r 10CFR50.73-

South Ctrohna Eltetric & Gia Compsey John L. SkousP O. Box 88 Vice President*

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JenkinsvWe, SC 290C$ Nuclear operatons'

- (AC3) 345-4040

SCE&G-

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July 2, 1992

Document Control DeskU. S. Nuclear Regulatory CommissionWashington, DC 20555

Gentlemen:

Subject: VIRGIL C. SUMMER NUCLEAR STATIONDOCKET NO. 50/395OPERATING LICENSE NO. NPF-12LER 92-004, REVISION 1 (ONO 920039)

Attached is Licensee Event Report No. 92-004, Revision 1, for the Virgil C.Summer Nuclear Station. This revision changes the previously reported rating ofthe power supply cards from 1200 ohms to 1250 ohms and documents the completionof one of the additional corrective items. lhis report is submitted pursuant tothe requirenents of 10CFR50.73(a)(2)(iv).

Should there be any questions, please call us at your convenience. -

Very truly yours

t

John L. Skolds

CAC:nkkAttachment

c: 0. W. Dixon S. R. HuntR. R. Mahan J. W. FlitterR. J. White L. J. MontondoS. D. Ebneter NRC Resident InspectorG. F. Wunder J. B. Anotts Jr.General Managers INP0 Records Center

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At approximately 0553 hours on May 21, 1992, tne reactor tripped from 9% power onlow-low steam generator water level in the "C" steam generator. Reactor power wasbeing maintainad at approximately 29% power when oscillations in feedwater flow,steam generator level, ara steam flow occurred due to the automatic cycling uf thesteam line power operated relief valves (PORVs). The automatic cycling was caused bya malfunction of Bank 2 of the S*.eu Oump System, which resulted in an elevatedreactor coolant system temperstw. and consequently elevated main staan linepressure. The cycli m of the PORVs resulted in feedwater flow decreasing below theminimum 13% flow setpon.t. When feedwater temperatura decreased below 225"F, afeedwater isolation to "C" steam generator occurred. An attempt was made to reducereactor power in order to transfer feedwater back to the emergency feedwater system.

I "C" steam generator level decreased below the low-low level reactor trip setpoint; before this could be accomplished, and a reactor trip occurred.

| The reactor protection system responded as designed. A post trip review revealed|

that six condenser steam dump valves did not fully open on demand. This was caussidby replacement of " current to pneumatic" transducers that had higher impedance thanthe original transducers. The higher impedance prevented the pcwer supply card fromdeveloping a full 20 milliamperes current, and the valves could not fully open on a100% demano signal. The original transducers had been replac.ed under the " EqualTo/Better Than" program.The installed transducers were replaced with the original lower impedancetransducers. The " Equal To/Better Than" procedure (Engineering Services 419) isbeing reviewed to determine if it needs any program enhancements.

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PLANT IDENTIFICATION:

Westinghouse - Pressurired Water Reactor

EQUIPMENT IDENTIFICATION:

Flow Control Valve, EIIS System Code - $0The higher impedance " current to pncematic" transducers are Rosemount Mode 3311 Seriestransducers.

IDENT!FICATION OF EVENT: -

In preparation fcr connecting the generator to the grid, with feedwater (FW) i

temperature at approximately 310*F and decreasing, reactor power was 1r. creased toapproximately 29% in order 'o maintain FW flow above the minimum 13% FW isolationsetpoint (FW isolation occurs when FW temperature is less than 225'F with FW flow lessthan 134). While the tutbine was rolling up, the main steam power operated reliefvalves (PORVs) cycled open and closed several times due to elevated main steam systempressure. The cycling of the PORVs resulted in FW floo decreasing celow the minimum13% flow setpoint. 3efore FW flow recovered to greater than the 17% low flow reset, FWtemperature dropp_d below 225'F causing FW isolation to "C' SG. An attempt was made to

redure reactor power in order to transfer FW bac< to emergency feedwater system. "C"SG level dropped below the low-ion SG level reactor trip serpoint and a reactor tripoccurred from approximately 9% power.

