ML18100A943

LER 94-005-00:on 940210,turbine Trip Occurred Due to Loss of Direct Current Control Power to electro-hydraulic Control Sys.Caused by Error in Design,Mfg,Const & Installation. EHC Power Supplies Monitored for stability.W/940311 Ltr

ML18100A943
Person / Time
Site:	Salem
Issue date:	03/11/1994
From:	HAGAN J J, PASTVA M J Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-005, LER-94-5, NUDOCS 9403180072
Download: ML18100A943 (7)

Text

e Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station U. s. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Dear Sir:

SALEM GENERATING STATION LICENSE NO. DPR-70 DOCKET NO. 50-272 UNIT NO. 1 LICENSEE EVENT REPORT 94-005-00 March 11, 1994 This Licensee Event Report is being submitted pursuant to the requirements of Code of Federal Regulation 10CFR50.73(a)

(2) (iv). Issuance of this report is required within thirty (30) days of event discovery.

Sincerely yours, MJPJ:pc Distribution

.,r.f"lr-.rn 94031eAonootR PDR PDR . S t'"'""1i;i11L your hands. 95-2189 REV 7-92 NRC FORM 366 (5-92) .* NUCLEAR REGULATORY COMMISSION PPROVED BY OMB NO. 3150-0104 EXPIRES 5/31 /95 LICENSEE EVENT REPORT (LER) (See reverse for required number of digits/characters for each block) ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503. FACILITY NAME (1) DOCKET NUMBER (2) PAGE (3) 1OF05 Salem Generating Station -Unit 1 05000 272 TITLE (4) Turbine Trip Due To Loss of Direct Current Control Power To Electro-Hydraulic Control Syst. EVENT DATE (5) LER NUMBER (6 REPORT NUMBER (7) OTHER FACILITIES INVOLVED (8\ FACILITY NAME DOCKET NUMBER NUMBER MONTH DAY

• SEQUENTIAL YEAR YEAR REVISION NUMBER MONTH DAY YEAR *05000 FACILITY NAME DOCKET NUMBER 02 10 94 94 005 00 03 11 94 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check one or more (11) MODE (9) 1 20.402(b) 20.405(c) x 50.73(a)(2)(iv) 73.71 (b) I POWER I I 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.71 (c) LEVEL (10) 99 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vii)

OTHER -20.405(a)(1

)(iii) 50.73(a) (2)(i) 50.73(a)(2)(viii)(A) (Specify in Abstract U--J--........:....:....:....:....:......:.._

____

_____ 1--4--_;_;;__;___;_;;___--I below and in Te>d, NRC 20.405(a)(1

)(iv) 50.73(a)(2)(ii) 50.73(a)(2) (viii)(B)

Form 366A) 20.405(a)(1

)(v) 50.73(a)(2)(iii) 50.73(a)(2)(x)

LICENSEE CONTACT FOR THIS LEA 12) NAME TELEPHONE NUMBER (Include Area Code) M. J. Pastva, Jr. -LER Coordinator (609) 339-5165 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13) CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE TONPRDS CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE TONPRDS SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MONTH DAY YEAR l YES SUBMISSION DATE (15) j (If yes, complete EXPECTED SUBMISSION DATE) NO x ABSTRACT (Limit to 1400 spaces, i.e., ai:iRroximately 15 single-spaced typewritten lines) (16) On 2/10/94, at 1258 hours0.0146 days <br />0.349 hours <br />0.00208 weeks <br />4.78669e-4 months <br />, a control power failure of the turbine Electro-Hydraulic Control (EHC) system occurred causing a turbine/reactor trip. The Unit was stabilized in Mode 3, at approximately 1315 hours0.0152 days <br />0.365 hours <br />0.00217 weeks <br />5.003575e-4 months <br /> (same day). Insufficient margin between the EHC.overvoltage protection*

setpoints and normal EHC power supply voltage allowed a variation in voltage to actuate the overvoltage protection circuitry.

The margin resulted from design/installation of the EHC power supplies and use of a 17.3VDC setpoint.

A contributor was EHC procedures that did not record power supply voltages in a manner that would reveal a reduced margin to trip. No component failures were identified as contributors to this event. EHC power supplies were monitored and no problems or transients/pulses were recorded.

The overvoltage protection circuits were replaced and the circuits' setpoints were reset to 17.9 +/-.1 voe, and the EHC +15 voe bus wiring was reworked.

Procedure changes have been implemented to ensure adequate margin below the overvoltage protection setpoint.

