Text

Rev 0 to Tornado Resistance Design Review Criteria,San Onofre Nuclear Generating Station Unit 1
	ML13333B091
Person / Time
Site:	San Onofre
Issue date:	11/26/1985
From:	Atalay B, Hampshire D, Sellers C; CYGNA ENERGY SERVICES
To:	;
Shared Package
ML13330B136	List: ML13330B135; ML13333B091; ML13333B092;
References
	DC-85028-01, DC-85028-01-R00, DC-85028-1, DC-85028-1-R, NUDOCS 8612010110
	Download: ML13333B091 (74)
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TORNADO RESISTANCE DESIGN REVIEW CRITERIA SAN ONOFRE NUCLEAR GENERATING STATION UNIT 1 FOR SOUTHERN CALIFORNIA EDISON COMPANY 2244 WALNUT GROVE AVENUE ROSEMEAD, CA 91770 Cygna Document Number DC-85028-01 Revision 0 October, 1985 Prepared by v

t k

U. Hamps i e Date Structural Review by/

Day ate Systems Review by Izz11 C. D. Ilers Date Approved by 4k

.1 gh ae Cygna Energy Services 101 California Street, Suite 1000 San Francisco, California 94111 8612010110 861121 PDR ADOCK 05000206 P

PDR

TABLE OF CONTENTS Page 1.0 Introduction 1-1 2.0 Design Review Approach 2-1 2.1 Identification of Structures, Systems and Components 2-1 2.2 Deterministic Evaluation 2-2 2.3 Probabilistic Evaluation 2-4 2.4 Design Basis Tornado 2-5 3.0 Loads 3-1 3.1 Tornado Loads 3-1 3.1.1 Tornado Wind Load 3-2 3.1.2 Tornado Differential Pressure Load 3-3 3.1.3 Tornado Missile Load 3-4 3.2 Straight Wind Loads 3-6 3.3 Normal Operating Loads 3-7 4.0 Load Combinations 4-1 5.0. Acceptance Criteria 5-1 5.1 Concrete Structures 5-1 5.2 Steel Structures 5-2 5.3 Reinforced Concrete Masonry 5-4 5.4 Piping Components 5-5 5.5 Pipe Supports 5-6 5.6 Electrical Raceway Supports 5-9 5.7 Tanks and Miscellaneous Equipment 5-12 SotenClfri Edison Company Page i San Onofre Nuclear Generating Station Unit 1

,iiiiii~g~iniII~IDocument No. DC-85028-O1, Rev. 0

TABLE OF CONTENTS (continued)

Page 5.8 Material Allowables and Design Strengths 5-15 5.9 Component Evaluation 5-17 5.9.1 Boundary Perforation 5-17 5.9.2 Loss of Operability 5-18 5.9.3 Structural Failure 5-19 6.0 Structural Evaluation Methods 6-1 6.1 Tornado Wind Load Evaluation 6-1 6.2 Differential Pressure Evaluation 6-3 6.3 Tornado Missile Loads 6-4 6.3.1 Local Impact Effects 6-4 6.3.2 Global, Structural Effects 6-6 7.0 Alternate Tornado Shutdown System Selection Criteria 7-1 7.1 General Criteria 7-1 7.2 Existing Systems 7-1 8.0 Bibliography 8-1 Appendix A Alternate Tornado Resistance Criteria for Reinforced Masonry Walls Southern California Edison Company Page ii

_San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

1.0 INTRODUCTION

This document describes the criteria being used in the tornado resistance design review for San Onofre Nuclear Generating Station Unit 1 (SONGS 1).

The design review is being performed for the resolution of SEP Topics 111-2 and III-4.A on "Wind and Tornado Loadings" and "Tornado Missiles," respectively.

The NRC has summarized their position on SEP-Topics 111-2 and III-4.A for SONGS 1 in SER's contained in [4] and [5].

The review criteria have been defined to comply with the NRC criteria and specifically, to ensure the availability of structures, systems, and components that are required to assure:

a.

capability to shutdown the reactor and maintain it in a safe shutdown condition, and

b. the capability to prevent accidents which could result in an increase of offsite exposures.

These criteria are used to evaluate the current straight wind and tornado design resistance of SONGS 1, as well as to quantify the upgrades required for different tornado wind speeds as defined in [14], and to determine the design basis tornado event.

The straight wind and tornado wind speeds being considered are those corresponding to probabilities of occurrence down to 10-7 per year.

_Southern California Edison Company P.age 1 - 1 San Onofre Nuclear Generating Station Unit 1 II IIII Document No.

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2.0 DESIGN REVIEW APPROACH The approach used in the design review involves five basic steps.

First, structures, systems and components required for plant shutdown are identified.

Next, they are deterministically evaluated against SEP criteria to determine availability following a tornado event.

For structures, systems and components which do not pass the deterministic evaluation, a probabalistic evaluation is pursued. The evaluations are performed for four tornado events of specific occurrence probability.

Plant modifications required to control the plant after each tornado event are conceptualized and their appropriate cost estimated. A cost/risk evaluation is performed based on these modification costs relative to plant risk which defines the Design Basis Tornado.

This approach is shown in the flow charts of Figures 2.1 and 2.2.