EVENT DATE: May 21, 1992 at 0553 hours.

REPORT DATE: June 19, 1992

This-report was initiated by Off-Normal Occurrence report 92-039.,

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CONDITIONS PRIOR TO THE EVENT:

Made 1, 29% reactor power

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DESCRIPTION OF EVENT:

On May 21, 1992, at approximately 0517 hours, Operations personnal began a main turbinestartup. Reactor power was raised from 1% to approximately 15% power. Atal roximately 0521 hours, the main turbine began to roll up to 1600 revolutions perminute (RPM).

As the main turbine re whed 900 RPM, FW temperature began to decrease at 13*F perminute. With 90 RPM acceleration rate selected, it would take another 10 minutes forthe main turbine to reach 1800 RPM. However, in that time FW temperature woulddecrease from approximately 310*F to 210*F. With a FW isolation signal generated by acombination of low FW temperature (less than 225'F) and low FW flow (13%), a FWisolation signal became a concern. The actual time for the turbine to reach 1800 RPMtook approximately 4.5 minutes longer than anticipated.

A decision was made to increase reactor power and dump steam to the condenser to raisefeedwater flow above it's setpoint. Reactor power was raised to 29% power. Tnecontrol room personnel received indication that Bank 1, steem dump valves, were fullyopen and Bank 2 was modulating open, which was expected for this bank. Bank 2, did notstop the reactor coolent system temperature rise. When this temperature reachedapproximately 574*F, main steam line pressure reached the main steam PORVs setpoint of1148 pounds per square inch (psig).

The FORVs began to cycle open and closed in response to main steam line pressure. ThePORVs cyc;ing caused oscillations of stcam flow, SG water level, and FW flow. FW flowon "C" FW line decreased to the 13% setpoint, while FW temperature was still above225*F. However, befor? FW flow could increase above the bistable reset point ofapproximately 17%, FW temper 1ture decreased to below 225*F and "C" FW isolation valveclosed.

To preclude a reactor trip on low-low water level in "C" SG, an attempt was made toreduce reactor pcwer to the point that the emergency feedwater system could sustainwater level (approximately 3% reactor powar). This was unsuccessful and the reactortripped at 0553 hour:; on low-low level . With the exception of the previously mentionedproblems, tne plant response was normal. The plant was stabilized in Mode 3 until thecause of the malfunctions could be determined and corrected.

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CAUSE OF EVENT:

The cause of the slow turbine roll up is unknown. Engineering and Instrument andControls personnel performed troubleshooting on tne turbine acceleration cor trolcircuitry. No abnormalities or equipment failures were found. Odring the subsequentmain turbine startup arid with 90 RPM acceleration rate selected, the turbineaccelerated as expected with no anomaly in acceleration rate.

The cause of the steam duma malfunction was the inability of the power supply card todrive open the six Rosemount current to oneumatic (I/P) transoucers. Under the " EqualTo/Better Than'' (ETBT) program, the Rosemount Model 3311 transoucurs were used toreplace the Fisher Type 546 transcucers in orcer to imorove equipment reiiability.

The Rosemount transducers were chosen due to their low tendency to drift and theirstability. The Fisher Type 546 transoucers had a high failure rate of both new andrepaired treasducers. Some fisher transoucers did not meet the required accuracy of 1%of the output range en initial installation. The ETBT evaluation ccmoared the fisherType 546 and the Rosemount Modt) 3311 in function and performance in several areas.These were air consumption at 20 psig, output capacity at 20 psig, operatingtemperatura limits, accuracy, humidity limits, remote output pressure reading, directcurrent input, air output, and vibration effects. In tnese areas, the transducers were

compatible, so the evalua'.. ion concluded that the changing of transducers did notconstitute a design t hange and the replacement was authorized. The post maintenancetesting was a valve stroke using the transducer and a simulated input.

