05000499/LER-1998-001, :on 980115,failure to Meet TS Requirements for Inoperable Sdg 21 Noted.Caused by Failure of U3 Operational Amplifier in DG Voltage Regulator Circuit.Replaced Voltage Regulator Board for Sdg 21 & Complete Post Maint Test
| ML20203A988 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 02/16/1998 |
| From: | Head S HOUSTON LIGHTING & POWER CO. |
| To: | |
| Shared Package | |
| ML20203A970 | List: |
| References | |
| LER-98-001, LER-98-1, NUDOCS 9802240180 | |
| Download: ML20203A988 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(1) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4991998001R00 - NRC Website | |
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NRC FORM'366 U.S. NUCLEAR RELULATsRY CLCSION APPROVED B Y OMC NO. 31604)104 (445)
EXPIRES 04/30/98 N
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THE PAPERWORK REDUCTIO. WA NOTO ttPROJECT TidlLfrV NAl4E (t)
DOCKET NUnisoih (t)
PAGE (3)
South Texas, Unit 2 05000 499 1 OF4 TITLE top Failure to nect Technical Specification requirenrnts for inoperable Standby Diesel Generator 21 EVENT DATE (6 LER NUMBER (6)
REPORT DATE (7) l OTHER FACILITIES INVOLVFD {0}TBER MONTH DAY YEAR YEAR LE ) N1 AL R
M6NTR DAY YEAR f ACiUTV NAME tga DOCKET NU 05000 01 15 98 98 001 00 02 16 98
' Ac'uiv hAME ooCxu NUMet R 05000 OPERhflNO l
THIS REPORT 18 SUBMITIED PUIItijANT IC THE REQUI tEMENTS OF 10 CFR 9: (Check one or more) (11)
MODE (9) 202201(b) 202203(a)(2 (v)
X 50.73(a)(2)(1) 50.73(a)(2)(viii)
POWER l(X) 20J203(a)(1) 202203(a)(3)(1) 50.73(a)(2)(ll) 50.73(a)(2)(x)
LEVEL (10) 202203(a)(2)(1) 202203(a)(3)(61) 50.73(a)(2)(iii) 73.71 202203(a)(2)(ll) 20.2203(a)(4) 50.73(a)(2)(lv)
OTHER
- u
{
gy 202203(a)(2)(3) 50.36(c)(1) 50.73(a)(2)(v) gecg gbelow or s
20.2203(a)(2)(lv) 50.36(c)(2) 50.73(a)(2)(vii)
LICEN1 EE CONTACT FOR THtt LEll112)
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NAw I LLEPHONE NUMitrR (incluos Area Code)
Scott M. Ilead - Licensing Su wrvisor (512)972-7136 COMPLETE ONE LINE FoR EACH COMPONENT F AILURE DE BCPIBED IN THIS REPORT (13)
'%sE sYtIEM COMPONENT MANUFACTURER REPORTABLE
CAUSE
SYSTEM COMPONENT MANVrACTIIRER I REPORTABLE TO NPROS TO NPRDS l
X EK AMP l'076 N
7,A w
j SUPPLEMENTAL REPORT EXPLCTED (14)
EXP ECTED MONTH DAY YEAR SUsMsSSION YES DATE (15)
X NO (if yes, comnieta EXPECTED SUBMISSION DATE).
AB BTRACT (Limit to 1400 spaces, t e., approximately 15 single-spaced typewntten innes) (16)
On January 15,1998, Unit 2 was in Mode I ret 100% power. On January 15,1998, the results of a failure analysis were received regarding abnormal voltage regulation indications noted for Standby Diesel Generator 21 during previous testing. Per Nuclear Regulatory Commission Regulatory Guide 1.9, it was determined that a condition had existed that could have resulted in a start failure if a dicsci start demand had occurred. A conservative decision was made Standby Diesel G2nerator 21 inoperable during the time that this condition existed. During part of the time that the diesel was conservatively considered to be inoperable, the required actions of Technical Specification 3.8.1.1 had not been performed. The period ofinoperability when Technical Specification actions were not taken staned at 0106 hours0.00123 days <br />0.0294 hours <br />1.752645e-4 weeks <br />4.0333e-5 months <br /> on December 28,1997 and ended at 1947 hours0.0225 days <br />0.541 hours <br />0.00322 weeks <br />7.408335e-4 months <br /> on December 30,1997 when the diesel was removed from senice for troubleshooting. Standby Diesel Generator 21 was returne(' to operable status on January 1,1998, at 2320 hours0.0269 days <br />0.644 hours <br />0.00384 weeks <br />8.8276e-4 months <br />. The cause of this occurrence was the failure of the U3 operational amplifier in the diesel generator vohage regulator circuit.
