ML14138A117
| ML14138A117 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 02/01/1983 |
| From: | Paulson W Office of Nuclear Reactor Regulation |
| To: | Dietch R Southern California Edison Co |
| Shared Package | |
| ML14079A147 | List: |
| References | |
| TASK-03-02, TASK-3-2, TASK-RR LSO5-82-02-006, LSO5-82-2-6, NUDOCS 8302070429 | |
| Download: ML14138A117 (13) | |
Text
February 1, 1983 Docket No. 50-206 LS05-82-02-006 Mr. R. Dietch, Vice President Nuclear Engineering and Operations Southern California Edison Company 2244 Walnut Grove Avenue Post Office Box 800 Rosemead, California 91770
Dear Mr. Dietch:
SUBJECT:
SEP TOPIC 111-2, WIND AND TORNADO LOADINGS SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 Enclosed is an evaluation of SEP Topic 111-2. This evaluation compares your facility as described in the Safety Analysis Report you supplied on May 4, 1982, and other information on Docket No. 50-206 with criteria used by the staff for licensing new facilities.
The evaluation identifies structures and portions of structures which cannot withstand the postulated tornado loads.
This evaluation will be a basic input to the integrated safety assess ment of your facility. This topic may be changed In the future if your facility design is changed or if NRC criteria relating to this topic is modified before the integrated assessment is completed. You are requested to respond to the factual correctness of this SER within 30 days of receipt of this letter.
Sincerely, rlglim1l signed by:
Walt Paulson, Project Manager Operating Reactors Branch #5 Division of Licensing
Enclosure:
As stated cc w/enclosure:
See next page 8320 02' 05000206___
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NRC FORM 318 (10-80) NRCM 0240 OFFICIAL RECORD COPY USGPO:1981-335-980
Mr. R. Dietch cc Charles R. -Kocher, Assistant General Counsel James Beoletto, Esquire Southern California Edison Company Post Office Box 800 Rosemead, California 91770 David.R. Pigott Orrick, Herrington & Sutcliffe 600 Montgomery Street San Francisco, California 94111 Harry B. Stoehr San Diego Gas & Electric Company P. 0. Box 1831 San Diego, California 92112 Resident Inspector/San Onofre NPS c/o U. S. NRC P. 0. Box 4329 San Clemente, California 92672 Mayor City of San Clemente San Clemente, California 92672 Chairman Board of Supervisors County of San Diego San Diego, California 92101 California Department of Health ATTN:
Chief, Environmental Radiation Control Unit Radiological Health Section 714 P Street, Room 498 Sacramento, California 95814 U. S. Environmental Protection Agency Region IX Office ATTN:
Regional Radiation Representative 215 Freemont Street San Francisco, California 94111 Robert H. Engelken, Regional Administrator Nuclear Regulatory Commission, Region V 1450 Maria Lane Walnut Creek, California 94596
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SYSTEMATIC EVALUATION PROGRAM TOPIC 111-2 SAN ONOFRE 1 TOPIC:
111-2, WIND AND TORNADO LOADINGS I.
INTRODUCTION The safety objective of this review is to assure that safety-related structures, systems and components 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 SAFETY 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 load 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 Regulatory Guides 1.76 and 1.117. Codes and standards used for the review of structures at the San Onofre 1 facility are given in 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 reviewed in this topic to determine their ability to withstand these values from Topic II-2.A. Appropriate values for the.San Onofre 1 site are a 250 mph windspeed (corresponding to 160 psf dynamic pressure) and a 1.5 psi (216 psf) differential pressure. The evalua tion and conclusions are based on a Safety Analysis Report supplied by the licensee, information available on Docket No. 50-206 and the information developed by the staff given in Enclosure 1 to thi's SER.
For those structures examined by the staff which cannot withstand the postulated tornado loads, limiting capacities were determined and are given in terms of strength and corresponding windspeed.
-2 V.
EVALUATION is a report entitled, "Wind and Tornado Loadings" pre senting our contractor's findings concerning the San Onofre 1 facility.
The report identifies limiting structural elements and their associated windspeed. The intent is to verify the SAR submitted by the licensee.
No analyses were performed for safety-related systems and components.
