05000324/LER-1992-001, Supplemental LER 92-001-01:on 920202,unit Scrammed During Main Turbine Control Valve Testing.Caused by Excessive Cycling of Turbine Control Valves.Hydraulic Accumulators a & B Disassembled

Supplemental LER 92-001-01:on 920202,unit Scrammed During Main Turbine Control Valve Testing.Caused by Excessive Cycling of Turbine Control Valves.Hydraulic Accumulators a & B Disassembled

ML20056H179
Person / Time
Site:	Brunswick
Issue date:	09/02/1993
From:	Mcgowan J, Warren C CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BSEP-93-0137, BSEP-93-137, LER-92-001, LER-92-1, NUDOCS 9309080338
Download: ML20056H179 (5)

LER-2092-001, Supplemental LER 92-001-01:on 920202,unit Scrammed During Main Turbine Control Valve Testing.Caused by Excessive Cycling of Turbine Control Valves.Hydraulic Accumulators a & B Disassembled

Event date:
Report date:
3242092001R00 - NRC Website

text

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FBE227amaT2:CLh"*J:NEDLTIM Carolina Power & Ught Company

%Mciz:nzmaaxn,TmuczTa Brunswick Nuclear Plant P. O. Box 10429 Southport, N.C. 28461-0429 September 3, 1993 FILE: B09-13510C 10CFR50.73 SERIAL: BSEP-93-0137 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 BRUNSWICK NUCLEAR PLANT UNIT 2 DOCKET NO. 50-324 LICENSE NO. DRP-62 SUPPLEMENTAL LICENSEE EVENT REPORT 2-92-001-01 Gentlemen:

In accordance with Title 10 of the Code of Federal Regulations, the enclosed 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, September 1983.

Supplemental Licensee Event Report 2-92-001-01 was mailed en September 1, 1993. Due to the inadvertent omission of the report date on form OMB 3150-0104 please disregard that report and replace it with this supplement.

Very truly yours, M13w C. Warren, P ant Manager Unit 2 Brunswick Nuclear Plant JFM/jfm Enclosure cc: Mr. S. D. Ebneter Mr. P. D. Milano BNP NRC Resident Office 080r+

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NRC FORM 306 U.S. NUCLEAR REGULATORY COWtSSION APPROVED OMB NO. 3150-0104 (5/92) WPIRES: 5/31/95 LST1M Alf D BURDEN AR RTEPONSE TO COMPLY WITH T HIS INF ORV AnDN CD11.lCTIDN REOVtST 50 D HR5 5 05hN ARD LICENSEE EVENT REPORT (LER) COMMus R,GiRDe euRDtN i5num iO ,He i~,ORunON AND Rt CORDS MANAGIM(NT !! RANCH lMNE4B 7714t U $ NUCLi AR fit GULATORY C OMMf55sDN. WA$mNGTON. DC 205% DOO1 ANDTO THE FAPERWORK RE DUCTION PROJf CT (3150 0104L OrnCE OF Mr NAC,lMINT A,ND fluDGET. W ASHilicTON. DC 20503 f AC IWV NAMI 1i DOC k iT NUVE4[ R (2} J%[ (3)

Brunswick Steam Electric Plant, Unit 2 05000324 l 1 of 4 1Ill F .4 <

UNIT 2 SCRIJ4 DURING MAIN TURBINE CONTROL VALVE TESTING f

EVENT DATE (5i LER NUMBER t61 REPORT DATE 17} OTHER FACILITIES INVOLVED (8)

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LICENSEE CONTACT FOR THIS LER (12)

NAMI it'i['PHONf NUMt i R Jeanne F McGowan, Regulatory Compliance Specialist (919) 457-2136 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DrSCRIBED IN THIS REPORT (13) m POni Ante l mr onT ABLE t Auti su u M ct w oN!Ni M Anes tum a ( AL8f SYSTLM COMPONE N T MANJF ACTUkFR

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/ b TF2 - ..mt t ;4C0 rpaces, 2 .e. apprcximatel) fifteen single space t ypewritten lines) (26) t i Jar a:y 9, 19 s , '

ut ; wa< geratir3 at apprcximately 100% steady state power. An

c nc:ater icr .cw electittydraul:c (EH3 fluid pressure was receised. EHC pressure cwings cu*

• re.g t< pr wr rety i t' abcut a power to c1tse #4 turbine control valve (TCV) w:,ch Ic: ac"d t !a EC p r + < ni . E w;n: r .

'n Februar, ., I H2, reactor power was reduced to

qprcx mately ~A M T~J t esting bega During #2 TCV testing, the Centrol Operator (CO) did m:t havt .

