05000324/LER-1991-019

LER 91-019-01:on 911112,LLRT Failure of Two MSL Inboard & Outboard Isolation Valves Resulted in Condition Outside Design Basis.Root Cause Analysis in Process.Msls C & D Inboard & Outboard MSIVs Repairs complete.W/930812 Ltr

ML20056D622
Person / Time
Site:	Brunswick
Issue date:	08/12/1993
From:	Jonathan Brown, Jones T CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BSEP-93-0128, BSEP-93-128, LER-91-019-01, LER-91-19-1, NUDOCS 9308170190
Download: ML20056D622 (6)

LER-2091-019,

Event date:
Report date:
3242091019R00 - NRC Website

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Carolina Power & Light Company

• E;acntrariawamimmante Brunswick Nuclear Plant P. O. Box 10429 Southport, N.C. 28461-0429 August 12, 1993 FILE: B09-13510C 10CFR50.73 SERIAL: BSEP-93-0128 i

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555 i

BRUNSWICK NUCLEAR PLANT UNIT 2 ,

DOCKET NO. 50-324 LICENSE NO. DRP-62 SUPPLEMENTAL LICENSEE EVENT REPORT 2-91-019-01 Gentlemen: Y In accordance with Title 10 of the Code of Federal Regulations, the enclosed -l '

Supplemental Licensee Event Report is submitted. The original report fulfilled the requirement for a written report within thirty (30) days of a reportable occurrence and was submitted in accordance with the format set forth in NUREG-1022, Septenber 1983.

Very truly yours, ,

M Wm  ;

M. Brown, Plant Manager - Unit 1 )

Brunswick Nuclear Plant l l

TMJ/ ,

a Enclosure l cc: Mr. S. D. Ebneter Mr. P. D. Milano BSEP NRC Resident Office _]

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9308170190 DR 930812

• ADOCK 0500 4 y f

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NRC FORM Y6 U S NUCLEAR REGULATORY COMM$SION APPROVED OMB NO 315D-0104

• EXPIRES 4/3^#92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH TH!$ INFORMATION COLLECTION REQUEST. 50 0 HRS FORWARD COMMENTS REGARDING BUR EN ESMME T THE RECORDS AND REPORTS MANAGEMENT BRANCH LICENSEE EVENT REPORT (LER) (P-630) U S NUCf. EAR REGUt ATORY COMM!SSiON, WASHINGTON, DC 20555, AND TO THE PAPERVN i:iEDUCTICN PROJECT (3150 01G4). OFFICE oF MANAGE' MENT AND BUDGET. WASHINGTON. DC 23503 F ACILITY NAME (1) Brunswick Steam Electric Plant D@C NUMMR Q PAGE (3)

Unit 2 05000324 1

mLE f4i LLRT Failure of Two Main Steam Lines' Inboard and Outboard Isolation Valves Resulting in a Condition Outside the Plant Design Basis.

EVE NT DATF (E) LER NUMBER 46) REPORT DATE (7) CTHER FACluTIES INVOLVED 19)

MONTH DAY YEAR VF AR SEQ REV NQ MONTH DAY YEAR FACILITV NAME DOCKET NUMBER NO 11 12 91 91 -

019 -

01 08 12 93 THis REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR g (Check one or mme of the followmg) (11)

OPfliATfNG MODE (9) S 20 do2?tu 20 doHci 50 73talmim) 73 71(el b

POWC R 20 4h(1gi) 50 36(n)(1) g 50 73(a) A(v) 73 71(c) }

ttvEt (10j ooo 20 4%@M SD 36(c)Q SO 73(a)Q(vu) OTHER (Specify m Abstract and Tert) 20 415[an1)(m) 50 73tajmp) $0 73(alm (vmHA)

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20 43$(a)(1)(w) y SC 73(sjm(n) 50 73(a)Atvm)(B)

?O 4DStan(inv) 50 73(ejf2)(ni) 50 73(almb)

