ML18038A992

LER 93-011-00:on 930525,facility Started W/Invalid LLRT Having Been Performed on Drywell Head Seals.Initial Investigation Determined That RTV Applied W/O Approved Procedure.Incident Investigation Being Conducted

ML18038A992
Person / Time
Site:	Browns Ferry
Issue date:	11/01/1994
From:	Jay Wallace TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18038A990	List: ML18038A989 ML18038A992
References
LER-93-011-01, LER-93-11-1, NUDOCS 9411070287
Download: ML18038A992 (16)

Text

NRC FORM 366 (5-92)U.S NUCLEAR REGULATORY CQBIISSION APPROVED BY (NQI NO.3150-0104 EXPIRES 5/31/95 LZCENSEE EVENT REPORT (LER)(See reverse for required number of digits/characters for each block)ESTIHATED BURDEN PER'RESPONSE TO COMPLY ,WITH THIS INFORHATIOH COLLECTION REQUEST: 50.0 HRS.FORlJARD COHMEHTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS HANAGEHENT BRANCH (MNBB 7714), U.S.NUCLEAR REGULATORY COHMISSION

~WASHINGTON, DC 20555-0001 AND TO THE PAPERWORK REDUCTION PROJECT (3140-0104)

~OFFICE OF MANAGEMENT AND BUDGET WASHINGTON DC 20503.FACILITY NAME (1)Browns Ferr Nuclear Plant BFN Unit 2 DOCKET NWSER (2)05000260 PAGE (3)1 OF 8 TITLE (4)An invalid local leak rate test on the dryweli head seals resulted in a condition prohibited by Technical Speci f ications HOHTH DAY YEAR YEAR EVENT DATE 5 LER NWSER 6 SEQUENTIAL NUMBER REVISION NUMBER HONTH DAY YEAR REPORT DATE 7 OTHER FACILITIES INVOLVED 8 DOCKET NUHBER FACILITY NAHE NA 05 25 93 93 011 00 1'1 01 FACILITY NAHE NA DOCKET NUMBER OPERATING INXJE'9)N THIS REPORT IS SUBMITTED PURSUANT 20.402(b)TO THE REQUIREMENTS OF 10 CFR=Check one or mor e 11 50.73(a)(2)(iv) 20.405(c)73.71(b)LEVEL (10)000 20.405(a)(1)(i) 20.405 (a)(1)(i i)20.405(a)(1)(iii) 20.405(a)(1)(iv) 20.405(a)(1)(v) 50.36(c)(1)50.36(c)(2) 50.73(a)(2)(i)(B) 50.73(a)(2)(ii) 50.73(a)(2)(iii)

LICENSEE CONTACT FOR THIS LER 12 50.73(a)(2)(v) 50.73(a)(2)(vii) 50.73(a)(2)(viii)(A) 50.73(a)(2)(viii)(B) 50.73(a)(2)(x) 73.71(c)OTHER (Specify in Abstract below and in Text, NRC Form 366A NAHE James E.Wallace, Compliance Licensing Engineer TELEPHONE NUHBER (Include Area Code)(205)729-7874 C(NPLETE ONE LINE FOR EACH C(NP(NJENT FAILURE DESCRIBED IN THIS REPORT 13 CAUSE SYSTEH COHPONENT HANUFACTURER REPORTABLE TO NPRDS CAUSE SYSTEM COMPONENT HANUFACTURER REPORTABLE TO NPRDS SUPPLEMENTAL REPORT EXPECTED 14 YES (If yes, cceylete EXPECTED SUBHISSION DATE).NO EXPECTED SUBMISSION DATE (15)MONTH DAY YEAR 01'5 95 ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)(16)On October 2, 1994, during the Unit 2 Cycle 7 refueling outage, TVA was removing the Unit 2 drywell head when it was noticed that a sealant material (i.e.i RTV)i used to adhere the 0-ring seals in their grooves on the bottom flange, displaced from the grooves.This condition occurred when the drywell head was reset on the lower flange during the Unit 2 Cycle 6 refueling outage.This condition existed when Unit 2 was restarted on May 25, 1993.It was determined that the excessive amount of RTV in the 0-ring grooves caused the LLRT performed during the last outage to be invalid..This event is reportable in accordance with 10 CFR 50.73 (a).(2)(i.)(B) as a condition prohibited by BFN Technical Specifications.