> t' reter t re scram log:c for trv 'F: trip (Ieceived as expected) before the 'Al' tz:p gnal wu :ac" ved cam og a reactcr scram. Follcwing the r ea ct c r scram, ECIC aatr , . call 3 : nit l at e d a nf .n3 ect ed . EPCl initiated but level recovered prior to iniectien.

T% cause cf this er"nt war nit 2 oyn t rapped in the Turbira Control Valve Fast Closure (TCVFC) 12 9 c: cat.ng 2 pretsute pel t ar t at icn m 3 the TCVFC Frersure Switch #1 (2-EHC-PSL-1756) causing it t o tr;p The gas s

• i an EHC accun ulat or was f ound t m be salid with EHC f luid. It is bel 2esed that a seal failure cf t h. accumulatcro arsociat ed with t his line allowed nitrogen t o ent er t h< EHC flu d. ~ne accrul at er seal failure is attributed to excessive cycling which began atter ir talle icm cf t he part ial are conve rsion modif ication during the last Unit 2 refueling outa ? '3e; 3 r a l Elm tr:c and Carolina Fowor & Light are investigating the cause and developing a

! plan fer arr ect A ve actic t til rplementation of the corrective action, reactor power was j ' enced 'O dnt: ore the EHF fyrtom crrillatirns. The EH2 accumulatorr. were rebuilt. During t he I m. 1-cevary +he CC was unaria to :ere* the 'A' Eeactor Feed Pump (EFP) t urbine due t o a failed ie et :% ay c eli 2 n t he F TP I t ' - logic. The 'IP RFP also had a bound pcmp shaft assembly due t o failure "f wer r: JT cap screwr The rafety significance of this event war minimal. Safety ryt t rw f r_* .- -d as esigmd. U-th I cimilar event was repcrted :n H R 017 (SCPJN during TCV /Tr' tes .ng du to p:oceduta] c d rwitch problems).

T' ause cl as s i f : cat ic.n fc: t his event per tr.a criteria cf NUE E ;- 1;22 is Design, Manufacturing, C nstrn~t cn/I <tallataen.

63RC FORM 366A U. S. FJUCLEAA REGULATORY COMMISSION APPROtfED OMB NO. 3150-0104 (5/92) EXPlRES: 5/31/95 ESTIMATED BURDEN PER RISPONSE TO COMPL Y WTTH TNS INFORMATION COLLECTION 84EQUEST: 50 0 HRS. FORWARC LICENSEE EVENT REPORT (LER) COMMcNT3 rec,ARo,No ,URnEN EsT,M A1E T O TNE ,N ORM AT,0N ANo TEXT CONTINUATION RECORDS MANAGEMENT BRANCH (MNBB 7714), U .S . WLEAR REGULATORY COMMISSION. WA9ttNGTON. DC20555-000L AND TO THE PAPERWORK REDUCTION PROJE CT (3160 0104). OFHCE OF MANAGEMENT AND BUDGET, WA$HINGTON, DC 20503.

FACILITY NAME (1) DOOKET NUMBER W LER NUMBER IE9 PAGE (3)

$FOUENTIAL REVISION Brunswick Steam Electric Plant ""'" """""

05000324 2 of 4 Unit 2 92 - 001 - 01 1

TEXT Uf more space os required, use additwat NRC form 366A %I (1h I 1

TITLE l l

UNIT 2 SCRAM DURING MAIN TURBINE CONTROL VALVE TESTING l

l INITIAL CONDITIONS  !

On February 1, 1992, Unit 2 was operating at 87% power. Periodic Test (PT) 4 0. 2. 5, Turbine Control Valve and Extraction Steam Stop Valve Testing, was scheduled to be performed during the shift. On February 2, 1992, at 0313 hours0.00362 days <br />0.0869 hours <br />5.175265e-4 weeks <br />1.190965e-4 months <br />, the Control Operator commenced a power reduction to 00% to perform the weekly valve testing. A briefing was held and at 0345  !

hours the valve testing commenced. The High Pressure Coolant Injection System (HPCI) and '

the Reactor Core Isolation Cooling System (RCIC) were operable and in standby.

EVENT NARRATIVE On January 29, 1992, Unit 2 was operating at approximately 100% power. An annunciator for low EHC 11uid pressure was received. EHC pressure swings occurred and reactor power was reduced to approximately 85% to close #4 TCV which reduced the EHC pressure swings.

