ML19254E195

LER 79-096/01T-0:on 791015,capacitor Failed in Integrated Control Sys Resulting in Unit Trip from 68.8% of Full Power. Caused by Blown Muffler on Generator Output 345 Kv Breakers. Damaged Mufflers Replaced & Offsite Power re-established

ML19254E195
Person / Time
Site:	Davis Besse
Issue date:	10/25/1979
From:	Batch S TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19254E193	List: ML19254E192 ML19254E195
References
LER-79-096-01T, LER-79-96-1T, NUDOCS 7910310306
Download: ML19254E195 (4)

Text

U. S. NUCLE AR REGULA RY C ,I al .

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LICENSEE EVENT REPORT CONTROL 83 LOCK: l l l l l l l (PLE ASE PRINT OR TYPE ALL REQUIRED INFORMATION) i e o 1 lOfH D Bl Sl Il@!tb010 -

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I4 75 REPoR T DAT E bJ

? e txJ bl OUCK E r r.U'AS E H OATE EVENT DES. 'PTION AND PROBABLE CONSEQUENCES h o 2 l At 1227 hours0.0142 days <br />0.341 hours <br />0.00203 weeks <br />4.668735e-4 months <br /> a capacitor failed in the Integrated Control System (ICS) causing an ICJ o a i response which resulted in a unit trip from approximate 1v 63.8 of full power. WhileI o 4 l reclosing the generator output breaker at approximately 1250 hours0.0145 days <br />0.347 hours <br />0.00207 weeks <br />4.75625e-4 months <br /> 345KV "J" bus triorhd O 5 I which resulted in a loss of of f site power. Both emergencv generators s Carted and pro--l 0 6 vided essential loads with power. The loss of reactor coolant psmps placed the unit I o 7 l in violation of T.S. 3.4.1.

The loss of off' site power placed the unit in the action I o s ! I statement of T.S. 3.8.1.1. Adequate core coolinn existed throughout the occurrences J SYSTEM CAUSE C AUSE COVP. VALVE SUCCDE COYPONENT CODE SUBCOGE SUBCODE CODE CODE 7

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_17191 21 22 23 24 26 21 23 ATT ACHY ENT 29 NPRO4 Ju F RIVE COUP 31 32 CO*.*PON E N T AC TION FUTUPE FFFECT SH U T DT. N MANUrACTUHER TAKEN ACTION ON PL A?.T M E Tr+ G D HOUHb 2. SUBVITitD FCRM BUS. SUPPU E R

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l33C l@lJ4 F l@ l3bC l@ 30 3' 40 41 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h 1 The cause of the loss of of f site power was a part of a blown muffler on one of the i i o du generator output 345KV breakers causing a fault to ground when the breaker was reclosell.

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! The damaged mufflers on both generator output breake s were replaced and reinforcing j i a j bands installed on all the mufflers in the switchyard. Offsite power was re-estab- 1 Ii.I41 I lished hv 1333 hours0.0154 days <br />0.37 hours <br />0.0022 weeks <br />5.072065e-4 months <br />. Three reactor coolant pumps were restarted by 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br />. 80 l

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% POWER OTHER STATUS ISCOV FY OlSCOVERY DESCRIPTION ST s l1 l5l d@ 0l0 0 l@hecoverv f rom trin l l Al@l N\ l ACTivlTY CO TENT AYOUNT OF ACTitlTY LOCATION OF RELE ASE l NA l liisl 7 8 9 AELE zl ASED@OF 10 11 NA RELE ASEl z44I@l d5 80 PERSONNEL E XPOSURES NUVSER D ESCRIP TICN l

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q 80 7 8 9 11 12 , LOSS OF DE;CniPTiON On C AY AGE TO FACILITY s,y Q TYPE l l1 l 98 ]9 l Dl@lia Damace to a non-seismic steam line restraint ,,, do 7 KSU D PTION [M w 12101 LdE8l Press ESCR: release to northern Ohio media (AP and LTI) l llllll1lll $ 06 69 8:) i 7 8 3 70 NAVE OF PREPARER Stan N. Batch pgoyg 419-259-5000.' Ext. 236  ?

