ML20042G941

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LER 90-004-00:on 900413,ESF Group Isolations & Diesel Generator Starts Occurred Due to Equipment Malfunction & Personnel Error.Equipment Repaired,Manual Disconnect Operating Location Labeled & Personnel trained.W/900510 Ltr
ML20042G941
Person / Time
Site: Cooper Entergy icon.png
Issue date: 05/10/1990
From: Horn G, Myers J
NEBRASKA PUBLIC POWER DISTRICT
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CNSS903669, LER-90-004, LER-90-4, NUDOCS 9005160314
Download: ML20042G941 (7)
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                                     .  .                                 COOPER NUCLEAR STATION .

Nebraska Public Power District - " * * "A"E *a'Es %""*>'?^ "'" CNSS903669 " ' May 10, 1990 U.S. Nuclear Regulatory Commission Document Control Desk-Washington, D.C.- 20555

Dear Sir:

Cooper Nuclear Station Licensee'. Event - Report ,90-004, : Revision '0, is being. forwarded as an~ attachment to this letter. 9 SineSrely,- L/ t G. in Horn:. Division Manager of Nu'elear Operations Cooper Nuclear Station GRH:bj s At'tachment cc: K. D. Martin ' L. G. Kunc1 R..E. Wilbur V. L..Wolstenholm G. A. Trevors INPO Records Center ANI Library NRC Resident Inspector R. J . . Singer CNS Training , CNS Quality Assurance 9005160314 DR 90031o ' - gk ADOCK 05000298 F PDC 1: 

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j j l l Ns i' l l l l l l l l l [ gg !!5ii( ' l l l 1 I I l ' ' l I I I I l'I SuPPLEASENTAL A890AT EXPGCTt0 He MONTM OAv YEAR SuemeS$ ION Yt$ 489 v.e. ees eer IJrotCTt0 SventistION DATil NO l l l AsefuCT ro ,, . ,e a A. ,- ,, ,,N P,, .-. en r , nei on April 13,-1990, at 9:10 P.M., during the 1990 refueling outage, an l automatic start of both diesel generators, Group 6 Isolation and a half scram and half Group 1, 2, and 3 Isolations occurred. These actuations were caused by loss of power to the Startup Station Service Transformer. An equipment malfunction caused the manual disconnect for the Startup Station Service i Transformer to be improperly seated and resulted in a transformer protective relay actuation when the B Core Spray Pump was started. l l Subsequent to correction of the manual disconnect seating, while restoring the l plant to the normal shutdown electrical lineup, at 3:11 A.M., on April 14, operation of an incorrect breaker control switch caused a momentary loss of , power to a critical bus resulting in Diesel Generator #1 start, Group 3 and 6

solations, and a half scram and half Group 1 and 2 Isolations. Operation of the incorrect switch was due to cognitive personnel error by the licensed operator.

Following the actuations, proper plant response was verified, the isolations l- reset, and plant systems returned to normal. The plant was in a refueling outage with fuel being reloaded into the core. l l Corrective action includes repair of the equipment involved, labeling at the ' I manual disconnect operating location, and training. l 1 Nnc e me temi l

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TEXT CONTINUATlON W",,7."4R""d'v?Aa,'.=wAsMtNGTOes. DC 2060 Op asAseAotugist AND SUDGET 9 ACILITY NAAf8 H) DOCK 8T NVIilB6R 428 LSR NUh00$R ($1 PADS (31 vtan 3 sa i,a, 6 jc sy,N Cooper Nuclear Station 0 l5 l0 l 0 l 0 l 219 l8- 9l0 - 0l0l4 - 0[0 0 l2 0F 0 l6 ftXT I# neue assee 4, seguset, use anime, ant MIC Alene MsJ t1h A. Event Descriotions ESF actuations occurring.atl Cooper Nuclear Station as'a. result of power. interruptions to the-critical buses are described in the following report.- A diagram of the AC Electrical Distribution System is'provided

  • in Figure 1.