Systems and components important to safety not housed within safety "related structures should be addressed by the licensee.
Original Design and SAR Conclusions According to the Safety Analysis Report and other information supplied by the licensee, structures at the site-were designed for straight wind pressures given below. The straight wind pressures represent the velocity pressure adjusted by a shape factor for the structure. Forces were only applied to the windward face. The forces were not varied with height except for the vent stack.
Code Used Reactor Auxiliary Building 15 psf UBC 1964 Fuel Storage Building 20 psf UBC 1964 Refueling Water and Condensate American Petroleum Storage Tanks 20 psf Industry Spec 650-1964 Turbine Building 15 psf UBC 1961 Vent Stack Top hal-f 128 psf Kaiser Steel Spec Bottom half 93.6 psf May 1960 Control and Administration Building 15 psf UBC 1964 The combination of D+L+W was utilized.
The diesel generator building and sphere enclosure building were designed for a 260 mph tornado and a 1.5 psi pressure drop.
The licensee has determined that limiting windspeeds for as-built structures at the site are as follows:
-3 Total"tornado wind velocity (mph) corresponding to calcullated pressure drop capacityl!
Total tornado external (differential pressure) (VT=transla wind velocity (mph) tional velocity -
VR=rotational (dynamic pressure) velocity)
Control Building 8" masonry blockwall 140 112 (VTZ95 8" concrete wall 204 R
9" concrete wall 250 200 (VT-3 9) 12" concrete wall 260 R
l'-l" concrete wall 260 2'-10" concrete wall 260 Roof 260 Fuel Storage Masonry blockwall 135 108 (VT=96 Building Roof -
178 R
Robertson barrier wall 260 Stack Cylinder 260 Foundation 260 Ventilation W 8X15 roof beams 158 Equipment Room Walls 159 127 (VT-108)
Reactor Auxiliary
- walls 126 122 (VT)193 Building
- 3 roof holorib 135 R
- 1 walls
.5.3 Roof beams 260 Turbine Building Masonry block walls 1043/
85 (VTI172 Gantry crane 1604/
260 Roof 260 Footnotes (see next page)
-4
- 1. Values shown above as limiting windspeed derived from differential pressure do not agree with those reported by licensee. Calculations provided by the licensee assume pressure drop loading is linearly proportional to velocity when, in fact, it is a function of the square of the rotational velocity. The staff has taken the values provided by the licensee and corrected them to account for this difference.
This results in the values shown above being greater than those reported by the licensee. The values shown assume a constant ratio for transla tional velocity to rotational velocity.
- 2. Connection capacity not accounted for.
- 3. Wind blowing from north or south; capacity represents overturning capacity.
- 4. Wind blowing from east or west.
GENERAL NOTES No venting is assumed which would reduce the differential pressure load.
77 -,7 7 17
-5 We-have reviewed the submittals by the licensee and have determined limiting windspeeds which various structures can withstand.
Discussion Current criteria for straight wind loading is given in Standard Review Plan 2.3.1 which references ANSI A58.1, Exposure C. Current criteria requires design for straight wind with a probability of exceedance in one year of 10-2 and of 10-7 for a tornado.
Straight wind loads differ from tornado loads in that straight 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 wind loads. Additionally, straight wind design includes such aspects as gust factors and variation of force with height whereas tornado design does not. Buildings at San Onofre 1 were original y designed as stated previously. ANSI A58.1, 1972, specifies a 10-1 wind which is approximately 70 mph at an elevation of 30' above grade.
Per current criteria, load combinations involving dead, live, wind, pipe reactions, and thermal are allowed a 30% increase in allowable stresses for concrete structures if working stress methods are used and a 50% increase in 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; therefore, the load factors.used in the original design are the same as current criteria. The magnitude of the straight wind loads, including localized effects, used in the original design is comparable to current criteria below 30 feet above grade and is less than that required by current criteria (ANSI A58.1, 1972 Exposure C) above 30 feet above grade. The results of a site-specific windspeed study indicate that an appropriate 10-2 windspeed for the San Onofre 1 site is 55 mph. Using the 55 mph basic windspeed and the corresponding ANSI A58.1, 1972 load distribution with height results in conservative original wind loads.
