ML17348A276

LER 89-020-01:on 891223,reactor Trip Occurred Due to Closure of MSIV 4A.Caused by Corroded Terminal Board Installed in Incompatible Svc Environ.Procedures Revised to Improve Installation of boxes.W/900531 Ltr

ML17348A276
Person / Time
Site:	Turkey Point
Issue date:	05/31/1990
From:	HARRIS K N, POWELL D R FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-90-200, LER-89-020, LER-89-20, NUDOCS 9006120016
Download: ML17348A276 (6)

Text

ACCELERATED DISTRIBUTION DEMONSTPATION SYSTEM i t REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)ACCESSION NBR:9006120016 DOC.DATE: 90/05/31 NOTARIZED:

NO , DOCKET FACIL:50-250 Turkey Point Plant, Unit 3, Florida Power and Light C 05000250 AUTH.NAME AUTHOR AFFILIATION POWELL,D.R.

Florida Power&Light, Co.HARRIS,K.N.

Florida Power'Light Co.RECIP.NAME

'RECIPIENT AFFILIATION

SUBJECT:

LER 89-020-01:on 891223,Unit 4 reactor trip&Unit 3 reactor shutdown required by Tech Specs due to corrosion.

W/9 ltr.DISTRIBUTION CODE IE22T COPIES RECEIVED:LTR ENCL SIZE: TITLE: 50.73/50.9 Licensee Event Report (LER), ncident Rpt, etc.NOTES RECIPIENT ID CODE/NAME PD2-2 LA EDISON,G INTERNAL ACNW AEOD/DSP/TPAB DEDRO NRR/DET/EMEB9H3 NRR/DLPQ/LPEB10 NRR/DREP/PRPB11 NRR/DST/SICB 7E NRR/DST/SRXB 8E RES/DSIR/EIB EXTERNAL: EG&G STUART,V.A LPDR NSIC MAYS,G NUDOCS FULL TXT COPIES LTTR ENCL 1 1 1 1 2 2 1 1 1 1 1 1 1 1 2 2 1 1 1 1 1 1 4 4 1 1 1 1 1 1 RECIPIENT ID CODE/NAME PD2-2 PD AEOD/DOA AEOD/ROAB/DSP NRR/DET/ECMB 9H NRR/DLPQ/LHFB11 NRR/DOEA/OEAB11 NRR/DST/SELB 8D-*BST/'S~B8D1 REG LE~02 I LE 01 L ST LOBBY WARD NRC PDR NSIC MURPHYiG A COPIES LTTR, ENCL 1 1 1 1 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE!CONTACT THE DOCUMENT CONTROL DESK, ROOM P 1-37 (EXT.20079)TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 34 ENCL 34 P.O.ox14000,Juno Beach,FL 33408-0420 NAY 3>tS90 L-90-200 10 CFR 50.73 U.S.Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.20555 Gentlemen:

Re: Turkey Point.Units 3 and 4 Dockets No.50-250 and 50-251 Reportable Event: 89-020 Revision 1 Date of Event: December 23, 1989 Unit.4 Reactor Trip and Unit 3 Reactor Shutdown Required by Technical Specifications Due to Corrosion in Electrical Terminal Boxes for Main Steam Isolation Valves The attached licensee Event Report is being submitted pursuant to the requirements of 10 CFR 50.73 to provide supplemental information on the subject event.Very truly yours,<<M J K.N.Harris Vice resident Turkey Point Plant Nuclear KNH/DRP/DWH/rat attachment cc: Stewart E.Ebneter, Regional Administrator, Region ZI, USNRC Senior Resident Inspector, USNRC, Turkey Point Plant~0(~6l200f (s<)00<'~g~DOCK 0500(O~~~ng 8 PDC an FPL Group company pp~