UCENSEE CONTACT FOR THIS LER (12)

MME Theresa M. Jones, Regulatory Compliance Specialist TELEPHONE NUMBER (919) 457-2039 COMPLETE ONE LINE FOR EACH COMPONENT F AILURE DESCRIBED IN THis REPORT (13)

GAUM SY ST EM COMPONENT MANurACTURER REPORTABLE CAUSE EYSTEM COMPONENT MANUFACTURER REPORTABLE +

TO NPRDS TO NPRDS X SB ISV R344 Y SUPPLEMENTAL PEPORT EXPECTED (14) EXPECTED MONTH DAY YEAR SUBMISSION YES pf yas cuee E@LCTED SubMtS$10N DATE)

NO DATE  !

X (15) l l

ABSTRACT {Le to 1470 wees i e awmommer feean w@e um typwen imey (16) l On November 12, 1991, the Unit 2 reactor was shutdown in refuel / maintenance outage. i Local leak rate testing (LLRT) of the main steam isolation _ valves (MSIVs) had been performed. The results of testing indicated that MSIV leakage on main steam lines l (MSLs) C and D had exceeded the Technical Specification (TS) limit of 11.5 standard cubic feet per hour (scfh), but the actual amount of leakage could not be determined. MSL C outboard MSIV leakage was caused by an indication across the in-body seat. It is believed the indication resulted from the disk closing on a piece of metal that had spalled off the body bore during a previous closure. MSL C inboard MSIV leakage resulted from poor disk to in-body seat contact caused by low spots. Low spots are generally the result of in-body seat deformation from thennal expansion and contraction. It was believed that MSL D outboard MSIV leakage resulted from the disk not seating completely against the in-body seat. The disk outside diameter was contacting a raised lip (tooling mark) on the in-body seat surface. It was believed that low spots also caused leakage of the MSL D inboard valve. MSLs C and D MSIVs repairs were completed and a repeat of the testing revealed zero leakage in both MSLs (ies MSL C = 0.173 scfh and MSL D = 0.266 scfh) .

This event is considered potentially safety significant based on the inability to determine the amount of leakage. A previous failure of two MSIVs to meet the TS required 11.5 scfh leakage requirement has been reported in LER 1* SS-025, That LER involved the outboard MSIV on two separate MSLs. On December 7, 1932, the results 1 of testing indicated that MSIV leakage on MSL D had again exceeded Technical l Specification limits (LER 2-92-010).

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NRC FORM Sf4A U S NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3150 0100

' EXP!RES: 630/02 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS INWRMAN CMECM REWESt M O HRS FORWARD COMEMS LICENSEE EVENT REPORT (LER) REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS TEXT CONTINUATION MANAGEEM WNCH F53% U S NUCLEAR REGULATORY COMMISStON, WASHINGTON, DC 20555. AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104L OFFICE OF MANAGEMENT AND BUDGET. WASHINGTON, DC 20 sos IActuTV NAME (1) DOCKET NUMBER c) LER NUMBER (0) PAGE (3)

Brunswick Steam Electric Plant 05000324 vEAR SEQ REV 2 Unit 2 NO. NO 91 019 01 TExr e mm. .p.c. . r.92n.a us. .Hhonal NRC Form 3fMiA s) (17)

Title:

LLRT Failure of Two Main Steam Lines' Inboard and Outboard Isolation Valves Reeultina in a Condition Outside the Plant Desion Basis.

INITIAL CONDITIONS On Novenber 12, 1991, the Unit 2 reactor was shutdown in day 62 of the 1991 refuel / maintenance outage. Local leak rate testing (LLRT) of the main steam isolation valves (MSIVs) had been performed to satisfy technical specification (TS) primary containment leakage rate surveillance requirements. The referenced TS requires that the primary containment leakage rate be limited to less than or equal to 11.5 standard cubic feet per hour (scfh) for any one main steam line (MSL) isolation valve when tested at 25 psig.

