ML19323G990

LER 80-047/01T-0:on 800523,safety Injection Occurred Due to High Steam Line Flow Signal Coincident w/lo-lo Tave.Caused by Loss of Vital Bus 1-III Which Removes Power from Feedwater Flow/Steam Flow Comparators for Steam Generators

ML19323G990
Person / Time
Site:	North Anna
Issue date:	06/04/1980
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19323G989	List: ML19323G988 ML19323G990
References
LER-80-047-01T, LER-80-47-1T, NUDOCS 8006090361
Download: ML19323G990 (4)

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RErCmT Dara 80 EVENT DESCRIPflCN AND PRCSASL5 CONSEQUENCES h Ia # 2i l At 0146 on May 23, 1980, with the unit at hot standby, actuation of the I A l Emercency Core Coolina System was initiated on hich steam line finw sional 1 lo,. l coincident with lo-lo Tave due to a loss of Vital Bus 1-III. Since this was an l l TTTI I inadvertent actuation (equipment performed the intended injection functic.1) and I I o 6sj l the reactor was alreadv shutdown, the nublic health and safaty were not l l") f7) l , s sn-end. o n en .-* , k i n n,*e,n-* *n T.e. c o.1.o i. l I1tdl I I s.

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Virginia Electric and Power Company Norch Anna Power Station, Unit #1

Attachment:

Page 1 of 3 Docket No. 50-338 Report No. LER 80-47/01T-0 l

Description of Event At 0146 on May 23, 1980, a Safety Injection occurred due to high steam line flow signal coincident with lo-lo T . This event resulted from the loss of Vital Bus I-III. At 0146, oniy* Train A of Safety Injection was actuated because the loss of Vital Bus 1-III deenergized the Solid State Protection System output cabinet for Train B. When power was restored to Vital Bus 1-III at 0148, Train B of Safety Injection was actuated. There was no release of radioactivity j during the transient.

As a result of the Safety Injection, the contents of the Boron Injection Tank (BIT) were flushed to the Reactor Coolant System which caused the concentration of the BIT to fall below the Tech. Spec, limit of 20,000 PPM borated water. Although the Tech. Spec. Limiting Condition for Operation was not met following the event, the BIT did perform its intended function.

As a result of the Safety Injection, the Refueling Water Storage Tank (RWST) level dropped below the 478,058 gallon limit required by T.S. 3.1.2.8.b.1 because the safety injection pumps draw suction from this tank to provide for the cold leg injection. Therefore, the RWST performed its function as intended.

As a result of the Safety Injection, the level in the Emergency Condensate Storage Tank (ECST) went below the value given in T.S. 3.7.1.3.

This is an expected occurrence following an ECCS actuation since the i auxiliary feedwater pumps take suction from this tank and start on a SI

) Signal to feed water to the steam generators. The ECST performed its j design function.

i During the Safety Injection the following unexpected events occurred i

which are contrary to Technical Specifications.

Upon receiving the Safety Injection Signal, emergency diesel generator 1H automatically started as designed; however, it tripped shortly thereafter on overspeed. The trip was reset and the diesel was

successfully restarted to verify operability. This is a second occurance of diesel overspeed following a Safety Injection. The periodic test on IJ diesel generator was in progress at the time of the Safety Injection following preventative maintenance on the IJ diesel. The required one hour run on the IJ diesel had been completed and the diesel was paralleling the normal power supply to the emergency bus.

Also, fcllowing the Safety Injection a hi-hi containment pressure alarm was locked in due to a failed compstator card due to blown fuses.

The card fails in the safe (tripped) mode. The card was replaced and recalibrated.

The ECCS actuation is reportable per T.S. 3.5.2 and 6.9.2. However, Regulatory Guide 1.16 states that ECCS actuations are reportable under Unit 1 T.S. 6.9.1.8.i which requires a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> notice and written follow up. This report is intended to meet the additional requirements of the 90 day report for T.S. 6.9.2.

The other events included in this discussion are reportable as 30 day items by T.S. 6.9.1.9.b.

This is the sixth actuation of the Emergency Core Cooling System reportable under T.S. 6.9.2.

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Attachment 2 of 3 Probable Consequences of Occurence The purpose of the Emergency Core Cooling System is to ensure adequate cooling of the reactor in the event of a loss of coolant accident. Although the safety injection system performed its intended function to inject borated water into the Reactor Coolant System, an actual accident condition did not exist and therefore the SI was not required. As a result, the health and safety of the general public were not affected.

Cause of Event The cause of the Safety Injection was the loss of Vital Bus I-III which removes power from feedwater flow / steam flow comparators for all three steam generators producing a high steam line flow signal. The loss of Vital Bus 1-III also cuts off supply of cooling water to the Reactor Coolant Pumps. The loss of coolant flow requires the operator to trip the Reactor Coolant Pumps which was done at 0141 stopping flow thru the RTD bypass lines. Due to ambient losses, the temperature in these lines dropped to the lo-lo T setpoint which together with the high steam line flow signal produc$3'the Safety Injection Signal.

The loss of Vital Bus 1-III was caused as a result of starting "A" Reactor Coolant Pump. The start of "A" RCP on Unit I at 0136 on 05-23-80 with the other two RCP's on Unit I and all three RCP's on Unit 2 running caused a reduction in voltage on "A" Reserve Station Service to which "1J" emergency bus is connected. At this time "1J" diesel was tied to this bus and it picked up load. The normal feeder breaker, 15J11, was tripped by directional overload relays. This caused a load rejection fror "1J" diesel. It is postulated that this load rejection caused a surge in voltage which was transmitted thru the battery charger and the batteries to 1-III inverter which blew two fuses, cau ing a loss of Vital Bus I-III.

The low levels in the RWST and ECST, and the loss of boric acid from the BIT, are all normal results of a Safety Injection and are expected to occur.

, The IH diesel generator tripped on overspeed following its automatic start because the governor failed to operate properly. Possible sticking or worn parts caused the governor to operate sluggishly.

The fuses in the comparator card for hi-hi containment pressure were apparently blown when Vital Bus 1-III was restored.

Immediate Corrective Action The Safety Injection Signal was reset at 0149 and Safety Injection was terminated by the control room operators in accordance with the applicable Emergency Procedure at 0151 when Reactor Coolant System letdown was established and cold leg injection flow was secured.

The operators refilled the RWST and ECST and reborated the BIT to their proper limits as required by the appropriate Technical Specification ACTION statements.

The governor on diesel generator 1H was replaced with a rebuilt govtrnor and several adjustments were made by the vendor representative.

The diesel generator was retested by special testing and determined to be operable.

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Attachment:

Page 3 of 3 The comparator card for hi-hi containment pressure was replaced.

The Vital Bus 1-III was restored by switching the power supply from the inverter to the voltage regulating transformer which was done at 0148 on 05-23-80. The blown fuses in the inverter were later replaced and the inverter put back in service.

Scheduled Corrective Action Operating procedures will be changed to caution against starting a Reactor Coolant Pump or other large loads if an Emergency Diesel Generator is tied to the same Reserve Station Service Bus as the Reactor Coolant Pump. Also, procedures will be changed to caution against adding large loads above prescribed Reserve Station Service loads.

The governor from "1H" Emergency Diesel Generator will be sent to the manufacturer for inspection. Diesel governors are scheduled to be replaced with rebuilt governors on a rotating basis for both Unit 1 and 2.

Fuses on all four inverters will be replaced.

Actions Taken to Prevent Recurrence A standing order was issued to avoid starting a Reactor Coolant Pump if an Emergency Diesel Generator is tied to the same Reserve Station Service Bus as the Reactor Coolant Pump.

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