2.1 Identification of Structures, Systems and Components The Normal, Abnormal and Emergency Operating Instructions are reviewed to determine structures, systems and components required to place and maintain the plant in a safe shutdown condition. Based on this review the normal and emergency methods for plant shutdown are evaluated and the necessary components required to perform this effort identified.

To assure that a failure of one of these components does not threaten the operability of the entire system, a review of the associated P&IDs is performed and redundant/alternate equipment noted. These components, along with their associated power supply and any structures they may be locate in or connected to, comprise the structures, systems and components to be evaluated.

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2.2 Deterministic Evaluation The review of these structures, systems and components centers around those safety related structures, systems and components that were identified by the NRC [4], [5] as not being able to withstand the postulated tornado loads or as not being adequately protected from tornado missiles. The evaluation performed by the NRC was based on criteria used for licensing new facilities.

The SER's were based on a tornado wind speed of 250 mph and a pressure drop (differential pressure) of 1.5 psi occurring in 4.5 seconds.

Two postulated missiles were considered, namely a 3 foot steel rod with a total horizontal velocity of 229 ft/sec and a utility pole with a total horizontal velocity of 152 ft/sec. Using these tornado and missile parameters it was concluded that the required concrete thickness for an adequate missile protection barrier would be 10 inches for the utility pole missile and 6 inches for the steel rod missile. It was further concluded that masonry walls, generically, would not provide adequate protection against tornado missiles.

The following structures were considered to have inadequate resistance to withstand a tornado with a wind speed of 250 mph and a pressure drop of 1.5 psi:

1.

Reactor Auxiliary Building (portions 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

7.

Vent stack Southern California Edison Company Piage 2 - 2 W 'San Onofre Nuclear Generating Station Unit 1 Document No.

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The systems and component items listed in Table 2.1 were considered to be located either in the open or in buildings with inadequate strength and were therefore considered not to be protected from tornado missiles.

The sphere enclosure building and the diesel generator building were considered in the NRC review to be capable of withstanding the 250 mph tornado, as well as being adequately protected from the effects of tornado missiles.

Systems and components that were considered to have adequate tornado missile protection are listed in Table 2.2.

Table 2.3 defines the scope of equipment targets that are evaluated as part of the deterministic tornado resistance design review.

The deterministic evaluation will be based on the assumption that all inadequately protected structures and components are subjected to the site specified tornado and straight winds of [14] and struck by the two specifically defined NRC missiles [5].

The resultant loads will be used to determine the structural adequacy of the components and structures to perform their required safe shutdown functions. If components are determined to fail at a given windspeed, based on the criteria of Table 2.4, modifications required to protect them are conceptualized in order to allow an overall cost risk analysis.

This methodology is shown in Figure 2.1.

In addition to the potential failure of safety related structures, systems, and components by postulated tornado missiles, safety related active components are also reyiewed for potential failure due to sand impingement.

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For those active components not located in protected structures a review is performed to determine if sand could enter into the component's casing or affect exposed bearings.

If it is determined that no visible pathway is available for sand to enter the component's casing or affect the bearings, the component will be considered protected and no further evaluation is required.

2.3 Probabilistic Evaluation For those structures, systems and components considered to have adequate tornado missile protection by deterministic evaluation, no further evaluation is performed. However, equipment not protected is evaluated to determine what modifications would be required to comply with these criteria considering their probability of strike and failure. The methodology used to determine if structures, systems, and components are protected from postulated tornado missiles is outlined on Figure 2.2.

To determine the probability of failure a Monte Carlo simulation methodology and a simulation computer code TORMIS, which quantifies tornado wind load and tornado-generated missile risk, is used.

The TORMIS-simulation code requires three imputs as follows:

1.

Three dimensional model of the plant structural and support configuration;

2.

Site specific missile database, and;

3.

Site specific windfield database.

Using the three database inputs, TORMIS determines, for each structure and component, the probability of strike and failure for each of the site specific missiles.

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The plant model--is determined by a review of layout drawings.

The site specific missile database is determined by a site inspection.

The site specific windfield database was determined in a previous analysis [14].

The probability of strike and failure for each of the structures and components is determined for tornado wind speeds with a probability of occurrence from 10-4 to 10-7 per year.

At each of these probable wind speed occurrences a risk simulation using a set of TORMIS code options is performed.

To facilitate comparison among alternate damage criteria, four definitions of the impact event are utilized

[24].

1. Missile impact

2. Missile impact with a velocity greater than a specified value

3. Barrier damage evaluation for a specified thickness.

4. Barrier damage evaluation for an alternate thickness greater than the thickness in event 3 above.

This methodology is shown in Figure 2.2 and the criteria used to determine if failure will occur is outlined in Table 2.4.

2.4 Design Basis Tornado Once it is determined that a structure, system or component will fail a conceptual modification and associated cost to protect it is developed. This information is used to perform a cost/risk evaluation for each of the wind events. Based on this evaluation it is determined at what probable wind speed occurrence it is cost beneficial to backfit the plant.

The windspeeds associated with this probability of occurrence represent the SONGS 1 Design Basis Tornado.

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Upon determination of the Design Basis Tornado a review of the safe shutdown systems will again be performed. This review is performed to define the minimum set of structures, systems and equipment available to place and maintain the plant in a safe shutdown condition. If sufficient systems and equipment are not available, modifications will be implemented to protect those necessary components.

