ML20052G514
| ML20052G514 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/10/1982 |
| From: | James Shea Office of Nuclear Reactor Regulation |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| Shared Package | |
| ML20052G515 | List: |
| References | |
| TASK-03-02, TASK-3-2, TASK-RR LSO5-82-05-013, LSO5-82-5-13, NUDOCS 8205180428 | |
| Download: ML20052G514 (9) | |
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r May 10,1982 Docket No. 50-245 L505 05-013 Mr. W. G. Counsil. Vice President Nuclear Engineering and Operations Northeast Nuclear Energy Company Post Office Box 270 Hartford, Connecticut 06101
Dear Mr. Counsil:
SUBJECT:
SYSTEMATIC EVALUATION PROGRAM TOPIC III-2, WIND AND TORNADO LOADINGS - MILLSTONE UNIT 1 Enclosed is a copy of our draft safety evaluation of SEP Topic III-2.
The evaluation identifies structures and portions of structures which are unable to withstand current licensing criteria tornado loadings for your site. The Gas Turbine Generator Building may not meet the tornado loadings as stated in your FSAR.
You are requested to examine the facts upon which the staff has based its evaluation and respond either by confirming that the facts are correct or by identifying errors and supplying the correct information.
We enc 6urage you to supply any other material that might affect the staff's evaluation of this topic or be significant in the integrated 8N assessment of your facility.
S:
Your response to the gas turtine generator concern is requested within
- j 30 days of receipt of this letter.
l Sincerely".'
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ff James J. Shea Project Manager Operating Reactors Branch No. 5 Division of Licensing
Enclosure:
As stated 820 5180 7M cc w/ enclosure:
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? . Millstone Unit 1 Docket No. 50-245 Revised 3/30/82 Mr. W. G. Counsil CC William H. Cuddy, Esquire State of Connecticut Day, Berry & Howard Office of Policy & Management Counselors at Law ATTN: Under Secretary Energy One Constitution Plaza Division Hartford, Connecticut 06103 80 Washington Street Hartford, Connecticut 06115 Ronald'C. Haynes, Regional Administrator Nuclear Regulatory Commission Region I Office 631 Park Avenue King of Prussia, Pennsylvania.19406 Northeast Nuclear Energy Company ATTN: Superintend 9nt Millstone Plant P. O. Box 128 Waterford, Connecticut 06385 Mr. Richard T. Laudenat Manager, Generation Facilities Licer. sing Northea:t Utilities Service Company P. O. Box 270 Hartford, Connecticut 06101 Resident Inspector c/o U. S. NRC P. O. Box Drawer KK Niantic, Connecticut 06357 Ffrst-Selectman of the Town of Waterford Hall of Records l 200 Boston Post Road l Waterford, Connecticut 06385 John F. Opeka l Systems Superintendent l Northeast Utilities Service Company P. O. Box 270 t Hartford, Connecticut 06101 l U. S. Environmental Protection Agency Region I Office ATTN: Regional Radiation Representative JFK Federal Building Boston, Massachusetts 02203
~ 1 SYSTEMATIC EVALUATION PROGRAM TOPIC III-2 MILLSTONE 1 TOPIC: III-2, WIND AND TORNADO LOADINGS I. INTRODUCTION The safety objective of this review is to assure that safety-related structures are adequate to resist wind and tornado loadings including tornado pressure drop loading. II. REVIEW CRITERIA The review criteria governing this topic is General Design Criteria 2, design bases for protection against natural phenomena. III. RELATED SAFCTY TOPICS AND INTERFACES 1. Tornado missiles are reviewed in SEP Topic III-4.A. 2. Structures which are considered safety related are given in SEP Topic III-1. 3. Wind and tornado parameters are given in SEP Topic II-2.A. 4. Design Codes, Criteria and Loading Combinations are reviewed in SEP Topic III-7.B. IV. REVIEW GUIDELINES 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 1.76 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 cr.pacity for withstanding these values from Topic II-2. A. Appropriate va".ues for the Millstone site are a 300 mph windspeld (corresponding tc 230 psf dynamic pressure) and a 2.25 psi (324 ps') differential pressure. For those structures which do not meet the acceptance criteria, structural capacities were determined and limiting components identified. These capacities are given in terns of strength and corresponding windspeed.
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- V.
