ML20084F602

AO 50-244/73-09:on 731021,instability of Transmission Sys & Loss of Outside Power Occurred Resulting in Reactor Trip. Caused by Procedures Permitting Generation of 435 Mwe When One Transmission Line Was Out.New Procedures Initiated

ML20084F602
Person / Time
Site:	Ginna
Issue date:	10/31/1973
From:	Amish K ROCHESTER GAS & ELECTRIC CORP.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084F607	List: ML20084F602 ML20084F634
References
AO-50-244-73-09, AO-50-244-73-9, NUDOCS 8304210185
Download: ML20084F602 (4)

Text

-

O O

, <. , , . . -4 ..

'< ~j t

.tp --

gx .....

.s .3 ROCHESTER GAS AND ELECTRIC CORPORATION e 89 EAST. AVENUE, ROCHESTER. N.Y. l M t9

• E f TH W A *d t S H  ? t L E ..= 0 5. E

";;a";,R ""lll:'

October 31, 1973

. c0 < i cii ,

x 9 t. i ,

//

e Mr. John F. O' Leary, Director Directorate of Licensing -'

9 nov ge.Q*r en

$2j

• %g g

$ b[

U. S. Atomic Energy Commission washington, D. C. 20545  % .

Subject:

Ab _ al Occurrences 7 -9 Excessive Cooldown Rate 73-10 Malfunction of Safety Injection Pump Suction transfer from Boric Acid Storage Tanks to Refueling Water Storage Tank R. E. Ginna Nuclear Power Plant, Unit No.1 Docket No. 50-244

Dear Mr. O' Leary:

In accordance with Technical Specification Section 6.6.2a, the attached reports of Abnormal Occurrences numbers 73-9 and 73-10 are hereby submitted. .

Additional information and further action taken by Rochester Gas and Electric Corporation will be reported as information becomes available.

Very t ly yours,

~

j V S)

Keith W. Amish Attachments xc: Mr. J. P. O'Reilly J

,V r 7 /h r t[;I t

( 8304210185 731031 2 i PDR ADOCK 05000244 79*

COPY SENT REGION -

m .__ . _ a p q 1, l

Q Q s-ATTACHMENT 1 Report Number: 50-244/73-9 Report Date: October 31, 1973 Occurrence Date: October 21, 1973 Facility: R. E. Ginna Nuclear Power Plant, Unit No.1 Docket No. 50-244 Identification of Occurrence: Excessive Cooldown Rate Condition Prior to Occurrence: Steady State Power at 435 MWe net Description of Occurrence: Instability of the transmission system and lo::s of outside power to Ginna Station occurred on October 21, 1973 at approxi-mately 0552 hours0.00639 days <br />0.153 hours <br />9.126984e-4 weeks <br />2.10036e-4 months <br /> resulting in a reactor trip. The sequence of this loss occurred as follows:

Of the four 115 Kv transmission lines from Ginna Station (Nos. 908, 911, 912 and 913), Circuit 912 had been taken out of service at 0512 hours0.00593 days <br />0.142 hours <br />8.465608e-4 weeks <br />1.94816e-4 months <br /> for safety reasons for construction on a new substation. Circuits 767 and 751 (34.5 Kv) were supplying auxiliary power for the station. A ground fault on Circuit 908 caused the loss of this line, leaving only Circuits 911 and 913 in service. The system demand during the early morning was light compared to the generator output and electrical power swings caused Circuits 911 and 913 to trip which isolated the plant's substation (13A) from the 115 Ky system.

The loss of the four 115 Kv circuits overloaded Circuit 759 which was supply-ing Circuit 751 and it burned open at a remote location. The loss of outside power on Circuit 751 plus loss of all power from Station 13A which supplies power to Circuit 767 resulted in a loss of all outside power to Ginna Station.

• From analysis of the electrical recordings and computer printouts, it is con-cluded that an electrical disturbance on the instrument buses within the plant was created during the loss of power which caused an overpower delta temp-erature reactor trip signal to trip the reactor. The loss of outside power also generated a turbine trip signal.

