ML19308D325

RO-77-20:on 770302,cooldown Rate in Excess of Tech Spec Limit Occurred Due to Loss of Ics,Causing Reactor Trip, Turbine Trip & Atmospheric Steam Dump Valves to Open.Caused by Output Diode Failure in B Inverter.Diode Renewed

ML19308D325
Person / Time
Site:	Crystal River
Issue date:	03/10/1977
From:	Stewart W FLORIDA POWER CORP.
To:
Shared Package
ML19308D324	List: ML19308D323 ML19308D325
References
NUDOCS 8002270774
Download: ML19308D325 (2)

Text

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@ l During normal operation in Mode 1, excess cool-down rate as defined by T.S.3.3.9.1 was l 7 U is

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CAU!.;L DESCR;PTION ,

g l An output diode failure in "B" inverter caused loss 'o f vital AC to the ICS, this in turn  !

7 o9 ,gg J l tripped the Rx/ turbine and caused the atmos dump valves to open to 507.. The failed j GO f component was renewed and "B" inverter restored to service.

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y Supplementary Informatio_n

1. Report No.: 50-302/77-20

2. Facility: Crystal River Unit #3

3. Report Date: 10 ifarch 1977

4. Occurrence Date: 2 March 1977

5. Identiftention of occurrence: .

During normal operations in Mode I, an excessive cool-down rate as defined by T.E.3.4.9.1 una experienced, in that the cool-down rate was approximately 164 F per 15 min.

6. Conditions Prior to Occurrence:

On March 1977 Crystal River #3 was in normal ifode I condition at 40*: power. -)

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7. Description of occurrence:

At approximately 1948, 2 !! arch 1977 the loss of "n" AC inverter caused the l Joss of "B" vital AC bus. Pouer was lost to the TCS causing a neactor trip, turbine trip, and the atnospheric steam dump valves to open 50".. A chech af ter the Reactor trip revealed that the "A" breaker supplying power to the control rod driva motors had also tripped due to the time required to swap the bun to the start-up transformer. The main feeIwater pumps tripped due to loss of vacuun and steam generator feed was continued via the emergencg feedwater pumps. Reactor coolant temperature decreased from 530 F to 416 T l in approximately 15 minutes. Plant normalization was begun innediately vacuum I was re-established at 2230.

8. Designation of Anparent Cause of Occurrence:

The cause of this occurrence was an output diode failure in "B" AC inverter j causing the chain of events previously described. 1

9. Analysis of Occurrence:

At all times the Reactor Coolant temperature / pressure parameters remained within the Region of Acceptable Operation set forth in Technical Specification 3.4.9.1, Figure 3.4-3. Prior to resuming Start-up and Power Operation, an engineering evaluation was performed to determine the effects of the cool-down on the fracture toughness properties of the Reactor Coolant System. Based on this evaluation, it was determined that the Reactor Coolant System remained acceptable for continued operatton.

10. Corrective Action:

Trouble shooting of "B" AC inverter revealed that output diode had failed. The diode was renewed and "B" AC inverter was restored to operating condition.

11. Failure Data: ,

1 l

l No previous failures of this type have been experienced.

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