The Startup Station Service Transformer and its associated electrical 

                                 . bus had previously been removed from service for testing.and inspection-
                                                                                              ~

during the 1990 Refueling' Outage. The= clearance.for the Startup Station ~. Service Transformer included opening the manually operated tower mounted disconnect on the-incoming 161KV line. The. clearance for the transformer was released during the evening of April 12 and house loads were shifted.to the Startup Station Service Transformer. At 9:10 P.M., on April 13, while attempting to start the "B" Core Spray Pump, a Startup Station Service Transformer neutralutime overcurrent lockout . relay actuated, resulting in loss of the Startup Station Service Transformer, automatic starting of both diesel generators, Group 6 j Isolation, as well as a half scram'and half Group 1, 2,jand 3 ; Isolations, as designed.-- Both 4160V critical; buses automatically transferred to the Emergency Station Service Transformer, which re-energized the buses as designed. The half Group 2 Isolation resulted in temporary loss of shutdown cooling,'and the; Group 6 Isolation' caused the Reactor Building Ventilation System to isolate and the' Standby Gas i' Treatment System co start. i In response to Control Room, indications, operators verified proper plant response, The actuations were reset, the diesel generators restored to . standby, and shutdown cooling and Reactor Building ventilation restored  ! to normal by 11:30 P.M. Refueling operations which had'been in progress were suspended until the systems were returned to normal. A Nebraska Public Power District utility line crew was called in'to assist in investigation of the lockout relay actuation. After

determining that e disconnect link was not properly seated on the tower i mounted-disconnect on the incoming 161KV line,'the operating'linkaSe wa8 l

repaired, the disconnect reopened and reclosed, and proper seating verified by a lineman climbing the tower. Following re-energization of the Startup Station Service Transformer, , . power supplies were being transferred from the Emergency Station' Service > l' Transformer to the Startup Station Service Transformer. Buses 1B, 1G and 1A had been transferred, and personnel were in the process of ' transferring the IF Bus when operation of an incorrect breaker control l- switch caused a momentary loss of power to the IF Bus at 3:11 A.M., on [ April 14. The loss of power caused the #1 Diesel Generator to start, Group 3 and 6 Isolations, as well as a half scram and half Group 1 and 2 ' Isolations, as-designed. Nac e senA <s=

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*Aciury NAase tip                                            oocast NUMSem W                               LER NUMg6R tel                   PA96 (35 YEAm       -

88 $$^b  :' : 7* *$*' Cooper Nuclear-Station o l5 l0 l0 l0 l 2l 9 l8 9l0 - 0 l0l 4 - 0]O O l3 ~ OF 0 l6 text w me. m =e-w. w. Mm w me s.,in 3 sam nn A. ' Event Descrintions'(Continued): " I The power loss was immediately apparent through control room 1 indications, and.the operator quickly closed the correct breakers, restoring power to Bus IF. As a result of the half Group 2 Isolation, shutdown cooling was temporarily lost, and as a result of the Group 6 Isolation, the Reactor Building Ventilation System isolated and the Standby Gas' Treatment System started. The'ESF actuations were reset,;the diesel generator returned to standby, and Reactor Building ventilation and shutdown-cooling restored to normal operation by 4:30 A.M. B. Plant Status The plant was in a refueling outage, with fuel being reloaded into the-core. Reactor Coolant temperature remained at 73 degrees Fahrenheit. C. Basis For Report . i. Unplanned actuations of Engineered Safety Features (ESP), reportable in accordance with 10CFR 50.73 (a)(2)(iv). D. Cause The root cause of'the first loss of power was.a slippage in the disconnect operating mechanism such that operation of the m'echanism resulted in incomplete closure of the disconnect link. The disconnect is located approximately 35 feet above the ground on a transmission line structure. The disconnect links are operated by a gearbox, vertical shaft, linkage, and rotating bushing. . Investigation by the line crew found that the vertical shaft had slipped relative to the gearbox, , preventing full seating of the disconnect link. Due to the partial ' engagement an overcurrent condition developed when the starting current of the core spray pump was imposed. The cause of the second loss of power was cognitive personnel error by licensed operators. The operator performing this evolution failed to verify that the correct breaker control switch was selected prior to its operation. The personnel involved were aware that Breakers IFS and 1FA-are interlocked such that only one can be closed. A caution sign is located on the panel near Breaker 1FA indicating that 1AF must be closed prior to closing 1FA, The procedure being used also indicated the complementary relationships between these breakers, y fenC Perin 3EBA (6498

