05000318/LER-1983-043, Updated LER 83-043/03X-1:on 830809,following Reactor Trip, Steam Generator Safety Valve Failed to Reseat.Caused by Missing Pin.Valves Inspected to Ensure That Blowdown Ring & Pin Not worn.W/840330 Ltr

Updated LER 83-043/03X-1:on 830809,following Reactor Trip, Steam Generator Safety Valve Failed to Reseat.Caused by Missing Pin.Valves Inspected to Ensure That Blowdown Ring & Pin Not worn.W/840330 Ltr

ML20087N875
Person / Time
Site:	Calvert Cliffs
Issue date:	03/30/1984
From:	Lyons W, Mahon C, Porter R BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF ADMINISTRATION (ADM)
References
LER-83-043-03X, LER-83-43-3X, NUDOCS 8404050121
Download: ML20087N875 (4)

LER-2083-043, Updated LER 83-043/03X-1:on 830809,following Reactor Trip, Steam Generator Safety Valve Failed to Reseat.Caused by Missing Pin.Valves Inspected to Ensure That Blowdown Ring & Pin Not worn.W/840330 Ltr

Event date:
Report date:
3182083043R00 - NRC Website

text

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EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h gl At 1810 following a Reactor Trip a Steam Generator safety valve failed l lTTil l to reseat. At 2230 the valve was cacced shut. The Power I.evel-liich trin l 1014 l l was reduced as per T.S. 3.7.1.1.a. The remaininc safety valves remained l l o 15 l l onerable rinrina thi s event. On 19 Am m ist the vnive hnr1 heen renniverl. I l0l6ll tested and returned to service. l l0l7ll Sitailar events: none. l FETF I "

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h l TIT ll The valve opened on high pressure and failed to rescat due to a worn l l1l1ll locking pin allowing rotation of the blowdown ring. The vendor reports l lil2ll this has been a rare occurence. To prevent future recurrence Preventive l l1l3ll Maintenance items have been approved to inspect the valves to ensure the I gl blowdown ring and pin are not worn. No further corrective action required. =

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1V lLER NO.~ .

'83-43/3X

, DOCKET NO. -

50-318 3 LICENSE ~NO. 1DPR.69

-EVENT DATE. .08-09-83

. UPDATE REPORT DATE 03-30-84 JATTACINENT

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- :CAUSE DESCRIPTION AND CORRECTIVE' ACTIONS'(CONT'D)

?On August 9,?1983 at 1'810, Calvert' Cliffs Unit 2 experienced a sudden pressure excursion and trip due_to a problem with the Turbine Throttle and Governor jalves. ~ During this excursion, pressure 'in the Main Steam header reached .1027 PSIA. x his exceeded the ' set pressure:of twelve of the Main Steam Safety valves.

g One. valve, 2-MS-3994-RV, did'not" reseat.1 Nhen the operators realized that the valve was partially open and should have m - reseated, they' called in maintenance ~ personnel. Rey t'irst attempted to further lift the valve, by 'means'of- the renual lifting lever,' to blow free any foreign fmatter which might.have been trapped between the disc and the seat. his had no Japparent effect. ,ne valve was then gagged shut to stop the steam flow, and uf frepair action was initiated. Power Level-liigh ~ trip. setpoint was reduced in accordance.with T.S. 3 7 1.1.a. All remaining Main Steam Safeties remained

? operable!during this event.

In operation,Ethe safety valve stays shut as long as the upward force felt due cto steam. pressure;is less than the downward force exerted by the spring. If,

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sg  : however,- the steam pressure increases enough to overcome the spring tension,

[the valve opens. :Once the disc has lifted a sufficient distance, a back pressure

will;be built up under the disc and disc holder due to a flow restriction between'the outer edge of the blowdown ring and the disc holder. he steam

-pressure -is1then effecting a nuch larger area thah before and will cause the Walve to stay open until the steam pressure drops to a point somewhat lower

. 'than the lift pressure.. If the blowdown ring is moved upward, the~ flow resis-V  ? tance is greater, causing-a higher back pressure and a-longer blowdown. -Con-

- .versely, if the ring were moved downward, the restriction'becomes less and the valveLwill close at a higher. pressure (closer to the opening setpoint).

In the case 'of this. failure, a vibration had existed between the blowdown ring

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"and'its'lo6 king pin for some time, causing-damage to'both parts. -Over a period

, Lof-possibly several years, the end of the pin became flattened to the point s where-it noflonger' prevented rotation of the ring. When the ring was allowed

/to rotate freely, fit' unscrewed and moved upward toward the seat.

'Ihe normal setting of the ring is approximately 0.047 in. below contact with

-the' disc holder.1 Evidence-indicates that the ring, in this case', unscrewed

- ;itself'uring d normal operation to the point where it contacted and actually 3 applied pressure td the-disc holder. . E en, when the valve lifted, the ring

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x- , further unscrewed to a position approximately.0.140 in, above its original setpoint.: In this condition the pressure in the steam header would have had to mdrop to around 750 PSIG before the valve would try to rescat. Even then it icould not ihave'done:so~, because the ring was still holding the disc holder

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(and?theretore the disc) approximately 0.093 in, off the seating surface. This W the position in which it was found upon disassembly.

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LER'NO. . 83-43/3X

< DOCKET;NO.. 318

LICENSE NO.. . DPR 69

. EVENT DATE 08-09-83

. UPDATE REPORT-DATE 03-30-84 cATTACHMENT - PAGE 2

.CAUSE DESCRIPTION AND CORRECTIVE ACTIONS (CONT'D)

' The.' valve was disassembled and inspected revealing minirral damage:

(1) .small, corresponding nicks in the disc and nozzle (apparently caused by something caught between Lthem), and; (2) damaged areas on the blowdown ring and its locking

. pin (evidence of the above described situation).

1he ' damage' to the disc and seat was corrected by_ grinding and lapping both

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to mirror surfaces. The blowdown ring and the locking pin were both replaced

,from spares. .The valve was returned to service on August 12, 1983

.The vendor reported this problem is a very rare occurence. To prevent future recurrence Preventive Maintenance items have been approved to inspect the safety valves and to ensure the blowdown ring and pin are not worn. No-further corrective action required.

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B ALTIMORE G AS AND ELECTRIC COMPANY P.O. B O X 14 7 5 ~

, S ALTIM O R E. M A R YL A N D 21203 NUCLEAR POWER DEPARTMENT

- CCLVERT CLIFFS NUCLEAR POWER PL ANT LUSBY. MARYLAND 20657 .

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March 30, 1984~

U.~ S. Nuclear Regulatory Cormtission Docket NO. 50-318 Document Control Desk' License No. DPR-69 Washington, DC 20555

Dear Sirs:

-The attached supplemental report to LER 83-43/3X, Revision 1, is being sent to you as required by 10 CFR 50.73 Should you have. any questions regarding this report, we would be pleased to_ discuss them with you..

Very.truly yours,_

UMl]

-L.B. Russell (

Plant Superintendent LBR:wn.:mst -

cc:- Dr. T. E. Marley Director, Office of Management Information and Program. Control

-Messrs: ' A. E. Lundvall, Jr.

-J.'.A. Tiernan 1

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. - .