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LER 90-006-00:on 900517,inadvertent Unit 2 Train B ESF Actuation Occurred Due to Shorted Light Socket in Diesel Generator Sequencer B Test Circuit.Personnel Replaced Light Socket W/Acceptable Replacement.Mod scheduled.W/900618 Ltr
	ML20043H276
Person / Time
Site:	Mcguire
Issue date:	06/18/1990
From:	Mcconnell T, Sipe A; DUKE POWER CO.
To:	; NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
	LER-90-006-03, LER-90-6-3, NUDOCS 9006250011
	Download: ML20043H276 (9)
	v • d • e

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Subject:

McGuire Nuclear Station Unit 2 Docket No. 50-370 Licensee Event Report 370/90-06 Gentlemen Fvrsuant to 10 CFR 50.73 Sections (a)(1) and (d), attached is Licensee Event Report 370/90-06 concerning an inadvertent Unit 2 Train B Engineered Safety Features actuation. This report is being submitted in accordance with 10 C7R 50.73(a)(2)(iv). This event is considered to be of no significance with respect to the health and safety of the public. Very truly yours, r/q a.mM T.L. McConnell e DVE/ADJ/cb1 Attachment xc: Mr. S.D. Ebneter American Nuclear Insurers Administrator, Region II c/o Dottie Sherman, ANI Library + U.S. Nuclear Regulatory Commission The Exchange, Suit 245 101 Marietta St., NW, Suite 2900 270 Farmington Avenue Atlanta, GA 30323 ~ Farmington, CT 06032 INPO Records Center Mr. Darl Hood Suite 1500 U.S. Nuclear Regulatory Commission 1100 Circle 75 Parkway Office of Nuclear Reactor Regulation Atlanta, GA 30339 Washington, D.C. 20555 M&M Nuclear Consultants Mr. P.K. Van Doorn 1221 Avenue of the Americas NRC Resident Inspector ; New York, NY 10020 McGuire Nuclear Station g

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         *LER 370/90-06 Page 2-f      +   June 18, 1990 bxc  B.W. Bline L.G. Bost J.S. Warren R.L. Gill C.L. Hartzell (CNS)

R.S. Matheson (ONS) P.R. Herran S.S. Kilborn (W)

,               R.E. Loper-Ibanez M.A. Mullen R.O. Sharpe (MNS)

G.B. Swindlehurst K.D. Thomas M.S. Tuckman L.E. Weaver R.L.~ Weber J.D. Wylie (PSD) J.W. Willis QA Tech. Services NRC Coordinator (EC 12/55) MC-815-04 (20) 1 l i

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        "' An Inadvertent Unit 2 Train B Engineered Safety Features Actuation Occurred Because Of A Shorted Limht Soeket On The Dienel Generator Load Senneneer Panel IVSNT DAtt een                     Lim esubstta les                        RIP 0af Daf t 17e                       OtMth D ActLiitts INv0Lygp 401 MON T .e     Day    vtam     vl A81          ,D, gNn" 6
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1 On May 17, 1990, at 2321, there was an inadvertent Engineered Safety Features (ESF) l l actuation from the Unit 2 Train B Diesel Generator Load Sequencer. The Unit 2 ) l Train B Motor Driven Auxiliary Feedwater (CA) pump automatically started and l injected water into Steam Generators C and D. Operations personnel immediately ! placed the 2B CA pump in recirculation and wrote an emergency work request for ; Instrument and Electrical (IAE) personnel to investigate the reason for the 2B CA . pump automatically starting. IAE personnel determined the cause to be a shorted l light socket in the Diesel Generator Sequencer ; test circuit. No other components l re-aligned due to the sequencer relays closing because of other interlocks on the l associated components or because the components were already energized. Train B 1 components were in service during this event. Unit 2 was in Mode 1 (Power l Operation) at 100 percent power when this event occurred. This event is assigned a l cause of Equipment Failure because the light socket, rated at a nominal 125 VDC, i developed a short. The measured voltage for Train B Bus is 131 VDC. IAE personnel replaced the light socket with an acceptable replacement. A modification is scheduled to replace all light sockets in DC circuits of this nature during the , upcoming outages. l 4 l l 884Gm ate