EVALUATION is a report entitled, " Wind and Tornado Loadings" presenting 1 our contractors' findings concerning the Millstone 1 facility. The report identifies limiting structural elements and their associated windspeed. No analyses were performed for safety-related systems and components. Systems and components important to safety not housed within structures noted in this SER should be addressed by the licensee. Original Design According to the FSAR and other information available on Docket 50-245, Class I structures at Millstone 1 were originally designed for a wind velocity of 115 mph with gusts up to 140 mph and roof loads of 60 psf. Additionally, it is stated that safety related systems which are required to function for long periods during or following the postulated accidents are housed in structures designed to withstand short-term tornado winds up to 300 miles per hour. These designs are based upon allowing steel to approach yield stress and concrete to approach ultimate stress. The FSAR states that although some 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 regarding tornado design. Information there states that concrete is allowed to approach 85% of ultimate. The reactor building superstructure above elevation 108.5' depends on the roof and roof panels for stability. The roof can withstand 40 psf vertical load and failure of the roof will result in failure of the wall panels; therefore, no credit is taken for tornado design of the : ;;istructure. I 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, other information supplied by the licensee is that 1) the intake structure was designed for dead i 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 tornade loads, but the combination is unknown. Additionally, the licensee is not certain whether operating pipe reaction loads and snow loads were included in the load combination as live loads. 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. I t - -, - ~ w w-,, - - -,y.- --,,y -,,,,,,,y e ..,,e, e.-w-----+ ---=----
. 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 building below the operating floor (elevation 108.5'). Although it could not be found, it is reasonable to assume that all structures designed for 300 mph winds would also be ds-igned for the 2.5 psi pres-sure drop since both loads are ccused by thi same phenomena. Since the 300 mph wind and the 2.5 psi presgure diffe.entf al'are greater than or equal to current criteria for 10-' tornado leads per SEP Topic II-2.A, only a limited confirmatory reanalysis was uildertaken. We have analyzed the ventilation stack, the reactor building and the gas turbine generator building to determine whether the 300 mph wind and 2.25 psi loads can be resisted and to determine limiting structural elements in those structures. Although the ventilation stack was not designed to resist tornado loads and it is currently not a Category I structure, it is a unique structure whose failure about the base can affect Category I structures and therefore, was analyzed. The results of the analyses are shown below in terms of limiting windspeeds. For elements found to have low tornado wind resistance, the element was examined for straight wind design per the requirements of ANSI A58.1. The wind capacity then reported is based on stress 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 Structure El ement* Failure ** (mph) Pressure Ventilation Pipe Foundation 1 214 117 Stack *** Reactor Building 14B17.2 Roof 2 75 29 Beams 3 74 26 1 127 41 North and South 3 77 27 Side Steel 2 85 37 Columns 1 131 44 Gas Turbine Intermediate 2 139 99 Generator Concrete Columns 1 220 124 Building
. Footnotes The first element identified for each structure is the limiting element. Additional elements that have also been found to be inadequate are subsequently listed. Note that this table dees 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 stae.k to circumferential stresses could not be determined because the placement of the hoop rein-forcement is not known. 4 w
' 1 The results indicate that the reactor building below the operating floor (elevation 108.5') 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 limiting 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. 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. The ventilation stack was 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 allowablar.; 2) working stress methods allowing stress in the steel to reach yield and concrete to reach.85 fc' and 3) ultimate strength methods. Although ACI has not approved ultimate strength design of stacks due to lack of experimental evidence, the stack was analyzed by ultimate strength methods to provide an indication of possible actual strength.
The results in terms of windspeed (mph) are given below. VENTILATION STACK WSD WSD Failure (ACI Code (fy,.85 fc' Location Allowables) Allowables) USD Stack cylinder 186 254 >300 (107 feet from top) Stack base 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. i ""=ame-m ms. ve.
_6 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 ( variation of force with height whereas tornado design does not. i 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 uniformly with height since the licensee has stated that this was the case for the intake structure. Converting to pressure by standard practice 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. Tha 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, l 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 permitted for load combinationsinvolving all operating loads (dead load, live load, wind load, operating pipe reaction loads and thermal loads). Since it is uncertain whether pipe reaction loads end snow loads were included in the original 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, f t 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 4 significantly reduced if vertical loads (e.g., snow or rain) induce be.. ding. l
. VI. CONCLUSIONS It is concluded that some structures and portions of others 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. Our evaluation of the gas turbine building intermediate columns indicates that this structure maynot withstand the FSAR tornado loads. The licensee should determin~e whether other Category I structures are similar in construction and may require upgrading. 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 cverturning 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 load-ings. The effect of their failure on the spent fuel pool needs.to be considered. l I l l _}}