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                                                                                       ~ W.W..e.'i"ll""oa.UOGE CF MANAQ5aeENT ANO M^e'M?'hi.*#.'& t"?.Ci-     "

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0 l0l 4 - 0l0 Ol4 0F 0-l 6 rext uni . w .asm.wmacr maawon E. ' Safe ty Sinnificance None. The Group Isolations-occurred as designed, the diesel generators started as' required, and the critical buses automatically transferred to the 69KV off-site power source. F. Safety Imolications - a None. -The disconnect at the Startup Station Service Transformer'is , 

        ,                 -operated infrequently, and would not'normally be used during operation-                                         .;

as the Startup Station Service Transformer is required to be operable by.  ; the Technical Specifications._ Back up power for' critical loads is-supplied by the Emergency. Station Service Transformer and the Diesel 

                          -Generators.

During normal power operation,-power to the station auxiliaries is supplied by the Normal Station. Service Transformer, except that one reactor recirculation pump M-G set is powered from the Startup' Station Service Transformer. A fast transfer from the Normal to tho'Startup Station Service TransformerLis provided. If the disconnect'at the Startup Station Service Transformer were improperly restored while at power,-an overcurrent condition would most likely be created when. power from the Startup Station Service Transformer would be required during.a reactor recirculation pump M-G set transfer to the startup power source, a unit shutdown, or upon fast transfer following:a reactor trip. The loss of the Startup Station Service Transformer would result in ESF actuations similar to those reported'in this LER, loss-of non-essential power, and a reactor trip. Procedures and operator' training at4 in place to accomplish recovery under these circumstances, i During plant operation, the 1A, 1B, 1F and 1G Buses are normally povered ' from the Startup or Normal Station Service Transformer. If Bus IF or 1G were aligned to the Emergency Station Service Transformer and a similar error was made during restoration, a similar ESF actuation would occur, without significant effect on the plant. G. Corrective Action A " caution" label will be placed near the manual disconnect operating mechanism identifying the special need for verifying disconnect closing. Additionally, the associated procedure will be reviewed and revised as i required. Switchyard training for operators will be enhanced to l emphasize the need for verification of disconnect closure and the methods to accomplish this verification. This will ensure that discrepant conditions are corrected if the linkage mechanism should malfunction. NRC Pese 30GA 1640) -

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                                                                                           "MWla"# 'T&J8"#32:I?T M ai,Ci OF MANAGEM6#T ANO evDGET.WASM4NOTON,DC 20003-FACILifY MaaSSlu                                        00CMtf NUtdSGA 42)                      Ltm afUhseth ($1                     PAtt(31 vs.a       s '* m .a6     f   'lg' Cooper Nuclear Station                                   .                .
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0 l0l 4 - 0l0 0 l .5 ,0F 0-l 6 i Text wm , ww Am.wanc wassawon . ~l i i G. Corrective ~ Action (Continued) The procedure involved in;the'second event is slated for review as part j of_the procedure upgrade; program. This review will include the' i misoperation discussed in this' report. This event will'also be covered in industry events training. H. Similar Events  ! 5 review of previous ESF actuations found none_which were the result of j improper restoration of manual disconnect switches or the misoperation j of breaker controls on the electrical distribution panel. j 1 1 

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