The Fisher transducers on steam duma valves were replaced with the Rosemounttranscacers between Maren 1,1991 ano April 18, 1991. On the steam cuma valves to theconcenser, two steam duma valves could be isolated by a single isolation valve, sotheir transducers were replaced and the valves were stroke tested.

The power supply cards for steam dump valve {/P transducers were rated to suppiy full~

load current (20 milliamperes) at an impedance of 1250 ohms and were bench tested to |supply full load current up to 1900 ohms imoecance. The impedance of the fishertransducers is 176 onms and of the Rosemaunt transducers a iaaximum of 410 ohms. Witheither two or three valves in steam dumo banks 1, 3, and 4; the Rosemount transmitters

|would not exceed the power supply, capacity In Steam Dump Bank 2, however, there are 6

|condenser valves. With the Rosemount transducers installed, the power supply card

! could not suppiy the necessary current to fully open the valves.

With the Bank 2 condenser dump valves not able to fully respond, reactor coolanttemperature increased. This also increased main steam line steam pressure up to themain steam line 90RVs setpoint resulting in the valves being activated.

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ANALYSIS OF EVENT:

This recort is being submitted pursuant to the requirements of 10CFR50.73(2)(a)(iv).Notification to the NRC Operations Center via the Emergency Notification System wasmade at 0843 hours on May 21, 1992, per the requirements of 10CFR50.72(b)(2)(ii).

With the exception of the steam dumo operaticn and the turbine roll up, the plant4

responded as expected. The decreasing of reactor power was by control rod insertion.As creviously stated, the faulty Bank 2 steam dump valves caused reactor coolanttemperature and main steam line pressure to increase resulting in main steam line PORVs

| actuation. Because the PORVs were cycling open and closed; steam generator level,steam flow, and FW flow oscillations began to occur. FW flow decreased to 13% on "C"FW line and failed to increase above it's reset point of approximately 17% before FWtemperature cecreased below 225'F. This logic closed the "C" FW isolation valve. Thereactor power was runback in an attempt to prevent a reactor trip on low-iow steam,

_ generator water level. This was unsuccessful and the reactor tripped on low-low steamgenerator water level. The reactor coolant system cooled down to approximately 530*Fduring the transient and was stabilized in Moce 3.

IMMEDIATE CORRECTIVE ACTIONS:;

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following the raactor trip, the operating snif t placed the olant in a stable conon cionin accordance with Emergency Operating Procedure (EOP) 1.0, " Reactor Trip / SafetyInjection Actuation," and E0P-1.1, " Reactor Trip Recove - Operations personnel and"

coeration of the steam dumpth? Independent Safety Engineering Group investigater .a

system. Instrument and Controls personnel performen tests of the I/P transducers todetermine the response and loading of the Rosemount transducers. Once the cause of thesteam dumo system operation was identified, the Rosemoult 3311 transcucers on Bank 2,steam dumps, were replacec with the Fisher Type 546 tr nsducers.

The turbine acceleration control circuitry was analyria and the cause of the slow rollup was not discovered. The plant was authorized for i restart and turbine acceleration

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! rate was monitored. It accelerated at 00 RPM with no anomalias.|-

I 'A search of the other installed Rosemount transmitters confirmed that ne more thanthree valves are driven by a single power supply card. Therefore the only suchapplication of the Rosemount transducers in the plant was on the Bank 2 steam dumps.

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-ADDITIONAL CORRECTIVE ACTIONS:

The following additional actions were initiated by SCE&G to prevent a similarreoccurrence:

1. The " Equal To/Better Than" procedure (Engineering Services - 419) is currentlyunaergoing an Engineering review to determine if this program needs anyenhancement. This review will be complete by July 31, 1992. Any identifiedenhancements will be implemented on a schedule commensurate with theirsignificance.

2. The calibration frequency of the Fisher Type 546 transducers that are on Bank 2 ofthe steam dump valves have been increu.ed to counteract their tendency to drift.

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PRIOR OCCURRENCES:

LER 84-009, dated March 5, 1904

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