ML20027D918

Updated LER 82-005/01T-1:on 820628,during Refueling Shutdown,Main Steam Check Valve B Found in Degraded Condition.Caused by Set Screws Which Lock Valve Disc tail- Piece to Rockshaft Loosened by Vibration.Set Screws Staked

ML20027D918
Person / Time
Site:	Robinson
Issue date:	11/03/1982
From:	Cox H CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20027D908	List: ML20027D907 ML20027D918
References
LER-82-005-01T, LER-82-5-1T, NUDOCS 8211100388
Download: ML20027D918 (3)

Text

NRC FORM 36e. UPDATE REPORT - PREVIOUS REPORT DATED U. S. NUCLEAR REGU ORY COMMISSION (7 77) -

• JULY 12' 1982 LICENSEE EVENT REPORT CONTROL BLOCK: l l l l l l l (PLEA 3E PRINT OR TYPE ALL REQUIRED INFORMATION) 1 6 0

lo l1l lS lC l11 lB lR l2 7 8 9 LICENSE E CODE 14 1 gl6 l0 l- l0 l0 l0 l0 l0 p p l0 lgf LICENSE NUMBEH 2h 26 f f f f lglb7 CATl 68lg LICENSE TYPE JO COWT lolil 7 8 S$n"C60 dl015 61 lo 10DOCK 10ET12 NUMBER 16 11 @l0 68 16 69 12EVENT 18DATE 18 12 l@l1 74 76 l 1 REPORT l 0 l 3DATEl 8 l 280 l@

EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h o 2 lOn June 28, 1982, at approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> with the plant at refueling shutdown, I j o ,3 i j "B" Main Steam (MS) Check Valve was discovered in a degraded condition. Inspection l iol4ll revealed that the set screws which lock the valve disc tail-piece to the rockshaf t l 101 s l l had ~ 1oosened due to vibration. This allowed the shaf t to move axially and partially l l o l 6 l l 811P out of cne shaft bushing. 'Ihis event is being reported pursuant to Technical l O 7 i S P ecification 6.9.2.a.9. "B" MS Check Valve was found closed, and therefore was l demonstrated capable of perfonning its intended function, so there was no threat to 10181 I the public health and safety. l 7 8 3 80 DE CODE SUBC E COMPONENT CODE SUBCODE 1,U E p

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,_ SEQUENTI AL 0,CURRENCE REPORT REVISION LE R RO EVENT YE AR REPORT NO. CODE TYPE h RE nU l 8l 2l [ __j l 0l 0l 5l 24 26 y

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_ 21 22 23 31 AK N AC O oN PL NT ET HOURS SB ITT D FO 9 8. SUP lF 33 lg[34Z J g {35g l36Zl@

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[dAiRESlg l l 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS i o l"A" and "C" MS Check Valves were inspected, and the set screws were found to be l i i l loose on both valve disc tail-pieces. All three valves have been modified to l

, 7 gcorrect a past modificaticn deficiency. This modification prevents excessive l In addition, the tail-piece set screws have been

, 3 l axial movement of the rockshaft. l staked to prevent loosening. These actions were completed on July 9, 1982. No l i 141 l fu rther action is considered necessarv. I 7 8 9 80 ST S  % POWER oTHER STATUS dis O RY DISCOVERY DESCRIPTION N/A l B [gl INSERVICE INSPECTION I1 l5l 'L_J@

H l 0l 0l 0l@l l l ACTIVITY CONTENT RELEASED OF RELE ASE AMOUNT OF ACTIVITY LOCATION OF RELEASE N/A N/A 1 6

@ @l l l l PERSONNEL EXPOS ES NUMBER TYPE DESCRIPTION y l 0 l 0 l 0 l@l Z l@] N/A l PERSONNEL INJU IES NUMBER DESCRIPTION N/A ITTil8 I9 01010 l@l 7 11 12 80 l

LOSS OF oR DAMAGE TO FACILITY TYPE DESCRIPTION Q Wgl 8211100388 821103 N/A 80 l

7 8 9 iO PUBLICITY . PDR ADOCK 05000261 NRC USE ONLY ISSUED D S PDR 13_L_I l_N_18l ESCRIPTioN N/A l l l l l l l l l l l l l l :j 7 8 9 10 68 69 80 E NAME OF PREPARER PHONE:

SUPPLEMENTAL INFORMATION LER-82-005, REVISION 1 I. Cause Description and Analysis On June 28, 1982, at approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> with the plant in refueling shutdown, "B" Main Steam (MS) Check Valve was discovered to be in a degraded condition. The MS Check Valves had undergone an In-Service Inspection in which the valves were usually verified to be seated by crawling the pipes.

However, the degraded condition of "B" MS Check Valve was not discovered until the rockshaf t end caps were removed for stamping of the shaf t end with a position mark to facilitate future inspections. Upon removal of the end caps on "B" MS Check Valve, it was noted that one end of the rockshaft had partially slipped out of its bushing and was pinned against the end of the bushing. Disassembly and inspection of the valve revealed that the set screws which lock the valve disc tail-piece to the rockshaf t had loosened, apparently due to vibration, and allowed the shaf t to move axially, resulting in the above configuration.

This event is the result of a modification performed on the MS check valves in 1978. This modification, in addition to increasing the rockshaf t diameter, modified the bushing retainer and end cap configuration. The modification to the bushing retainers and end caps increased the clearance between the end of the rockshaft and the end cap such that, if the set screws were to loosen, the rockshaft could slide out of the bushing on one end. This clearance is now identified as a deficiency of the modification.

The configuration of "B" MS Check Valve which resulted in this degraded condition was caused by a modification developed by CP&L personnel and is plant spe cific . However, subsequent investigation and design analysis by the valve vendor reveals that these same conditions could exist in an unmodified valve. Specifically, if the set screws loosened and the rockshaft moved axially to the most extreme position, the remaining bushing to shaf t engagement would not provide sufficient bearing surface for continuous operation. The valve vendor is reporting this item under 10CFR21.

This event resulted in a condition which requires corrective measures to prevent operation in a manner less conservative than assumed in the safety analysis report and is being reported pursuant to Technical Specification 6.9.2.a.9.

"B" MS Check Valve was found closed, and therefore was demons trated capable of performing its intended function. Thus, there was no threat to the public health and safety.

II. Corrective Action An inspection of the remaining two MS Check Valves was performed, and the set screws were found to be loose on both valves. A modification has been implemented for all three valves. This modification consisted of replacing the damaged bushing and bushing retainer on "B" MS Check Valve and adding

a retaining block at each end of the rockshaf t on all three valves. These retaining blocks reduce the clearance between the shaf t end and the end cap and will prevent axial movement to the extent which would allow the rockshaf t to slip out of its bushing.

Additionally, the tail-piece set screws, which also limit axial movement of the rockshaf t, were replaced with longer set screws and machined to fit, thereby allowing the set screws to be staked without damage to the threads. This action will prevent the screws from loosening due to vibration.

All modification work was completed on July 9, 1982.

III. Corrective Action To Prevent Recurrence The corrective actions described above are suf ficient to prevent recurrence of this event . However, since the modification deficiency aspect of this event could potentially arise in future modification, this LER will be reviewed by on-site engineering personnel involved in modification develop-me nt . This review was completed on September 1,1982.

Additionally, the MS Check Valves will be routinely inspected during the next refueling outage with special attention being directed to the condition of the rockshaf t/ bushing configuration and the set screws.

No further action is considered necessary.

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