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LER 93-012-00:on 930607,noted That HPCS Initiation Signal Resulted in Auto Start of Div 3 DG & ESW Sys.Caused by Failure of Div 3 Reserve Battery Charger.Procedures Used for Insp & Maint of Battery Being modified.W/930707 Ltr
	ML20045G217
Person / Time
Site:	Perry
Issue date:	07/07/1993
From:	Routzahan L, Stratman R; CENTERIOR ENERGY
To:	; NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
	LER-93-012, LER-93-12, PY-CEI-NRR-1674, NUDOCS 9307130057
	Download: ML20045G217 (7)
	v • d • e

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CENTERi??R ENERGY PERRY NUCLEAR POWER PLANT Maif Address-.

O. BOX 97 Ro M A h ahan

- 10 CENTER ROAD PERRY, OHIO 44081 VICE PRESIDENT NUCLEAR PERRY, OHIO 44081 (216) 259-3737 July 7, 1993 PY-CEI/NRR-1674 L U.S. Nuclear Regulatory Commission Document Control Desk Vashington, D.C. 20555 Perry Nuclear Power Plant Docket No. 50 440 LER 93-012

Dear Sir:

Enclosed is Licensee Event Report 93-012 for the Perry Nuclear Power Plant.

Sincerely, !

f-cW s fg Robert A. StrAtman RAS:LKRtss

Enclosure:

LER 93-012 cc: NRC Project Manager l NRC Resident Inspector ;

NRC Region III i l

'i 120049 :

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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 f5 92i '

EXPIRES 5/31/95 ESilMATED BURDEN PER RESPONFE TO COMPLY WITH 1HiS INFORMATION CCMECTION REQUESf; 50 0 HRS. I'OHWARD LICENSEE EVENT REPORT (LER) COuutNTs ntoARDiNG auRoEN EsTiuiTt TO THc inrOiwiATiON AND RECORDS MANAGEMF NT BRANCH (MN8B 7718. U.S. MA: LEAR REGULATOriY COMMtSSiON, W ASHINGTON, DC 205550001, AND TO THE FAPEHWORK REDUCTION PROJECT (3150 0104), OFTICE OF (See reverse for required numtier of digits / characters for each block) MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

F ACILITY NAME {1) DOCKET NUMBER (2) PAGE (3)

Perry Nuclear Powr Plant, Unit 1 05000 440 1 OF 6 TITLE (4)

Voltage Fluctuations in Battery Charger Output Cause High Pressure Core Spray Actuation EVENT DATE (5) LER NUMBER (6'. REPORT NUMBER (7) OTHER FACILITIES INVOLVED (8)

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MCWTH DAV YEAR YEAR MONTH DAY YEAR Nuuw n NuweR 05000 F ACidiY NAME DOCKET NUMBER

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06 07 93 93 012 00 07 07 93 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR O (Check one or more) (11)

MODE (9) 1 20 402(b) 20 405(c) X 50 73(a)(2)0v) 73.71(b)

POWER 20 405(aH110) 50.36(c)(1) X 50.73(a)(2)(v) 73.71(c)

LEVEL (10) 082 20 405(a)(1)(n) 50.36(c)(2) 50.73(a)(2)(vn) x 01HER 20 405(a)(1)(m) 50.73(a)(2)h) 50.73(a)(2)(vin)(A) PP'W 'n Abw ct below and in Test, NRC 20.405(a)(1)(m) 50.73(a)(2)Di) 50.73(a)(2)(vni)(B) Form aceA) T.S.

20 405(3)(1)M 50 73(a)(2)(m) 50,73(a)(2)(x) 3/4 3.5.1.q LICENSEE CONTACT FOR THIS LER (12)

AAME TELLPHONE NUMHf H pnchsde Area CorJej

, Linda K. Routzahn, Compliance Engineer Extension 5781 (216) 259-3737 I

COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCdlBED IN THIS REPORT (13) -

cAusE s erM cowOu r l WWi ACTURER CAu$[ $YS TEM COMPONE NT MANUFACTURER O

B FJ BYC P319 N SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MON TH DAY YEAR ns SUBMISSION X NO P m. mmwe o a w o NPM'ssoN DoCi DATE (15)

ABSTRACT (umet to 1400 spaces. i e , apprommately 15 singte-spaced typewntten lines) (16)

On June 7, 1993, receipt of a High Pressure Core Spray (HPCS) in. . tion signal resulted in auto start of the Division 3 Diesel Generator and Emergency Service Water System, followed by High Pressure Core Spray injection with suction ~from the Suppression Pool. The cause of the event was failure of the Division 3 Reserve Battery Charger to maintain stable output voltage. The voltage transient tripped the

. 125 VDC to 120 VAC Topaz inverter, which affected the supply to Division 3 transmitters and the associated output signals. Once level transmitter output signals decreased to indicate vessel level 2, the divisional master trip units provided a HPCS initiation signal. Control Room operators secured the system after confirmation of inadvertent initiation.