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Table 2.1 Systems And Components Not Protected From Tornado Missiles Per NRC Review (Based on 250 MPH Tornado Wind Velocity) 1 Atmospheric dump valves and steam dump control system 2

Turbine and motor-driven auxiliary feed pumps (Auxiliary Feedwater System) 3 Water source -

Condensate Storage Tank 4

Component Cooling Water System 5

Salt Water Cooling System 6

Chemical and Volume Control System 7

Refueling Water Storage Tank 8

Instrument Air System 9

Spent fuel pool storage and spent fuel pit cooling system 10 Boron Injection System 11 Ventilation system for the control room 12 Control Room 13 Safety Injection System

14 Instrumentation for shutdown 15 Emergency power (AC and DC) 16 Main Steam and Main Feedwater System

_________Southern California Edison Company Page 2 -7

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Table 2.2 Tornado issile Protected System and Component Per NRC Review (Based on 250 sph Tornado Wind Velocity) 1 Reactor Coolant Pressure Boundary 2

Steam Generators 3

Pressurizer 4

Charging Pumps 5

Diesel Generators 6

Diesel Fuel Supply 7

No. 2 125 VDC Bus, Battery and Battery Chargers 8

Control Rod Drive System 9

Liquid Radwaste System 10 Gaseous Radwaste System 11 Reactor Core and Fuel Assemblies 12 Main Steam System Inside Containment 13 Feedwater System Inside Containment 14 RHR System Inside Containment 15 Boron Injection System Inside Containment 16 Spent Fuel Pit Boundary 17 Instrumentation Inside Containment

_________Southern California Edison Company Page 2 -8 San Onofre Nuclear Generating Station Unit 1 2

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Table 2.3 Potential Targets to be Evaluated in the Tornado Resistance Design Review 1 Main Steam Lines & Associated Relief and Dump Valves outside containment up to and including the Turbine Stop Valves 2

Main Feedwater Pumps and Piping outside containment 3

Motor Driven and Turbine Driven Auxiliary Feedwater Pumps and Piping 4

Condensate Storage Tank 5

Component Cooling Water Surge Tank 6

Component Cooling Water Pumps and Piping in backyard 7

Component Cooling Water Heat Exchanger 8

Refueling Water Storage Tank 9

Auxiliary Feedwater Storage Tank 10 Remote Shutdown Panel 11 Control Room and Control Room HVAC 12 RCP Seal Water Return Valve 13 Salt Water Cooling Pumps and Piping 14 Volume Control Tank 15 Boric Acid Tanks, Pumps and Piping 16 Gaseous Nitrogen System 17 Dedicated Manual Transfer Switches at Auxiliary Feedwater & Charging Pumps 18 Instrument Air System 19 Auxiliary Feedwater System Flow Control Valves 20 Primary Plant Make-up Water Storage Tank 21 Auxiliary Salt Water Cooling Pump and Piping 22 Recirculation Heat Exchanger 23 Steam Generator Blowdown Valves and Piping 24 CCW Piping and Valves in Valve Alley 25 Spent Fuel Pit Heat Exchanger 26 Instrument A.C. Power Supplies 27 4160V Switchgear Southern California Edison Company Pace 2 - 9 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

Table 2.3 (cont'd) 28 480V Switchgear 1, 2, & 3 29 4160V/480V Transformers 1, 2 & 3 30 480V Motor Control Centers 31 No. 1 125V D.C. Bus, Battery and Battery Chargers 32 D.C. Power Cables 33 A.C. Power Cables 32 Safe Shutdown Instrumentation Cables Southern California Edison Company Page 2 - 10

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TABLE 2.4 COMPONENT CRITERIA EVALUATION Failure Mechanism Component Boundary Loss of Structural Perforation Operability Failure Piping Section 5.9 NA Section 5.4, 5.5 Active Valves Treated as Piping Note 1 Note 1 Passive Valves Treated as Piping NA NA Instrumentation NA Strike = Failure Strike = Failure Tanks Treated as Piping NA Sections 5.2, 5.7 Heat Exchangers Treated as Piping NA Section 5.2, 5.7 Air/N 2 Tubing Strike = Failure Strike = Failure Strike = Failure N2 Cylinders Treated as Piping NA NA Pumps/Operators Treated as Piping Note 1 & 2 Note 1 Elec. Cabling NA Strike = Failure Strike = Failure Elec. Cable Trays NA NA Sections 5.2, 5.6, 5.9 Elec. Conduit NA NA Sections 5.2, 5.6, 5.9 Elec. Switchgear NA NA Sections 5.6, 5.9 Transformers 5.9 NA Section 5.9 MCCs 5.9 NA Section 5.9 Note 1:

Missile impacts and wind loads are assumed at the eccentric center of mass (i.e, valve operator C.G.). Seismic qualification calculations are used to extrapolate seismic loads to acceptable wind/impact loads.

Note 2:

Missile impacts are assumed to occur at the most critical location affecting the structural aspect of operability. For example, for pumps this may be the bearing supports or drive shaft.

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TABLE 2.5 SAN ONOFRE TORNADO MISSILE SUBSET CHARACTERISTICS Weight Final per Unit Length/Depth Missile Description Depth Length Amin Ratio Weight (lb.)