RC Form 345 I9 531 LICENSEE EVENT REPORT (LER)U.S, NUCLEAR REQVLATORY COMMISSIOrt APPROVKD OMS NO,3150-0104 EXPIRES.5/31/SE FACILI'TY NAME (1)DOCKET NVMSER (2)PA E Turkey Point Unit 3 0 s 0 0 025 OioF04 nit 4 Reactor rip n nit eac or u own equire y ec njca pec~'tea sons Due To Corrosion In Electrical Terminal Boxes For Main Steam Isolation Valves EVENT DATE(5)MONTH OAY YEAR YEAR Ppoi SEOVENTIAL HuMEER LER NUMSER (5)R E v ter ore HU ME E te MONTH DAY YEAR REPORT DATE (7)OTHER FACILITIES INVOLVED (~)FACILITY NAMES DOCKET HVMSERISI Turke Point Unit 4 0 s 0 0 02 5 I 0 2 0 3 I 9 0 0 5 0 0 0 OIIE RATINO MODE (5)POWER LEYEL 9 4 20.402(E)20.405(~l(1)(i)20.405(e)(1)IN) 20.405 I~)(1)I ii))20.405 4 I ll I (iv)20.405 (I)I I I (v I 20.405(e)50.35(c)(1)50.35(~l(2)50.73(~)(2)(i)50.73iel(2HII) 50.73(~l(2)(iii)LICENSEE CONTACT FOR THIS LER (12I 50.7Se)(2)(iv) 50.73(e)12)(vl 50.73(e)IS(vill 50.73(e l(2)(viii)(Al 50,73(e)(2)(v(EI (5)50.73(~)(2I(xl 0 THE RKOUIREMEHTS OF 10 CFR (I!IChectr One or more OI the IoriowinPI (11)THIS REPORT IS SVSMITTED PURSUANT T 73,71(E)73.71(cl O'THER ISpeciiyin AOttrect oeiow end in Text, HRc Form JSFAI NAME David R.Powell, Licensing Superintendent TKLEPrrQNK NUMBER AREA CODE 3 05 6-65 59 CDMPLETE ONE LINE FOR EACH COMPONENT FAILURE OESCRISED IN THIS REPORT l13)CAUSE SYSTEM COMPONENT MAHUFAC TVRER EPORTABI.E TO HPROS CAUSE SYSTEM COMPONENT MAHUFAC TURKR EPORTASLK TO NPRDS I,~.@P;,'.

@yy.)n4:%.BLK G080 Y SUPPLEMKNTAL REPORT EXPECTED (14)NO YES Iii yet, comPiere fXFECTfD SUdetiSSIOH Dayfi ASSTRACT ILimit to)400 NwceL I e., eporoximetery ir iteen tinpre torte ty ptrvntNn ir'nni (15)EXPECTED SVSMISSIOH DATE IIS)MONTH DAY YKAR At 2314, on December 23, 1989, with Unit 4 in Mode 1 at 94 percent pow-er, a reactor trip occurred due to closure of the 4A Main Steam Isola-tion Valve (MSIV).The sudden loss of steam flow fr om the 4A steam generator caused an increase in pressure in that steam generator.

The pressure increase caused the steam generator level to"shrink" to the low-low level setpoint of 15 percent.The Auxiliary Feedwater System re-sponded as designed.Corrosion across terminal board contacts supply-ing vital 125 VDC power to one of two 4A MSIV opening solenoid valves caused a fuse to blow.Upon de-energization, the opening solenoid failed to the vent position.This allowed air to bleed from the bottom of the MSIV piston.The MSIV disc dropped down into the steam flow, resulting in rapid closure of the MSIV.The accelerated corrosion rate was due to stray DC leakage currents.Upon inspection of the terminal boards supplying vital 125 VDC power to the opening and closing solenoid valves for the 3A, 3B and 3C MSIVs, corrosion was identified on one of the two terminal boards for each the 3B and 3C MSIVs.The 3B and 3C MSIVs were declared inoperable and Unit 3 entered Technical Specifica-tion (TS)3.0.1 at 2300"on December 24, 1989.The two terminal boards were replaced, the 3B and 3C MSIVs were declared operable, and Unit 3 exited TS 3.0.1 at 0455 on December 25, 1989.HRC Form 355 19 53) 41C S~iin 55¹A 983 LICENSEE EV REPORT{LERI TEXT CONTINUATI V 5 4QC" TAA aiGQLATQIlv CQ4IMI5$IQ4 AnnaQV8C Qu8 VQ 3158~18¹8~n<a85 8 5I 85 SACILITY IIAM¹III OOCKUT IIUM88I¹Ql t81 HUM8811 IUI 5¹QM¹4>>Al.

