ML20128G592

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Sser Input Re Potential Flooding of Cooling Tower Areas. Requirements of GDC 2 Met.Related Info Encl
ML20128G592
Person / Time
Site: Waterford Entergy icon.png
Issue date: 06/03/1982
From:
Office of Nuclear Reactor Regulation
To:
Shared Package
ML19263A633 List:
References
FOIA-84-455, FOIA-84-A-56 NUDOCS 8505300232
Download: ML20128G592 (7)
v • d • e


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l Supplement to the ' Safety Evaluation Report I Hydrologic Engineering Section '

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Waterford Steam Electric Stationi Unit 3 Docket Number 50-382

2. SITE CHARACTERISTICS 2.4 Fydrataoic Enoineerina' 2.4.2 Flood Potential 2.4.2.3 Local Intense Precipitation Waterford 3 has wet and dry cooling towers which are open at the top.

There are two open cooling tower areas A and B. Local intense precipitation which fatts directly over the e open areas plus' runoff from .

adjacent roofs will accumulate and pond on the floors of the dry cooling

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tower areas. A combination of floor drains and a network of drainage piping will convey this water to two sumps where a set of duplex pumps in each sum'p will remove water from the cooling tower areas.

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Design Basis Rainfall Event:

l In Section 2.4.2.3 of the Safety Evaluation Reports the staff concluded t

that the applic' ant's analysis of potential flooding in cooling tower l

L areas A and B did not meet the design criteria suggested in Regulatory j Guides 1.59 and 1.102 nor the requirements of GDC-2 because certain i

safety-related transformers and motor control centers located in the cooling tower areas could be flooded during a design basis rainfall -

event. The staff stated that safety related components in cooling tower 8505300232 850301 PDR FDIA PDR

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areas A and B should be flood protected to d.2 feet and 3.6 feet respectively.

Thestaffalsostatedthatlower'floodprEtectiohdepthswouldbeacceptable if additional or larger pumps were used to reduce ponding levels or if the j applicant could provide assurances that roof drains would not become clogged. The applicant subsequently presented an evaluation of the potential

. for blockage of roof drains. This evaluation showed that clogging of roof drains would be highly unlikely. However, as described belows the appl.icant conservatively assumed that 33 percent of the roof drains would be clogged during a design basis rainfall event. Based on the information presented by the applicant, the staff agrees that it is highly unlikely that all of the roof drains would become clogged. The' Staff further agrees that a 33 percent blockage of roof drains is a conservative assumption.

In Amendment 21 to the FSAR, the applicant presented a revised analysis ,

of potential flooding in cooling tower areas A and B. In this analysis roof drains were assumed to be 33 percent blocked. The applicant also assumed that one of the sump pumps in each cooling tower . area would be inoperable during a probable maximum precipitation (PMP) event. Amendment 21 also stated that the sump pumps in the cooling tower areas each have a i

i capacity of 325 gallons per minute (gpm). Initiallyr the FSAR had shown l

L these pumps as having a capacity of 140 gpm. This revised analysis by the -

l-applicant resulted in Lower ponding levels in the cooling tcwer areas.

t l These Levels however were not low enough to prevent flooding of the motor i

i control centers which are located on the floors of the dry cooling towers.

To further reduce ponding levels in the cooling tower arease the applicant ,

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proposed to allow water to flow into and pond in the Fuel Handling -

Building. Openings wiLL have to"6e provided betsien the cooling tower areas and the Fuel Handling Building. The applicant has determined that three 4-inch diameter openings have to be installed in the sills beneath exit doors located on each side of the Fuel Handling Building. Howevere to allow for some clogging o.f pipess.3 total of eight 4-inch diameter pipes wiLL be installed. The applicant has estimated that by al' Lowing f

water to pond in the Fuel Handling Buildings a maximum of 1.6 feet of water wiLL pond in the cooling tower areas and in the Fuel Handling Building. Themaximumheighttowhichwate[canpondinthecooling tower areas before flooding of essential poFtions of the transformers occurs is 3.0 feet. For the motor control centers it is 1.71 feet.

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The staff has reviewed the material presented by the applicant and has' performed' independent analysis. The staff therefore concludes thate with the eight 4-inch diameter opening installed as indicated by the applicants water depths in the cooling tower areas will remain below 1.6 feet following a PMP event and wiLL thus not affect _the safe operation

. of Wate,rford 3. -

i Combination of Events:

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Regulatory Guide 1.59 suggests that a sufficient number of combinations

. of flood causing events be tested or discussed to assure that the highest flood level has been determined. An alternative combination which should be considered is an operating basis earthquake (OBE)r -

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which fails the sump pumps, coincident with a rainfall event less

-s._. - m ._ .A severe than the PMP. This combination is considered appropriate since the pumps are not seismically qualified, and thu.s.cannot be shown to be operable following a seismic event. The staff therefore requested that .the applicant provide an analysis of the effects of a.

Standard Project Storm (SPS assumi'n g all four sump pumps in the cooling tower areas are inoperable.

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MThe applicant has described the sump pumps as designed to seismic Category 1 requirements but not classified as seismic Category 1 (FSAR Table 3.2-1). ,

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  • 3/The SPS is a storm used for design of flood control structures by the U.S. Army Corps of Engineers. Rainf all resulting from a SPS is generally equal to about 40 to 60 percent of the PMP.

