ML20039C326

Forwards LER 81-183/01T-0.Detailed Event Analysis Encl

ML20039C326
Person / Time
Site:	McGuire
Issue date:	12/16/1981
From:	Parker W DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20039C327	List: ML20039C326 ML20039C330
References
NUDOCS 8112290231
Download: ML20039C326 (4)

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' A.' 7 4 D, UKE POWER COMPANY Ibwen Urstmixo

M ace SocTn Curucu STurer. Cn.AH OTTE, d'. C. 26242 "I 0?Cf R S . j y W I L LI AM O. PA R K E R, J R, m Pa t s i o te , December 16, 1981 1, u ,,,,,, c , . . . ,0.

5TE4 4 Paoovenow 373-4083 Mr. J. P. O'Reilly, Director U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 Re: McGuire Nuclear Station Unit 1 Docket No. 50-369

Dear Mr. O'Reilly:

Please find attached Reportable Occurrence Report R0-369/81-183. This report concerns T.S.6.9.1.12(g), " Conditions arising from natural or man-made events that, as a direct result of the event require unit shutdown, operation of safety systems, or other protective measures required by technical speci. fica ,

tions." This incident was considered to be of no significance with,r 6pe,c f '.

to the health and safety of the public. f'  ?

VNytrulyyours, '

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Attachments s cc: Director Records Center Office of }bnagement and Frogram Analysis Institute of Nuclear Power Operations U. S. Nuclear Regulatory Commission 1820 Water Place Washington, D. C. 20555 Atlanta, Georgia 30339 Mr. P. R. Bemis Senior Resident Inspector-NRC McGuire Nuclear Station Q l 1 I 8112290231 811216 OTTTGT'iI, COPV l

PDR ADOCK 05000369 ~

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DUXE POWER COMPANY McGUIRE NUCLEAR STATION REPORTABLE OCCURRENCE REPORT NO.81-183 REPORT DATE: December 16, 1981

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FACILITY: McGuire Unit 1, Cornelius, NC IDENTIFICATION: Inadvertent Station Blackout during Loss of Offsite Power Test DISCUSSION: At 2136 on December 2, 1981 the Unit I reactor and turbine tripped on low reactor coolant (NC) pump frequency while a Loss of Offsite Power Test

was being attempted. The test was initiated by opening the switchyard power circuit breakers (PCB) and isolating Unit i from the power grid. The turbine generator was expected to "run back" from its operating load of 30% (315 MWe) to the unit's auxiliary load of 46 MRe while maintaining generating frequency

, within the reactor and turbine trip setpoints. Immediately following the trip of the last PCB, generator frequency increased to 62 Hz as speed control took over and closed the governor and intercept valves. Frequency then dropped to 60 Hz and the intercept valves opened to maintain speed. Covernor valves re-mained closed and the frequency again began to drop after hovering at 60 Hz for a short period. Frequency dropped to 58 Hz and then slowly drifted to 4

56 Hz. The governor valves never opened more than a crack before the reactor

and all four NC pumps tripped on under frequency signals from 2 out of 4 NC l pump motor busses. The NC system went into natural circulation cooling and the safety systems responded as designed. Operators immediately began recover-ing offsite power and the 6900 volt busses were charged after verifying that major pump motor breakers on the busses were tripped. Power was restored to all four 6900 volt busses about two minutes after the blackout started. NC pump B was started at 2140 and forced circulation of the primary system was reestab-lished. Within twenty minutes, NC pumps A and C were started; but, efforts to start NC pump D were unsuccessful because its number 1 seal was apparently cocked. No significant transient resulted from the trip.

Operators continued to recover the secondary side of the plant. The condensate (CM) system was started up using the appropriate Condensate and Feedwater System procedure. Hotwell pump (HWP) A was started about 2212, but the strainer differ-ential pressure rose rapidly ~so B HWP was started and A was tripped. About ten or fifteen minutes later, a seal oil (LG) system trouble alarm was received.

I While investigating this problem, water was noticed coming from the turbine end of the main generator. Operations staff personnel attempted to keep the generator t sealed by running the back up seal oil pump and controlling the system manually.

Other Operations personnel isolated the hydrogen cooler from the CM system and vented hydrogen to atmosphere. The LG system maintains an operating pressure 12 psig higher than the hydrogen pressure in the generator. When the operators reached the LG skid, the local gauge was pegged high (100 psig) due to the high hydrogen pressure. A large volume of water had leaked from the hydrogen cooler into the generator.

