ML20027C373

Advises That Gas Turbine Generator Bldg Can Adequately Resist Design Basis Tornado Loadings,Per SEP Topic III-2 Re Wind & Tornado Loadings.Technical Evaluation Rept & Final SER Encl

ML20027C373
Person / Time
Site:	Millstone
Issue date:	09/30/1982
From:	James Shea Office of Nuclear Reactor Regulation
To:	Counsil W NORTHEAST NUCLEAR ENERGY CO.
Shared Package
ML20027A802	List: ML20027A801 ML20027C373
References
TASK-03-02, TASK-3-2, TASK-RR LSO5-82-09-088, LSO5-82-9-88, NUDOCS 8210150382
Download: ML20027C373 (9)

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September 30, 1982 Docket No. 50-245 LS05-82-09-088 Mr. W. G. Counsil. Vice President Nuclear Engineering and Operations Northeast Nuclear Enefgy Company Post Office Box 270 llartford, Connecticut 06101

SUBJECT:

SEP TOPIC III-2, WIND AND TORNADO LOADINGS - MILLSTONE 1 We have reviewed your coments dated June 29, 1982, on the above topic.

We agree that the analysis we performed on the gas turbine building intennediate columns described in our SER dated May 10, 1982, contained conservative boundary condition assumptions.

You have analyzed these columns using actual boundary conditions and concluded that the columns can withstand the full design basis tornado loadings. We have subsequently perfonned approximate calculations on the columns and also conclude acceptability. For these reasons, we conclude that the gas turbine generator building can adequately resist the design basis tornado loadings.

Our final SER is enclosed and will be a basic input to the integrated safety assessment of your facility.

Sincerely, S68 77)

James Shea, Project Manager Operating Reactors Branch #5 DSCd Division of Licensing

Enclosure:

As stated cc w/ enclosure:

See next page.

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Hartford, Connecticut 06103 80 Washington Street i

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i Ronald'C. Haynes, Regional j

Administrator Nuclear Regulatory Commission i

Region I Office 631 Park Avenue I

Xing' of Prussia, Pennsylvania.19406 1

Northeast Nuclear Energy Company j

ATTN:

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Millstone Plant P. O. Box 128 i

Waterford, Connecticut 06385 l

Mr. Richard T. Laudenat t

Manager, Generation Facilities Licensing

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Northeast Utilities Service Company l

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Hartford, Connecticut 06101 Resident Inspector i

c/o U. S. NRC P. O. Box Drawer XX Niantic, Connecticut 06357 Ffrst-Selectman of the Town of Waterford Hall.of Records 200 Boston Post Road Waterford, Connecticut 06385

..s sd John F. Opeka Systems Superintendent Northeast Utilities Service Company P. O. Box 270 Hartford, Connecticut 06101 U. S. Environmental Protection Agency

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SYSTEMATIC EVALUATION PROGRAM

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i TOPIC 111-2 l

l MILLSTONE 1 i

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. TOPIC: III-2, WIND AND TORNADO LOADINGS I.

INTRODUCTION f

The safety objective of this review is to assure that,afety-related structures are adequate to resist wind and tornado loadings including 1

tornado pressure drop loading.

i II..

REVIEW CRITERIA The review criteria governing this topic is General Design Criteria 2, design bases for protection against natural phenomena.

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.!!I. RELATED SAFETY TOPICS AND INTERFACES

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1.

Tornado missiles are reviewed in SEP Topic III-4.A.

i 2.

Structures which are considered safety related are given in SEP l

Topic III-1.

J.

Wind and tornado parameters are given in SEP Topic II-2.A.

j 4.

Design Codes, Criteria and Loading Combinations are reviewed in SEP Topic III-7.B.

IV REVIEW GUIDELINES 1

I The currently accepted design criteria for wind and tornado loadings is outlined in Standard Review plan, Sections 3.3.1, 3.3.2, 3.8 and in Regulatory Guides 1."6 and 1.117. Codes and standards used for the review of structures at the Millstone 1 facility are given in Section 5 of Enclosure 1 to this SER.

Site specific windspeed and tornado parameters were developed in Topic II-2.A and the appropriate values were identified for use as input to the wind and tornado loading analyses. Structures important to safety were analyzed in this topic to determine their capacity for withstanding these values from Topic II-2.A.

Appropriate values for the Millstone

, site are a 300 mph windspe d (corresponding to 230 psf dynamic pressure) and a 2.25 psi (324 ps:) differential pressure. For those structures which do not meet the acceptance criteria, structural Jcapacities were detennined and limiting components identified. These capacities are given in terms of strength and corresponding windspeed.

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_ V.

EVALUATION is a report entitled " Wind and Tornado Loadings" presenting The our contractors' findings concerning the Millstone 1 facility.

report identifies limiting structural elements and their associated No analyses were performed for safety-related systems and windspeed.

Systems and components important to safety not housed components.

within structures noted in this SER should be addressed by the iteensee.