TOLEDO EDISON CO:IPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-32-79-1_1_ DATE OF EVENT: October 15, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Reactor trip and station power loss Conditions Prior to Occurrence: The unit was in Mode 1, with Power (>ntr) = 1665, and Load (Gross M4e) = 530. Description of Occurrence: At approximately 1227 hours on October 15, 1979, a capa-citor f ailed in the Integrated Control System (ICS) pulser circuit to the turbine eleccro-hydraulic control (DiC) system. This capacitor failure caused the turbine control valves to open which lowered the main steam line header pressure. The ICS responded to the low hevder pressure by increasing both reactor power and feedwater which resulted in a reactor protection system reactor trip at the reduced high flux setpoint of approximately 68.8 percent of full pouer. While reclosing the generator output breaker 34560 at approximately 1250 hours, 345KV "J" bus tripped which resulted in a de-energization of the Startup Transformer 01 and a station blackout. Both caergency diesel generators automatically started. The Steam and Feedwater Rupture Control System (SFRCS) actuated from the loss of all four reactor coolant pumps, both auxiliary feed pumps started, and natural circulation was established in the Reactor Coolant System (RCS). Natural circulation was verified by a reactor inlet to outlet temperature change of approximately 20 F. The loss of the reactor coolant pumps placed the unit in violation of Technical Specification 3.4.1 which requires at least one reactor coolant pump in each loop be in operation while the unit is in Modes 1 through 5. The loss of "J" bus placed the unit in Action Statement (c) of Technical Specification 3.8.1.1 which requires two independent cir-cuits between the offsite transmission network and the onsite Class lE distribution system while the unit is in Modes 1 through 4. Although the SFRCS actuated upon the loss of all four reactor coolant pumps, complete isolation of the steam generators did not occur until the SFRCS received a trip on feedwater differential pressure at 1259 hours. This was due to the low feedwater flou at 20 minutes after a reactor trip. The auxiliary f eedwater pumps maintained the feedwater to the steam generators and provided an adequate heat sink for the reactor decay heat. The Component Cooling Water (CCU) Pump 2 and Service Water (SW) Pump 3 (as 2) failed to automatically start when the diesels were started. The operators manually started both pumps to provide cooling to the Diesel Generator 2. Difficulty was experienced in re-energizing 13.8KV "A" and "B" buser f rom Startup Transformer 02. This was caused by sticking motor cutof f switch operating linkages in the string charging circuit. This required several attempts at closure for bus "A" and a slight tap for bus "B". Therefore, it was not until 1316 hours that bus "A" was re-energized and at 1333 hours bus "B" was re-energized from Startup Trans-former 02. This removed the unit from the Action Statement (c) of Technical LER #79-096

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T_0LEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PAGE 2 SUPPLEMENTAL INFORMATION FOR LER NP-32-79-11 Specification 3.8.1.1 and placed the unit in Action Statement (a) of Technical Speci-fication 3.8.1.1. Startup Transformer 01 was re-energized at 1810 hours on October 15, 1979, removing the unit f rom the Action Statement (a) of Technical Specification 3.8.1.1. Reactor Coolant Pump 1-2 was restarted at 1415 hours, removing the unit from viola-tion of Techn: cal Specification 3.4.1. Due to difficulties in the CCW interlock,2000the remaining reac;-r coolant pumps were not estarted until 1915 hours (Pump 2-2), hours (Pump 1-1), and 0135 hours on the next day (Pump 2-1). Desionation of Apparent cause of Occurrence: The cause of the unit trip wat the failure of the capacitor in the ICS pulser circuit at the reduced Reactor Protection System trip setpoint (the plant trip setpoint was limited to less than 70% of full power by Technical Specification 3.1.3.3 since a reactor control rod absolute posi-tion indicator was inoperable.) The cause of the station blackout was a blowing o of the internals of the muffler on generator output breaker 34560 when it opened for the trip which caused a fault to ground when the breaker was reclosed. These mufflers reduce the sound level when these air blast breakers actuate. The cause of the failure of the CCW Pump 2 and SW Pump 3 (as 2) to automatically start uas due to a failure of the linkage rod assemb'.y in the Diesel Generator 2 outlet breaker AD101. It was discovered the linkage was improperly manufactured in that only one of tao tackwelds had been cade on the assembly; the lone tackweld had failed. The cause of the sticking motor cutoff switch in the spring charging circuit of the 13.8 KV axr circuit breakers operating linkages was due to galling of the linkages which actuate the cutoff switch. The cause of the problem in the CCW interlock to the reactor coolant pump start cir-cuit is believed to be due to defective Couch relays. A relay in the 2-1 RCP circuit was found to have a contact burnt to ground. Corrosion at the base of the relays and relay contact / burning was also noted which may have contributed to the relay deficiencies. Analysis of Occurrence _: There was no danger to the health and safety of the public or to station personnel. Adequate core cooling existed throughout the occurrence and at no time did RCS conditions approach the saturation point. Corrective Action: The f ailed pulser circuit was repaired and proper operation of the ICS was verified. Since this was the third occurrence of problems with the capacitors, B&W investigated the cause of the f ailure (no previous failures resulted in unit trips). It was determined that voltage spikes occurred in the EHC system that exceeded the capacitor design voltage. A capacitor with a higher voltage rating has been installed. LER #79-096  : "~4 354

TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PAGE 3 SUPPLEMENTAL INFORMATION FOR LER NP-32-79-11 The damaged muf flers on both generator output breakers were replaced and a reinforcing band installed to strengthen all breaker mufflers. The cell switch linkage rod assembly in the Diesel Generator 2 outlet breaker has been replaced. The cell switch linkage rod assembly on Diesel Generator 1 outlet breaker as well as twenty-seven other breakers have been inspected with no further deficien-cies discovered. All breakers with cell switch actuators on C1 and D1 bus transfer switchgear were inspected with no further galling discovered. The sticking "A" and "B" bus motor cutoff switch operating linkages were replaced. Adjustment of the motor cutof f switches will be checked by a preventative maintenance program on a refueling outage frequency. All blown fuses wer2 ren' aced in the CCW interlock circuit. The relays on all four reactor coolant pump interlock circuits were replaced. Failure Data: There has been one previous loss of all reactor coolant pumps f rom a power failure, but the power f ailure did not originate at the switchyard (see Licensee Event Report NP-32-77-20). LER #79-096

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