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mi355Westinghouse Energy SystemsPittsbu@ Pemsylvania 15230 0355 jElectric Corporation

NSD-NRC-97-5175DCP/NRC0908

Docket No.: STN-52-003 r

June 11,1997 ;-

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Document Control Desk !

U.S. Nuclear Regulatory Commission 1

Washington, DC 20555

ATTENTION: T.R. QUAY

SUBJECT: OPEN ITEM AND RAI RESPONSES RELATED TO CONTAINMENT AIR BAFFLEAND PCS TANK ,

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Dear Mr. Quay:

Attached are responses for DSER open item 3.8.4.4.7 (OITS # 755) and requests for additional information i

220.106 through 220.110. The DSER open item is in response to an requirement included in the meetingsummary in an NRC letter dated May 15,1997. The summary documented a meeting between the NRCstaff and Westinghouse on structural modules during April 14-18, 1997.

The requests for additional information are related to the liner of the passive containment cooling system(PCS) storage tank and were transmitted in an NRC letter dated May 1,1997.

The SSAR revisions included in the responses will be included in SSAR Revision 14.

This transmittal completes the Westinghouse actions for these items except for the inclusion of the SSARchanges in a formal SSAR revision. The status for these open items is tabulated below. ,

DSER/RAI Number OITS Number W Status

3.8.4.4-7 755 Action N

220.106 5242 Confirm W

220.107 5243 Confirm W

'%220.108 5244 Confirm W g

220.109 5245 Action N

-220.110 5346 Action N-

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9706200031 970611 "PDR ADOCK 05200003:E PDRC

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NSD-NRC-97 5175 )- -DCP/NRC0908 -2- June 11,1997

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Please contact D. A. Lindgren at (412) 374-4856 if you have any questions.:

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Brian A. McIntyre, Manager-Advanced Plant Safety and Licensing

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Attachment' -

. cc: D. T. Jackson, NRC (w/ Attachment). N. J. Liparulo, Westinghouse (w/o Attachment)

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DSER Open Item ? < 4.4-7 (OITS # 755)

NRC letter dated May 15,1997 " Summary of meeting to discuss Westinghouse AP600 structuralmodules"

" Westinghouse will update the design calculations for the containment air baffle to includeconsideration of air Dow fluctuations and the potential for How induced vibration / fatigue failure."

Westinghouse response

The design erWations for the air baffle utilize wind loads from wind tunnel tests. Use of these loadsin the design cae.ulations is justified below.

Dynamic excitation

Pressures in the air baffle flow path were determined in a series of wind tunnel tests as described inSSAR section 3.3. The wind tunnel modeled a boundary layer representative of open terrain (ANSI

exposure C). The 110 mph design wind has frequency content in the range of 0.1 to 1.5 hertz withmaximum energy between 0.3 and 0.4 hertz. This is shown in the power spectral density of the inputtime history used to represent the wind in the wind tunnel tests (see for example Figure 17 b ofWCAP-13323 which shows the spectrum of the average chimney pressure). The frequency content ofthe wind varies linearly with the wind velocity. Wind velocities in the tests are defined in terms of , -the mean hourly wind speed at the roof elevation. The mean hour!y wind speed at the roof elevationiis 110 mph for the test and 213 mph for the tornado. Thus the range of frequencies in a tornadoeculd increase to 0.2 to 3.0 hertz.

The wind fluctuation will not cause dynamic amplification of wind loads on the air baffle since thelowest frequency of the air baffle is at 16 hertz.

The containment vessel has a fundamental frequency of the axisymmetric structure at 7 hertz. This isalso su0iciently away from the range of wind pressure frequencies that dynamic amplification will besmall. Since the tornado loads applied as static pressure are not critical to the containment vessel anyslight amplification will not affect the overe:i vessel.

The containment vessel has a local mode comprising radial vibration of the equipment hatch. Thisoccurs at a frequency of about 3.7 hertz which is 20 percent higher than the frequency range of thetornado. Dynamic amplification would be small because the tornado gusts are random with most ofthe maximum energy below I hertz. The equipment hatch and penetration insert plate are within theauxiliary building and are not exposed to the wind loads. The containment vessel adjacent to th:equipment hatch is exposed to v;;nd loads as shown in SSAR Figure 3.8.4-1. Wind effects at thebottom of the air baffle are attenuated by the annulus air flow path and pressure loads on the vesseladjacent to the equipment hatch are small in comparison with those due to the safe shutdownearthquake. Therefore design for the safe shutdown earthquake is sufficient to envelope the dynamiceffects of the wind.