The 4 TCVs had experienced oscillations during power ascension to 100% after the Unit 2 refueling outage. A plant modification had been installed to convert the Unit 2 High Pressure (HP) turbine from a full arc to a partial arc valve admission. During the investigation of the ccntrol valve oscillations, the lead / lag potentiometers in the pressure regulator control loops were found at zero (0). The system was aligned after installation of the Partial Arc Conversion Modification. Per the lineup instructions, lead / lag potentiometers are moved to zero (0) from their operational settings at the start of pressure control adjustments. Upon completion of the pressure control adjustments they are to be returned to their "as-found" settings. The lead / lag potentiometers were not returned to the required "as-found" positions upon completion of the pressure control section of the line-up instructions. Unit 2 was shutdown to correct the potentiometer settings. The unit was returned to 100% power after the adjustments were made.

Af ter restart, the valves continued to oscillate causing steam line pressure swings. The EHC pressure regulators began to alternately control the valve demand signals due to the pressure swings. Reactor power was reduced due to scram potential of the unstable pressure regulators. Based on the manufacturers recommendations, a bias adjustment was made to separate the control functions of the pressure regulators, allowing the backup pressure I regulator to control the valve demand signals. This did provide better valve stability: j h w ver, after approximately seven days of 100% power operation the valve oscillations j becaue larger and the EHC hydraulic pressure was observed to be moving greater than 150 )

psi. Reactor power was reduced to 85% while a root cause determination was made. Based  ;

on a recommendation from the manufacturer, the hydraulic accumulators were tested and it  !

was discovered that leakage past the seals had resulted in the accumulators being filled j with EHC fluid. The reduction in mechanical dampening from the leakage into the gas end of the accumulators was corrected by depressurizing the gas end and recharging it to the correct p1 tssure in accordance with PT 33.1, EHC Accumulator Precharge Check, on February 1, 1992. The unit was expected to return to 100% power after performing control valve testing to assure correct mechanical response of the accumulators.

, On February 2, 1992, at 0313 hours0.00362 days <br />0.0869 hours <br />5.175265e-4 weeks <br />1.190965e-4 months <br />, the Control Operator commenced reactor power reduction to 80% to perform PT 40.2.5, Turbine Control Valve and Extraction Steam Stop Valve Testing.

A briefing was held and at 0345 hours0.00399 days <br />0.0958 hours <br />5.704365e-4 weeks <br />1.312725e-4 months <br />. the valve testing commenced. At 0509 hours0.00589 days <br />0.141 hours <br />8.416005e-4 weeks <br />1.936745e-4 months <br />, while

I r---- -= . j NRC FORM 366A U. S. f60 CLEAR REGULATORY COMNtSSIOM APPROVED OMB NO. 3150-0104 j

{5/92)

EXP!RES: 5/31/9b

( STIM AT E D BURDEN PE R RE SPONSE TO COMPL Y WITH THIS INf DHMATION COLLE CTION RIOUf 5T: f.O.0 HRS F ORW ARD  !

. LICENSEE EVENT REPORT (LER) COMME Nis RtGAnn,NG BURotN tsTiMATr TO THc ,NroRiaAT,oN ANo TEXT CONTINUATION RICORDS MWAGEMINT BRWCH NNbB M O. U S. NUCLI AR REGULATORY COMMISSION. WASHINGTON, DC 20f 55 0001. AND TO i THE P APf. RWORK Rf, DUCTION PROJECT 0160 0100 Of rice Of l i

MANAGEMLNT AND BUDGLT, WALHINGTON, DC 20t.03 I

f ACPJTY NAME M) DOCKET NUMBER G) LE R NUMBER (C) PACE (3)

LIQUINTIAL REVISION Brunswick Steam Electric Plant " " " * "

05000324 3 of 4 Unit 2 92 - 001 - 01  ;

TVKT Uf mue space is requeed. use addaronalIVRC form 366Ks! O h testing the #2 TCV, a reactor scram occurred due to the actuation of an EHC Reactor ,

Protection System (RPS) pressure switch (2-EHC-PSL-1756). Following the reactor scram, l ECIC automatically initiated and injected. HPCI initiated but level recovered prior to j allowing injection.

Preliminary investigation into this event revealed that the accumulator piston seals were  !

subjected to excessive cyclic wear due to the hydraulic occillations in the EHC system.

The EHC Accumulators were rebuilt and placed back in cervice. The unit was returned to 82% power and evaluations of the accumulator seal failure continued. The unit was to (

remain at 82% power to minimize control valve oscillations and until the root cause could l be determined and the corrective acticna implemented. The unit remained at 82% power until both undts were shutdown in April due to Diesel Generator Building seismic concerns.  ;

i CAUSE OF EVENT The cause of the event was the excessive cycling of the turbine control valves. This caused the failure of the EHC Accumulator seals. The seal failure allowed nitrogen into the EHC lines, causing a pressure perturbation on the TCVFC Pressure Switch No. 1 (2-EHC-PSL-1756). This perturbation caus M the opening of the TCVFC Pressure Switch No.1 during testing of TCV #2. Extensive benc;. 7 sting of the TCVFC Pressure Switch No. 1 showed no 4 defects or unusual sensitivity to pressure perturbations. It was concluded that the pressure seen by the switch did drop into the trip setpoint range and the switch did react to that pressure by opening.