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Background

The Diesel Generator [EIIS DG) Load Sequencing System [C1!S:EK] functioris to energize the necessary Blackout or Loss of Coolant Accideni (LOCA) loads in a prescribed sequence, and in such a manner that the Diesel Generator or auxiliary trensformer [EIIS:XFMR] is not momentarily overloaded. The sequencer is maintained in a standby condition at all times during plant operation and can be actuated by , either a LOCA signal from the Solid State Protection System (SSPS) [EIIS:JC] or a 2 ! out of 3 phase Undervoltage signal sensed on the 4.16 KV essential bus (EIIS:EB). Depending on the accident conditions present (LOCA, Blackout, etc.), the sequencer will operate to energize the loads required for these conditions. The automatic loading is accomplished by timer (EIIS:TMR] relays (EIIS:RLY) through either a committed sequence or an accelerated sequence mode. The time settings on these relays must be properly set to ensi-e the loads will be energized when they are - needed. Various types of alarms 'T. IS: ALM] are provided to depict system status. l Status indicating lights [EIIS:IL] located on the sequencer panel [EIIStPL] have been provided for testing purposes. Their status during normal sequencer standby ; conditions or during sequencer actuated conditions have little significance. The Committed Sequencer timer relay circuit consists of an arrangement of 10 timer relays (see drawing on page 7 of 7). The Committed Sequence Sub Test indicating light indicates that the committed sequence test is enabled and monitors re-closure of test contacts. On October 31, 1986, Design Engineering personnel completed Design Study MGDS-0084; task 3114B, Cutler-Hammer E29 Indicating Light Units. This Design Study documented that there was a history of light unit failures caused by deteriorated internal composition resistors. As reported in this Design Study, the findings of inspections completed on August 15, 1986 at McGuire Nuclear Station were as follows: Unit I had Cutler-Hammer E29NM Indicating Light Units. These light units are designed for 125 VDC applications. The 125 Voltage DC system [EIIS:EJ] normally operates between 132 to 136 VDC measured. There was definite evidence of overheating on the light units. Unit 2 had Cutler-Hammer E29NY1 Indicating Light U-its. There were no visual signs of deterioration; however, a visual inspectr on would not exclude the possibility of an internal resistance problem exi sting. Also, this Design Study reviewed all indicator light uait applications at McGuire that use Cutler-Hammer E29NM, E29NM1, and E29NY1 indicator lights. All of the E29 indicating light units in the Units 1 aid 2 Diesel Generator Load Sequencers are in DC circuits with the exception of a lew devices which are in AC circuits. l

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tx, ins.sw a i f actiety seamt up ooCEif NUantam tal tsa =uantam toi paos (si n aa " W'Mt' "'MW McGuire Nuclear Station, Unit 2 o ]s jo jo jo l3 ; 7l0 9l0 0l0 j6 Og0 l3 or l7 text w- . s=w me s mau nn ( The indicating light used for the Committed Sequence Sub Test light was an E29NY1 rated at 120 VAC/132 VDC with two internal resistors (1200 ohms, I watt and 1800 ohms, 2 watt), and a slide base bulb socket. As a result of the Design Study, Design Engineering personnel recoc: mended that all Cutler-Hammer type NM, NM1, and NY1 indicating light units should be replaced with Cutler-Hammer E29NY11 units, which are designed to operate at 135 VDC, utilize a bayonet base bulb socket, and fit the existing control panel cut-outs. Nuclear Station Modifications (NSMs) MG-12139 and MG-22139 were approved by McGuire Projects personnel for Design to begin on May 25, 1988. The purpose of these modifications are to replace all Cutler-Hammer E29 type NM, NM1, and NY1 indicating , light units used in Quality Assurance (QA) and non-QA condition DC circuits at McGuire with E29NY11 indicating light units. This is to eliminate the overheating problem of NM and NMI indicating light units which can fail and short with time, causing a unit trip. Also, the purpose is to eliminate the possibility of I electrical shorting of NY1 indicating light units if not properly installed. If , the E29NY11 light unit fails due to overheating the result would be the bulb burning out which will leave the circuit open and not closed as in the case of the j shorted light sockets. i Description of Event On May 17, 1990 at 2321, Operations Control Room (EIIS:NA) personnel received a signal that the 2B CA [EIIS:BA) pump [EIIS:P] automatically started. The 2B CA pump was injecting water into Steam Generators [EIIS:SG) C and D. At 2323, Operations personnel isolated the 2B CA pump flow from Steam Generators C and D. Operations personnel placed the 2B CA pump in recirculat an flow at 2324. At 2330, on May 17, 1990, Operations personnel wrote emergency work request 141179 for IAE personnel to investigate and repair the reason that the 2B CA pump automatically started. At approximately 2330, Operations Control Room personnel reviewed the Events Recorder (EIIS:IQ] printout. This identified that the 2B Diesel Generator Sequence load groups had energized. An Operations person was then dispatched to the Diesel Generator Load Sequencer 2B panel and reported to IAE personnel that something smelled as if it was melted inside the panel. On May 18, 1990, IAE personnel determined that the Committed Sequence Sub Test Indicating light located in the Diesel Generator Load Sequencer panel had shorted. When the light socket shorted, a voltage drop occurred across the committed sequence timer relays causing the relays to energize. One of the relays signalled the 2B CA pump to auto start. Other components that would have started due to the load sequencer relays closing were already energized since Train B was in service. Other components that also received a signal from the load sequencer, did not receive an auto start signal because of interlocks with other protection systems (i.e. SSPS) not being satisfied. IAE personnel lifted the lead from the light socket which allowed Operations to re-align the relays in the load sequencer panel back to standby. At 0242 on May 18, 1990, Operations personnel reset the 2B Diesel Generator Load Sequencer and at 0244, Operations personnel turned the 2B CA pump off.