The power plant responded to the HPCS Initiation as expected. The reactor power, pressure, and level transients were within the limits of the USAR analysis.

Erratic Reserve Charger output and internal control voltages were noted during subsequent testing. All charger components which were considered capable of causing the noted malfunction were replaced, and no further erratic voltages were observed.

Submittal of this report also satisfies the requirements for Technical Specification 3.5.1, action g. which requires a Special Report following any Emergency Core Cooling System actuation and injection into the Reactor Coolant System.

NRC wnu u n m

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NRC FORM 366A' U.S. NUCLEAR HEGULATOnY COMMISSION APPROVED DY OMB NO. 3150-0104 EXPIRES 5/31/95 ESTIMAYED BURDEN P( A AESM96E TO COMPLY WTTH THtS LICENSEE EVENT REPORT (LER) E%^AidfEM"nl#ELAr"iO72,,400 TEXT CONTINUATION "

$U E *cS'M "'*N"TO 'Elisi E THE PAPERWOAK REDUCTION PRG1ECT (3tSO4104). OFFCE OF M ANAGEMENT AND SUDGET, WASHINGTON, DC 20M3 FACILITY NAME {t) DOCKIT NUMBE R (2) Lf R NUMBER (4) P AOg (13 g blGUL NT tA. Hk v&o4 NUMBER NUMBEA Perry Nuclear Power Plant, Unit 1 05000 440 2 OF (,3 TLXT pf more stance on repree, m* accatoroet coo **s of NHC Fwm 3rtA) (11; I. Introduction At 0424 hours0.00491 days 0.118 hours 7.010582e-4 weeks 1.61332e-4 months on June 7, 1993 an inadvertent High Pressure Core Spray (HPCS) [BG) initiation occurred due to the effect of unstable output voltage from the Division 3 Reserve Battery Charger (BYCJ on divisional trip unit power and logic circuits. Prior to the event the plant was operating at 82 percent power, with reactor pressure at 994 psig and saturated conditions.

The Emergency Core Cooling System discharge to reactor coolant system and Engineered Safety Features actuation are being reported pursuant to the requirements of 10CFR50.73(a)(2)(iv). Partial loss of Division 3 instrumentation is reported pet the requirements of 10CFR50.73(a)(2)(v). Appropriate notifications vere made pursuant to the reporting requirements of 10CFR50.72(a),

10CFR50.72(b)(2)(iii)(d), and 10CFR50.72(b)(2)(ii). An unusual event was simultaneously classified due to HPCS flow to the reactor, and terminated at-0430.

Submittal of this report also satisfies the requirements for Technical Specification 3.5.1, action g. which requires a Special Report following any Emergency Core Cooling System actuation and injection into the Reactor coolant System. This was the seventh High Pressure Core Spray injection cycle to date.

The injection nozzle usage factor is currently less than 0.70.

II. Description of the Event Approximately six hours prior to the event, the Unit 1 Division 3 Reserve Charger and the Unit 2 Division 3 Battery [BTRY] had been aligned to supply Unit 1 Division 3 125 VDC Bus ED1C. The Unit 1 Division 3 Charger and Battery had been removed from service in preparation for a battery load test.

On June 7, 1993, at approximately 0424 hours0.00491 days 0.118 hours 7.010582e-4 weeks 1.61332e-4 months , with the plant at 82 percent power and ascension to 35 percent power planned, a High Pressure Core Spray Initiation )

signal was received. The initiation signal resulted from the effect of Division l 3 Reserve Battery Charger output voltage fluctuations on the divisional analog trip unit power and logic circuits. The Division 3 Diesel Generator [DG) and Emergency Service Vater System auto-started. Ten seconds following the initiation signal, the HPCS Pump auto-started. Approximately 4 seconds later the pump had developed sufficient discharge pressure to begin injecting from the Suppression Pool to the reactor vessel. Control Room Operators verified the HPCS initiation to oe inadvertent and secured the HPCS Pump at approximately 0425 hours0.00492 days 0.118 hours 7.027116e-4 weeks 1.617125e-4 months . The HPCS Discharge Check Valve indicated closed at approximately 0425 hours0.00492 days 0.118 hours 7.027116e-4 weeks 1.617125e-4 months .