4 tiV a¹v'5 I Q 4 VUMU¹a SAQ8 151 Turkey Point Unit 3 TE3IT III~Mines is isnvvnIS.Sw sa¹¹nannI HSIC Savin I¹5 I I ITI o 5 o o o 2 5 8 9-0 2 0-0 1 02 OF 0 4 DESCRIPTION OF THE EVENT Unit¹At 2314, on December 23, 1989, with Unit 4 in Mode 1 (Power Operation) at 94 per-cent power, a reactor trip occurred due to cl'osure of the 4A Main Steam Isolation Valve (MSIV)(EIIS:SB, Component:ISV).

The sudden loss of steam flow from the 4A steam generator caused a pressure increase in that steam generator.

The increased pressure resulted in"shrink" of the 4A steam generator level to the low-low level setpoint of 15 percent.The Auxiliary Feedwater System and one Code Safety Valve on the 4A steam generator responded as designed and the Unit was stabilized in Mode 3 (Hot Standby).At 0013, on December 24, 1989, the NRC was notified of the Unit 4 reactor trip in accordance with 10CFR50.72(b)(2)(ii).

Instrument Air is provided to each MSIV through two solenoid valves for opening and maintaining the MSIV open and through two different solenoid valves for clos-ing the MSIV.Vital 125 VDC power is supplied to the opening and closing solen-oid valves.Train A power from one terminal box feeds one opening and one clos-ing solenoid valve for a MSIV.Train B power from another terminal box feeds the other opening and closing, solenoid valve for the same MSIV.An investigation into the unexpected closure of the 4A MSIV revealed corrosion buildup between terminal board contacts in one of the two terminal boxes (EIIS: EJ, Component:JBX) providing 125 VDC vital power to the MSIV opening and closing solenoid valves.The corrosion created a short circuit which, in turn, caused the fuse to an opening solenoid valve to blow.Upon loss of power, the de-ener-gized solenoid valve failed to the vent position, allowing air to bleed from the bottom of the MSIV air piston.The MSIV disc dropped down into the steam flow, resulting in rapid closure of the MSIV.Unit 3 An inspection of the terminal boxes feeding vital 125 VDC power to the 3A, 3B and 3C MSIV opening and closing solenoid valves was conducted on December 24, 1989.Corrosion buildup was found on one terminal board (EIIS:EJ, Component:

BLK)associated with the 3B MSIV and one terminal board associated with the 3C MSIV.Since the operability of the 3B and 3C MSIVs was in question, a decision was made to declare both MSIVs inoperable.

Technical Specificat",ion (TS)3.8.1.b requires the MSIVs to be operable and cap-able of closing in 5 seconds or less.If an inoperable MSIV cannot be restored to an operable status within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, TS 3.8.3 requires the reactor to be shut down in accordance with TS 3.0.1.With more than one MSIV inoperable, TS 3.0.1 is entered at the time inoperability is declared.TS 3.0.1 requires that within one hour action shall be initiated to place the unit(s)in Mode 3 (Hot Standby)within the next six hours.VAC SQAM 588A 4~11 VAC 5wa~A 555 i LICENSEE EV REPORT ILERI TEXT CONTINUATI V 5 VOC'AA AECULAEOAY CQMMI55(QV

>>~4QYEC QVe VQ JIEO OIIIA E t~I+E$4 5I 55 5ACILIYY NAME ll>OOCIIE'Z IIVMEEII IEI LEII IIUMIEII IE>5EOMEVY<AI VVV+CY'5iOV VOM 5~~AOE 13I Turkey Point Unit 3 EE5IE Ill mar 5AAle i5~~.ver AAA~h'AC~IA'51 lltl o so oo 250 8 9-0 0-0 03 o~0 4 At 2300, on December 24, 1989, with Unit 3 operating at 100 percent power, the 3B and 3C MSIVs were declared inoperable.

