ML19317F160
| ML19317F160 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 04/18/1977 |
| From: | Heineman R Office of Nuclear Reactor Regulation |
| To: | Stello V Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8001080881 | |
| Download: ML19317F160 (4) | |
Text
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DISTRIBUTION APR 1 81977
/ CENTRAL FILES _ ASB READING N RR LEADING i
I DSS READING R. HEINEMAN l
A. HAIKALIS- > " - #
j A. CARRICO HEMORANDUM FOR:
Victor Stello, Jr., Director, Division of Operating Reactors, NRR FR0!!:
Robert E. Heineman, Director, Division of Syste::s j
Safety, NRR I
SUBJECT:
RESPONSE TO OPERATING EXPERIENCE !*EfiORANDUM HO. 7-FLOODING OF TUP,BINE BUILDING AT OCONEE l
50*AM f'
Suraary of Occurrence l
The subject memorandum addresses a potential safety problem that could result from flooding the turbine building by a failure of the circulating water systen.
The specific conditions producing such an event were:
(a) the source of circulating water, Lake Keowee, was located at a higher elevation than the condenser water box, (b) a manway was opened to inspect the condenser, (c) a 78-inch pneumatic-piston operated iso-lation valve on the discharge side of the condenser was closed with a i
jackscrew in place, (d) the inadvertent operation of the pneumatic piston of the discharger isolation valve caused the attendant jackscren to fail and the valve to open, and (e) the static head of the water on l
the lake caused circulating wa'ter to back-flow through the open valve j
and r.anway flooding the turbine building floor. A safety related electric oil pump for one of the three auxiliary feedwater turbine pumps i
was inundated.
Other non-safety related components were also rendered inoperable.
In addition, a potential existed for flooding the safety i
related components in the auxiliary building unich is separated from the turbine building by a 21-inch curb. Approximately one and one-half i
million gallons of water back-flowed into the turbine building in 32 l
minutes.
_Present Review Process Standard Review Plan Sections 10.4.1, ilain Condenser, and 10.4.5, Circulating Water Systea, of NUREG 75-037, outline our review procedure i
and acceptance criteria for assuring that flooding the turbine building will not cause unacceptable flooding of areas housing safety related i
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systems or components.
Section.10.4.1, Paragraph I Areas of Review, item 2c of the SRP deals with "the means provided to deal with flooding from a complete failure of the main condenser and to preclude damage to safety related equipment from the flooding."
The circulating water systems, Section 10.4.5, Paragraph I Areas of Review, item 2 of the SRP covers "a malfunction, failure of a component, or failure of a circulating water pipe do not have unacceptable adverse effects on the in the innediate area." functional performance capabilities of safety relate This is the upper bound.
In both sections of j
the SRP, the acceptance criterion is that a failure of piping or of a i
component should not cause unacceptable flooding of areas housing safety related equipment so that their functional performance capabilities will not be precluded.
Plant layouts and drawings are used to assure that access opening to safety related areas are at an elevation well above the conservatively estimated flooding elevation.
i Planned Action Sections 10.4.1 and 10.4.5 of the Standard Review Plan contain th necessary criteria and review procedures to bound the problem in such a way that any flooding of the turbine building will not prevent safety related couponents from performing their safety function.
in response to Operating Experience Memorandum Ho. 7, we see no baisTherefo cedures nor any changes in the Standard Review Plan.upon wh j
based on the following:
Our position is 1.
Oconee and other operating reactor plants received
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Huclear Plants reviewed in accordance with Sections 1 10.4.5 of tha SRP should not have safety related components located in their turbine building, j
2.
As presently stated, our analysis assumes the worst break such that j
the building is continually being flooded at the maximum flow rate.
l Under these conditions, we require that all safety related equipment should be protected.
The type of protection is in most cases plant dependent.
We recomend that OR plants be afforded similar protec-tion after a case-by-case review is completed especially in view of 1
l the fact that the circulating water and condenser are non-seismic l
sys tems.
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In our review process we assume that the turbine building is flooded and the flood level is detemined by conservatively estimating the circulating water system flow rate. Access openings to safety related areas must be located above the maximum attainable flood level'in the turbine buildirg.
In addition, we consider the potential for flood paths such as passageways, pipe chases, and/or cableways which join the flooded space to other reas that contain safety components necessary for safe shutdosa.
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The flooding that occurred, as outlined in Operating Experience b
Pemorandum ilo. 7, dumped 1.5 X10 gallons in 30 minutes which corresponds to a flow rate of 50,000 gal / min.
Plants under review i
for a CP or OL meet one of the following:
a.
Nuclear Plants that use cooling towers for a heat sink to cool the ci culating water have a water inventory of about 7 to b
gallons. The entire inventory of the cooling tower is 8 X 10 than assumed to be dumped into the turbine building in 10-15 rainutes.
1l b.
liuclear plants that use a heat sink with an unlimited supply of cooling water assume that the turbine building is flooded until s
there is flow out the turbine building and over the plant grade, i
These assumptions represent a " worst case" review process and i
therefore, are more conservative than the flooding that occurred in Operating Experience Memorandum !'o. 7.