Fatigue of eir bafile

The mean hourly wind speed at the roof elevation for the design wind at a worst location (ANSIexposure D) is 131 mph. Wind loads are proportional to the square of wind velocity. The air baf0eis designed for differential pressures due to tornado wind loads (mean hourly wind speed at the roofelevation of 213 mph) with all stresses less than yield. The tornado loads used in design of the airba0le were established conservatively and exceed the wind tunnel test results by 50%. Hence, the

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stresses in the air bame and its attachments to the containment vessel are expected to be less than(131/213)2/1.5 = 25% of yield due to the 110 mph design wind. Assuming that inward and outwarddifferent'ial pressures are equal to the maximum value, this results in a maximum stress range of 50%of yield.

Section QB1 of AISC N690 establishes allowable stress ranges for repeated variation oflive loads.Repeated variations are to be evaluated when the number of cycles exceeds 20,000. This corresponds |

to about 14 hours of cyclic loading at a frequency of 0.3 hertz. Loading condition 1 applies when the 1

number of cycles is greater than 20,000 and less than 100,000 (which corresponds to about 70 hours |

of cyclic loading).

The allowable stress range given in AISC is related to the type of member and connections. Thecontainment air baffle is described in SSAR subsection 3.8.4. The load carrying elements for windloads are:

air bame panels constructed from sheet metal in accordance with AISI. This code does not.

require evaluation of cyclic loads, it is however generally similar to AISC so the conclusionson other members should also be applicable to these panels.horizontal beams consisting of built up members with fillet welds ioaded primarily along the.

weld.U-plate attached to containment vessel.

bolts esaching panels to horizontal beams and the beams to the U plate attachment to the - :.

containment vessel I.

The welded connections are represented by stress category B with an allowable stress range of 49 ksi.The bolted connections are represented by stress category D with an allowable stress range of 28 ksi.Since the stress range of the design wind is less than these allowable stress ranges, the air bamedesign meets code requirements for up to 100,000 peak design load cycles due to the 110 mph designwind.

The design wind of i10 mph has a mean recurrence interval of once in 50 years for a plant sited atthe worst location in the U.S. For such a site the wind velocity for a mean recurrence interval of 5years is 77 mph (ASCE-7-95, Table C6-5) which has peak wind loads that are 50% of the 110 mph i

wind. Each severe wind may have a series of peak gusts that would contribute to fatigue. However,the number of equivalent full cycles would be significantly less than 100,000. Cyclic stresses due to |

wind loading will therefore not result in fatigue failure. J

Air BafDe Turning Vane Loads

The air bame turning vane at the bottom of the shield building annulus and entrance to thecontainment cooling air flow ennulus has been conservatively designed for the peak pressure |

differences (both positive and negative) that occur across the air bame at the shield building inletelevation. These loads were measured utilizing a model of the AP600 shield building and air cooling |

Ilow path that produced an air cooling path pressure loss bounding the AP600 plant as part of the |

wind tunnel testing program. The tests showed that the differential pressures from the shield buildmg j

annulus to where the containment cooling annulus flow is fully developed is about 25% of thedifferential pressure opposite the air inlets. Thus the turning vane structure is loaded to a smallpercent of its yield loading even in the event of tornado wind speeds, and any loads produced by iocaleddies or flow separation are much smaller and would be highly dampened due to the high stiffness ofthe structure.

The turning vane has been designed to minimize the occurrence of localized eddies or flow separation

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from the turning vane surface both by its streamlined shape and by holes through the turning vane 1

. surfaces. The occurrence of eddies is funher discouraged due to the fact that the air stream velocity is '

rapidly reduced as the air passes the vane and enters the plenum formed at the bottom of the airannulus, causing a reduction in dynamic head and an increase in the static pressure of the air. Notethat any loads imposed on the turning vane due to local eddies or flow separation, should they occurat all a:!!.c higher air velocities, would not be continuous or imposed for a long time period since the ,

air f'.ow rate at any given location is oscillating between greatly different maximum and minimumI

vrJues. Thus the resultant pressure and the area over which it is applied are very small, and their7

j frequency is constantly changing.