An initial investigation of this event determined that the RTV was appli.ed without an approved procedure, without proper authorization, and was not incorporated into the design prior to installation.

Before reinstalling the drywell head, documentation will be provided as to limiting the amount of RTV allowed for the drywell head installation to ensure that it does not interfere with the LLRT.To further determine the root cause of the event and corrective actions to preclude recurrence, TVA is currently conducting an inci.dent i.nvestigation on this event after which a supplemental report will be submitted.

The event date of'his report'is May 25, 1993, when Unit 2 was restarted wi.th an invalid LLRT having been performed.

9411070287

'741101 PDR ADOCK 05000260 S PDR NRC FORM 366 (5 92) 0 0 NRC FORN 366A (5-92)U.S NUCLEAR REGULATORY CQHIISS ION LICENSEE EVENT REPORT TEXT CONTINUATZON APPROVED SY MB NO.3150-0104 EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO COHPLY NITH THIS INFORHATIOH COLLECTIOH REQUEST: 50.0 HRS~FORllARD COHHENTS REGARDING BURDEN EST IHATE TO THE IHFORHATIOH AND RECORDS NANAGEHENT BRANCH (HNBB 7714), U.S.NUCLEAR REGULATORY COHNI SSI ON/llASHIHGTOH

~DC 20555-0001, AND TO THE PAPERlQRK REDUCTION PROJECT (3150-0104), OFFICE OF IIANAGEHENT AND BUDGET, IIASHINGTOH DC 20503 FACILITY NAKE (1)DOCKET NINER (2)LER NWSER (6)YEAR SEQUENTIAL NUHBER REVISION NUHBER PAGE (3)Browns Ferry Unit 2 05000260 93 011 00 2 of 8 TEXT If more s ce is r fred use additional co les of NRC Form 366A (17)I~PLANT CONDITIONS At the time this event was discovered, Unit 2 was shutdown for a scheduled refueling outage.Units 1 and 3 were shutdown and defueled.DESCRIPTION OF EVENT Ao Event On October 2, 1994, TVA was removing the BFN Unit 2 drywell head during a scheduled refueling outage.While removing the drywell head, personnel observed an excessive amount of sealing material (i.e., RTV-102)on the lower flange.The sealant had been used to facilitate installation of the drywell head 0-rings during the cycle 6 refueling outage.Additionally, approximately three inches of the inner 0-ring protruded from its groove (the drywell head flange 0-ring configuration is shown on page 7).Based on the observations of the 0-rings[SEAL)when the drywell head[NH]was removed this outage, it was concluded that an invalid LLRT had been performed before the restart of Unit 2 on May 25, 1993.Specifically, the RTV was in the area between the O-rings, and the inner 0-ring seal was broken.Thus, the excessive amount of RTV obstructed the LLRT test volume.Further details of this event are provided below.On May 13, 1993, during the Unit 2 Cycle 6 refueling outage, the drywell head seal failed its initial as-left LLRT.RTV-102 was placed in the 0-ring grooves to augment the sealing characteristics of the 0-rings.The drywell head was subsequently reset, the bolts were retorqued, and the LLRT was reperformed on May 15, 1993.The followup LLRT measured 0.0036 SCFH of seal leakage which was within the acceptance criteria for this test.The use of RTV-102 was not documented on applicable drawings;therefore, the use of this material should have required a design change to implement the addition of the RTV to the 0-rings.On May 16@1993'fter the drywell head was instal)ed and leak rate tested, a Design Change Notice (DCN)was processed to justify the use of RTV-102 to augment the sealing characteristics of the 0-rings.However, the engineering evaluation for the DCN failed to identify that excessive RTV would be forced out of the 0-ring groove upon compression of the 0-rings by the head flange.This amount would have been sufficient to obstruct the LLRT test volume.