EVENT NARRATIVE The ref erenced testing is accomplished by draining the MSL, closing the inboard and outboard MSIVs, prcasurizing the space between them to 25 psig with air while providing a vent path for any leakage, and measuring the leakage rate. In the event of a leakage rate equal to or-greater than 11.5 scfh the test procedure directs that the associated MSL be filled with water between the reactor vessel and the inboard MSIV to seal any leakage past the inboard MSIV. The space between the MSIVs is again air pressurized and the leakage rate resulting from leakage past the outboard MSIV is measured. This method of testing indicates the total MSL leakage, the leakage associated with the outbourd MSIV and, by subtraction, the leakage associated with the inboard MSIV.

The MSIVs are Rockwell Model 1612, 24", Y-type globe velves.

On September 17, 1991, the initial leakage testing of main steam lines (MSLs) C and D was conducted. In each case the line would not pressurize to the required air pressure; therefore, the amount of leakage past the outboard MSIV was nonquantifiable. Specifically, MSL C could only be pressurized to 21 psig and MSL D could not be pressurized above 3 psig.

During the testing, the test volume in MSL C experienced water intrusion but the volume in MSL D did not, indicating possible leakage of the MSL C inboard MSIV. Work requests were initiated to repair the outboard MSIVs on MSLs C and D. Inspection of the valves revealed the following:

MSL C outboard MSIV

1. Galled stem.

2. Indication on in-body seat.

3. Raised " lip" on in-body seat face.

4. Bonnet backseat deformation (indented contact pattern).

5. Raised metal on body bore.

MSL D outboard MSIV

1. Poor disk to in-body seat contact.

2. Disk outside diameter contacting raised " lip" on seat face above in-body seat.

3. Indented cont act pattern on bonnet backseat.

4. Steam cuts exhibited on inside diameter of packing gland / follower piece. j

.A second leakage test was performed on November 12, 1991, following repair of the MSLs C and l D outboard MSIVs. The results of these tests indicated that both outboard MSIVs were no I

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NRO FORM 3DCA U S f(JCLEAR REGULATORY COMM$SION APPRCNED OME NO. 3150-0134 EKPIPES 413'vD2 ESTIMATED BURDEN PER RESPONSE TO COMPtY 1MTH THIS M RMAD N NECD N RE UEST. SH HRS F RWAR C MMENTS LICENSEE EVENT REPORT (LER) REGARD!NG BURDEN ESTIMATE TO THE RECORDS AND REPORTS TEXT CONTINUATION u^o^ocut"T SRAucH (R430i. u s NUCtEAR eeoutaTOR< COMM>SsiON.

WASHINGTON DC 20%5, AND TO THE PAPERWORK REDUCTION PROJECT (31500104J OFFICE OF MANAGEMENT AND BUD 3ET, WASHINGTON, DC 20503 i ActuTY NAME (1) DOCEET NUMDER (2) LER NUMBER (5) PAGE (%

Brunswick Steam Electric Plant 05000324 YEAR SEO REV 3 No- NO Unit .2 ,

91 ,

019 01 T E n %. . . . .... - -~., NRC - w .m ,

longer leaking. Given that the outboard leakage was eliminated the testing revealed that both MSLs C and D inboard MSIVs exhibited leakage. MSL C inboard MSIV was determined to have a leakage rate of 32.47 scfh. The leakage rate associated with the MSL D inboard MSIV is nonquantifiable because the test volume would not pressurize. Work requests were initiated to repair MSLs C and D inboard MSIVs. Inspection of the valves indicated the following:

fML C inboard MSIV

1. In-body seat showed inadequate contact with disk.

2. In-body seat had two small pin holes.

3. Contact indications on outside diameter of disk. t

4. Slight gall marks in body bore.

5. Indications on bonnet backseat.

MSL D inboard MSIV

1. In-body seat has two " low spots".

2. Gall marks on body bore.

3. Bonnet backseat had slight indention marks.

The MSLs C and D inboard MSIVs repairs were completed and a subsequent repeat of the testing revealed zero leakage in both MSLs (ie: MSL C = 0.173 scfh and MSL D - 0.266 scfh).