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NRC FORM 366A' U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104

- E.XPIRES S/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LER) l"ZTEb'"fSEno"! E#ofE d%ITS '

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THE FAPEAWOW PLDUCTON PAGJECT (31RO100. OFFICE OF M ANAGEMENT AND BUDGET, WA$HtNGTON. DC 20503 7 ACluTV ,4 A,AL D) DOCKET NUMS[R (2) LE R NUMBER (5) PAGE (); 8 gp M OUL NT AL Fttv$ON NUMBER NUMBEA Perry Nuclear Power Plant, Unit 1 05000 440 3 OF6 012 ~

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93 00 7uTw n.u-.a,.u..am. m m. n .w mc m m on In parallel with the llPCS initiation, alarms for Division 3 DC System Trouble and I!PCS Out Of Service, and a status light for Trip Unit Gross Fail vere received.

Operators observed the Division 3 DC Bus voltage to be approximately 150 VDC and the instrument bus power supply to be de-energized. With the instrument power supply de-energized, Operators had no indication of IIPCS flow, discharge pressure, Division 3 reactor level or dryvell pressure indications. At this point HPCS was considered. inoperable, due to loss of monitoring capability. At approximately 0430 hours0.00498 days 0.119 hours 7.109788e-4 weeks 1.63615e-4 months the Division 3 DC bus voltage returned to normal and the instrument bus power supply re-energized restoring HPCS instrument indications.

Voltage excursions on the 125 VDC bus occurred five times during the next hour, as evidenced by lov level alarms on the sequence of events recorders. Event duration ranged from several milliseconds to several seconds. Since the initial Division 3 initiation signal had not been reset, subsequent initiations did not 7

occur.

By 0600 hours0.00694 days 0.167 hours 9.920635e-4 weeks 2.283e-4 months the Unit 1 Division 3 Charger and Battery were realigned to supply the Unit 1 Division 3 125 VDC Bus and the Division 3 Reserve Charger and Unit 2 i Division 3 Battery were secured. At 0616 hours0.00713 days 0.171 hours 0.00102 weeks 2.34388e-4 months , the Division 3 Initiation signal ]

vas reset and HPCS returned to standby readiness condition. The Division 3 -l Diesel Generator was synchronized to the Division 3 4160. Volt Bus and loaded for ;

one hour. Following the diesel run, both the diesel and the Division 3 Emergency l Service Water System were secured and returned to standby readiness condition. i At 0713 hours0.00825 days 0.198 hours 0.00118 weeks 2.712965e-4 months , HPCS vas declared operable. !

i III. Cause of Event The event was caused by the failure of the Division 3 Reserve Charger to maintain a stable output voltage. Charger components which most likely caused the voltage i fluctuations have been replaced. The removed components have been forwarded to the vendor for additional failure analysis. The chargers supply power to a 125 VDC to 120 VAC Topaz inverter [INVT), which in turn feeds a 120 VAC to 24 VDC instrument power supply [JX). The 24 VDC supply provides power to the HPCS instrumentation and analog master trip units. Once the 125VDC Bus voltage vent to approximately 150 volts, the Division 3 instrument power supply inverter units tripped on high voltage. The analog master trip units continued to power their associated transmitters, but with a decreasing voltage. The decreasing voltage caused a decrease in transmitter outputs. Once the output signal from the Division 3 Reactor Level Transmitters decreased to indicate less than vessel level 2, the Division 3 Reactor Level master trip units tripped, energizing their output relays and providing the (sealed in) HPCS initiation signal. ,

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IV. Analysis of Event The power plant response was as expected. This event is described in USAR Chapter 15.5. Reactor Pressure Control and Reactor Level Control Systems responded as expected to changes in reactor level and pressure. As HPCS flow to the vessel increased, reactor power decreased slightly causing a slight drop in reactor pressure. Reactor Level Control responded reducing feed flow to the vessel. Once the HPCS pump was secured the Reactor Level Control System readjusted feed flow and restored vessel level to within its normal band with no reactor operator interaction. Once Reactor Level Control stabilized, reactor power and pressure returned to pre-transient values.

The Rosemount Master Trip Units and Transmitters responded to the instrument bus power loss as expected. HPCS initiation logic responded as expected. The Division 3 Diesel Generator, Emergency Service Vater, and High Pressure Core Spray Systems responded as expected to an initiation signal.

I The impact of this event, inclusive of fatigue, is enveloped by design phase analysis for the reactor, reactor internals, and HPCS piping. Design specifications account for 10 cycles of inadvertent HPCS initiation with injection of 40 degree F vater. Engineering reviev of USAR Chapter 15, Section 15.5.1, " Inadvertent HPCS Startup," identified no irregularities or deficiencies for this event. The event is bounded by the existing safety analysis and is not considered to be safety significant.