NRC FQDI 366A (5-92)U.S.NUCLEAR REGULATORY COB(I SSION LICENSEE EVENT REPORT TEXT CONTINUATION APPROVED BY (NB NO.3150-0104 EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS.FORIIARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEHENT BRANCH (MNBB 7714)~U.S.NUCLEAR REGULATORY COMMISSION, IIASHINGTON, DC 20555-0001, AND TO THE PAPERNORK REDUCTION PROJECT (3150-0104)

~OFFICE OF MANAGEHENT AND BUDGET~MASHINGTON DC 20503 FACILITY-NAME (1)Browns Ferry Unit 2 DocKET ROBER (2)05000260 LER NUMBER (6)YEAR SEQUENTIAL NUMBER 93 011 REVISION NUMBER 00 PAGE (3)3 of 8 TEXT If more s ce is r ired use additional co ies of NRC Form 366A (17)BFN Technical Specification 4.7.A requires that a LLRT of primary containment penetrations be performed once per operating cycle.The LLRT performed on the drywell head during the last refueling outage was determined to be invalid.Thus, this event is reportable pursuant to 10 CFR 50.73 (a)(2)(i)(B) due to a condition prohibited, by the BFN Technical Specifications.

The event date of this report is May 25, 1993 when Unit 2 was restarted with an invalid LLRT.The discovery date of this event was October 2, 1994, which initiated the 30-day timeclock for reportability purposes.As described further in Section IV of this report, TVA has not observed any abnormal leakage from the drywell 0-rings during the past operating cycle.An Incident Investigation (II)of this event is in progress.B.Ino erable Structures Com onents or S stems that Contributed to the EventI None Co Dates and A roximate Times of Ma'or Occurrences:

May 13, 1993 The drywell head LLRT failed three times.May 14, 1993 May 15, 1993 May 25, 1993 October 2, 1994 The drywell head was lifted, the grooves were cleaned, RTV-102 was placed in the 0-ring grooves, the drywell head was reset, and the bolts were retorqued.

The drywell head, LLRT was performed.

Unit 2 was restarted.

This condition was detected when the drywell'ead was lifted at the start of the next refueling outage.D~Other S stems or Seconda Functions Affected: None.

0 I' NRC FORH 366A (5-92)U.S NUCLEAR REGULATORY CWI SSION LICENSEE EVENT REPORT TEXT CONTINUATION APPROVED BY QGI NO.3150-0104 EXPIRES 5/31/95 ESTINATED BURDEN PER RESPONSE TO COHPLY WITH THIS INFORHATION COLLECTION REQUEST: 50.0 NRS.FORWARD COHHENTS REGARD IHG BURDEN ESTINATE TO THE INFORHATION AND RECORDS HANAGENENT BRANCH (HNBB 7714)~U.S.NUCLEAR REGULATORY COHHISSION, WASHINGTON, DC 20555-0001

'ND TO THE PAPERWORK REDUCTION PROJECT (3'l50-0104), OFFICE OF HANAGEHENT AND BUDGET, WASHINGTON DC 20503 FACILITY MANE (1)Browns Ferry Unit 2 DOCKET NNSER (2)05000260 YEAR 93 LER NOSER (6)SEQUENTIAL NUHBER 011 REVISION NUHBER 00 , PAGE (3)4 of 8 TEXT If more s ce is r uired use edditionsl co ies of NRC Form 366A (17)ED Method of Discove This condition was discovered when the drywell head was being lifted off its lower flange during a scheduled outage after operating cycle 7,.F.0 erator Actionst None'G.Safet S stem Res onses: None ZZZ~CAUSE OF THE EVENT A.Immediate Causes The RTV was applied without an approved procedure, without proper authorization, and was not incorporated into the design prior to installation:"'A'de'Sign change notice was issued without correctly specifying the limit for the amount of RTV applied.Bo Root Cause: The root cause(s)of this event has not yet been determined.

TVA is currently conducting an Incident Investigation (II)of this event.The results of the II will be provided in a supplemental report.ZVo ANALYSIS OF THE EVENT The top portion of the drywell is removable during refueling operations.

The drywell head is connected to the remainder of the drywell via a flange connection held together by 208 bolts.This flange connection is sealed via a double captured seal ring arrangement.

