ML19319A907
| ML19319A907 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 02/25/1977 |
| From: | Stello V Office of Nuclear Reactor Regulation |
| To: | Heineman R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19319A906 | List: |
| References | |
| NUDOCS 7912300133 | |
| Download: ML19319A907 (5) | |
Text
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R. E. Heineman, Director, Division of Systems Safety
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MEMORANDUM FOR:
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V. Stello, Jr., Director, Division of Operating Reactors
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FROM:
OPERATING EXPERIENCE MEMORANDUM NO. 7
SUBJECT:
FLOODING OF TURBINE BU.LDING AT OCONEE A
t PROBLEM With Oconee Units.1 and 2 at full power operation and Unit 3 shutdown for refueling, partial flooding of the turbine building occurred; a common. turbine building serves the three Oconee nuclear units. The gravity flow of circulating water from Lake Keowee continued for abo 1
The full 30 minutes through opened manways in the Unit 3 condenser.
water. level in Lake Keowee provides about a 25 foot head referenced to
- the basemenf floor' of
- the turbine' building. The back flow of_ water from V
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the lake through one of six condenser outlet valves was stopped after an
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accumulation of 16 to 24 inches of water in the basement of the Oconee Units 1 and 2 remained at power operation.
be'lding.
PRESUMED CAUSE The Unit 3 main condenser was isolated for inspection; manways were open.
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The six 78 inch mac ually operated inlet valves and the six 78 inch As a backup measure f
pneumatic-piston operated outlet valves were closed.
a jackstrew was installed on each outlet valve to preclude inadvertent opening. ' Solenoids' to each outlet valve were energized to provide clos air to the pneumatic driven outlet v lves.
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oloss of AC-power.to' the solenoids occurred. Air'"to open" was intro,
duced to each-of the six-pneuinatic pistons of the outlet valves. The driving 1 force of one piston was sufficient to fail the attendant jack-screw' and one valve opened.
This resulted in backflow of water from
-Lake Keowee through opened condenser manways to the turbine building, c
AC power was restored after about 30 minutes reenergiring the solenoids, and properly securing each of the six outlet valves.
An isolated air supply to the pneumatically operated valves would have precluded this event. These outlet valves are of course designed to fail i
open upon loss of power to the solenoid control valve.
SAFETY SIGNIFICANCE
' A. o rA 9au-i m
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Twenty one inch curbs betweenl the ccrc:rl; ;'.;c:d auxiliary and turbine' buildings at the Oconee Station prevented water flowing to the auxiliary
. building. Water accumulated to a depth of about 16 inches along the M-.. %__...
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Within the turbine building, an electrically driven oil pump for one gms hogegpump of the three steam-driven emergency t
an becamefinoperable as a result of _the flooding. The emergency feedwater A
pump.was the only affected safety equipment.
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. All' hotwell, booster, and main feedwater pumps, which are located on
- the floor of the turbine-building-basement, could have become inoperative 1 f the. f1 coding had not been' stopped.
~If flooding 'of the. auxiliary building had occurred the pumps of the LPCI and the HPCI. systems,'and all sources of water to the secondary side of all steam generators, could have become inoperable.
Wc&uL~y%%-
4 REPAIR To preclude recurrence of this incident, the lir'.iee, Duke Powe I
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 E
shutdown.
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The Oconee flooding incident occurred as a result of the inadvertent opening
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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
'j concerns regarding the consequences of an unisolable break in the circulating water system piping in' side the turbine buildina~rlt should be noted that, li a
-I ity'hM cd 4 is locateif at an elevation higher than that of 7
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' the source of circulating water, the adverse consequences of an unisolable j
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- N-break in the circulating water. piping would be minimized.
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-b) Manually operated' valves.at the condenser inlet are
- closed and mechanically locked; c) air to pneumatic-piston valves be blocked and the pistons vented; d) Screw jacks be placed at condenser cutlet valves; and, e)' Lock closd the emergency condenser discharge valve to the gravity drain system.
Additionally, the licensee is reviewing other potential flooding modes to determine necessary facility modifications to preclude, regardless Consideration is being of the source, unacceptable flooding levels.
3 given to a gravity drain system from the basement of the turbine building.
i DDR ACTION _
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D0R has-reviewed the sources of cooling water to the main condenser for-operating facilities to determine whether a hydrostatic head exists that It has been deter-could cause a flooding event as occurred at Oconee.
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 sucn events from t
.6 None of the" facilities affecting safety-related plant shut down equipment.
are equipped with Seismic Category I circulating water system piping.
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Salient d5 sign teatures for;each of. the ten facilities are outlined
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belowi i
1.
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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.c,. pw& 4 k~J 2[.4 rojan, the' turbine building has-prowisions-for-directing-T
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-Lu GW 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 a g A ~ 4 h W p M p# 'b equipment is located at sdf4c4cnt elevation.
d#T At Humboldt Bay, other design basis events envelopes postulated Ab W 5.
floodingpw~ M% A @ [~ '
6.
At Rancho Seco, the condenser and turbine are located outdoors with appropriate grading of the yard to preclude flooding of safety equipment.
RECOMMENDATIONS
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Section.Wd Circulating Water System, of the Standard Review Plan contains the bases.for acceptance of the CW 5.
However, there are no 3
explicit requirements related to the type of flooding event that occurred at Oconee.. We reconraend 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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- We also recommend that: facilities now-under. review be' evaluated to' I
tassure that design and operational ethods are appropriate -to preclude.
theioccurrence 'of similar' events.. This applies to those facilities wh'e're~ elevation differences between the-source of circulating. water and the circulating system could potentially jeopardize the operation of safety-related equipment.
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-PRINCIPAL 00R PERSONNEL Reviewers:
-B.,C. Buckley F. Clemenson
- j Project Manager:
J. D. Neighbors Victor Stello, Jr., Director-Division of Operating Reactors Office of Nuclear Reactor Regulation 9
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