Subset (Typical) d (in)

(lb/ft)

(in2)

Min.

Max.

Min.

Max.

1*

Rebar 1.00 2.67 0.79 36.0 36.0 8

8 2

Gas Cylinder 10.02 38.64 9.45 4.0 10.0 129 323 3

Drum, Tank 19.98 23.55 311.60 2.3 6.0 90 235 4*

Utility Pole 13.50 32.06 143.10 31.1 31.1 1122 1122 5

Cable Reel 42.21 140.70 126.60 0.5 0.6 247 297 6*

3" Pipe 3.50 7.58 2.20 34.3 34.3 76 76 7*

6" Pipe 6.63 18.90 5.60 27.2 27.2 284 284 8*

12" Pipe 12.75 49.60 14.60 14.1 14.1 743 743 9

Storage Bin 38.40 112.50 40.50 1.0 7.8 360 2808 10 Concrete Frag.

36.00 326.25 324.00 1.0 3.0 979 2936 Wood Beam 12.00 9.50 48.00 12.0 12.0 114 114 40 Wood Plank 12.00 3.30 12.00 8.0 12.0 26 40 13 Metal Siding 48.00 25.00 24.00 2.0 4.0 200 400 14 Plywood Sheet 48.00 15.02 50.74 2.0 2.0 120 120 15 Wide Flange 11.29 27.87 8.16 8.0 60.0 210 1573 16 Channel Section 5.11 11.88 3.49 9.0 80.0 45 405 17 Light Eqpt.

46.48 44.02 4.63 0.5 5.0 85 853 18 Heavy Eqpt.

67.07 88.67 15.70 0.5 8.0 248 3956 19 Steel Frame, Grating 43.31 12.37 2.22 1.0 7.5 45 335 20 Large St. Frame 97.41 47.23 11.00 1.0 5.0 383 1917 21*

Vehicle 66.00 250.00 2474.00 2.9 2.9 3988 3988 Denotes membership in NRC standard spectrum of missiles Southern California Edison Company Pag 12 San Onofre Nuclear Generating Station Unit 1

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Figure 2.1 DETERMINISTIC EVALUATION FLOWCHART NRC Missiles Site Specific

Utility pole Windfield

Steel rod Database Targets OK at 10-7 yes windspeed no OK at 10-.6 yes wi ndspeed no Targets OK at 10-5 yes windspeed 0

Targets OK at 10-4 yes windspeed Component and Structure Qualification Levels Southern California Edison Company Page 2 -13 San Onofre Nuclear Generating Station Unit 1 Document No. OC-85028-01, Rev. O

Figure 2.2 PROBABILISTIC EVALUATION FLOWCHART Missile Plant Windfield Database Model Database Begin TORMIS Evaluation Probability of:

missile impact

missile impact at velocity > allowable

missile penetrating barrier No.

1

missile penetrating barrier No.

2 Damage/Failure probability vs windspeed curve Southern California Edison Company Page 2 -

14 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

3.0 LOADS In addition to the extreme environmental condition loads directly related to the postulated tornado event, the design review also takes into consideration sustained (dead weight) loads as well as live loads and operating loads that may exist concurrently with the tornado event.

The tornado loads are defined in Section 3.1 below.

3.1 Tornado Loads Tornado intensities in terms of wind speed and pressure drop have been defined as functions of annual probability of occurrence for the SONGS 1 site in a report entitled "Tornado Hazard Analysis Relating to SEP Topic 111-2 at San Onofre Unit 1" [14].

Based on available historical and technical data it is concluded in

[14] that the Western Region tornado defined in USNRC Regulatory Guide 1.76 [1] is not appropriate for use at SONGS 1. Instead, the wind effects described in [14] are used in computing structural effects and missile characteristics at the San Onofre Unit 1 site.

The significant tornado properties for use in the tornado evaluation as specified in [14] are summarized in Table 3.1.

A tornado can potentially cause damage to a structure through three principal interaction mechanisms:

(1) pressure forces created by air flowing around and over the structure, (2) pressure forces created by relatively rapid changes in atmospheric pressure, and (3) impact forces created by tornado-propelled missiles [15].

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For the structural evaluation, then, the tornado parameters are used to define the following three categories of structural tornado loadings:

Tornado Wind Load [WW]

Tornado Differential Pressure Load [W ]

Tornado Missile Load [Wmi The total tornado load, consisting of a combination of the above three tornado load categories (Wy, Wp, Wm) is designated Wt.

The individual tornado load components are addressed below in Sections 3.1.1, 3.1.2, and 3.1.3, while the combination of the components into total tornado load, Wt, and combination of Wt with other operating and live loads are discussed in Section 4.0.

3.1.1 Tornado Wind Load The tornado wind load, Ww, expressed as a maximum velocity pressure is obtained from the representative tornado wind speed using the following expression [6]:

P = 0.00256 V2 in which:

P = maximum wind load pressure [psf]

V = representative tornado wind speed [mph]

The possibility of load reduction as a result of local shielding effects may be taken into account when determining the representative tornado wind speed, V, in this expression.

Southern California Edison Company Page 3 - 2 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

The maximum velocity pressure applies at the radius of the tornado funnel at which the maximum velocity occurs.