The dual 0-ring configuration and the intermediate leak rate testing tap permits leak rate testing of the drywell head flange seal.As stated previously, an excessive amount of RTV was observed on the lower flange of the drywell head.The RTV was found to be uniformly distributed around the lower flange surface from near the inner radius of the flange across the 0-rings outward past the 0-ring grooves.Examination of the RTV on the lower flange of the drywell head

NRC FORM 366A (5-92)LICENSEE EVENT REPORT TEXT CONTINUATION FACILITY NAME (1)DOCKET NQIBER (2)U S.,NUCLEAR REGULATORY C(MIIISSION PAGE (3)LER NIIQER (6)REVISION NUHBER YEAR SEQUENTIAL NUMBER APPROVED SY (MRI NO 3150-0104 EXPIRES 5/31/95 ESTIHATED BURDEN PER-RESPONSE TO COMPLY MITN THIS INFORHATION COLLECTION REQUEST: 50 0 NRS.FORMARD COHHENTS REGARDING BURDEN EST IHATE TO THE INFORHATION AND RECORDS HAMAGEHENT BRANCH (HMBB 7714), U.S.NUCLEAR REGULATORY COHHISSION, llASMINGTOM, DC 20555-0001, AND TO THE PAPERllORK REDUCTION PROJECT (3150-0104), OFFICE OF HANAGEHENT AND BUDGET, MASNINGTOM DC 20503 Browns Ferry Unit 2 05000260 93 011 00 5 of 8 TEXT If more s ce is r ired use additional co ies of MRC Form 366A (17)indicated that it was adhering tightly to the flange surface.The'LLRT volume between the inner and outer 0-rings was completely filled.Approximately three inches of the inner 0-ring flange groove was empty because the 0-ring had been dislodged and was crushed between the flange surfaces, with a small portion extending from between the flange surfaces into the drywell interior.Examination of the outer 0-ring indicated that it was seated in its associated groove and compressed along the entire circumference of the drywell head flange.Only one 0-ring is required to provide the seal between the upper and lower flange surfaces for the drywell head.Therefore, the drywell head was effectively sealed.Additionally, a calculation was performed to,determine the pressure in the drywell that would'be required to overcome the bolt preload and lift the head.This calculation showed a pressure in excess of twice the design basis accident drywell pressure.No abnormal nitrogen makeup[LK)requirements for drywell inerting were observed during operating cycle 7 (See chart 1 on page 8).The average amount of nitrogen consumed for the first 81 days was less than the amount that was used during operating cycle 6 when the drywell head was sealed without RTV[see chart 2 on page 8).However, the average amount of nitrogen consumed did increase over the remainder of the operating cycle 7.This increase was due to a drywell air compressor problem.If the drywell air compressor problem had not occurred, TVA believes that the nitrogen consumption would have continued to follow the trend of the first 81 days (i.e., less than cycle 6 nitrogen consumption).

During the last two operating cycles, the amount of nitrogen consumed was significantly below the Technical Specifications limit.Based on the examination of the joint flange, and the amount of nitrogen used to maintain the inerting of the drywell during the operating cycle, TVA has determined that an effective seal was in place.Vo CORRECTIVE ACTIONS A.Immediate Corrective Actions: Before reinstalling the drywell head during the Unit 2 Cycle 7 refueling outage, documentation will be provided as to limiting the amount of RTV allowed for the drywell head installation to ensure that it does not interfere with the LLRT.A Problem Evaluation Report (PER)has been initiated and an II is in progress.

HRC FORH 366A (5-92)U.S.N)CLEAR REGULATORY CQBIISSIOH LICENSEE EVENT REPORT TEXT CONTINUATION APPROVED BY (WB HO.3150-0104 EXPIRES 5)31/95 ESTIHATED BURDEN PER RESPONSE TO COHPLY llITH THIS INFORHATION COLLECTION REOUEST: 50.0 NRS.FORIIARD COHHENTS REGARDING BURDEN EST IHATE TO TNE INFORHATI ON AND RECORDS HANAGEHENT BRANCH (HNBB 7714), U.S.NUCLEAR REGULATORY COHMISSION, MASNINGTON, DC 20555-0001