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EVAL.UATION: ThelossofOffsitePowerTestwasthefirstthn(of,thetu'rbine L control system in which turbine speed was controlled with a load on3 the generator.g A severe drop in electrical load, from 315 MWe to 46 MWE, added gthe di' ficuljy '"'

of the test. <'

The turbine speed transient thatendedinareactortripwasthefesultofak,.,

improperly set up turbine control system. Damagetothegenerator,hydrogengool-er was apparently caused by starting A liWP with a flow path throut,'poligher ' '

demineralizer cells A, C, and D. ,

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As the CM system is currently designed, seven flow patbs exist between the ifW, ' '

discharge header and the generator hydrogen cooler. Four of the paths are tWough.

polishing demineralizer cells A, B, C and D. Two demineralizer bypass paths [are '

controlled by valves ICM-422 and ICM-423. The seventh path'is a line which gonnects the HWP discharge directly to the condensate bocster pump suction and is contgolled ~

by valve ICM-420. Valve ICM-420 is normally closed and opens.only when a turbine ,

runback is in progress. Valves ICM-422 and ICM-423 operate f rom a. single, controIIer g.

e la H tolimitdifferentialpressureacrossthedemineralizerswhenthecontrollerd,ye,cs-automatic. When the controller is in manual the valves may be positioned as'n sary by a manual loader in the control room. Of the four valves involved ii~h t isolation of each demineralizer cell, 2 inlet and 2 outlet, 2 are operatu by the demineralizer control logic and 2 may be positioned nanually. If a cellsia in -

service and flow drops below a preset limit, the ccrresponding " hold" pump startP ,

and a " hold" valve opens to allow recirculation flew through the cell. 'This pre '

vents loss of the filter coating material which covers the sedeens. The deminer-alizer outlet valves do not automatically close on loss of flow thaough a cell in service, but maintain their operating positions uni u s repositioneT by the cell?' ,%

control system. Cells may be isolated by selecting the " hold" mode on the local control panel. Each cell has its own set of control switches and indication lights- ' ' ,

on the local panel. A set of switch modules is also located in the control room fo'r' '

controlling the operating modes of the cells. Each module., one for ecch cell, has a .

" hold" pushbutton and light, and a " filter" pushbutton and light. These switchen are redundant to the switches on the local panel and are not normally used because .\

station Chemistry personnel have responsibility for operatingqhe cells. During the event the control room operator called the chemistry techtician on duty and asked the status of the polisher demineralizer cells. Based on-the infirmation he~

received he assumed all the cells were ioolated, but'in fact cells A, C'and D were not isolated. Some of the misunderstanding between Operations and Chemistry personnel might be attributable to what is meant by a cell being in " hold". A cell might be said to be in " hold" when the flow has dropped on a cell that was in service.

The hold pump would be running and the water would be recirculating to protect the filter. This condition differs from the " hold" mode because the cell is not iso-laced and the " filter" status light is illuminated.

None of the seven flow paths valves have status lights in the control room. The demineralizer cell valves have status lights on the local panel. Valve ICM-420 has a computer status point.

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b There are three interlocks which prevent starting the first INP when all three pumps are tripped. If ICM-420 or ICM-422 is not closed, INP starts are prevented (ICM-423 closes before ICM-422). Pump start is also prevented if the controller

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, fnr ICM-422 and 1CM-423 is in automatic mode. No interlocks are installed on the demineralizer cell isolation-vnives to. prevent ilWP starts. -

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m, Inspec. Mon of thc paerator determined that no permanent damage had occurred other

, Mhan damage tg Bbt!s at the exciter end of the cooler.

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CORRECTIVEACTION:fThespeedcontrolsontheturbinegeneratorwillbereadjusted

,by Westinghoate personnel to respond more quickly.

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' -4 Work is underway to'teplage the n.amaged hydrogen cooler with the cooler coil from a'

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.- The' stator and rotor of the generator have been heated and dried ou using fans, f heaters, and specially constructed housing structures. Electrical leakage tests

! ,,1 " \ q ,*aere conducted on the insulation to determine the residual moisture present during the drying prcices';.

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!,* A task force ha[, een,; b formed to review this incident and to determine whether T* , procedural or destgrechanges are required.

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• S_AFETYANALYSISI'.Thereactortripandensuingtransientpresentednodangerto A

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the NC syst'em. Development of the capability for a unit to withstand a separa-

\_ tion fEcm its electrical load and offsite power and yet continue to supply auxil-(f, iaryyllads will increare the safety and reliability of the station. The health s aind saf ety of- the 1"ablic was not af fected by this incident.

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