The tangential velocity varies with the radial distance from the center of the tornado core.

One idealization of this variation is shown in Figure 3.1 which is obtained from

[15].

This variation, as described in [15], may be taken into account for design purposes.

In cases where structural dimensions are large compared to the size (radius) of the tornado this consideration may result in a reduced average velocity pressure. It should be noted that only the tangential wind velocity component is characterized by this variation.

For calculating effective tornado wind velocity pressures on structural surfaces, shape factors and pressure coefficients from ASCE Paper No. 3269 [16] or ANSI A58.1 [26] are used.

Gust factors are taken as unity.

The effective wind velocity pressure thus obtained is considered constant with respect to height when applied to exposed structures [6].

3.1.2 Tornado Differential Pressure Load The differential pressure variation with respect to tornado radius is shown schematically in Figure 3.1.

The maximum values of the differential pressures and associated rates of pressure change for the tornado wind speed probabilities of interest are included in Table 3.1.

The differential pressure, as shown on Figure 3.1., has its maximum at the core of the tornado, where the 'tangential wind speed is zero.

This is reflected in the methodology used for combining the load effects on structures from the two Southern California Edison Company Page 3 - 3 San Onofre Nuclear Generating Station Unit 1 Document No.

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different load phenomena, Ww and Wp, as discussed further in Section 4.0.

3.1.3 Tornado Missile Loads Tornado and severe wind missile loading characteristics are based on the missiles and relative velocities of [5].

Specifically, these missiles and their associated velocities relative to Table 3.1 windspeeds are presented in Table 3.2.

All exposed components and structures will be assumed to be struck by these missiles and evaluated for potential damage in accordance with Section 5.0. Both missiles will be assumed to travel at the stated horizontal velocity regardless of their actual aerodynamic characteristics or probability of injection.

This deterministic evaluation will be supplemented by the probabilistic evaluation described below in order to bound the actual damage potential of safe shutdown components.

For the probabilistic evaluation described in Section 2.3, tornado and severe wind missile loading characteristics will also be developed using site-specific missiles and plant data.

The TORMIS methodology [24], [25], which has been reviewed and accepted by the NRC for plant-specific wind borne missile analysis [29], is used for this analysis.

Conservative inputs and assumptions are used to quantify the missile loads for each target and risk level.

Specifically, the following analysis procedure is followed.

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Site-Specific Missiles: A site-specific survey of SONGS 1 is conducted to develop information on the potential types of missiles at the plant.

This data is collected in a form consistent with the basic missile sets identified in [24].

The numbers and locations of missiles are quantified and the missile threat to the SONGS 1 shutdown systems determined.

Site-Structures and Targets:

Shutdown systems and scenarios that comprise the targets for the missile load and impact analysis are modeled for the TORMIS analysis. Tornado-proof structures that tend to shield these targets from certain missile sources or directions are included.

Non-tornado proof buildings are also considered potential sources of missiles.

Tornado and Straight-Wind Frequency Risk:

The combined tornado and straight windspeed frequencies developed in [414]

are used in the analysis.

These windspeed frequencies are used with the TORMIS tornado windfield model for windspeeds greater than the tornado cross-over windspeeds. Tornado windfield characteristics are based on site specific data in

[14] as available. For windspeeds below the tornado cross over windspeeds, straight wind profiles and site-specific directional characteristics are used.

Missile Injection Criteria:

The minimally restrained missile injection criteria is used in the TORMIS methodology [24],

[25].

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Missile Impact Characteristics and Local Damage Probabilities: A spectrum of missile impact characteristics (missile type, mass, velocity) is developed for each target. In addition, impact (hit) probabilities, failure probabilities, and local effects damage probabilities are estimated using the TORMIS methodology. The local effects analysis includes perforation of steel targets and scabbing of reinforced concrete targets.

An assessment of the missile effects on critical equipment is made based on the missile definition and estimated impact velocities (Table 2.4).

3.2 Straight Wind Loads The curves describing the annual occurence probabilities for fastest mile straight wind velocity and maximum tornado wind velocity, respectively, in [14] intersect between the 10-4 and 10-5 probability levels.

Wind speeds due to straight wind and tornadoes are not directly comparable in terms of effects on structures since effective pressure calculations and pressure distribution are treated differently for straight winds and tornadoes. The straight wind case is, however, conservatively considered the controlling event for the 10-4 annual occurence probability, which is at the upper end of the range of interest between 10-and 10-Higher probability straight wind (i.e., lower wind speeds) are thereby not included in the evaluation.

Straight wind velocities are obtained from [14].

Transformation of wind velocity to effective pressure applied to structural surfaces is performed in accordance with ANSI A58.1-1982 [26], using gust factors corresponding to Exposure D. Exposure D, as defined in [26],

represents coastal areas extending inland 1500 feet from the shoreline or 10 times the height of the structure under consideration, whichever is greater.

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The velocity pressure, q,, at height Z is determined by the following equation [26]:

qz = 0.00256 Kz (IV)2 where:

V = basic wind velocity [mph]

Kz = velocity pressure exposure coefficient I = importance factor = 1.0 The parameter Kz is obtained from [26].

The importance factor, 1, is taken as unity for this design review because the occurrence probabilities are accounted for by varying V directly. Pressure and drag coefficients are obtained from [16] and [26] as applicable to different types and shapes of structures and components.