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SSAR Revisions: Nonej

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g . NRC REQUEST FOR ADDITIONAL INFORMATION

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RAI #220.106 (OITS # 5242)

In SSAR Subsection 3.8.4.1.1, Westinghouse states that the conical roof supports the passivecontainment cooling system (PCS) tank, which is constructed with a stainless steel liner on reinforcedconcrete walls. However, there is no description of the tank liner (e.g., con 6guration of the liner,thickness of the liner, interface between the liner and reinforced concrete walls, collection of leakagepast the liner, and Ogures for design details of the liner). Westinghouse needs to include a descriptionof the tank liner in the SSAR. Additionally, Westinghouse needs to include the configuration of thetank liner and the welding requirements in the SSAR Hgures.

Westinghouse response

The description of the PCS tank liner is included in the SSAR as shown below. Welding andinspection activities are included in subsection 3.8.4.2

SSAR Revisions

Revise subsection 3.8.4.1.1 as shown below. ;

3.8.4.1.1 Shicid Building

The shield h1.ilding is the shield building structure and annulus area that surrounds the containmentbuilding. It shares a common basemat with the containment building and the auxiliary building. Theshield building is a reinforced concrete structure. The Ogures in Section 1.2 show the layout of theshield building and its interface with the other buildings of the nuclear island.

The following are the significant features and the principal systems and components of the shieldbuilding:

Shield building cylindrical structure.

Shield building roof structure.

Lower annulus area.

Middle annulus area.

Upper annulus area.

Pasi, containment cooling system air inlet.

Passive containment cooling system water storage tank.

Fire water storage tank| =

Passive containment cooling system air diffuser.

Passive containment cooling system air baffle.

Passive containment cooling system air inlet plenum.

The cylindrical section of the shield building provides a radiation shielding function, a missile barrierfunction. and a passive containment cooling function. Additionally, the cylindrical section structurallysupports the roof with the passive containment cooling system water storage tank and serves as a

220 mT Westinghouse

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'. NRC REQUEST FOR ADDITIONAL INFORMATION

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major structural member for the nuclear island. The floor slabs and structural walls of the auxiliarybuilding are structurally connected to the cylindrical section of the shield building.

The shield building roof is a reinforced concrete shell supporting the passive containment coolingsystem tank and air diffuser. Air intakes are located at the top of the cylindrical portion of the shield

I building. The conical roof supports the passive containment cooling system tank as shown in Figurej 3.8.4-7., " hich ' cc-:? red " "5 2 st2!-W :!c? " e er 9r~ced ccrrete "2!!c The air diffuser

is located in the center of the roof and discharges containment cooling air upwards.

| The passive containment cooling system tank has a stainless steel liner which provides a leaktight| barrier on the inside surfaces of the tank. The wall liner consists of a plate with stiffeners on thej concrete side of the plate. The Door liner is welded to steel plates embedded in the surface of the| concrete. The liner is welded and inspected during conctruction to assure its leaktightness. Leakage,| if it were to occur, is collected at the base of the cylindrical walls. This permits monitoring for| leakage and also prevents degradation of the reinforced concrete wall due to freezing and thawing of| leakage.

I| The fire protection system tank is shown in Figures 3.8.4-8. It is a 9 inch high stainless steel tank at;| the top of the passive containment cooling system tank. It is constructed with a series of radial beamsI separating the upper and lower steel plates. The upper plate is connected to the concrete roof by

| welded studs located over the radial beams.

The upper annulus of the shield building is the volume of the annulus between elevation 132'-3" andthe bottom of the air diffuser. The middle annulus area, the volume of annulus between elevation100'-0" and elevation 132'-3", contains the majority of the containment vessel penetrations. Thearea below elevation 100'-0" is the lower annulus of the shield building. There is a concrete Doorslab in the annulus at elevation 132'-3", which is incorporated with the stiffener attached to the

containment vessel.

A permanent flexible watertight and airtight seal is provided between the concrete Door slab atelevation 132'-3" and the shield building to provide an environmental barrier between the upperand middle annulus sections. The flexible watertight seal is utilized to seal against water leakage fromthe upper annulus into the middle annulus. The seat is designated as nonsafety-related andnonseismic; it is not relied upon to mitigate design basis events. The seal is able to accommodateevents resulting in containment temperature and pressure excursions that result in lateral shellmovement inward or outward.