It should be noted that structures at San Onofre 1 are shielded on three sides because of the way the plant is situated. Higher terrain exists immediately adjacent to the plant on the north and east sides and San Oncfrc 2 and 3 structures exist to the south. (A seawall to the west provides some partial shielding.) According to ANSI A58.1, 1972, section A6.3.5 on shielding and channeling, reductions in velocity pressures due to shielding by adjacent buildings or terrain is not per mitted. However, a variation in the wind profile with height is permitted due to effects of adjacent buildings or terrain. The code handles this aspect through its exposure A, B, and C categories-and the corresponding requirements for use of a particular exposure. The code is cautious in allowing force reductions due to shielding from adjacent buildings because, although these buildings may reduce loads for certain wind directions, they may also increase loads due to buffeting and channeling.
For instances such as these, the code recommends wind tunnel testing and that all results of this testing, both load increases and load decreases be considered in the design. The intent of the above discussion is not to rely on terrain and location for acceptability of wind loads
-6 since wind tunnel testing has not been performed, but rather to suggest that load reduction due to location is a possibility at the San Onofre 1 site.
Some structural capacities and the corresponding windspeed calculated by the staff may be lower than meteorologic data may indicate has occurred in the vicinity of the site. The previously described load reduction due to shielding effects may be one reason to account for this discrepancy. Other possible reasons are that windspeeds experienced in the vicinity of the site did not actually occur at the site and that reserve margin exists before structural collapse occurs. Of course, this possible shielding described above will only occur for straight winds and not for a tornado if it strikes the site.
It appears that allowable stresses were increased by 1/3 for load com binations involving wind. The 1/3 increase in allowable stress utilized by the licensee for structures does not imply structural failure since increases of 30% and 50% in allowable stress above code allowable are permitted for load combinations involving all operating loads (dead load, live load, wind load, operating pipe reaction loads, and thermal loads).
Since pipe reaction loads or any thermal loads were not included in the original design in combination with wind loads, it may be possible to overstress some structural elements if these loads are combined with wind.
Although it is possible to overstress some structural members due to the additional loads, 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 load and would, therefore, provide margin to accommodate the additional loads; however, at San Onofre 1 many walls do not possess excess capacity above the straight wind load.
The staff has analyzed the storage building above the reactor auxiliary building, the turbine building enclosure wall, the fuel storage building, and control room. The results in terms of limiting wind speed at which acceptance criteria for limiting structural elements is exceeded is given below.
.V7VQ
Cause of Wind Corresponding Structure.
Element(b)
Failure(C)
Speed (mph) Pressure (psf Storage Building West Side Concrete 3
46 9
Block Wall 2
51 14 1
80 16 North Side Concrete 2
34 6
Block Wall 3
35 4
1 54 8
12W27 Roof Beam 2
152 120 Turbine Building Concrete Block 3
60 15 Enclosure Wall Wall 2
64 22
.1 102 27 Fuel Storage Building Concrete Block 3
66 19 Wall 2
80 33
- 1.
127 41 12W19 Roof Beam 2
73 27 3
80 28 1
124 39 12W19 Edge Beam 2
40 9
3 466 10 3163 Control Room East and South Side Reinforced Concrete Walls MowS
>to
- a.
The ratings of some structural components are not definitive but rather are estimates based on approximate modeling.
- b. Note that this table does not imply that all inadequate elements have been identified. Structural details not included in this review are windows, doors, and roof decks.
- c. Key:
1 = tornado dynamic pressure; 2 = differential pressure; 3 = high wind dynamic pressure. Tangential windspeeds are listed for differential pressure failures.
-8 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 85 mph at San Onofre 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 for 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%. Similarly, the straight wind capacities given for masonry walls do.not include the stress increase allowed for tornados. Prior to increasing stress allowables in masonry walls an evaluation of increased stresses on anchor bolt safety factors in addition to the magnitude of thermal and pipe reaction loads would have to be performed.
The results obtained by the staff indicate that a substantial number of structures cannot withstand the design basis tornado loads. The staff has determined that the control room can withstand the design basis tornado loadings. Based on original design specification, the sphere enclosure building and diesel generator building would have adequate capacity to resist the design basis tornado and the vent stack would not. There are numerous portions of systems and components not inside structures which have not been investigated by the staff.