3.3 Normal Operating Loads Normal operating loads include deadloads (0), live loads (L), thermal operating loads (T ) and pipe reaction Loads (Ro).

The live load (L) is taken to include lateral and vertical liquid pressure as well as lateral earth pressure as applicable.

Thermal operating loads (TO) and pipe reactions (R0 ) are considered as applicable for individual structures, unless they are shown to be secondary and self-limiting in nature.

Based on engineering judgement and accepted industry practice, the total operating loads (To + R0 ) are assumed to be enveloped by 5% of the dead loads (D),

except for pipe reactions from main stleam and feedwater systems, which are considered explicitly.

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Table 3.1 Maximum Tornado Load Parameters and Associated Probabilities of Occurrence [14].

Annual Probability 10-4 10-5 10-6 107 Maximum Horizontal Windspeed [mph]

59(1) 98 136 176 Radius of Maximum Rotational Speed [ft]

52.7 74.3 97.0 Pressure Drop [psi]

0.23 0.47 0.77 Rate of Pressure Drop [psi/sec]

0.11 0.23 0.38 Notes:

(1) At the tornado occurrence probability of 10-4, the straight wind speed of 70 mph is controlling.

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Table 3.2 Tornado Missile Velocities Horizontal Velocity

'issile Vlocity (FT]SEC)

Missile Basis 1x10-1x10 1x1O-1x10-7 Steel Rod 0.6VT 62 87 120 156 1"0.D. x 3' Lg.

Weight = 8lbs Utility Pole 0.4VT 41 57 79 103 13.5"0.D. x 35'Lg.

Weight = 1,4901bs VT = Total tornado or straight wind velocity Southern California Edison Company Pege 3 - 9 San Onofre Nuclear Generating Station Unit 1 II Document No.

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0

Tornado core w

V/A Constant z

Oo-VR *Constant z

z I

4I R c Rjdius C

R ad'us A c CM U

(b)

FU 3

0 Tornado core Ib)

FIGURE 3.1 Variation of wind and atimospheric-pressure change with radius (15]

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4.0 LOAD COMBINATIONS The consideration of tornado loading constitutes an extreme environmental condition for which the following load combination is applicable:

0 + L + T + Ro t

where:

D = Dead Load including any permanent equipment L = Live load including any moveable equipment loads and other loads which vary in intensity and occurrence, such as lateral soil and liquid pressure.

To = Thermal effects and loads during normal operating or shutdown conditions. These effects are assumed to be 2.5% of dead loads (D).

Ro = Pipe reactions during normal operating or shutdown conditions. Major pipe reactions from main steam and feedwater systems are considered explicitly, while other pipe reactions during normal operating or shutdown conditions are assumed to be 2.5% of dead loads (D).

Wt = Loads generated by the tornado under consideration.

The tornado loading, Wt, includes load contributions from:

tornado wind pressure, Ww; tornado differential pressure, Wp; and tornado missile loads, Wme These three load components are combined and considered separately for each particular structure in a conservative manner. Credit is taken for the fact that maximum values of the wind velocity and the differential pressure do not coincide in time'and space as shown in Figure 3.1.

Thus, the maximum Southern California Edison Company Page 4 -

1 San Onofre Nuclear Generating Station Unit 1 I. Document No. DC-85028-01, Rev. 0 IIIIIIIIIIlIIIIIIIIIIII ll1IIII

value of WW is combined with one half of the maximum value of Wp.

The most adverse combined effect of the individual tornado load components is included in the load combination as Wt.

In general the following three combinations are considered for any particular structure or component [6]:

1. Wt = WP

2. Wt = W + Wm

3. Wt = W + Wm + 0.5 Wp For consideration of high probability, extreme straight wind loads, W, the following load combination is applicable:

D + L + T0 + Ro +W Load symbols in this combination are as defined previously in this section.

Southern California Edison Company Page 4 - 2 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

5.0 ACCEPTANCE CRITERIA 5.1 Concrete Structures For evaluation of extreme environmental conditions, including tornado effects, the strength design method for concrete is used and the following structural acceptance criteria apply:

D + L + To + R t < U where:

D, L, TO, Rot Wt = Loads as defined in section 4.0. A load factor of 1.0 is implied for each load.

U = Section strength required to resist design loads based on the strength design methods described in ACI 349 [13].

The criteria above is first satisfied without inclusion of missile impact load, Wm. When including the concentrated impact load due to Wm in the combination, local section strength capacities may be exceeded provided there is no loss of function of any structure or component required for safe shutdown of the plant; in which case, maximum allowable ductility ratios are as defined in [3], unless higher values are demonstrated to be applicable.

For evaluation of higher probability (greater than or equal to 10-4) straight wind effects, the above acceptance criteria are applicable with Wt replaced by W.

__Stouthern California Edison Company Page 5-1 San Onofre Nuclear Generating Station Unit 1

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5.2 Steel Structures For evaluation of extreme environmental conditions, including tornado effects, the following acceptance criteria apply.

a.

For elastic working stress methods [12, Part 1]

D + L + T o

+ R + Wt < 1.6S

b.

