ML20086B198

Ro:On 701126,emergency Diesel Generator B Started & Immediately Tripped.Caused by Activation of Low Coolant Pressure & High Crankcase Pressure Trips.Low Coolant Pressure Setpoint Reduced to 9 Psig from 12 Psig

ML20086B198
Person / Time
Site:	Robinson
Issue date:	12/07/1970
From:	Utley E CAROLINA POWER & LIGHT CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8311170096
Download: ML20086B198 (3)

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Carolina Po>ver & Light Company $2 Raleigh, North Carolina 27602

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December 7, 1970 _

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Dr. Peter A. Morris 'O

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Division of Reactor Licensing U. S. Atomic Energy Commission Washington, D. C. 20545 Re: FACILITY LICENSE NO. DPR-23 DOCKET NO. 50-261

Dear Dr. Morris:

In accordance with Section 6.6.2 of the H. B. Robinson Unit No. 2 Technical Specifications, the Company reports a malfunction of emergency diesel generator "B" following a reactor trip and partial loss of plant auxiliary power.

The malfunction occurred on November 26, 1970, with the unit operating at 70 E' gross electrical load. An export load rejection was initiated to test the transient behavior of feedwater heater drain revisions. Breakers were aligned in the normal manner as per plant procedures with 4160V buses 1, 2, and 4 on the unit auxiliary trans-former and 4160V bus 3 on the start-up transformer. The generator breaker was opened manually from the Control Room to initiate the export load rejection.

Following an unplanned reactor trip, emergency diesel generator "B" started and immediately tripped.

Sequence of Events

. 1. Generator breaker was opened manually from the Control Room.

2. Unit carried its auxiliaries for a short period of time.

3. Reactor tripped due to steam generator "C" low level and steam flow / feed flow mismatched, thus tripping turbine-generator.

4. 4160V buses 1, 2, and 4 did not transfer to start-up trans-former aut':atatically since genera _

ped manually.

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Dr. Peter A. Morris December 7, 1970

5. Emergency diesel "A" started and energized bus E-1.

6. Bus E-2 remained energized from start-up transformer per original lineup.

7. Safety injection was initiated by high steam flow and low T avg.

8. Diesel generator "B" started on S. I. signal but tripped due to low coolant pressure and high crankca'se pressure.

The malfunction of emergency diesel generator "B" was investigated by representatives of Carolina Power &

Light Company, Ebasco Services, and Fairbanks Morse '

Company. Failure of the diesel to start was_ determined to be ~

due to activation of the low coolant pressure and high craniciase pressure trips. The low ccolant pressure trip functioned because the coolant pressure trip set point was above the coolant pressure at the location of the pressure switch. This appears to have occurred because the coolant temperature control valve activated during the cooler weather. The crankcase pressure trip was determined to be due to insufficient margin between the operating crank-case pressure and the trip set point.

Corrective Action

1. The actual pressure at the coolant pressure switch was measured with a test gauge. Minimum pressure was deter-mined to be 12-13 psig. The low coolant pressure set point was therefore reduced to 9 psig. Original' set point was 12 psig.

2. The crankcase pressure was reduced to -4" H2 O at full load and normal operating temperature. This was accomplished by enlarging the flow restricting orifice diameter in the air line to the crankcase ventilation eductor from 0.50" to 0.625". The crankcase pressure trip set point remains-at 40.5" H20.

These modifications were accomplished under the technical supervision of the vendor representative. The engine was returned to service after a complete test.

A telephone report of this abnormal occurrence was made to the Director of Region II Compliance by Mr. Don Kirkpatrick (AEC Compliance Inspector) who was on site . November 27, 1970. A telegram was sentLto Region II on November 27, 1970 as required by Section 6.6.1 of our Tech-nical Specifications.

Yours very trul ,

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cc: Mr. J. A. Jones l- l(7 E. E. Utley /. ,

Manager

.' Generation & System Operations ]$N