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! On May 18, 1990 at 0252, the NRC was notified of this event as directed by RP/0/A/5700/10, NRC Immediate Notification Requirements. At 0530, IAE personnel replaced the light socket with an E29NM1 Cutler-Hammer indicating light unit and replaced the lifted lead. Also, IAE personnel wrote work request 600132 to replace three other indicating lights in the Diesel Generator Load Sequencer Panel that lookea charred and were suspect to potential failure. ' Conclusion This ESF Actuation [EIIS:JE] event is assigned a cause of Equipment Failure because the Diesel Generator Load Sequencer Panel Committed Sequence Sub Test Indicating Light Unit failed by shorting. When this indicating light shorted, the timer relays re-aligned and started the timer sequence to load components from Train B. All components were either already energized or had other interlocks that prevented them from starting except for the 2B CA pump. Therefore, the 2B CA pump auto started. The type of indicating light that was installed in the Committed Sequence Sub Test Circuit and that failed causing the 2B CA pump to auto start was a Cutler-Hammer E29NY1. IAE personnel replaced the E29NY1 light with an E29NM1 l!ght. Cutler-Hammer E29 type NM, NM1, and NY1 indicating light units currently installed in McGuire Unit 1 and 2 DC circuits have experienced failures due to overheating. The E29NY1 and E29NM units have a slide base bulb socket which is subject to electrical shorting if its installed incorrectly. Failures of these Cutler-Hammer E29 light units have resulted in unit trips. As documented in the Design Study MGDS-0084/00, information based on tests conducted by Transmission Department personnel in 1977 and past experience with Cutler-Hammer indicating light units with internal composition resistors showed i that the resistance values for these light units decrease with time due to heat. The decrease in resistance is permanent. The composition resistors are made of carbon. Carbon has a negative temperature coefficient of resistance (= -0.0005). The resistance value will drop with an increase in temperature. As the resistance value decreases, current will increase and cause the temperature in the light unit to rise. With time, the light unit can fail and short due to heat dissipation. 1 NSMs MG-12139 and MG-22139 were Design complete on August 7, 1989 ano January 19, ; 1990 respectively. Both NSMs include replacement of all the indicating lights for both trains of the Diesel Generator Load Sequencer Panels to Cutler-Hammer E29NY11 indicating light units. These modifications are not field complete, but are i scheduled to be complete before the end of the next respective refueling outages. The use of E29NY1 and E29NM light units had already been prohibited at the station prior to this event and based on the acceptable substitutes list the E29NM are , replaced by E29NM1 and E29NY1 are replaced by E29NY11. The Bill of Materiale j required the Committed Sequence Sub Test indicating light to be an E29NM light unit; therefore, the replacement was required to be an E29NM1 light unit which will be replaced when the NSMs MG-12139 and MG-22139 are implemented.