Corrective actions included replxing the voltage regulator board for Standby Diesel Generator 21 and completion of a satisfactory post maintenance test and surveillmee test.
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TEXT CONTINUATION FACILITY NAME 01 DOCKET LER NUMBER {6)
PAGE (3)
South Texas,' Unit 2 05000 499 T$e?
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2 OF4 98 001 00 TEXT tif more space is required, use additional copies of NRC Form 366A) (17)
DESCRIL'110RDEEYENT:
On January 15,1998, Unit 2 was in Mode I at 100% power. On January 15,1998, the results of a failure analysis were received regarding abnornal voltage regulation indications noted for Standby Dksel Generator 21 during previous testing. Per Nuclear Regulatory Commission Regulatory Guide 1.9, it was deternuned that a condition had existed that could have resuhed in a start failure if a diesel start.imand had occurred. A conservative decision was nude to consider Standby Diesel Generator 21 inoperable during the tinr that this condition existed. During pait of the line that the diesel was conservatively considered to be inoperable, the required actions of Technical Specification 3.8.1.1 had not been performed.
During surveillance testing perfornrd on December 27,1997, abnormal vohage regulation symptoms were obsened and diagnosed as an indication problem. Other conditions regarding perfornunce of Standby Diesel Generator 21 were normal and surveillance testing acceptance criteria were met. On December 30, 1997, Standby Diesel i
Generator 21 was renoved from service to troubleshoot the cause of the observed indication abnormalities. Static checks revealed some loose fuse to fuse clip connections serving the metering circuit; with higher than expected resistance readings. This condition was corrected and the diesel was started for a post maintenance test on December 31,1997. During the post maintenwcc test, abnormal indication symptcms were again obsen'ed but were much nore pronounced than those observed on December 27,1997. Analysis determined that the observed cenditions were p.ely due to vohage regulator control problems. The vohage regulator and instantaneous preposition boaid were considered the likely suspect components and were replaced.
Following replacenrnt of the suspect conponents, Standby Diesel Generator 21 perfomed satisfactorily during subsequent board alignments and during post maintenance testing. Surveillance testing was completed satisfactorily and Standby Diesel Generator 21 was declared operable at 2320 hours0.0269 days <br />0.644 hours <br />0.00384 weeks <br />8.8276e-4 months <br /> on January 1,1998. The operability of Standby Diesel Generators 22 and 23 was verified to denenstrate that a comnen nude failure did not exist.
A failure analysis was perforned on the Standby Diesel Generator 21 vohage regulator and instantaneous preposition board. The results determined that operational amplifier U3 on the vohage regulator board had failed with all pins open circuited. The operational amplifier U3 provides the firing signal that turns on one phase of the three-phase rectifier that provides excitation current to the rotor field of the generator. Since the diesel generator is self-excited, the failure of this phase of the regulator woald cause a drop in one phase of the generator output voltage. This drop in one phase of the output voltage was one of the symptoms observed.
