ML20084B202
| ML20084B202 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 07/20/1972 |
| From: | Clemenson F, Connery L US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Long C US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084B161 | List: |
| References | |
| NUDOCS 8304060177 | |
| Download: ML20084B202 (3) | |
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UNITED STATES
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ATOMIC ENERGY COMMISSION J.?. '.
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3 li,77.6 Jul, t 01372 Docket No. 50-254 To Files e4 Thru:
Charles G. Long, Chief, Auxiliary & Power Conversion Systems
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Branch, L QUAD-CITIES, UNIT 1 - TURBINE BUILDING FLOODING INCIDE'iT This meno reports the APCSB findings and reccamendations in response to a technical assistance request (TAL-32) from the Assistant Director of Operating Ecactors following the June 9, 1972, Quad-Cities Turbine Building riooding Incident.
An abnormal occurrence took place uhile making modifications to the main condenser circulating water butterfly valves and its associated control system during a scheduled naintenance outage.
The occurrence was due to uator hammer which caused the rubber expansion joint, located below one of the train condenser unter boxes, to rupture.
Rupture of the expansion joint permitted the circulating water to flood the turbine building to a level of 15 feet 6 inches in the 6 minute interval before the supply breakers on all major cicctrical equipment in the area could be racked out of service. The circulating water pumps were delivering about 510,000 gpm to the condenser.
Flooding of the turbine building resulted in the loss of the following safety related equipment housed in the turbine building:
(a)
The cooling water pumps for 2 out of the 3 station emergency diesel generators.
(b)
All 4 residual heat removal system service water pumps.
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(c)
The station seismograph.
In addition, the condensate pumps were made inoperable.
In the Quad-Cities design, as in many other large power plants, the trend has been to design the circulating water system such that it is possibic to reverse the flow on a regular basis to assist in keeping the tubes and water boxes clean.
Also, due to tne size of these lines and valves, 120 inches, the trend has been toward butterfly valves. This type valve can be quickly operated i
and enable flow reversal to be performed while the plant is operating at i
reduced power.
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Eight of these valves are on the Quad-Cities Unit I condenser.
To hold down cost and ucight of the valves and their actuators they have mounted a hydraulic cylinder actuator on each valve.
Then with two hydraulic control units (one serving as a spare) they sequentially operate the eight valves.
Before modification the valves were main-tained in position by the hydraulic system.
Limit switches sensed any drift in valve position.
Due to frequent drift of the butterfly valves the hydraulic control unit operated excessively. Therefore, it was decided to modify the cystem by manually pinning the valves in position once they vere properly positioned.
The abnormal occur-rence took place when (1) the circulating water pumps were operating, (2) the valves had not been pinned in position, and (3) they were venting and filling the hydraulic control unit. Apparently a valve started to drif t and the circulating water flow caused the valve to slam shut and created water hammer.
Due to the venting and filling operation, the hydraulic unit was unabic to control the motion cf the valve.
FINDINGS 1.
The feature of being able to reverse the direction of flou of the main condenser circulation while at pouer is advantageous on most large nuclear plants where mud and debris can bc,
deposited.
(Dresden 2 and 3, Quad-cities 1 and 2.)*
2.
The applicant has taken positive steps to protect the safety related equipment located in the turbine building.
It is not cicar that the redesign of the hydraulic control system vill under all circumstances fail in such a manner to retain control of valve motion while ocing actuated.
Therefore, the applicant's proposal does not give assurance that the valve will not again slam shut and cause the rubber expansion joint to rupture.
Ue believe that the hydraulic control system should be modified so that if hydraulic pressute falls below a predetermined value, the inlet and outlet lines to each hydraulic actuator will be automatically valved closed and thereby prevent the butterfly valve from being rapidly closed by the forces developed by the recirculating water flow.
3.
We recommend that all plants be examined to determine: (a) if flooding of the turbine building is possib1c, (b) the effects of flooding on safety related equipment should be evaluated, k
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To Files For exampic, from the information presented in the flatch Unit 1 FSAR it appearn that the lower areas of the control building, housing many essential systena, could be flooded via the passageway and cabicuays connecting these two areas.
- Trends in Large Valvint; for Condenser Circulating Water Systems Vol. 30, l'roceedings of the American l'ower Conference 1968.
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