For plastic design methods [12, Part 2]

D + L + T + R + Wt < Y where:

D, L, TO, Ro, W = Loads as defined in Section 4.0. For each load a load factor of 1.0 is implied.

S = Required section strength based on elastic design methods and allowable stresses defined in Part 1 of the AISC specification [12].

Y = Section strength required to resist design loads and based on plastic design methods described in Part 2 of the AISC Specification [12].

Loads due to straight wind are considered for wind velocities corresponding to an annual occurrence probability of 10-4 or greater. These loads represent extreme environmental effects and are subject to the same acceptance criteria shown above with Wt replaced by the straight wind load, W.

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2 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

The criteria above are first satisfied without inclusion of missile impact load, Wi.

When including the concentrated impact load due to W in the combination, local section strength capacities may be exceeded provided there is no loss of function of any system or component required for safe shutdown of the unit.

In an inelastic evaluation for missile impact effects on steel structural elements, the maximum allowable ductility ratios, Wd, are as follows [8], unless a more detailed ductility capacity analysis is performed:

Stress Component Maximum Ductility or Member Type Ratio, id = e/e Tension due to flexure 10.0 Columns with 1/r < 20 1.3 Columns with 1/r > 20 1.0 Tension 0.5 (e

/ey) where:

1/r

=

slenderness ratio

=

effective member length r

=

least radius of gyration e

=

strain e

=

yield strain eu

=

ultimate strain Southern California Edison Company Paqe 5 - 3 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

5.3 Reinforced Concrete Masonry For evaluation of the reinforced concrete masonry-walls at SONGS 1, subjected to extreme environmental conditions including tornado effects, the following acceptance criteria are used:

D + L + T0 + R0 + Wt < U where:

D, L, To, Ro, W =

Loads as defined in Section 4.0 U = Masonry section strength based on elastic design methods and allowable stresses defined in ACI-531-79 [33] and increased by factors shown in Table 5.1.

Note:

The live load, L, in the combination is considered as its full value as well as being completely absent.

The criteria above are first satisfied without inclusion of missile impact loading, Wi.

When including the concentrated impact load due to Wm in the combination, local section strength capacities may be exceeded provided there is no loss of function of any system or component required for safe shutdown of the unit.

Loads due to straight wind are considered for wind velocities corresponding to an annual occurrence probability of 10-4. These loads represent extreme environmental effects and are subjected to the same acceptance criteria shown above with Wt replaced by the straight wind load, W.

In cases where the above criteria provide unacceptable results, the capacity of reinforced masonry walls to resist straight wind, tornado and missile impact loads will be determined by alternate Southern California Edison Company Page 5 -

4 San Onofre Nuclear Generating Station Unit 1 I I Document No. DC-85028-01, Rev. 0

criteria [28].. These criteria are included in Appendix A. These alternate criteria are based on testing and detailed analytical studies and state that the determination of ultimate, lateral wind pressure load capacities for the reinforced concrete block walls is based on the following criteria [28]:

o Maximum reinforcement steel ductility = 45 o

Maximum compressive strain in concrete blocks = 0.004 o

Reinforcement steel strain hardening modulus = 0.01E (where E =

Modulus of Elasticity) o Maximum wall deflections do not exceed the stability limit of the wall These criteria are consistent with the seismic reevaluation of the SONGS 1 masonry walls.

5.4 Piping Components Piping components essential for the safe shutdown of the unit are subject to the acceptance criteria outlined below for load combinations including tornado effects.

The purpose of these criteria is to ensure the pressure retaining ability of the pipes.

The potential for perforation of the pipe wall by a tornado propelled missile is evaluated using the methods described in Section 5.9.1.

Unless alternative approaches, such as non-linear evaluations, are found to be necessary, the following stress criterion is used for Southern California Edison Company Page 5 - 5 San Onofre Nuclear Generating Station Unit 1 IlIll Document No.

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the structural response considerations of piping components potentially exposed to wind and tornado loads:

max MA+M m no + 0.75i

< 3.OSh [< 2.0 S where:

P max = peak internal pressure [psi]

D = outside pipe diameter [in]

tn = nominal pipe wall thickness [in]

i = stress intensification factor MA = resultant moment loading on cross section due to sustained loading [in.lbs]

MB = resultant moment loading on cross section due to extreme wind or tornado loading [in. lbs]

Z = section modulus of pipe [in 3 Sh = basic material allowable stress at design temperature

[psi]

S = basic material yield strength at design temperature [psi]

This criterion is consistent with the consideration of other extreme environmental loads, such as the Safe Shutdown Earthquake, in the ASME Boiler and Pressure Vessel Code [23].

5.5 Pipe Supports The following documents and criteria will be used to evaluate the adequacy of pipe supports:

o AISC Steel Construction Manual, 8th Edition [12].

o Stress Limits - ASME Code,Section III, Division 1 [23].

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Supporting structure designs will be checked for conformance to the AISC Manual for Steel Construction.

When a member is subjected to both axial force and bending moment, stresses shall be proportioned to satisfy the following requirement provided that; fa

< 0.15:

Fa fa

+

fbx +

fby

< 1.0

[30]

aFa 6Fbx SFby where:

fa is the calculated axial stress, tensile or compressive.

Fa is the allowable compression stress.

fbx and fby are the calculated bending stresses due to moments Mx and My, respectively.

