05000336/LER-1993-018

LER 93-018-00:on 930805,letdown Manual Isolation Valve 2-CH-442 Developed Leak Which Exceeded TS Limits.Root Cause Has Not Been Determined.Valve Replaced & All Code Required Post Intallation Tests Successfully completed.W/930903 Ltr

ML20056H457
Person / Time
Site:	Millstone
Issue date:	09/03/1993
From:	Scace S, Temple W NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-018, LER-93-18, MP-93-704, NUDOCS 9309090363
Download: ML20056H457 (4)

LER-2093-018,

Event date:
Report date:
3362093018R00 - NRC Website

text

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September 3, _'993 MP-93-704 Re: 10CFR50.73(a)(2)(i)

U.S. Nuclear Regulatory Commission  !

Document Control Desk i Washington, D.C. 20555

Reference:

Facility Operating License No. DPR-65 Docket No. 50-336 Licensee Event Report 93-018-00 Gentlemen: ,

This letter forwards Licensee Event Report 93-01S-00 required to be submitted within i thirty (30) days pursuant to 10CFR40.73(a)(2)(i). the completion of any nuclear plant shutdown required by the plant's Technical Specification. ,

Very truly yours, i I

NORTHEAST NUCLEAR ENERGY COh1PANY  !

P j)k Stepien E. Scace tact./

Vice President - hiillstone Station SES/C.lD:ljs l

Attachment:

LER 93-018-00 l cc: T. T. h1artin. Recion 1 Administrator i P. D. Swetland. Senior Resident Inspector, hiillstone Unit Nos.1, 2 and 3 G. S. Vissing, NRC Project hianager, hiillstone Unit No. 2 i

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LICENSEE EVENT REPORT (LER) F F o0 MC"ON AND LE OPOS MANA3EVEN* 5;ANOs 7

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• 3' n' DC PN r F ACIL'TY NAME (1) DOOKET NUMBER (2) PAGE(h I Wstone Nudear Powe Staton Unrt 2 05000336 1 OF 03  :

i ma s, Letdown iso:aton vane 2-CH-442. Leakage Above 1.0 GPV '

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LICENSEE CONTACT FOR THIS LER f12) nen m ws u, m :._ s.n cn W.!bam J. Temde. Sde Licensing (203) 437-5904 f COMPLETE ONE LINE FOR E ACH COMPONENT FAILURE DESCRIBED IN THtS REPORT (13) i i

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• EAR YEs O f X / ,es c:cwe E c c TED s 2v ssos D ATt : ScATE UBM$o S's)N 10 30 93 ABSTRACT . m u e caees ;e ap.r c.na e3 E m e m a e: ta,ee m men osi On Augun i 1%3 at 1439 houn with the plant m Mode 1 at 1003 power. Letdown Manual isolanon Vahe 2-Cil-442 (nonsolataNe from the Reactor Coolant System) deieloped a leak which e>.ceeded the Techrucal f Specthcation Lmatung Cond:non for Operat on (LCO) 3.4.6.2. Reactor Coolant Synem "umdennhed" leakage hmn of 11 paHon per mmute. No attempt was made to quanufy th:s leakage as "idennhed" leakage. The Techrural Speaftauen Action 5tatement requaes that the leaka;e rate be reduced to vc: thin hmits wnhm 4 houn or be m Cold shutdoe.n wnbm the neu M houcs. Operatorn personnel immediately began a contro!!cd plant shutdown unhnn; Operaung Procedure. OP 2205, " Plant Shutdown.' and Abnormal Operating Procedure. AOP 25 M.

• Reactor Coolant Syuern Leak." On August 6.1993, at 0433 hours0.00501 days <br />0.12 hours <br />7.159392e-4 weeks <br />1.647565e-4 months <br />, the plant wu m Slode 5. 3 9 hourt aber the conneMed shutdown was m:nated. During the controDed plant shutdoun there uere no challenges to the plant safety nsiem3 AH other wtems and controls rernamed o;,eraNe durm; this ume period.

Tho esem a bemp reported pursuar:t to the reqmrements of Parapaph 50.73(a)(2Hi). the complenon of any

, nuch:ar plant <hutdown requned by the plant's Technmal Specihcations.

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FACIA NAVE n , DOOy,E- teJMBE R 2 2 LE A NUMBE A C PAGE73i ,

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1. Descrmuon of Ev- ,

On August 5.1043, at 1434 hours0.0166 days <br />0.398 hours <br />0.00237 weeks <br />5.45637e-4 months <br />. with the plant in Alode 1 at 100"c power. Letdown N1anual isolation  !

Vahe 2-CH-442 (nomsolatable from the Reactor Coolant Synem) developed a leak which exceeded the  !