The failed operational amplifier U3 degraded Standby Diesel Generator 21's vohage regulation capability in the enrrgocy nude. This condition prevented Standby Diesel Generator 21 from fulfilling its design safety function. A consenative decision was nude that the vohage regulator control malfunction could have resuhed in the failure of the Standby Diesel Generator to start in response to an Enrrgency Mode start signal anytime after the last successful surveillance test conducted on December 27,1997. Therefore, the period ofinoperability was determined to start at 01% hours on December 28,1997, which was the conclusion of the last satisfactory surveillance test. Standby Diesel Generator 21 was inoperable for approximately 118 hours0.00137 days <br />0.0328 hours <br />1.951058e-4 weeks <br />4.4899e-5 months <br />. From 0106 hours0.00123 days <br />0.0294 hours <br />1.752645e-4 weeks <br />4.0333e-5 months <br /> on December 28,1997 until the es\\wp\\nl\\ntc-ap\\lera98\\0082. doc stb 30512 3 0
wRp sitwa mA U.S. NUCLEAH RECULA107.Y COMDSSION 14 H)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME on DOCKET LER NUMBER [0)
.PAGE01 South Texas, Unit 2 05000 499
",RMY M$
3 OF4 98 001 00 TEXT tllmore space is required, use additional copies of NRC Form J66A) (l7)
. DESCRIPIlotLODiVENT (CONTINUED):
diesel was taken out of service at 1947 hours0.0225 days <br />0.541 hours <br />0.00322 weeks <br />7.408335e-4 months <br /> on December 30,1997 for troubleshooting, tne required actions c r Technical Specificatkm 3.8.1.1 had not been perforned.
This occurrence is classified as a Valid Failure of Standby Diesel Generator 21. Including this Valid Failure, there have teen 3 Valid Failures of Standby Diesel Generator 21 in the last 20 Valid Tests,3 Valid Failures in the last 50 Valid Tests, and 3 Valid Failures in the last 100 Valid Tests. During this period, Standby Diesel Generator 21 suncillance testing was already at increased frequency since a Valid Failure that occurred on November 11,1997, and remained on an increased frequency of at least weekly in accordance with tie South Texas Pro.iect Technical Spccificatic,ns. The 3 Valid Failures of Standby Diesel Generator 21 have been determined to be unrelated.
Currently, Standby Diesel Generator 21 has returned to a normal surveillance test frequency of at least once every 31 days.
A review of equipnent history did not indicate any other occurrences regarding Standby Diesel Generator failures at the South Texas Project attributed to malfunctioning vohage regulator operational amplifiers. A review of the Equipnent Performance and Infonnation Exchange System did not reveal any problems experienced at other plants attributed to the type of failure reponed in this occuiTence.
CAUSFm0F EVENT:
0 The cause of this occurrence was the failure of the U3 operational amplifier in the diesel generator voltage regulator circuit.
ANAIJSIS_OF EVENT:
Faihire to nect the requirrnrnts of Technical Specifications is reponable pursuant to 10CFR50.73 (a)(2)(i)(B).
The S:andby Diesel Generators are part of the Class IE 4.16kV AC Power System. The Class IE 4.16kV AC Power System is composed of three trains designed to provide a reliable source of power to safety-related equipruent essential to all modes of plant operation including emergency shutdown and accident mitigation following any design basis event. Upon loss of offsite power, each of the three SDGs start automatically and supply backup power to their associated 4.16 kV buses. Two trains of Standby Diesel Generators will provide safe shutdown capability and mitigate the South Texas Project analyzed design basis events. Standby Diesel
' Generators 22 and 23 remained operable during this occurrence. There were no adverse safety or radiological consequences from this event.
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NRC %AM 364A H 95)
U.S. NUCLEAR RE;ULATO3Y COZMESION LICEBISEE EVEbrF REPORT (LER)
TEXT CONTINUATION
. FACILITY NAME (1)
DOCKET LER NUMBER [6)
PAGE (3)
SouthTexas, Unit 2 05000 499
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"fJAP "17f$
4 OF4 98 001 00 TEXT (If more spac e is required, use additional copies of NRC Form 366A) (17)
CORRECTIVE ACTIONS
1.
Tic voltage regulator tuard for Standby Diesel Generator 21 was replaced.
2.
A satisfactory post maintenance test and surveillance test was completed for Standby Diesel Generator 21.
ADDIT 10NALJb'EORhMT10N:
l A component failure analysis of the operational amplifier U3 and funher review ofindustry information is planned.
The Standby Diesel Generator is a Cooper Bessenrr nudel KSV-20 engine rated at 5500KW. Tir voltage regulator is an NEl Parson Peebles Electric Products nxxlel 7212400100. The operational amplifier U3 is a RCA nudelCA3094AE.
No Licensee Event Repons have been submitted in the last two years by the South Texas Project to the Nucla r a
Regulatory Commission regarding failure to nret Technical Specifration 3.8.1.1 for an inoperable Standby Diesel Generator due to a conqunent failure.
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