GhUSE OF EVENT A Ioot cause analysis is in progrecs and the results will be provided in a supplement to this '

report.

CORRECTIVE ACTIONS 1 MSLs C and D inboard and outboard MSIVs repairs are complete. Additional corrective actions resulting from the root cause determination will be reported in the supplement to this report.

l SAFETY ASSESSMENT This event is outside the current design basis of Unit 2. A safety assessment of this event has not been completed at this time. Available data indicates that. it is not reasonable to assume a loss of MSL or condenser integrity during a LOCA or an earthquake, therefore the MSLs and the condenser would delay the release of MSIV 3eakage. However, given that the amount of leakage which would have eccurred through MSL D MSIVs has not been quantified, the degree to which the radiological limits of 10CFR100 would have been approached during a design basis accident bas not been determined. The assessment of this event will continue and will be reported in the supplement to this report.

PREVIOUS SIMILAR EVENTS A past failure of two MSIVs to meet the TS required 11.5 scfh leakage requirement has been reported in LER 1-88-025. That LER involved the outboard MSIV on two separate MSLs.

EIIS COMPONENT IDENTIFICATION Sys t ern /Comrenent FIIS Code  ;

MSIV SB/ISV l

NRCFORM 3904 U $ NUCLEAR REGULATORY COMMIS$0N APPROVED OMB NO. 31$04100 .

' EXPIRES' &sof02 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INF RMATCN C LLECTON MEST; $0.0 HRSJORWARD COMMEMS LICENSEE F. VENT REPORT (LER) REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS TEXT CONTINUATION MANWENT BRANCH N U S. NUCLEAR REGULATORY COMM:SSON, WASHlNGTON DC 205S5, AND TO THE PAPERWORK REDUCTION PROJECT (3150-01ML OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503 F ACILITY NAME tt) DOCKET NUMBER (2) LER NUMBER (e) PAGE(3)

Brunswick Steam Electric Plant 05000324 YEAR SEQ PEV 4 Unit 2 NO NO.

91 019 01 TEXT (if mme spne a reautred tme addtanal NRC Fo'm 366A e) (17)

SUPPLEMENTAL CAUSE/ CORRECTIVE ACTION ,

Q MSL C OUTBOARD MSIV The leakage of the MSL C outboard MSIV resulted from the indication across the in-body seat.

Although no foreign material was found during the inspection, it is believed the indication was caused by the disk (main disk or poppet) closing on a piece of metal that had spalled off

-the body bore during a previous closure. This conclusion was substantiated by the raised metal on the body bore. Body bore-to-disk galling is a common problem with this type of valve. Corrective actions included lapping the in-body seat to remove the indication, removing the raised lip, and honing the body bore to remove the raised metal. The bonnet backseat surface was " skim cut" to remove the deformation (indented contact pattern). The ,

raised lip on the in-body seat was determined to be a tooling mark interjected during a previous seat repair, and is not suspected to have affected valve closure. A new (lighter) disk was also installed. Installation of the lighter disk is recommended by the vendor to minimize or eliminate galling. New and improved parts (disk, stem, stem-disk, and disk-piston) being supplied by the vendor as replacements for discontinued parts are being used ,

whenever an MSIV is required to be rebuilt. Other corrective actions included installing a new stem and increasing the bonnet backseat bore inside diameter to achieve greater clearance between the stem and backseat bore. This reduces the propensity of the stem contacting the bonnet backseat during valve stroking. Also, taller spacer rings have been installed.

Taller spacer rings are less likely to become cocked and cause galling.