The A +15VDC power supply was replaced and additional testing will be conducted to evaluate transient effects. During the next Unit 2 outage, voltage readings of the Unit 2 EHC 15VDC power supply will be taken to verify adequacy of the overvoltage protection margin to trip setpoint.

NRG FORM 366 (5-92)

BLOCK NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 REQUIRED NUMBER OF DIGITS/CHARACTERS FOR EACH BLOCK NUMBER OF DIGITS/CHARACTERS TITLE UP TO 46 FACILITY NAME 8 TOTAL 3 IN ADDITION TO 05000 DOCKET NUMBER VARIES PAGE NUMBER UP TO 76 TITLE I 6 TOTAL 2 PER BLOCK EVENT DATE 7 TOTAL 2 FOR YEAR 3 FOR SEQUENTIAL NUMBER LER NUMBER 2 FOR REVISION NUMBER 6 TOTAL 2 PER BLOCK REPORT DATE UP TO 18 FACILITY NAME 8 TOTAL-DOCKET NUMBER OTHER FACILITIES INVOLVED 3 IN ADDITION TO 05000 1 OPERATING MODE 3 POWER LEVEL 1 CHECK BOX THAT APPLIES REQUIREMENTS OF 10 CFR UP TO 50 FOR NAME 14 FOR TELEPHONE LICENSEE CONTACT CAUSE VARIES 2 FOR SYSTEM 4 FOR COMPONENT EACH COMPONENT FAILURE 4 FOR MANUFACTURER NPRDS VARIES 1 CHECK BOX THAT APPLIES SUPPLEMENTAL REPORT EXPECTED 6 TOTAL 2 PER BLOCK EXPECTED SUBMISSION DATE LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 DOCKET NUMBER 5000272 PLANT AND SYSTEM IDENTIFICATION:

Westinghouse

-Pressurized Water Reactor LER NUMBER 94-005-00 PAGE 2 of 5 Energy Identification System (EIIS) codes are identified in the text* as {xx} IDENTIFICATION OF OCCURRENCE:

Turbine/Reactor Trip Due To Loss Of Direct current Control Power To Electro-Hydraulic Control System Event Date: 2/10/94 Report Date: 3/11/94 This report was initiated by Incident Report No.94-045. CONDITIONS PRIOR TO OCCURRENCE:

Mode 1 Reactor Power 99 % Unit Load 1136 MWe DESCRIPTION OF OCCURRENCE:

On February 10, 1994, at 1258 hours0.0146 days <br />0.349 hours <br />0.00208 weeks <br />4.78669e-4 months <br />, a turbine/reactor trip {JC} occurred due to a turbine trip signal while above the P-9 reactor power interlock setpoint.

The turbine trip was initiated from a direct current (DC) control power failure of the turbine Electro-Hydraulic Control (EHC) System. Emergency Operating Procedure (EOP)-TRIP-1, "Reactor Trip Or Safety Injection" and EOP-TRIP-2, "Reactor Trip Response" were entered and the Unit was stabilized in Mode 3, at approximately 1315 hours0.0152 days <br />0.365 hours <br />0.00217 weeks <br />5.003575e-4 months <br /> (same day). At 1403 hours0.0162 days <br />0.39 hours <br />0.00232 weeks <br />5.338415e-4 months <br /> (same day) the NRC was notified of this event in accordance with 10CFR50.72(b)

(2) (ii). ANALYSIS OF OCCURRENCE:

The turbine EHC system controls steam flow through the turbine to govern turbine speed and load during startup, normal operation and shutdown.

In addition, the system trips the turbine if required.

The two +15-volt DC control power supplies (A and B) to the system are utilized via an auctioneering circuit. Over-voltage protection of the EHC power supplies is provided.

Loss of both power supplies is indicated by a Control Room overhead alarm annunciator "EH DC PWR FAIL" first out window (F-32). The turbine/reactor trip occurred due to a DC control power failure of the turbine EHC System which caused a turbine trip signal while above LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 DOCKET NUMBER 5000272 ANALYSIS OF OCCURRENCE: (cont'd) LER NUMBER 94-005-00 PAGE 3 of 5 the P-9 reactor power interlock setpoint (>/=50% rated thermal power). Emergency Operating Procedure (EOP)-TRIP-1, "Reactor Trip Or Safety Injection", was entered. Main Steam was isolated in accordance with EOP-TRIP-2, "Reactor Trip Response" to limit cooldown of the Reactor Coolant System {AB}. The Unit was stabilized and placed in Mode 3 and Integrated Operating Procedure IOP-8 was entered. This event resulted from insufficient margin between the overvoltage protection setpoints and normal EHC power supply voltage. Consequently, a variation in voltage actuated the overvoltage protection circuitry.