Origird Desien According to the FSAR and other information available on Docket 50-245, Class I structures at Millstone 1 were origina.11y designed for a wind velocity of 115 mph with gusts up to 140 mph and roof loads of 60 Additionally, it is stated that safety related systems which psf.

are required to function for long periods during or following the postulated accidents are housed in structures designed to withstand These designs short-term tornado winds up to 300 miles per hour.

are based upon allowing steel to approach yield stress ard concrete The FSAR states that although some to approach ultimate stress.

damage to these structures may occur, this damage would under no circumstances impair the functions of the safety related systems.

In response to NRC staff questions, Amendment 15 gives additional Information there states information regarding tornado design.

The reactor that concrete is allowed to approach 85t of ultimate.

building superstructure above elevation 108.5' depends on the roof The roof can withstand 40 psf vertical and roof panels for stability.

load and failurs of the roof will result in failure of the wall panels; therefore, no credit is taken for tornado design of the superstructure.

The reactor building below 108.5' is designed to withstand at least 2.5 psi internal pressure without exceeding yield point of steel or 85%

of concrete stress.

Relating to wind and tornado loadings,.ot,her information supplied by the licensee is that 1) the intake structure was designed for dead load, live load, wind load and wave load; 2) the gas turbine building was designed for dead load, live load and tornado loads; 3) the radwaste/ control building was designed for dead load, live load and wind load; and 4) the turbine building was designed for tornado loads, Additionally, the licensee is not but the combination is unknown.

certain whether operating pipe reaction loads and snow loads were included in the load combination as live loads.

1 The licensee stated that as a result of IE Bulletin 80-11. " Masonry Wall Design " any external masonry walls determined to be safety related will be modified to withstand a 300 mph wind and a 2.5 psi pressure drop.

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Discussion The original tornado design at Millstone 1 was a 300 mph tornado wind load for structures housing safety related systems which are required to function for long periods during or after postulated accidents and a 2.5 psi tornado pressure drop for the reactor l

building below the operating floor (elevation 108.5'). Although t

it could not be found, it is reasonable to assume that all structures designed for 300 mph winds would also be designed for the 2.5 psi pres-Since the sure drop since both loads are caused by the same phenomena.

300 mph wind and the 2.5 psi presqure differential are greater than or equal to current criteria for 10-' tornado loads per SEP Topic II-2.A.

We have only a limited confimatory reanalysis was undertaken.

• analyzed the ventilation stack, the reactor building and the gas turbine generator building te determine whether the 300 mph wind and 2.25 psi loads can be resisted and to determine limiting structural Although the ventilation stack was l

elements in those structures.

not designed to resist tornado loads and it is currently not a Category I structure, it is a unique structure whose failcre about the base can affect Category I structures and therefore, was analyzed.

The results of the analyses are shown below in terms of limiting For elements found to have low tornado wind resistance, windspeeds.

the element was examined for straight wind design per the requirements

- I The wind capacity then reported is based on stress of ANSI A58.1.

limits for wind design with no allowable stress increase; therefore, there would be additional capacity beyond that shown.

TABLE 1.

SUMMARY

OF LIMITING STRUCTURAL ELEMENTS Cause of Windspeed Corresponding j

Element

• Failure **

(moh) pressure Structure j

Pile Foundation 1.

214 117 Ventilation t

Stack ***

i Reactor Building 14B17.2 Roof 2

75 29 i

l Beams 3

74 26 i

1 127 41 j

North and South 3

77 27 Side Steel 2

85 37 l

Columns 1

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_1 element. Additional elements that have also been found to be inadequate are subsequently listed. Note that this table does not imply that all inadequate elements have been identified or that entries are listed with respect to the ~most critical loading combination. Structural details not included in this review are windows, doors and roof decks.

Key: 1 - tornado dynamic pressure; 2 - differential pressure; 3 - high wind dynamic pressure. Tangential wind speeds are listed for differential pressure failures.

To conform to the applicable structural acceptance criteria, conclusions on the stack and pile foundation strength were drawn from mathematical models based on ultimate strength prin-ciples. The resistance of the stack to circumferential stresses could not be determined because the placement of the hoop rein-forcement is not known.

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-s-The results indicate that the reactor building below the operating floor (elevation 108.s') is adequate to withstand tornado pressure and wind loads. Above the operating floor, structural elements were found to be inadequate to withstand the postulated tornado loads with the liiniting elements given in Table 1.

The concern above the operating floor is the spent fuel pool since there are no other safety related systems or components at this level. The failure of structural elements on the spent fuel pool needs to be considered by the licensee.

The gas turbine building was analyzed and the results indicate that the roof slab, roof steel and reinforced concrete walls can withstand the tornado loads.

It was found that the intermediate columns were the limiting elements and that they cannot withstand the postulated tornado loads; however, the staff has made conserva-tive assumptions regarding boundary and conditions.

The licensee has analyzed the structure using actual boundary condi-tions and concludes that the structure can resist the full tornado loads.

The staff has performed approximate calculations and concludes the same.