Any roof decks at the site consisting of built-up roofing as opposed to structural roof slabs made of concrete were not investigated by the staff.
It is expected that such roofs will have minimal resistance to differential pressure.
A comparison of limiting windspeeds obtained by the licensee.and those obtained by the staff is given below.
-9 Tornado rotational wind velocity Total tornado external wind (mph) or calculated pressure,drop velocity (mph) (dynamic pressure) capacity (differential pressure)
Licensee Staff Licensee Staff Control Room Southwall (1'-l" thk)
>260
>250
>1.5 psi
>1.5 psi Eastwall (9" thk) 250
>250
.89 psi
>1.5 psi Fuel Storage Building Concrete blockwall 135 127 92 80 W12X19 roof beams (middle of roof) 190 124 73 Turbine Building Concrete blockwalls 104 102 72 64 Reactor auxiliary building Westside blockwalls 153 80 103 51 Northside blockwalls iZG 54 34 Roof beams
>250 257 152
-10 As--can be seen, in some instances,.the capacities calculated by the staff and-by the licensee compare well while in other cases, there are larger discrepancies. This can be attributed mainly to differences in modeling. For example, steel roof beams would be subjected to uplift as a result of both differential and dynamic pressures for which they had not been originally designed. This would result in compression in bottom flanges which are usually unbraced. The staff has calculated capacity using elastic design with allowable stress increases and accounting for a long unbraced
-compression flange whereas the-licensee has used plastic design and calculated full plastic section capacity. In the plastic analysis, location and adequacy of bracing as required by the AISC to permit development of full plasticcapacity was not reviewed by the licensee.
The primary reason for the large differences in the reactor auxiliary building masonry block wall capacities is again due to modeling differences. The staff conservatively assumed a cantilever due to the type of connection between the top of the block wall and the upper slab whereas the licensee assumed the wall to be simply supported.
If it can be shown that the connections are such that the walls behave as simply supported, then the capacities would be twice those calculated by the staff shown on pages 7 and 9 of this SER. Not all capacities reported by the licensee were reviewed by the staff; rather, a sampling approach was-used.
The ventilation stack analysis submitted by the licensee, did not address the following factors which could significantly reduce its capacity: 1) a comparison of extreme fiber stresses to allowable stresses which include allowable stresses to preclude buckling; this should be done for various cross-sections over the height of the stack; 2) base connection adequacy, and 3) effects of vortex shedding.
VI.
CONCLUSIONS Based on the sampling conducted by the staff, it is concluded that portions of most structures cannot withstand the postulated design basis tornado loads of 250 mph wind and 1.5 psi pressure drop.
The licensee should: 1) implement modifications for the following structures in order to meet the design basis tornado loads, 2) demonstrate that the consequences of failure if subjected tornado loads are acceptable or 3) demonstrate adequate resistance for smaller tornado loadings and that the risk associated from larger tornado loadings is acceptable.
1.--. Storage building (portion of the Reactor Auxiliary Building which-is above grade)
- 2. Turbine building
- 3. Fuel storage building
- 4. Portions of the control and administration building other than the control room
- 5. Ventilation equipment room
- 6. Turbine building gantry crane In this SER, the staff considers the 4Kv room and battery room as part of the control and administration building and the 480v switch gear room 'as part of the fuel storage building.
For the numerous safety-related.components not inside structures, the licensee should demonstrate the acceptability for tornado loads or that the consequences of failure are acceptable. This should be reviewed in conjunction with SEP Topic III-4.A, "Tornado Missiles."
The licensee should determine the effects of pipe reaction loads and thermal loads in conjunction with wind loads in order to show that the original wind design is comparable to present wind criteria-and to use the higher stress allowables. The licensee should determine whether any anchor bolts exist in exterior masonry walls and assess whether calculated wall capacity for-tornado resistance should be decreased to assure anchor bolt functionality.
Extreme fiber stress comparisons, base connection adequacy and the effects of vortex shedding need to be addressed in order to establish vent stack capacity.
The need to implement modifications in order to assure that structures, systems and components can adequately resist Wind and tornado loads will be determined during the integrated assessment.