ML20052C112
| ML20052C112 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood, 05000000 |
| Issue date: | 04/26/1982 |
| From: | Tramm T COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 3986N, NUDOCS 8205040384 | |
| Download: ML20052C112 (6) | |
Text
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Commonwoelth Edison l' O '~
One First N;tionIl Ptits. Chicago,11tinois AddrIse R: ply to: Post Offica Box 767 Chicago, Illinois 60690 April 26, 1982 y
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Of fice of Nuclear Reactor Regulation G"
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4 Mr. Harold R. Denton, Director 2
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U.S. Nuclear Regulatory Commission N
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Subject:
Byron Station Units 1 and 2 Braidwood Station Units 1 and 2 Auxiliary Building Flooding NRC Docke t Nos. 50-454, 50-455, 50-456 and 50-457 Re ferences -(a):
Ma rch 25, 1982, letter from T.R.
Tramm to H. R. Den to n.
(b):
April 12, 1982, letter from T.R.
Tramm to H. R.
Denton.
Dear Mr. Denton:
This is to provide information regarding the auxiliary building flooding analysis for Byron and Braidwood Stations.
Review of this information should close Outstanding Item 12 o f the Byron Safety Evaluation Report.
Enclosed is a revised response to FSAR question 10.47.
It contains additional information on check valves in drain piping.
This revised response will be incorporated into.the Byron /Braidwood FSAR at the earliest opportunity.
4 Please direct questions regarding this material to this o f fice.
One signed original and fif teen copies o f this letter and the enclosure are provided for your review.
Very truly yours, y
ffMW T. R.
Tramm Nuclear Licensing Administrator 3 00l
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/ 7 jg ogy 3986N E
l April 20. 1982 QUESTION 10.47 "Your response to 010.30 has not provided an adequate analysis to demonstrate that drainage of leakage water away from safety-lEZ related components or systems is adequate for worst case flooding resulting from postulated pipe breaks or cracks in high or moderate energy piping near these safety-related compo-nents or systems.
The analysis must show that drainage by natural routes such as stairwells or equipment or hatches by the non-seismic Category I drainage system under failed con-ditions is adequate to prevent the loss of function of safety-related components and systems.
As an example, show that a crack in one essential service water pump room will not flood out the other redundant pump before operator action can be taken to isolate the leak assuming a failed non-safety grade sump alarm system.
Worst case locations should be assumed for this example and for other safety-related systems listed in FSAR Table 3.6-1.
It is our position that unless drainage capability by natural or by failed non-seismic Category I draina'ge systems can be demonstrated, you should provide the follouing for all areas housing redundant safety-related eilipment.
1.
Leak detection sumps shal! be couippeu with redundant safety grade alarms which annunciate in the control room.
Verify that if operator action is required on receipt of the alarm that flooding of redundan t safety grade equip-ment will not occur within 30 minuLcc; or 2.
Provide separate watertight rooms and independent drainage paths with leak detection sumps for each redundant safety-related component."
RESPONSE
A confirmatory analysis has been completed to insure that the Byron /
Braidwood design will accommodate flooding as a result of high and moderate energy line breaks with no adverse effects on the capability to safely shut the plant down.
Design features such as enclosure of safety related equipment by structural walls, separation of re-dundant safety systems, and drainage into stairways and open areas prevent a loss of safe shutdown capability in the event of moderate or high energy line breaks in the auxiliary building.
The auxiliary building flooding study examined 114 separate areas in the auxiliary building.
20 of these areas were large general areas and the remaining 94 were considered subcompartments.
Sub-compartments are enclosed by structural walls and open into other
April 20, 1982 PLg3 2 i
areas only by doorways.
The limiting high or moder, ate energy line break in each area was defined by surveying the lines in the area and determining the limiting failure.
Pipe breaks and cracks were defined following the guidelines in Standard Review Plan Section 3.6.1.
Through-wall cracks were postulated in Category II systems following the Standard Review Plan guidelines.
This approach is justified because of the Byron /Braidwood design criteria for Category II piping systems in the auxiliary building.
The Category II piping is both designed and supported to withstand seismic loads.
The allowable stresses are the same as those used with equivalent Category I pipe.
As a result, Category II systems are no more likely to be loaded beyond design than Category I systems.
Maximum flood levels were defined for a break within an area and for breaks outside the area which might raise the flood level.
Fluids are considered to drain from subcompartments and general areas by way of doorways, stairwells, open hatches and floor drains.
