ML19317D927
| ML19317D927 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 01/20/1975 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317D923 | List: |
| References | |
| RO-269-74-09, RO-269-74-9, NUDOCS 7912100606 | |
| Download: ML19317D927 (2) | |
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l DUKE POWER COMPANY OCONEE UNIT 1 l
Ep Report No.:
UE-269/74-9 Report Date: January 20, 1975 Event Date:
December 4, 1974 Facility:
Oconee Unit 1, Seneca, South Carolina Identification of Event: Reactor Building Cooling Unit Logic Error Conditions Prior to Event: Unit in Refueling Shutdown Description of Event:
On December 4, 1974, the annual Reactor Building Cooling Unit (RBCU)
Engineered Safeguard (ES) and Performance Test, PT/0/A/0160/03, was con-ducted for Oconee Unit 1.
The test confirmed that RBCU fans lA and 1B shifted from high speed to slow speed, as designed, when ES Channel 5 tripped.
RBCU fan 1C, which was idle with its controller in the " auto" position, started and went to high speed as the other two fans shifted to slow speed. When ES Channel 6 was tested, RBCU fans 1B and 1C shifted from high speed to slow speed, as designed; however, RBCU fan LA, which was idle with its controller in the " auto" position, started and went to high speed.
The Reactor Building Cooling System Design description in the Final Safety Analysis Report Section 6.3.2.1 states that upon receipt of a signal from the Engineered Safeguards Actuation System, the two operating fans reduce speed and the third fan starts in reduced speed.
If both ES Channels 5 and 6 are actuated, this description is accurate; however, if only one channel is actuated, the third fan starts and goes to high speed as was described above.
Designation of Apparent Cause of Event:
The normal operating configuration of the RBCU fans is two in high speed and the third fan idle with its controller in the automatic position.
If one fan fails, the third automatically starts in high speed and maintains normal Reactor Building ventilation.
'The apparent cause of this event is the interface between the normal and Engineered Safeguards logic. As the two operating fans shift to slow speed, in response to a single channel ES actuation, the idle fan senses the loss of a high speed fan and starts in fast speed.
The intent of the FSAR is that the actuation of a single ES channel will rest.lt in two fans in slow l
speed.
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Analysis of Event:
t Two Reactor Building cooling fans normally operate in high speed to maintain the Reactor Building environment.
In the unlikely event of an ES actuation, all three fans are utilized in slow speed to remove the heat in the Contain-ment atmosphere.
The speed of the fans is reduced to offset increased power requirements due to the increased density of the building atmosphere.
If an ES actuation had been required, and both ES Channels 5 and 6 had functioned properly, all three RBCU would have run in slow speed, as designed.
If only one rf these two ES channels had actuated, two fans would have operated in slow speed and one in high speed.
It'is possible that the high speed fan would have tripped; however, the two operating RBCU are sufficient for Reactor Building cooling under accident conditions and the Reactor Building Spray System provides full capacity, redundant cooling of the Reactor Building.
Thus, it is concluded that the health and safety of the public was not affected.
Corrective Action:
A design review of the RBCU fan logic is in progress and appropriate modifi-cations will be installed to ensure the proper operation of the Reactor Building Cooling Units.
In the interim, the fan which is not normally operating will have its controller in the off position. This will allow the fan to respond properly to an ES signal; however, it will not auto-matically start should an operating fan fail in normal operation.
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