The Lov Pressure Core Spray (LPCS) and the Low Pressure Coolant Injection (LPCI) systems are provided to assure that the core is adequately cooled following a loss of coolant accident (LOCA). They provide adequate core cooling capability for all break sizes following depressurization. The HPCS system is provided to assure that the reactor is adequately cooled in the event of a small break LOCA vhich does not result in rapid depressurization of the reactor vessel. .

Additionally, the Automatic Depressurization System (ADS) is provided to reduce pressure during small break LOCAs to allow LPCS and LPCI to perform their functions in time to prevent core damage. The various systems described above, are divided into three Emergency Core Cooling System (ECCS) divisions for operability and Technical Specification compliance purposes. In addition, although not relied on in accident analyses, the Reactor Core Isolation Cooling (RCIC) system provides the same function as the HPCS system. All but the HPCS system vere operable during this event, providing ECCS capability.

HPCS was inoperable for less than three hours during this event. Technical Specifications allow the HPCS system to remain inorserable for fourteen days provided the remaining two ECCS divisions and RCIC are operable.

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NRC FORM 366A- U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 aga E.XPIRES 5/31/95 E S* MATED BURDEN PER RESPONSE TO CouPtY WTTH THrs INF ORMATCN COLL 1CTION REQUE ST. 50 0 HR$ FORWARD LICENSEE EVENT REPORT (LER) CoMMtes nEatRowo eURoEN EsTuiTE To THE i~roRMATioN AND RECORD $ MANAGEMEV BkANCH (UN08 nt4h U.S. NUCLEAR TEXT CONTINUATION AmutATony COwsscN w As-NcToN. oc aces 5 om. AND TO THE PAPERWORK REDUCTION PRr.2ECT (31504104g orFICE OF MAN AGEMENT AND BUDGE 7, WASHtNGTON. DC 20503 F ACILITV NAME (1) DOCFET NUMBER (2) LE R NUMBER (4) PAGE (3)

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V. Previous Similar Events A previous similar event occurred at Perry in 1986. This event was reported in LER 86-41. In the 1986 event, the Reserve Charger was povering Division 3 Bus.

When its output voltage became unstable and resulted in a Division 3 HPCS initiation signal. No injection occurred during the 1986 event. A design change to the system battery chargers was evaluated to incorporate a very high speed, '

electronic high voltage shutdown circuit to allow protective coordination with the instrument power inverters. However, this type of circuit was not available from the manufacturer. In addition, based on the operating history of the charger dssign, the manufacturer did not recommend a design upgrade.

The integrated lov voltage electrical system response was also evaluated with no design change to the analog trip unit power and logic circuits recommended by the NSSS designer at that time. The conclusion of the NSSS designer was that the power system design met divisional safety requirements and that additional control components vould actually decrease safety system reliability.

VI. Corrective Actions Subsequent to the Reserve Charger being removed from service, tests were performed to monitor charger output and internal control voltages. Erratic output voltages were initially observed during the tests, but voltage stabilized after manual adjustment. Discussions with the vendor identified charger components most likely to have contributed to the voltage excursion. These suspect components, the sensing board, amplifier board and float voltage adjustment potentiometer, were replaced and have been forwarded to the vendor for ;

failure analysis. No erratic charger operation was observed during tests conducted after the components were replaced.

Procedures used for periodic inspection and maintenance of battery chargers are being modified to include detailed inspection and cleaning of float voltage adjustment and equalizing voltage potentiometers.

The Unit 1 and Unit 2 Division 3 Batteries were tested per the surveillance requirements of Technical Specification 4.8.2.1(b) following the over voltage transient. All tested attributes were found to be acceptable.

Engineering is evaluating the need for installation of a high voltage shutdown circuit; replacement of the Topaz 125 VDC to 120 VAC inverters; and the effect of the voltage level increase for divisional instrumentation and power supplies, appropriate relays and other equipment that may have a lov tolerance to overvoltage conditions.

NRC FORM 366A F92)

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Prior to this event the HPCS had been aligned to take suction from the Suppression Pool to support Suppression Pool Cleanup Operations. Initial !

estimates are that approximately 500 to 1000 gallons of Suppression Pool water l vere injected to the reactor. Reactor coolant samples were analyzed and determined to be within normal chemistry limits. The HPCS Suppression Pool '

Suction Strainer was inspected and found to be in an acceptable condition.

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ML20045G217

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Dear Sir:

Enclosure:

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