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The applicant's analysis of this comb'ination of events showed that

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there would be some flooding of motor control centers about 7 hour8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />.s after ponding in the cooling towers began. The applicant stated that reactiyation of even one of the sump pumps would, at an increasingly rapid rater reduce the total accumulated water level. ' There was no

- discussion or description of how the sump pumps would be reactivated

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nor how Long it would take to do so. Th'us the staf f was unable to conclude that a rainfall event coincident with an OBE would not result in flooding of motor control centers and transformers in the cooling tower areas.

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In analyzing the PMPs both the applicant and the staff determined that

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ponded v'ater in the cooling tower areas would peak at about the 5th or 6th hour. After this, levels would decrease because.the capacit'y of the sump pumps would exceed the amount of water coming in.

Thus consideration of a 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> PMP as a design basis event was adequate.

I For the coincident SPS and OBE events howevers storm duration is a much more critical parameter because the sump pumps are assumed to be

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inoperabler allowing water to accumulate for the entire duration of the storm.

l In Section 2.4.2.3 of the SERr a 48-hour PMP is estimated to be 43.5 .

' inches. The 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> SPS rainfall would be about 21.8 inches assuming that the SPS is equal to 50 percent of the PMP. Since ponding depth in 4

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  • # i the cooling tower areas is dependent on the duration of the rainfall

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event, the staff considered a SPS of 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> dur'ation. This eve'nt would produce a total rainfall of about 23 inches ,and would result in a ponding depth of about 1.9 feet in the cooling tower areas assuming that all four sump pumps are inoperable.- Since this is higher than.

the maximum allowable' ponding depth of 1.71 feets the applicant har-proposed to provide a portable pump with a pumping capacity of 100 gallons per minute (gpm) and sufficient head to pump over the cooling tower wall. This pump will be stored on pallets placed away from any non-seismic category I eqdipment which coul fall and gamage the pump.

InadditionithepumpwiLLbeincludedin'ifesurvhittancetesting program which will include a demonstration at least once per refueling that the pump will circulate water. As part of the station's emergency proceduress a provision wiLL be included for emplacing >the portable pump within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> of a seismic event if the installed pumps fail.

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, The staff has determined that a 100 gpm pump capable of Lifting water 75 feet vertically is adequate to prevent flooding of safety related  ;

l equipment in the cooling tower areas during a combined SPS-0BE event provided the pump is placed in operation within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

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Conclusion:

l The staff now concludes that with respect to potential flooding of the '

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cooling tower arease the station meets the requirements of GDC-2 and the criteria of Regulatory Guides 1.59 and 1.102. .

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I Wet and dry cooling towers at Waterford 3 are open at the top and could be affected by local intense precipitation which falls directly over the cooling towers and by runoff from adjacent roofs: Theie are two open cooling towers areas, A and B. These areas have. floor drains that flow into a sump for each area. Each sum of 280 gal / min.p is drained by two sump pumps which have a combined capacity Th.e pumps remove ponded water from the cooling tower areas to the exterior plant drainage system.

A rooftop draina'ge system has also been designed to. prevent roof ponding of water for rainfall rates up to 6 in./hr. More intense rainfall will either pond below roof parapets or overflow. Part of this overflow will enter the open cooling tower areas. - --

The applicant performed an analysis of' the effects of a 6-hr duration PHP on the open cooling tower areas and adjacent roofs. In this analysis the rooftop drainage system was assumed to be functioning and all sump pumps, w,hich are described as seismically designed were assume'd to be pumping water from each cooling tower area at a maximum ra,te of 280 gal / min. The computed ponding depths were 1.35 ft in cooling tower area A and 1.70 ft in cooling tower area B.

The applicant stated that all safety related equipment would be located above these ponding levels. ,.- ,

At the request of NRC, the applicant provided drawings and descriptions of safety-related components that are located in the coolin These consist of transformers and motor control centers (MCCs)gmounted tower areas.

on the floors of the dry cooling towers. Although these components will be partially inundated by water, the a3plicant has stated that the transformers are watertight for approximately tie lower 3 ft and the MCC's can withstand ponded water up to 1.75 ft without harmful effects. Thus the applicant's analysis shows that water levels in Cooling Tower Area B, assuming that roof drains and sump pumps function as. design, will be wi' thin 0.05 ft (5/8 in.) of flood'ag the MCC's

,and affecting the operability of the dry cooling towers. The margin in Cooling Tower Area A as calculhted by the applicant, is 0.4 ft (4.8 in.). These margins could easily be exceeded should the roof. drains become partially clogged or not function at their design c pacity or if a sump pump does not switch on when needed or does not operate at full capacity. Based on this, the staff concludes that the app.licant,'s analysis'and design are not conservative and that the flood protection for the cooling tower areas does not meet the design criteria suggested in Regulatory Guides 1.59 and 1.102 nor the requirements of GDC 2. -

The staff performed an independent analysis of potential flooding of these

  • cooling tower areas, assuming that one sump pump in each area is inoperable and that the roof drainage system is clogged with debris during the PHP. This

' analysis resulted in a ponding depth of 4.2 ft in Cooling Tower Area A and 3.6 ft in Cooling Tower Area B. These ponding depths would inundate the transformers and MCC's in the cooling tower areas and affect the safety of the .

plant. The staff wi11' require that all safety-related components in the cooling towers area be flood protected to these depths. Lower flood levels may be acceptable if t.he applicant can provide adequate assurances that the roof drains will not becom.e clogged during a design basis event. Additional or larger

' capacity pumps may also be used to reduce calculated ponding level. NRC will need to review the applicant's proposal prior to issuance of an operating license. The results of review will be provided in a supplement to this report.

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