/N 59 had not been exerosed in over three years. The mitial hit prenure for S/N $9 was aho higher than the nommal pressure of 2500 psia. Hourser, it was higher than S/N 100 at 0.1 percent above its nominal setpomt. Also, the subsequent h!t prenures were not conmient, and two of the three remaining tests had hit prenures outside the one percem ,

tolerance (one at 1.0 percent and the other at 1,7 percent abose 2$00 psia). The one test that did meet the tolerance hhed at a pressure of 2510 psia. While these values are not substantially above the nominSI preuute of 2500 psia, the relatisely wide differences in hit pressures that occurred m the three tests followmg the intual hit indicate there is a mechanical problem. For example, the last three hit pressures for vahe S/N 100 differed by 4 psi, while those lor S/N 59 differed by 30 psi.

This event posed no significant threat to pl:.nt safety during normal or accident conditions. ,

Pressurirer code safety vahes are sired to prevent the Reactor Coolant System from bems presurized above its safety hmit of 2750 psia. Specifically, the combined rehef capacit) of all vehes is greater than the mammum surge rate resultmp from a 100 percent load re.iecuon, anuming no sebetor tnp until the first Reactor Tnp System inp setpoint is reached. The plots and data .

tables dehneated m the Final Safety Analysis Repon (FS AR) and supportmp safety documents werc '

reviewed to determine the maMmum prenure which would occur, The rnaximum pressure was '

found to be 2613 psia. An increase in a safety valve setpoint from 2525 psia (nominal value plus one percent) to 2553 psia (highest lift pressure idenuhed dunng Wyle Laboratory's testing) is conservatively asumed to raise the peak prenure by the difference in hit pressures. Therefore, the peak transient prenure would be 2641 psia (2613 psia plus 26 psi). This is well below 2750 psia, '

the fauhed hmit of 110% design prenure. Thus, there is no safety impact on the FSAR results or concluaions.

r IV. Cntrective Action The dist insen for Pressurizer Safety S/N $9 was replaced with one specibcclly inspected to assure surface for the disc holder. Also, parts considered entical to the there proper operat was on a of flat, polished safety S/N matinh9 were thoroughly inspected per fit and function.for pro V, Addninnnt inforn9 tion Pressurizer safety vahes are Crosby Model Number HB-Bp-66 6M6 safety valves. A search of the SpRDS indicates the problem of setpoint drift is a common problem in the industry. Information from this hearch indicates the setpoints may dnft high or low. No specific failure mer.hanism was identihed in any of the reports. Millstone 3's origmal safety vah'es, which were removed from the

• System m Nosember,1965, and iested at Crosby in June,1966 also failed their set prenure test.

Whether these vahes failed high or low cannot be determined from the vendor test records. Sin't these vahes were removed from the pressunrer prior to issuance of the facihty Operating License, '

their failure was not reportable.

LERs67-036 and 69-010, *Setpoint Dnft on Main Steam Safety Valves Due to Unknown Causes*, discuss drift problems associated with Main Steam Safety Yahes. No failure mechanism was identihed for the drift. The corrective action for both events was to reset the subject valves and test or replace the other Main Steam Safeties on the estabhshed frequency.

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LER 67-009-02 describes previous setpoint drih problems with three Pressurirer Safety Yahes dunng bench testing at Wyle Laboratories. The reasons for the drift were undstermined. The vahes were reset to their pressure setpomt, and reworked such that no leakage was experienced when leak tested with air. The LER abo provides information about the vahes includmg a chronology whien covers esents from Nosember 1955 through February,1986. The following is a l chronological update from Februar), 1966 to the present.

2/66 Valve S/N 101 lifts dunng plant hea.up. This vahe was replaced by vahe S/N $9.

Vahes 60, 61, and 101 were sent to Wyle for testmp/ refurbishment. Valve S/N 61 was found to be hiting outside its acceptance entena. Vahes S/N 60 and S/N 101 were found to be liftmp withm acceptable hmit.  ;

3/88 Vahes S/N 60, 61, and 101 were received back from Wyle.

4/66 Noted that valve S/N 103 was leaking. During a Unit shutdown, S/N 103 was replaced with S/N 101. S/N 103 was sent to Wyle, r 9/$$ LER 87-009-02, update repon submitted.

12/$6 Received valve S/N 103 back from Wyle.

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!/86 Dunng refuehng, valve S/N 59,101, and 10: were replaced with S/N 60, 61, and 103. ,

to Dunny stanup, it was noted that S/N 103 was leaking a minor amount. S/N 101 was f 7/89 . hipped immediately to Wyle for refurbishment and resetting in case replacement of 5/N 103 was required.

t 9/89 Valves S/N 59 and 100 were sent to Wyle.

10/69 Valves S/N 19 and 100 reponed to be lifting higher than the allowed tolerance. l Received valves S/N 101 and 102 back from Wyle retested and certihed.  ;

Ei!K CODES Entem Onmannent<

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