The A power supply was set at approximately 220 millivolts (mV) below the overvoltage protection setpoint of 17.3 volts and the B power supply was set at approximately 340 mV below the overvoltage protection setpoint of 17.3 volts. Guidance for the power supply, Lambda Electronics, Division of VEEC Instrument Co., recommends a setpoint of 115% of the power supply voltage plus 1.0 volt (i.e. > 18 volts). The Westinghouse EHC field calibration procedure recommends an overvoltage protection setpoint of 17.3 volts. However, Engineering

& Plant Betterment analysis determined 18VDC as the maximum overvoltage protection setpoint.

Probable contributors to the insufficient setpoint margins: The power supply bus employed 18 gauge wiring, which may contribute to high line resistance which caused voltage drops from the power supply to the bus. Encountered high line resistance has required setting the power supply voltage relatively high in order to maintain proper bus voltage. Improperly crimped and loose wiring lugs in the power distribution panel wiring, confirmed by observed voltage transients during movement of the power supply output wiring. Recommendations in the Westinghouse EHC field calibration procedure required the overvoltage protection setpoint to be 17.3 volts, which was used by PSE&G. The potentiometer used to adjust the A power supply showed erratic response/high sensitivity to adjustments.

EHC calibration procedure did not record power supply voltages in a manner that would reveal a reduced margin to trip. No component failures were identified as contributors to this event. In addition, the loss of one 15 volt power supply resulting in loss

' LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 DOCKET NUMBER 5000272 ANALYSIS OF OCCURRENCE: (cont'd) LER NUMBER 94-005-00 PAGE 4 of 5 of the other could not be duplicated.

However, troubleshooting showed that the A power supply did not adequately control under large load transients.

At the time of this event, efforts were in progress to develop design changes to replace and upgrade the power supplies in response to previously encountered EHC power supply and distribution chassis problems, dating back to August 1992. APPARENT CAUSE OF OCCURRENCE:

The cause of this event is "Design, Manufacturing, Construction/Installation", as classified in Appendix B of NUREG-1022.

Methods used during installation and design of the EHC power supplies (i.e. wire size used) resulted in minimum margin between the overvoltage protection setpoints and normal EHC power supply voltage. In addition, EHC calibration procedures did not record power supply voltages in a manner that would reveal a reduced margin to trip. The conservative 17.3VDC setpoint contributed to the reduced margin. No component failures were identified as contributors to this event. PREVIOUS OCCURRENCES:

Review of documentation showed this event to be an isolated occurrence.

SAFETY SIGNIFICANCE:

This event did not affect the health and safety of the public. It is reportable as an automatic RPS actuation in accordance with 10 CFR50. 73 (a) (2) (iv). The RPS functioned as designed and the heat sink was maintained during this event. The reduction in Tav , requiring main steamline isolation, has been experienced during reactor trips (e.g.,Unit 1 LER 272/93-002-00 and Unit 2 LER 311/92-009-00).

Engineering is investigating Tavq reduction following trips and potential corrective actions are being assessed.

CORRECTIVE ACTION: EHC power supplies were monitored for voltage stability and no problems or transients/pulses were recorded.

The overvoltage protection circuits were replaced and the overvoltage

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--' . LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 DOCKET NUMBER 5000272 LER NUMBER 94-005-00 PAGE 5 of 5 CORRECTIVE ACTION: (cont'd) protection setpoints reset to 17.9 +/-.1 voe to provide greater margin to trip. The EHC +15 voe bus wiring was reworked to reduce voltage losses in the wiring. Procedure changes have been implemented to require recording of final EHC power supply voltage values in order to ensure adequate margin below the overvoltage protection trip setpoint.

The A +15VDC power supply, including its potentiometer, was replaced as a precautionary measure. The B +15VDC power supply potentiometer was cycled to assure proper performance.

Additional testing of the replaced A power supply and the overvoltage protection circuits will be conducted to evaluate transient effects. During the next Unit 2 outage, voltage readings of the Unit 2 EHC 15VDC power supply will be taken to verify adequacy of the overvoltage protection margin to trip setpoint.

PSE&G is continuing to investigate Tavg reduction following reactor trips and potential corrective actions are being assessed.

MJPJ:pc SORC Mtg.94-022