A possible contributor could have been leakage of the stem-disk (pilot disk) to disk-piston ,

seat due to alignment. Stem misalignment is caused by a lack of valve actuator support I resulting in actuator deflection. The vendor states that a certain amount of misalignment 2s not detrimental to the actuator performance, however it is not advisable because it may cause galling of the stem and cocking of the stem-disk. Brunswick has installed taller i spacer rings to provide additional stem support and increased the bonnet backseat bore '

internal diameter to reduce the chance of stem galling.

MSL D OUTBOARD MSIV It is believed that leakage of the MSL D outboard MSIV resulted from the disk not seating completely against the in-body seat due to the disk outside diameter coming into contact with a raised lip (tooling mark) on the in-body seat face. This was evidenced by the disk O.D.

showing signs of contacting the raised lip. Finding no indications / imperfections on either the in-body or disk seating surfaces further substantiated this analysis. The in-body seat was lapped and the tooling mark removed. A " skim cut" was performed on the bonnet backseat to remove the def ormation and the packing gland / follower was replaced. The disk was replaced and the bcnnet backseat insida diameter was enlarged. A taller spacer ring was installed.

MSL C TNPOARD M91V Leakage of the MSL C inboard MSIV is attributed to poor disk to in-body seat. contact caused by low spots. Poor or no contact in certain areas due to low spots is considered typical and a primary cause of leakage in valves. These low spots are generally the result of in-body seat deformation caused by thermal expansion and contraction. The pin holes or pits noted were not.large enough in diameter (approximately 1/32") to cause leakage. The in-body seat was lapped to a satisf actory sealing surf ace. Additional corrective actions included honing the gall marks smooth and taking a " skim cut" on the bonnet backseat to remove the indication. The disk was replaced and the bonnet backseat inside diameter enlarged. A taller spacer ring was installed.

MSL D INBOARD MSIV

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WASHINGTON DC 20%5 AND TO THE PAPERWORK REDUCTON PROJECT I (3150 010 4 OFFICE OF MANAGEMEPlf AND BUDGET, WASHINGTON, DC i "3

F AOUTY NA " - (1) DOCKET NUMBER c) LER NUMBER (6) PAGE (3)

Brunswick Steam Electric Plant 05000324 YEAR SEQ REV 5 Unit 2 NO NO 91 019 01 TEXT p ,w. we. . q,.o . . sone.:NaC rorm 3 sea .) (37; It is believed that low spots also caused leakage of the MSL D inboard valve. A loose stem-disk may have contributed to the leakage in that the disk could have cocked enough to prevent proper fit-up to the disk-piston seat. The loose stem-disk was determined to be caused by vibration loosening the locking pin (i.e., locking pin was found " wallowed outa). The in-body seat was lapped to a satisf actory sealing surf ace. The gall marks were honed smooth and .;

a " skim cut" taken to remove the indention marks from the bonnet backseat. Additionally, the' '

disk was replaced and the bonnet backseat inside diameter enlarged. A taller spacer ring was installed.

SUPPLEMENTAL SAFETY ASSESSMENT

• This event is considered potentially safety significant based on the possibility- for exceeding the 10CFR100 dose limits during a design basis accident. A dose analysis was l performed by first calculating the maximum allowable leakage without exceeding the limits and '

then the equivalent orifice necessary to produce this leakage. If the MSIV with the smallest  ;

leak was more than 0.01 percent open, the offsite dose limit may have been exceeded.  !

However, since the percent open la not known, the degree to which the radiological limits '

may have been approached can not be determined.

ADDITIONAL SUPPLEMENTAL INFORMATION .

t On December 7, 1992, the results of local leak rate testing indicated that MSIV leakage on MSL D again had exceeded the Techn;_al Specification limit of 11.5 scfh. Preliminary investigation indicated that the outboard MSIV appeared to have had excessive disk piston to valve bore clearance and an alignment problem (ie., the disk was not guiding properly into the in-body seat). MSLs A, B, and C tested satisfactorily. See LER 2-92-010.

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