ML20064F982
| ML20064F982 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 11/08/1978 |
| From: | TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML20064F981 | List: |
| References | |
| NUDOCS 7812060129 | |
| Download: ML20064F982 (1) | |
Text
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. ENCLOSURE SEQUOYAH NUCLEAR PLANT UNITS.1-AND 2 4'
FAILURE OF LACK DRAFT DAMPER IN MAIN CONTROL ROOM AIR HANDLING UNIT FINAL REPORT Description of Deficiency
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The failure of the backdraft damper in one of the two trains of the Main Control Room (MCR) air handling units ( AIIU) was discovered during a routine modification of the system.
The failure of the subject damper was the loss of all the blades from the damper.
The cause of damper blade failures was excessive wear of the nylon damper blade bearing due to oscillatory motion.
The oscillatory motion was probably caused by poor balance of the damper blades.
There have not been similar failures of backdraft dampers im to this time at any of TVA's other nuclear plants.
The backdraft a sper in the. other train of the MCP AHU's has been l
'nspect d and it has 1ost one of its damper blades.
It appears
..iat even though the failure of th>s latter damper is not as severe, the failure mode is similar to the failure experienced by the first backdraft damper.
Safety Implications If this damper failure had remained uncorrected, a single failure (power loss in the affected MCR AIIU train, for this case) would permit the air operated suction damper in that train to open.
The ductwork is arranged so that in this situation a partial short circuit of the air flow from the opposite train would occur.
See Sequoyah TSAR Figure 9.4-2 for further details.
This short circuit situation would reduce the supply of cooling air available to the f1CR.
Partial loss of cooling to the MCR could lead to unreliable operation of the instrumentation in the MCR.
'nreliable operation of MCR instrumentation could place in
- eopardy the safe operation of the plant.
Corrective Action _
i TVA has replaced the two failed backdraft danpers.
They were replaced with high pressure dampers equipped with stee] ball bearings.
Af ter irfstallation of the new backdraf t dampers, f u nc t.iona l testing'of them was performed with engineers from TVA Division of Engineering Design observing the test.
?o harmful oscillations were observed in either damper.
Each damper closed liqht when its associated air handling unit was off and opened to the proper position and held that position with a minimum of movement when the air handling unit was in encration.
The air handling units for the Main ContrM Room at Watts Bar t'uclear Pl ant are similar in design to those at Sequoyah.
Ilowe ve r, the backdraft dampers are of different, heavier construction with bearings made of metal instead of nylon.
7W206612T )
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