ML19317F298
| ML19317F298 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 02/17/1977 |
| From: | Nichols L Office of Nuclear Reactor Regulation |
| To: | Goller K, Neighbors, Schwencer A Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19317F294 | List: |
| References | |
| NUDOCS 8001090769 | |
| Download: ML19317F298 (1) | |
Text
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R. E. Heineman, Director, Division of Systems Safety MEMORANDUM FOR:
V. Stello, Jr., Director, Division of Operating Reactors FROM:
OPERATING EXPERIENCE MEMORANDUM NO. 7 FLOODING 0F TURBINE BULDING AT OCONEE l
SUBJECT:
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With Oconee Units 1 and 2 at full power operation and Unit 3 for refueling, partial flooding of the turbine building occurred i
common turbine building serves the three Oconee nuclear un ts.
I for about The gravity flow of circulating water from Lake Keowee co The full 30 minutes through opened manways in the Unit 3 condenser.
d to water level in Lake Y,eowee provides about a 25 foot head refe The back flow of water from the basement floor of the turbine building.
fter an the lake through one of six condenser outlet valves was stop e
the turbine accumulation of 16 to 24 inches of water in the base Oconee Units 1 and 2 remained at power operation.
building.
PRESUMED CAUSE
_The Unit 3 main condenser was isolated for inc.pection; man The six 78 inch manually operated inlet valves and the six 7 As a backup measure pneumatic-piston operated outlet valves were closed.
t a jackscrew was ins.talled on each outlet valve to preclude Solenoids to each outlet valve were energized to provide opening.
air to the pneumatic driven outlet valves.
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l Loss of AC power to the solenoids occurred. Air "to open" was intro.
t The j
duced to each of the six pneuiratic pistons of the outlet valves.
driving force of one piston was sufficient to fail the attendant jack-screw and one valve opened. This resulted in backflow of water from Lake Keowea through opened conc. iser manways to the turbine building.
AC power was restored after about 30 minutes reenergizing the solenoids, and properly securing each of the six outlet valves.
An isolated air supply to the pneumatically operated valves would have These outlet valves are of course designed to fail precluded this event.
open upon loss of power to the solenoid control valve.
SAFETY SIGNIFICANCE _
A, c vAsum-Twenty one inch curbs. between the==b n. cd auxiliary and turbine buildings at the Oconee Station prevented water flowing to the auxiliary Water accumulated to a depth of about 16 inches along the building.
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r Within the turbine building, an electrically driven oil pump for one of the three steam-driven emergency feedwater j* umps, and a hogwegpump Mt<b.4
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The emergency feedwater A
pump.was the only affected safety equipment.
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9 All hotwell, booster, and main feedsater pumps, which are located on the floor of the tm bine-building basement, could have become inoperative if the flooding had not been stopped.
If flooding of the auxiliary building had occurred the pumps of the LPCI and the llPCI systems, and all sources of water to the secondary side of all steam generators, could have become inoperable.
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REPAIR _
I To preclude recurrence of this incident, the licensee, Duke Power will take the following steps:
1.
Dual-coil, mechanically latched solenoids will be used to replace the present ones on the condenser outlet valves.
The latched solenoids do not change state with loss of power.
2.
The power for the controls of the condenser circulating water (CCW) system will be changed to provide automatic, uninterrupted, transfer to a backup power source.
3.
Position indicating lights for the condenser outlet valves will be placed in the control room.
4.
Procedures for opening the CCW system inside the turbine building will be revised as necessary to require, a) Vented inlet and outlet CCW pipes if all CCW pumps are shutdown.
The Oconee flooding incident occurred as a result of the inadvertent opening of a main condenser isolation valve in the circulating water system while the condenser was open for maintenance. The fact that flooding of the turbine building continued until the valve could be repositioned raised concerns regarding the consequences of an unisolable break in the circulating i
water system piping inside the turbine buildina' alt should be noted that, li a j
Mility'7MwEf if, located at an elevation higher than that of gg% } the source of circulating water, the adverse consequences of an unis j
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I break in the circulating water piping would be minimized.
b) Manually opern'.ad valves at the condenser inlet are closed and mechanically locked; t
c) air to pneumatic-piston valves be blocked and the pistons vented; d) Screw jacks be placed at condenser outlet valves; and, e)'Lockclosejtheemergencycondenserdischargevalvetothe gravity drain system.
Additionally, the licensee is reviewing other potential flooding modes to determine necessary facility modifications to preclude, regardless j
of the source, unacceptable flooding levels.
Consideration is being given to a gravity drain system from the basement of the turbine building.
DOR ACTION DDR has reviewed the sources of cooling water to the main condenser for operating facilities to determine whether a hydrostatic head exists that could cause a flooding event as occurred at Oconee.
It has been deter-mined that ten operating facilities have a positive head differential be-tween the water source and the condenser; however, during the initial plant design, provisions were incorporated to preclude such events from affecting safety-related plant shut down equipment. None of the# acilities f
are equipped with Seismic Category I circulating water system piping.
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Salient design features for each of the ten facilities are outlined a
below:
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Palisades, D. C. Cook 1, Pilgrim 1, and Nine Mile Point 1 have safety-related equipment located at an elevation higher than the postulated flooding level.
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- u. p& 4.i d 2[.4 rojan, the turbine building has-prwisions-for-directing T
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water the yard in the event of/ flooding.
3.
At Zion 1 and 2, no safety-related equipment is located in the turbine building. The turbine and auxiliary buildings are separated by barriers.
4.
At Monticello, at least one complete train of redundant safety-68.
equipment is located at sufficient-e+levat4on,.M-~ %- g-Za<.hD W u atwkn
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At Humboldt Bay, other design basis events envelopes postulated hb %
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At Rancho Seco, the condenser and turbine are located outdoors with appropriate grading of the yard to preclude flooding of safety equipment.
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RECOMMENDATIONSt/
ltwN Section. lwd Circulating Water System [ of the Standard Review Plan contains the bases for acceptance of the CW S.
However, there are no 3
explicit requirements related to the type of flooding event that occurred at Oconee. We recomend that consideration be given to the development of an NRR position to preclude such flooding events that could damage safety-related equipment.
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f We also recommend that facilities now under review be evaluated to assure that design and operational methods are appropriate to preclude the occurrence of similar events. This applies to those facilities where elevation differences between the source of circulating water and the circulating system could potentially jeopardize the operation of safety-related equipment.
PRINCIPAL DDR PERSONNEL 1
Reviewers:
B. C. Buckley F. Clemenson Project Manager:
J. D. Neighbors Victor Stello, Jr., Director Division of Operating Reactors Office of Nuclear Reactor Regulation
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