Unit 3 entered TS 3.0.1 and steps were taken to shut down the unit.Mode 2 (reactor critical with reactor power less than 5 percent)was achieved at approximately 0135 and repair work was ini-tiated.At approximately 0455, on December 25, 1989,.the two affected terminal boards had been replaced, the 3B and 3C MSIVs were declared operable, and Unit 3 exited TS 3.0.1.At 2347, on December 24, 1989, the NRC was notified of the Unit 3 shutdown in accordance with 10CFR50.72(b)(1)(i)(A).

CAUSE OP THE EVENT The root cause for the corroded terminal board was that it was installed in a service environment in which it was not compatible.

The results of the analysis of both the terminal box water inleakage and the terminal board accelerated cor-rosion rate, which caused the blown fuse to an opening solenoid valve for the 4A MSIV, led to the following conclusions:

1.The accelerated corrosion rate experienced on the affected terminal board was due to stray DC leakage currents.This phenomenon is created when a terminal board is continuously energized in a humid environment.

This corrosion aggravated an acceptable but weak.terminal board which caused a fault path through the terminal barrier between the positive and nega-tive leads supplying a 4A MSIV opening solenoid valve.2.Weep holes or lack of weep holes did not have an effect on the corrosion process.Terminal board corrosion under electrolytic conditions can occur as likely with or without weep holes.ANALYSIS OP THE EVENT The MSIVs are 26 inch air operated isolation valves.These full flow valves are held open against spring pressure by air from the plant Instrument Air System.The air pressure must overcome the weight of the valve disc and spring tension to hold the valve open.The MSIV disc opens into the steam flow such that steam flow acts to close and seat the.valve.Loss of vital 125 VDC power to an opening solenoid valve caused it to fail in the vent position.This allowed air to bleed from the bottom of the MSIV pis-ton.The MSIV disc dropped into the steam flow, resulting in rapid closure of the MSIV.The sudden loss of steam flow from the 4A steam generator caused an increase in pressure in that steam generator.

The pressure increas'e resulted in"shrink" of steam generator level to the low-low level setpoint of 15 percent.The Auxiliary Feedwater System and one Code Safety Valve on the 4A steam gener-ator responded as designed and the Unit was stabilized in Mode 3 (Hot Standby).The health and safety of the public were not affected by this event.VAC 50AM 55EA A Oll 4AC Iowan SAAA 9 9)'ICENSEE E T REPORT (LER)TEXT CONTINUATI V S 4>CCEAA AEGUCATGA4 COMMISS~O4 A~ioOV EO OMS 4O PS-GIGA EI~~IIES 9)I ES 9ACILITY NAME III OOCKET IIVMIEA Ill 4E A A LEII IIVMIEII I~I$9 G II l 4 T>A I, 4VV TV'$%4 4V4l 9 4 PAGE ISI Turke Point Unit 3 TEXT Ill~IAAF e teOvwed.vM Oarit~IVIIC~BI'Il llll o s o o o 5 8 9 020 0 104 or 0 4 CORRECTIVE ACTIOIS 1.FPL engineering design procedures (Quality Instructions) will be evaluated and strengthened where appropriate to reduce the probability of corrosion problems associated with electrical component applications in the future.This action will be completed by August 15, 1990.2.Terminal boards in each of the two terminal boxes supplying vi.tal 125 VDC power to the opening and closing solenoid valves for the Unit 3 and Unit 4 MSIVs have been replaced with Raychem splices.Weep holes were added to these terminal boxes to prevent potential water accumulation.

3.Walkdowns of plant areas outside the containment buildings have been per-formed to inspect terminal boxes in areas subJect to potential moisture intrusion.

4.Other terminal boards have been identified as being susceptible to stray DC current leakage corrosion.

These terminal boards are being inspected on a periodic basis.Replacement of the terminal boards with Raychem splices or application of a moisture resistant chemical coating to the ter-minal boards will be performed, if required, to relax the periodic inspect-ion requirements.

" 5.Terminal boxes have been identified for which weep holes are desirable.

Weep holes will be drilled in these terminal boxes by August 15, 1990.6.Procedures are being revised, as necessary, to improve the inspection and installation of terminal boxes.This action will be completed by July 27, 1990.ADDITIOHAL INFORMATION The terminal boards are General Electric Co.Model EB25.No similar Licensee Event Reports have been issued for Turkey Point Units 3 or 4.VIIC 9OIIM SAAA'A~1l