A "lo-lo steam generator level" signal in both steam generators caused auto-matic start of both steam and motor driven feedwater pumps. The automatic start of these pumps resulted in ambient temperature water from the condensate storage tanks being pumped into the steam generators. The operator recog-nized that the steam generator levels were increasing, secured the motor driven auxiliary pump and sent an auxiliary operator to secure the steam driven auxiliary pump by tripping the governor valve. Further review revealed that an additional signal was generated by the loss of outside power on buses 11A and 11B which placed the steam driven auxiliary pump in service. This signal remains in effect until the " loss of outside power" signal is cleared and thereby prevents operator action from the main control board. The pump can only be stopped locally. The cooling down of the secondary system cooled down the reactor coolant system to the point that the safety injection signal

l '

Attachmcnt I cont'd. 2

.O O~

. .- /-

was generated by a combination of low pressurizer pressure and level. The initiation of safety injection caused borated water to be pumped into the reactor coolant system.

l Investigation into the cooldown rate as indicated by the strip chart recorders l revealed that the cooldown rate as defined in the Technical Specifications, Section 3.1.2.1 Cooldown Item b. , may have been exceeded. The cooldown rate is difficult to determine accurately due to the loss of instrument buses l which disabled various indicators and recorders for a short period of time.

l Reco'nstruction of the information on the recorders when power was restored indicated that the change in temperature in the reactor coolant cold leg was l approximately 85 F in approximately 10 minutes. For this short period of time, the rate was in excess of the 1000F/hr. limit and is therefore reportable as an i abnormal occurrence as defined in Section 1.9b, " Violation of a limiting j condition for operation established in the Technical Specifications."

Designation of Apparent Cause of Occurrence: Loss of outside power was due to procedures permitting Ginna Station to generate 435 MWe when one trans-mission line was out. This condition also led to instrument bus disturbances l which generated false "lo-lo steam generator level" signals for both generators l and automatically started both steam and motor-driven auxiliary feed pumps.

l Analysis of Occurrence: The Electric System Planning and Operation Depart-

ment of Rochester Gas and Electric has determined that loss of outside power was due to a power instability. condition caused by. low. electrical-system demand.

l Westinghouse was contacted to determine what possible deleterious effect the l rapid cooldown could have had on the reactor vessel. Their initial analysis I

and comparison with similar instances at other faci'.ities indicate stress levels to be acceptable and the effect of this one cooldown cycle to be insignificant .

in the allowable fatigue life of the vessel.

With the exception of the instrument bus disturbances which generated inac-curate signals, no equipment malfunction or operator error was apparent.

i Corrective Action: The Electric System Planning and Operation Superintendent

! has ordered that whenever any transmission circuit from Ginna Station (Nos. 908, l 911, 912 and 913) is out of service, the Ginna Station electric load shall be

reduced to 240 MWe net. Initial analysis has determined that the system should l be stable with two lines out with the plant output as high as 300 MWe on the generator. The Plant Superintendent has issued similar orders to Ginna Station operators for power reduction on the occasion of line outage,s.

The Plant Operations Review Committee is reviewing the Ginna Station Emer-gency Procedure E-4 (Station Blackout Operation) to incorporate experience gained as a result of this occurrence.

The Engineering Department and Westinghouse are reviewing the logic for the operation and control of the auxiliary feedwater pumps in view of the rapid filling of the steam generators during this occurrence.

Westinghouse has been requested to provide a written report on the effects of the cooldown to the primary system.

Attachment 1 c . 3.

The Plant Operations Review Committee reviewed th'is occurrence and determined that there were no unresolved safety questions. The Nuclear Safety Audit and Review Board reviewed the occurrence and the action taken and concurred with the Plant Operations Review Committee.

Failure Data: There have been no previous instances of loss of power to Ginna Station due to electrical system instability.

9

+

9 e

G e

i l

l l

l l