Doors are considered to be open or closed to maximize the floo.d levels.
Non-watertight doors are assumed to have a 1/2 inch gap at the bottom.
The floor drain system in the Byron /
Braidwood plants is a Safety Category II system but is supported 1
to withstand seismic loads throughout the auxiliary building.
Credit is taken for the floor drain capacity since there is no potential failure mode for the auxiliary building drain pipes which would prevent drainage.
l No check valves are used in the drain system.
Flooding causad by back flow does not adversely affect the plant.
The floor drains are four inches in diameter.
Drains between redundant safety related subcompartments are six inches in diameter.
As a result, drain flow is limited at the floor drain inlet and will not back up.
The drains lead to the watertight auxiliary building sump room.
In the event of a sump pump failure, watt.
l will accumulate in this room.
The room will hold about 4000 f t.
i of water.
The water would then begin to back up into the RHR and Containment Spray Pump Rooms at elevation 343'.
No leaks j
or breaks will flood to the lowest safe shutdown equipment
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within 30. minutes except for a break of the 48 inch essential service water line.
This break, if all the leakage drained l.
into one units floor drain system, would damage the RHR pump l
room cubicle coolers in 21 minutes.
However, this line is be-tween the two units in a general area which would drain to both sump rooms.
At least one-third of the leakage would go to each unit, insuring that the coolers would not be flooded within 30 minutes.
Therefore, no check valves are required.
The auxiliary building is equipped with leak detection sumps which will detect any leakage above normal rates.
Also, plant personnel regularly check the general conditions in the auxiliary j.
building.
As a result, it is assumed that any isolable break is isolated 30 minutes after the break occurrence.
All systems which contain sufficient inventory to cause significant flooding can be isolated.
After isolation, the analysis was continued until the levels stabilized to insure that maximum ic lc Nere calculated in areas away from the break.
If isolation is not assumed, 34 areas would experience increasing flood levels after
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1 April 20, 1982 Page 3 30 minutes.
All but two of these areas are on elevation 330 feet
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or 346 feet.
In general, safe shutdown equipment is not located on these areas or is protected by watertighb doors.
The RHR pumps are not required for hot shutdown but are required for cold shutdown.
The pumps are not protected by waterproof doors but are elevated to prevent flood damage.
The two remaining areas are a surface condenser room on elevation 401 feet and a subcom-
'a partment on elevation 475 feet 6 inches.
Neither of these areas contain safe shutdown equipment.
Of the 114 areas analyzed, 84 will not be subject to flooding greater than 4 inches deep.
Electrical equipment is located at least 4 inches above the floor to eliminate flooding concerns.
These areas, therefore, required no additional analysis.
The remaining 30 areas could experience water levels greater than 4 inches.
Of these, 17 would_ not flood above 12 inches and 13 were predicted to ficod above 12 inches.
These 30 areas are primarily located in the lower levels of the auxiliary building.
These areas are individually discussed in the following paragraphs.
The auxiliary building basement is at elevation 330 feet.
All rooms and areas on this elevation can be flooded to at least a depth of 12 i nehes.
Au a result, these areas aave been designed to accommcoute ficoding. The floor drain sump and equipment drain pump rooms for Units 1 and 2 have been fitted with watertight doors.
These roonc can be. filled without affecting safe shutdown equip-ment.
The essential service water valve pits, if flooded, would result in failure of the motor operated valves.
The as-is position can be considered the safe position because the essential service water systemc are redundant and separated by structural walls.
The general area contains the essential service water pumps and strainers.
The doorways and penetrations leading into this area are waterti'ght. and the structural walls.are adequate to withstand the forces of flooding in adjacent areas.
In the event of a limiting crack of a 36 inch essential service water line within the area, a maximum flood level of 12 inches is predicted.
In general, this will not disable the essential service water pumps.
Even if the system in the area is affected, there will be no impact on the redundant system which is separated by a structural wall.
On the 346' feet level, flooding above the 4 inch level is predicted in four general areas and ten subcompartments.
A crack in a 48 inch essential service water line is predicted in the Unit 1 and 2 general floor areas which contain the blowdown condenser pumps, nitrogen storage area and various tanks and motor control centers.
None of the equipment in this area is safe shutdown equipment.
Two general piping areas which contain the auxiliary building collection sump pumps are located adjacent to the containments.
The area adjacent to Unit 1 is predicted to flood to 12 inches after a 20 inch essential service water line failure.