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,- NRC REQUEST FOR ADDITIONAL INFORMATION

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NRC REQUEST FOR ADDITIONAL INFORMATION*

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NRC REQUEST FOR ADDITIONAL INFORMATION*,

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RC REQUEST FOR ADDITIONAL INFORMATION. .

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RAI #220.107 (OITS # $243)

Westinghouse needs to provide a description of the procedures for the design and analysis of the tankliner in the SSAR.

Westinghouse response

A description of the procedures for the design and analysis of the tank liner is included in the SSARas shown below.

SSAR Revisions

Add the followirig paragraph after the third paragraph of subsection 3.8.4.4.1

| The liner for the passive containment cooling water storage system tank and the fire water storage tank ,

| is analyzed by hand calculation. The design considers construction loads during concrete placement, |

| loads due to handling and shipping, normal loads including thermal, and the safe shutdown earthquake. - ;

| Buckling of the liner is prevented by anchoring the liner using the embedded stiffeners and welded-

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| studs. The liner is designed as a seismic Category I steel structure in accordance with AISC N690| with the supplemental requirements given in subsection 3.8.4.

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NRC REQUEST FOR ADDITIONAL INFORMATION |"

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. RAI #220.108 (OITS # 5244)

In SSAR Subsection 3.8.4.4.1, Westinghouse provides a only brief description of the design approachfor the PCS tank. Additionally, the ANSYS and GTSTRUDL models were not provided in the SSAR.Westinghouse needs to expand its description of tne PCS tank design approach and include adescription of the models in the SSAR.

Westinghouse response

The description of the PCS tank design approach and of the models is included in the SSAR as shownbelow.

SSAR Revisions

Revise third paragraph of subsection 3.8.4.4.1 as shown below,

j The shield building roof and the passive containment cooling water storage tank are analyzed using~

| three-dimensional Unite element models with the A''SYc -d GTSTRUDL computer codes. The-

s j model is shown in Figure 3.8.4-9. It represents one quarter of the roof with symmetric or asymmetric"| boundaiy conditions dependent on the applied load. Loads and load combinations are given in

subsection 3.8.4.3 and include construction, dead, live, thermal, wind and seismic loads. Seismic loads

are applied as equivalent static accelerations. The seismic response of the water in the tank isanalyzed in a separate Snite element response spectrum analysis with seismic input de6ned by theDoor response spectrum.

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220.108-1

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RC REQUEST FOR ADDITIONAL INFORMATION*.

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220.108-2

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NRC REQUEST FOR ADDITIO'NAL INFORMATION.,,

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RAI #220.109 (OITS # 5245)

Operating experience with steel-lined water tanks indicate that the likelihood of water leakage cannotbe ruled out. Considering a sixty year design life and significant exposure to weather, specialprovisions for preventing degradation of the reinforced concrete tank structure should be provided inthe SSAR including the limitation of tensile stress in the reinforcing bars. Also, consideration shouldbe given to incorporate the recommendations for the design of reinforced concrete overhead tanks byAmerican Water Works Association. Please explain if Westinghouse considered these items and howthey were addressed. 'If not, explain why Westinghouse believes the items are not necessary.

Westinghouse response

The design of the passive containment cooling storage tank liner includes provisions for collection ofleakage through the liner (see response to RAI # 220.106). This prevents water leaking into theconcrete with the potential for degradation due to freezing and thawing of this water.

Stresses in the reinforcement are limited by following the provisions of ACI 349. These limitationsare considered adequate for a stainless steel lined reinforced concrete tank. Sustained conditions for

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the design of the reinforced concrete walls include the hydrostatic pressure and thermal gradients'

through the thickness of the wall.

Westinghouse reviewed the publications of the American Water Works Association but did not findrecommendations for the design of reinforced concrete overhead tanks.

SSAR Revisions: None

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RAI #220.110 (OITS # 5246)

In Westinghouse's submittal dated March 26,1997, the fire tank located inside the PCS tank is shownin the markup of SSAR Figure 3.7.212. However, no description of this tank was provided in SSARSection 3.8.4. Westinghouse needs to include a description of the fire tank in SSAR Section 3.8.4.

Westinghouse response

See SSAR revisions included in response to RAI 220.106.

SSAR Revisions: None

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220.I10-1

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