5.
The following assumption, e.g. failure of condenser or expansion joints, is considered since the circulating water system is a non-t safety related systen and it cannot be relied upon to function or l
naintain its integrity in tne event of an earthquake. f.ccordingly, any attempt to prevent flooding in tne event of an earthqucke should i
rely on a safety grade systen.
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I Robert E. Heiner.:an, Director I
Division of Systems Safety Office of Huclear Reactor Regulation cc: See Page 4 l
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W OEM #7 - Flooding of Turbine Bldg.
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> MEMORANDUM FOR:
R. E. Heineman, Director, Division of Systems Safety FROM:
V. Stello, Jr., Director, Division of Operating Reactors
SUBJECT:
OPERATING EXPERIENCE MEMORANDUM NO. 7 FLOODING OF TURBINE BUILDING AT OCONEE 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' 0conee nuclear units.
The gravity flow of circulating water from Lake Keowee continued for about 30 minutes through opened manways in the Unit 3 condenser. The full water level in Lake Keowee provides about a 25 foot head referenced to the basement floor of the turbine building. The back flow of water from the lake through one of six condenser outlet valves was stopped af ter an accumulation of 16 to 24 inches of water in the basement of the turbine building. Oconee Units 1 and 2 remained at power operation.
PRESUMED CAUSE The Unit 3 main condenser was isolated for inspection; manways were The six 78 inch manually operated inlet valves and the six 78 open.
inch pneumatic-piston operated outlet valves were closed.
As a backup measure a jackscrew was installed on each outlet valve to preclude in-advertent opening. Solenoids to each outlet valve were energized to provide closure air to the pneumatic driven outlet valves.
Loss of AC power to the solenoids occurred. Air "to open" was intro-duced to each of the six pneumatic pistons of the outlet valves. The driving force of one piston was sufficient to fail the attendant jack-screw and one valve opened. This resuited in backflow of water from Lake Keowee through opened condenser 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 precluded this event. These outlet valves are designed to fail open upon loss of power to the solenoid control valve.
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R. E. Heineman SAFETY SIGNIFICANCE Twenty one inch curbs between the 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 curbs.
Within the turbine building, an electrically driven oil pump for one of the three steam-driven emergency feedwater pumps, and a hotwell pump became inoperable as a result of the flooding. The oil pump was the only affected safety equipment.
All hotwell, booster, and main feedwater pumps, which are located on the floor of the turbine-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 HPCI systems, and all sources of water to the secondary side of all steam generators, could have become inoperable.
The Oconee flooding incident occurred as a result of the inadvertent opening of a main condenser isolation valve in the circulating water The fact that system while the condenser was open for maintenance.
flooding of the turbine building continued until the valve could be repositioned raised cor.cerns regarding the consequences of an uniso-lable break in the ciralating water system piping inside the turbine It should be noted that, if a facility's circulating water building.
system piping is located at an elevation higher than that of the source of water, the adverse consequences of an unisolable break in the circu-lating water piping would be minimized.
REPAIR To preclude recurrence of this incident, the licensee, Duke Power Company, 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 to not change state with loss of power.
The power for the controls of the condenser circulating water 2.
system (CWS) will be changed to provide automatic, 6ninterrupted, transfer to a backup power source.
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Robert E. Heineman 3.
Position indicating lights for the condenser outlet valves will be placed in the control room.
4.
Procedures for opening the CWS inside the turbine building will be revised as necessary to require, a) vented inle? and outlet pipes if all pumps are shutdown; b) manually operated valves at the condenser inlet to be closed and mechanically locked; c) air to pneumatic-piston valves be blocked and the pistons vented; d) screw jacks be placed at condenser outlet valves; and, t
e) lock in closed position the condenser emergency discharge valve to the gravity drain system when the condenser is isolated for inspection.
Additionally, the licensee is reviewing other potential flooding modes to determine necessary facility modifications to preclude, regardless of the source, unacceptable flooding levels.
Consideration is being given to a gravity drain system from the basement of the turbine building.
DDR ACTION 00R is reviewing the circulating water system for all operating facilities.
Determinations will be made whether a positive differential head exists between the water source and the CWS; and if so, whether design pro-visions prevent flooding of safety-related equipment.
Also, evaluations will be made to determine whether or not adequate design features exist to preclude damage of safety equipment from postulated leaks in the CWS.
RECOMMENDATIONS Section 10.4.5 Circulating Water System (CWS), of the Standard Review Plan contains the bases for acceptance of the CWS. However, there are no explicit requirements related to the type of flooding event that occurred at Oconee. We recommend 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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Robert E. Heineman We also recommend that facilities now under review the occurrence of similar events. This applies to those facilities where elevation differences between the source of circu of safety-related equipment.
PRINCIPAL D0R PERSONNEL F. C. Buckley Reviewers:
F. Clemenson Project Manager:
J. D. Neighbors 4
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Sh Victor Ste o, J irector Division of Operating Reactors Office of Nuclear Reactor Regulation
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