The area adjacent to Unit 2 is predicted to flood to 48 inches after a 48 inch essential service water line failure.
Neither of these areas contains safe shutdown equirment.
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April 20, 1982 Pcgo 4 I
The subcompartments predicted to flood are the two* RHR pump rooms, the two containment spray pump rooms and the valve operating area on each unit.
Upon failure of a 3 inch chemical and volume control system line, a flood level of 10 inches in the valve operating area could be expected.
No safe shutdown equipment is in this area.
The residual heat removal pump rooms and containment spray pump rooms are all interconnected and all contain safe shutdown equip-ment.
The floor of these rooms is at elevation 343 feet, 3 feet below the general area.
The containment spray pumps are used only during accident conditions and, therefore, are not required under normal conditions as defined in the Standard Review Plan.
- However, the containment spray pumps are elevated to prevent flooding from disabling the pump.
The RHR pumps are used during normal shutdown but are not required (except in LOCA conditions) to bring the plant to a safe hot shutdown condit.e7.
In a normal shutdown, the RHR system will be used when the reactor pressure is below about 400 psig to cool the reactor.
At this time, a 16 inch RHR system line in the RHR pump roon or a 24 inch Safety Injection System (RHR suction) line in the containment spray pump room will be pres-surized.
A failure of these lines, if not isolated, could cause flooding up to the level of the general area at elevation 346 feet.
The rcaulting flood of about three feet would not directly affect the RHR pumps which are elevated.
The RHR pump room cubicle coolers would be damaged by this level of flooding, resulting in a gradual increase in the subcompartment temperature.
Failure of the cubicle cooler is not expected for several reasons.
The line break in question is very unlikely.
The RHR system is in use only af ter the reactor is below 400 psig and 350*F.
A total rupture of the pipe would re-sult in an immediate low flow alarm in the control room which would result in the pump being taken out of service and the pipe isolated.
Additional control room indication of the break will result frcm the radiation monitoring system since the leaking fluid would be reactor i
fluid.
In the event of the total rupture of the pipe, cold shutdown will be attainable if the redundant cubicle cooler is undamaged.
To damage this cooler, both RHR pump rooms and spray pump rooms must be flooded and all doors must be open.
Using these assumptions, over ten minutes is available to isolate the line.
If the break is smaller, the radiation monitoring system will still alarm and time available for isolation will be much longer.
Therefore, a line break in this area will not impair the ability to safely shut down the plant.
On the 364 feet level, three subcompartments per unit could be flooded.
A failure of an 18 inch non-essential service water line in the blowdown condenser room could result in a 40 inch flood level.
A failure of a 12 inch component cooling line in either residual heat exchanger room (A or B), would result in a flood level of approximately 100 inches.
There is no safety related equipment in the blowdown condenser room.
Flooding of a residual heat exchanger room would not af fect the redundant train.
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April 20, 19821 Page 5 On the 383 feet level, a crack in the 6 inch diesel oil piping in either Unit 2 diesel oil storage tank room would result in a flood level of less than 6 inches.
This would ndt affect the other tank or the plant safe shutdown capability.
A crack in the 20 inch non-essential service water line in either Unit 1 or 2 auxiliary feedwater diesel driven pump room would result in a i
6 inch flood level.
This would have.no effect on the diesel driven auxiliary feedwater pumps or the redundant motor driven pumps.
On the 401 feet level, a failure of a 6 inch chilled water line would result in a 5 inch flood level in the boric acid transfer pump room.
No pump damage is expected and no safe shutdown equip-ment will be affected.
Non-essential service water line failures could flood two of the radwaste surface condenser rooms to levels of 10 and 36 inches repectively.
No safe shutdown equipment is affected, n
At elevation 475 feet, 6 inches, a failure of a 4 inch fire pro-tection line could result in up to 24 inches of water in cable spreading area E or K.
No damage is expected to the cables from a flood.
All cables with safety functions have redundant cables located in another cable spree. ding area separated by structural walls.
A 14 inch non-ersential service water line located in a room containing ventilt.t ion equipment and the chilled water ex-pansion tank could result in a 21 inch flood level.
No safe shut-down equipment is in this area.
As a result of this study, it is concluded that flooding will not adversely affect the capability to safely shut down the plant.
The architectural desian of the plant, the drain systems, the redundancy and separation of safety systems and the installation of watertight closures insure the plant safety.
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