Techmcal Specihcanon Limtung Condmon for Operation (LCO) 3.4.6.2. Reactor Coolant System i "umdennhed" leakage hmn of 1.0 gallon per mmute. So attempt was made to quanufy this leakage as t "idenuhed" leakage.  ;

\ ahe :-CH-442 had numerous leak scalar.: mjection applications dunng the months of June. July and f August to stop mmor bod) to bonnet leakage. The vahe was being momtored in the Control Room by a  !

closed cucuit television camera to provide real ume visual leak indicanon. On August 5,1993, at  :

approximately 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br />, the vahe was m the procer of bemp mjected to stop minor leakage so that a specially designed sealant retenuon clamp could be mstalled. During the m;ecuan process the leak rate i increased sigruncantly. It was determined that the leak rate exceeded the Technical Specihcation  ;

LCO 3.4.6.2. Reactor Coolant System "unidenuhed" leakage hmit of 1.0 gallon per mmute. Leakage i was esumated to be 4.3 galions per mmute. The Technical Specihcanon Acuon Statement requires that i the leakage rate be reduced to wrhm hmns withm 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> or be in Cold Shutdown within the next 36 i hours  ;

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Operanons personnel immediately began a controlled plant shutdown unlizmg Operating Procedure.  !

OP 2 05 " Plant Shutdown," and Abnormal Operaung Procedure. AOP 2566, " Reactor Coolant System l

Leak." On August 6.1993, at 0933 hours0.0108 days <br />0.259 hours <br />0.00154 weeks <br />3.550065e-4 months <br />. the plant was in N1 ode 5.19 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br /> after the controlled  ;

shutdown was irnuated. Dunng the controi'ed plant shutdowT) there were no challenges to the plant ufety (ruemt All other systems and controls remamed operable dunne this ume period. l i

l 11. Cause of Es ent j

The cause of the shutdown was a sudden change m vahe leakage which exceeded Technical Specihcauon hmus Sub>equent vahe disasembly has shown that one of the 4 body to bonnet studs failed. Detailed j metallurgical testing is bemp performed to determme the cause of the stud failure. The root cause of the  ;

ongmal leakage has not been determmed at this ume. l A 5 person lmestigauen Team was forrned to c'etermine among other thmgs the root cause of the vahe leakage event. The Invesuganon Team conclusions and recommendauons will be reviewed when  !

complete. Programmatic and procedure changes will be implemented.

l Addiuonally, a management lesel Independent Review Team was established to evaluate the cucumstances surroundmg not only this event but other recent operational issues regarding Niillstone 2.

Resuhs of this evaluanon will be distuned with the NRC at a management meeung.

Once the imestigation Teams have completed their evaluations of this event, a supplemental LER will be j subm:tted. -

l 111. Anahsis of Esent I Tlus esent is being reponed putsuant to the requiremems of Paragraph 5033(a)(2)(i). the completion of i any nuclear plant shutdown required by the plant's Technical Specihcations.  !

Prior to the leak sealant injection evolutions, structural evaluations were performed to confirm piping system structural mtegnty. The calculauon meluded the conservauve assumption that no creda was taken for one of the four studs. The results demonstrated structural mtegnty would be maintained.

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$ Although th:s actual event was mmated due to Reactor Coolant System leakare, post esent evaluauon to f date has determmed that the actual safety consequences were trummal (the safety implicauons and letsons to be learned are sigmfcam and are bemp evaluated). This is based upon the fact that the Reactor Coolam leakage of approximately 4.3 paljons per mmute is well withm the 44 gallon per minute capacny of each of the three Charpmp Pumps. All leakage was collected and processed by the }

contamment (ump and radwaste suttms. l 1 Complete bod) to bonnet failure would ha.e resuhed m a small break loss of coolam event that would base been unhm the bounds of the Reactor Coolant System Loss of Coolant Accident analysis.

Th- operators minated a comro!!ed plant shutdown and all safets systems were asailable. Operation was f perf ormed withm the requirements of the plants Techrucal Specificauon. j IV. Fm-m t Acym h

Valve :-CH-44: has beert teplaced and all code required post mstallauon tests have been successfully _l' completed.

I A directn e has beer promuipated that prohibits sealant type leak repairs on pnmary system valves.  !

Other safets related uhes mas be repaired by this method prouded a safety esaluanon is uniten and  !

approved pnor to the repair. Thn restnction will remain m effect pendmg the Insesugauon Team l conclusion and recommendauons. j 4

As discuwed abose, an Irnesugation Team has been formed to determine the root cause of this event.  !

d The InwQonon Tro n wnJuwm and scwunnendouon3 eli be wdencJ when winpicte. Subsequent l to tho, apprornate programmauc and procedure changes wil! be implememed.  ;

V. Ad unnal Infmrnoon .

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! Nmdar LERt 4 15, 51-5.31-033, 82-032, 53-5

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The lo!iowmp component failed dunne tlas esent: Letdou n Manual isolation Yah e. -CH 442  !

l Manubcturer: Velan Engneennp Comparues J

Model: W5-3 5 4 B- 13M S I 1

1 Ells Code: CB ISV VOSO (Letdown Manual isolation Vahe -CH-442)

CF (Reactor Coolam Sptem)

M % h k CF U1 Nh A. b $th I n

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