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McGuire Nuclear Station, Unit 2 o ls jo lo lo l3 l 7l0 9l0 -- 0 l0 l6 -- Ol0 l5 0F p rext m, a . w m== =ac w aser.nm The failed E29NY1 light unit had a manufactured date of May, 1979. This light may have shorted due to length of service which probably caused the breakdown in resistance. There is not a preventative maintenance (PM) program for replacing these light units. These NSMs will provide a permanent solution for DC circuit light units and the E29NY11 light units will not require a PM program. A review of the Operating Experience Program data base for the past twenty four months prior to this event revealed 2 events involving ESF actuations with a cause of Equipment Failure. Licensee Event Report (LER) 369/88-21 documented an auto start on the Turbine [EIIS:TRB] Driven CA pump caused by a blown fuse [EIIS:FU). LER 370/88-07 documented a Feedwater System [EIIS:SJ) isolation caused by a failed signal comparator card. The corrective actions for these LERs were specific to each event. These events involved failures on different components. Therefore, this event is considered not recurring. The problem of failures on Cutler-Hammer E29NY1 indicating light units is a recognized recurring problem. There have been several failures in the past where

   )             breakers have opened due to a short in these indicating lights. Recognition of this problem was what initiated the Design Study MGDS-0084/00.

This event is Nuclear Plant Reliability Data System (NPRDS) reportable. Industry reported to NPRDS four light socket failures during replacement of the 'ight units and four light socket failures due to unknown causes. These light sockets were not identified by manufacturer but all failures were listed as light unito shorting. Only three of the failures were on the Duke Power System and only one at McGuire. The McGuire failure was on a Load Control Breaker [EIIS:ED) and: caused the Breaker ' Trip Circuit [EIIS:72] to remain energized. The Industry search did not reveal any similar events on Diesel Generator Load sequencers occurring. There were no personnel injuries, radiation overexposures, or unconirolled releases of radioactive material as a result of this incident. CORRECTIVE ACTIONS: ; Immediate: 1) After pushing the CA Modulating Valve Reset button, Operations Control Room personnel manually closed the 2B CA pump discharge valves to the Steam Generators C and D and thereby placed the pump in a recirculation mode. - Subsequent: 1) Operations reset the Diesel Generator Load Sequencer and returned the 2B CA pump to off. 1

2) IAE personnel replaced the failed indicating light E29NY1 on the Diesel Generator Load Sequencer Panel for the Committed Sequence Sub Test light unit documented on work request 141179.

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3) IAE personnel wrote work request 600132 to replace three other indicating lights in the Diesel Generator Load Sequencer Panel that looked charred and were suspect to potential failure.

i Planned: 1) Unit 2 NSM MG-22139 will replace all Unit 2 Cutler-Hammer E29 type NM, NM1, and NY1 indicating light units used in QA and non-QA condition DC circuits at McGuire with E29NY11 indicating light units. This includes the Diesel Generator Load Sequencer Panel indicating 11ghts.

2) Unit 1 NSM MG-12139 will replace all Unit 1 Cutler-Hammer E29 type NM, NM1, and NY1 indicating light units used in QA and non-QA condition DC circuits at McGuire with E29NY11 indicating light units. This includes the Diesel Generator Load Sequencer Panel indicating lights.

SAFETY ANALYSIS: Unit 2 was in Mode 1 at 100 percent power with all Train B components in service at the time of the ESF actuation. During this event, the 2B CA Pump did auto-start, ) as designed, upon receipt of the start signal and pumped water into Steam t Generators C and D for approximately 2 minutes. During that time period, Operations personnel isolated the CA flow to Steam Generators C and D and placed the pump in recirculation mode. The 2B CA pump did operate for approximately 3 hours and 23 minutes. A small Reactor Power Mismatch was caused by the CA flow discharging into the Steam Generators; however, the Power Mismatch did not reach an alarm setpoint level of + 2 percent. Steam Generator water levels did not change during this event. The inadvertent actuation of the 2B CA pump did not adversely > affect any of the Unit 2 equipment or systems.

               ;This event did not affect the health and safety of the public.                                                                  ,

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ML20043H276

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