Following the scram on February 2, 1992, both of the EHC Accumulators were disassembled.

Removal of the piston revealed that the piston seal in both accumulators had f ailed. Both ,

seals had significant deterioration as indicated by excessive pitting. The f ailure of the seu s were due to the precoure oscillations during the period from January 5 to February 2, 1992. This was due to the instability experienced in the EHC system pressure regulator ,

as seen after the conversicn from full arc-1 admission to partial arc-2 admission. l Initially, hydraulic pressure oscillations in the order of apprcximately 70-100 psi were a seen. After electrcnic adjustment to the pressure regulator, hydraulic pressure ,

oscillations of approximately 25-50 psi were seen. The frequency range of these oscillations was 0.5 - 1.0 Hz. Typical hydraulic accumulator piston seals have a life of  ;

I - 2 x 10' cycles. Based on the time period and frequency of the hydraulic pressure oscillations, the EHC accumulators experienced in excess of 1 x 10' cycles.

4 As part of the Partial Arc Conversion Modification, new valve curves were used to pennit  !

operation f or partial are - 2 admission. The investigation of the failed EHC Accumulator j seals revealed that the valve curves were designed f or a reactor output of 105% . The power i uprate modification on the reactor had not been performed and the reactor output was 100%

rather than 105%. This caused the new valve curves to be inaccurate for the present ,

reactor operation. The resulting turbine instability caused turbine control valve oscillations and the EHC Ac.;umulator seal failure.

i COPRFCTIVE ACTIONS <

Corrective actions included the following: ,

l

1. The EHC hydraulic accumulators A and B were disassembled. The inner cylinder walls were checked for nicks and light scoring and any indications were removed with crocus cloth. All *O* rings, teflon rings, and piston seals were replaced. The

i lNRC FORM 366A U. S. NUCLEAR REGULATORY COISMISSIORI APPROVED OMB NO. 3150-0104 (5/92) EXPIRES: 5/31/95

, F STIM ATID 11URDEN PLA RfLPONSE TO COMPL Y WITH THIS INFORMATION COLLICTION RtOUEST: 50.0 HRS. F ORWARD

' LICENSEE EVENT REPO T L g r COMMINTS Rt GARDJNG BURDEN tSTIM ATE TO THE INF ORM A1 ION AND TEXT CONTINUATION RECORDS MANAGEMENT BRANCH (MNt!B 77141 US NUCLE AR

, REGULATORY COMMISSION, W ASHINGTON, DC 20b05 0001. AND TO THE PAPE RWORK REDUCT ION PROJECT (3160 01041, Of f sCE OF M ANAGI ME NT AND HUDGEI. WASHINGTON DC 20503.

i FACILITY NAME (1) DOCKET NUMBER (21 LER NUMBER 16) PAGE (3)

SL OUfNTIAL R[ VISION Brunswick Steam Electric Plant """"'" " " '"

05000324 4 of 4 Unit 2 92 - 001 - 01 TEXT W mcne space as re.7uked, use addmonalNRC form 366A's) (17) accumulators were reassen. bled and placed back in operation.

2. The accumulator testing frequency was increased to verify accumulator integrity.

l The increased frequency continued until the unit was shutdown in April, 1992.

3. Reactor power remained at a lower level to prevent the opening of TCv #4 which resulted in stable unit operation and eliminated abnormal EHC pressure oscillations.

The reduced power level continued until the unit was shutdown in April, 1992.

4. The causes f or errors made during the design and installation phases of the partial arc conversion modification were studied. Lessons learned were incorporated into redesign and repair activity. Af ter the April 1992 shutdown, the decision was made by plant management to return the Turbine to partial arc - 3 admission. This decision was based on the Stable operation of the unit during the first ten years when the unit was in partial arc -3 admission turbina operation. The modification was performed and the unit was able to achieve 100% operation without the previous oscillations experienced in partial arc - 2 admission.

SAFETY ASSESSMENT The saf ety significance of this event was minimal . Safety systems functioned as designed.

HPCI and RCIC initiated as required with RCIC injecting to restore vessel inventory. HPCI did not inject due to level recovery prior to the HPCI injection valve receiving an open signal.

PEEVIOUS SIMILAR EVENTS A previous similar event was reported in LER 1-90-017, Scram during TCV/TSV testing due to procedural and switch problems.

EIIS COMPONENT IDENTIFICATION System / Component EIIS Code ELECTROHYDRAULIC SYSTEM TG ACCUMULisTOR / SEAL ACC/ SEAL 3

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