The ventilation stack vas analyzed by different methods. Although the stack is not immediately adjacent to safety related structures and components, an extreme case of overturning about the foundation would affect safety related structures and components.

Since the stack is not in near proximity to safety related structures, a failure in the stack itself would be tolerable down to a limiting distance; however, our results indicate that the limiting failure based on strength, is the foundation. The stack was analyzed by

1) working stress methods with ACI code allowables; 2) working stress methods allowing stress in the steel to reach yield and concrete to reach.85 fc' and 3) ultimate strength methods. ACI has not approved ultimate strength design of stacks due to lack of experimental evidence; therefore, this v'alue is not relied upon as the actual capacity only to pm..de an indication of possible additional strength.

The results in terms of windspeed (mph) are given below.

VENTILATION STACK WSD WSD Failure (ACI Code (fy,.85 fe' Location Allowables)

Allowables)

USD Stack cylinder 186 254

>300 (107 feet from top)

Stack bass 172 238

>300 (8' above grade)

The pile foundation was found capable of withstanding 172 mph by working stress methods and 214 mph by ultimate strength.

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- Current criteria for straight wind loading is given in Standard Review plan 2.3.1 which references ANSI A58.1. Current criteria requires design for straight wind with a probability of exceedence in one year of 10-2 and a 10-7 tornado. Wind loads differ from tornado loads in that wind loads are considered in different load combinations, have different load factors in ultimate strength design of concrete and have different acceptance criteria than tornado loads. Additionally,,

. straight wind design includes such aspects as gust factors and o

variation of force with height whereas tornado design does not.

Millstone 1 was originally designed for 115 mph straight winds with gusts up to 140 mph.

It is uncertain what design codes were used in obtaining and applying these loads to structures.

It appears that the loads may have been applied unifomly with height since the licensee has stated that this was the case for the intake structure.

Converting to pressure by standard Dractice would result in 34 psf (115 mph) and 50 psf (140 mph). ANSI A58.1 specifies a 10-2 wind of 90 mph at 30 feet above grade and a 10-2 snow load of approximately 33 psf.

It appears that allowable stresses were increased by 1/3 for load combinations involving wind. Current licens-ing criteria load combinations involving dead, live, wind, pipe reac-tions and thermal are allowed a 30% increase in allowable stress for concrete structures if working stress methods are used and a 50% increase in allowable stress for steel structures if elastic design methods are used. The original design by the licensee utilized working stress design methods for steel and concrete design; there-fore, the load factors used in the original design would be the same as current criteria.

The magnitude of the straight wind load, including localized effects, are greater in the original design than required by current criteria.

The 1/3 increase in allowable stress does not imply structural failure since increases of 30% and 50% in allowable stress above code allowables are pemitted fer load combinationsinvolving all operating loads (dead load, live load, wind load, operating pipe reaction loads and themal loads). Since it is uncertain whether pipe reaction loads and snow loads were included in the originaJ design in combination with wind loads, it may be possible to overstress some structural ele-ments if these loads are combined with wind. Although this is possible.

it is unlikely to occur for structures that are able to withstand the design tornado loads since these loads are significantly more demanding than the wind loads and would, therefore, provide margin to accommodate pipe reaction loads and snow loads with the exception of some roofs.

The capacity of roof members designed to carry axial loads as a result of wind is siggificantly reduced if vertical loads (e.g., snow or rain),

induce bending.

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_ m The values presented above are given for tornado dynamic pressure (otherwise known as velocity pressure). differential pressure, and high straight wind pressure.

The allowable stresses for the tornado loads are according to SRP Section 3.8 which permits stress increases above code allowables for certain types of extreme loadings. The straight wind (non-tornado generated) capacity is also given because it becomes the controlling event for tornado velocities under approximately 90 mph at Millstone 1.

The straight wind capacity is calculated based on straight wind criteria (e.g., wind velocities vary with height).

The capacity given has been normalized to 30 feet above grade since this is the elevation at which basic wind pressures are given for straight winds and because the report performed by Mcdonald fqr SEP Topic II-2.A has normalized the straight wind probability curve to this elevation.

It should be noted that the straight wind capacities given above have not included the 50% increase in stress allowables for steel since the increase is only permitted for the load combination including pipe reaction loads and thermal loads.

If it can be shown that these loads do not significantly add to the loads applied to the wind resisting structure, wind velocities for steel can be increased by approximately 22%.

VI.

CONCLUSIONS It is concluded that some structures and portions of othtes cannot withstand the postulated tornado loadings of 300 mph wind and 2.25 psi pressure drop.

The need for modification of these structures will be determined during the integrated assessment.

The licensee should also determine whether snow loads, operating pipe reaction loads and thermal loads were considered with wind in the original design.

If these loads were not, the effect of combining them should be addressed.

It was determined that the limiting structural element of the ventilation stack is the foundation.

Should overturning about the foundation occur, structures and components important to safety would be impacted. Structural elements above the operating floor of the reactor building were unable to withstand the tornado loadings. The effect of their failure on the spent fuel pool needs to be considered by the licensee.

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