~AND TO THE PAPERlKNK REDUCTION PROJECT (3150-0104), OFFICE'OF HANAGENENT AND BUDGET/NASHINGTON DC 20503 FACILITY HAHE (1)Browns'Ferry Unit 2 DOCKET HWBER (2)05000260 LER HOSER (6)YEAR SEQUENTIAL NUHBER 93 011 REVISION NUHBER 00 PAGE (3)6 of 8 TEXT f more s ce is r ired use additions(co ies of NRC Form 366A (17)B Corrective Actions to Prevent Recurrencec The Unit 2 replacement of the drywell head 0-rings for the Unit 2, Cycle 7 restart will be performed using an approved procedure that addresses the use of RTV.Any further substantial corrective actions that result from the II will be provided in the supplemental report.VI~ADDITIONAL INFORMATION

'A.Failed Com onentsI Bi None Previous LERs on Similar Eventss None VII'ommitments 1.The Unit 2 replacement of the drywell head 0-rings for the Unit 2 Cycle 7 restart will be performed using an approved procedure that addresses the use of RTV.2.Documentation will provide instructions on limiting the amount of RTV allowed for the drywell head installation to ensure that it does not interfere with the LLRT.This corrective action will be completed prior to resetting the drywell head'.3.TVA expects to provide a supplemental report by January 25, 1995.Energy Industry Identification System (EIIS)system and component codes are identified in the text with brackets (e.g.,[XX].

0 NRC FORM'366A (5-92)U.S.WCLEAR REGULATORY CQIIISSIQI APPROVED SY QHI NO.3150-0104 EXPIRES 5/31/95 FACILITY NAIF (1)DOCKET MINGLER (2)LZCENSEE EVENT REPORT TEXT CONTZNUATZON ESTIMATED BURDEN PER RESPONSE TO CQiPLY IIITH THIS INFORMATION COLLECTION REQUEST 50.0 HRS FORMARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORHAT I OH AHD RECORDS MANAGEMENT BRANCH (NHBB 7714), U.S NUCLEAR REGULATORY CQOIISSIONg MASHINGTOH, DC 20555-0001, AND TO THE'APERHORK REDUCTION PROJECT (3150-0')04)

~OFFICE OF MANAGEMENT AND BUDGET/iIASHINGTOM, DC 20503 PAGE (3)LER IRHSER (6)Browne Ferry Unit 2 05000260 YEAR 93 SEQUENTIAL NUMBER 011 REVI SI OH NUMBER 00 7 of 8 TEXT lf more s ce is r ired use additional co ies of MRC Form 366A (17)NlAIN FLANGE 0-RINGS OUTSIDE DRYHELL INSIDE DRYHELL DRYWELL IIEAD FLANGE 0-RING CONFIGURATION 0

NRC FINDI.365A (5-92)U S IN)CLEAR REGLRATORY CtlelISSION LICENSEE EVENT REPORT TEXT CONTINUATZON APPROVED BY tNRI NO 3150-0104 EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE To COHPLY WITH THIS INFORNATION COLLECTION REOUEST: 50.0 HRS.FORWARD COHHENTS REGARDING BURDEN EST I HATE To THE INFORHAT ION AND RECORDS NANAGEHENT

• BRANCH (NNBB 7714)~U.S.NUCLEAR REGULATORY COHHISSION, WASHINGTON, DC 20555-0001

~AND To THE PAPERWORK REDUCTION PROJECT (3150 0104)~OFFICE OF NANAGEHENT AND BQ)GET, WASHINGTON DC 20503 FACILITY WUK (1)Browne Ferry Unit 2 DOCKET NN%ER (2)05000260 YEAR 93 LER IRISER (6)SEQUENTIAL NUHBER Oll REVISION NUHBER 00 PAGE (3)8 of 8 TEXT If more s ce is r ired use additional co les of NRC Form 366A (17)U2CG-U2C7 N2 USE COMPARISON

-CHART I 600 t 500-'400-;4J 300~Lu Q)I 200-.tV z 100 TECH SPEC LIMIT (542 SCFH/DAY)UZC6 and UZC7 N2 AVERAGE USE (SEE CHART 2)0 O N C)A (0 O W CO cv A r)pl DAYS U2CG-U2C7 N2 USE COMPARISON

-CHART 2 120 CI 80.40 z U2C7 N2 USE (Assumed Constant Average)y~UZC6 N2 USE (Actual Average)A ir compressor problems iU2C7),I U2C7 N2 USE (Actual Average)7)OAY 1 IU2C6)=9/I/92 OAY 1 (U2C7)=6/1/93 iV DAYS 4$