Fbx and Fby are normal allowable bending stresses

For tension a = 1.6

For compression and Kl/r > 126, a = 1.28 For compression and Kl/r < 126, a = 1.1 8 = 1.6 for unsupported length < Lu 8 = 1.1 for unsupported length > Lu All other terms in this and the following equation (K,1,r,Lu and bf) are as defined in the AISC Manual for Steel Construction [12].

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For angles in bending the following must be met:

1. Structural angles must be analyzed about their principal axes.

2. The normal allowable (0.6Fy) should only be used if the unsupported length is less than or equal to 76bf F 0.5 y

For miscellaneous steel as covered by AISC, allowable tension and bending stresses shall be assumed as equal to 1.6 times the AISC allowables for steel design using elastic methods. For allowable axial compression stresses, refer to above paragraph.

For the evaluation of concrete expansion bolts, the allowable loads as given in Table 5.2 shall be used. The interaction formula as shown below shall be used when tension and shear occur simultaneously:

Calculated Tension) 2 +

(Calculated Shear 2

1.

[30]

Allowable Tension Allowable Shear For the evaluation of rock bolt expansion anchors, the allowable loads as given in Table 5.3 shall be used.

The interaction formula as shown below shall be used when tension and shear occur simultaneously:

Calculated Tension2 +

(Calcul;ated Shear 2

1.

[30]

Allowable Tension

'Allowable Shear The allowable stresses on complete and partial penetration welds are Southern California Edison Company Page 5 - 8 9: -San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

shown in Table 5.4, and Table 5.5 shows the allowable stresses for fillet welds. Minimum AISC weld size requirements are not considered for installed supports.

Strength calculations of welds are considered sufficient.

5.6 Electrical Raceway Supports Members used in the cable tray and conduit (electrical raceway) supports shall be qualified considering the following member forces as appropriate:

Flexure about both axes Axial loads Shear In addition, local effects such as buckling of section web or flanges shall be considered. Consideration shall be given to the effects of unbraced lengths, slenderness ratios, and force interaction (e.g., combined bending and compression or tension).

The section properties of members shall be appropriately modified to consider the reduction in area due to bolt holes through the flanges of flexural members per Reference [12].

Welded joints and connections shall be adequately checked for the intended load transfer.

Allowable stresses and stress interaction equations shall be taken from the appropriate sections of the. codes and standards as specified in Ref. [34] and as summarized below:

Southern California Edison Company Page 5 - 9 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

a. Structural steel:

Smaller of 0.9FY or 1.5Fs in Bending, and 1.5Fs in Compression or Tension where:

F =

specified minimum yield stress for the type of steel being used, and Fs =

allowable as defined in AISC "Specification for the Design, Fabrication and Erection of Structural Steel for Buildings," [12].

b. Unistrut Structural Shapes:

Smaller of 0.9Fy or 1.5Fs in bending, and 1.5 Fs in compression or tension where:

F = minimum yield strength of material y

Fs = Allowable stress from A.I.S.I. Specification for the Design of Cold-Formed Steel Structural Members, 1980.

[31].

NOTE:

Section properties will be taken from Unistrut's General Engineering Catalog.

c. Bolts:

1.5 Fs where:

Fs = Allowable as defined in AISC "Specification for Design Fabrication and Erectiol of Structural Steel for Buildings" [12],

0 Southern California Edison Company Page 5 - 10 San Onofre Nuclear Generating Station Unit 1 Document No.

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d. Welded Connections:

1.5 Fs where:

Fs = Allowable as defined in A.I.S.I. "Specification for the design of Cold-formed Steel Structural Members",

Section 4.2.1. [31].

e. Through Bolts in Masonry Walls:

Allowables as specified in Table 5.6.

f. Unistrut Bolt Connections Pullout: One bolt (total for one bolt in a two bolt connection):

1. 8F Two bolts (total for two bolts in a four bolt connection):

2.7F Slip:

1.8F where:

F = Recommended Unistrut bolted connection pullout or slip allowable from Unistrut Engineering Catalog (The recommended Unistrut allowable has a factor of safety of 3.)

g. Conduit Clamps:

1.5F where F is the allowable design load as specified in Table 5.7.

h. Conduit Straps:

1.5F where F is the allowable design load as specified in Table 5.8.

Southern California Edison Company Page 5 - 11 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

i.

U-Bolt Conduit Tiedowns:

Allowables as specified in Table 5.9.

Base plate stiffness and prying effects will be considered in the qualification of the cable tray and conduit supports.

Hand calculations, Cygna proprietary computer program EPLATE, finite element analysis or any comparable method may be used to check the adequacy of the base plate and to determine loading on the anchor bolts.

Anchor bolts shall be analyzed according to the interaction equations and allowables as specified for pipe supports in Section 5.5.

5.7 Tanks and Miscellaneous Equipment Equipment listed in Table 2.3 as well as components required for the intended function of this equipment are evaluated for effects caused by extreme wind and tornado loading.

The objective of these evaluations is to ensure the availability of systems, components and power sources required to safely shutdown the unit, and maintain it in a shutdown condition, in case the postulated low-probability events were to occur.

Passive, load carrying steel components such as atmospheric pressure tanks, are subjected to acceptance criteria as defined for steel structures in Section 5.2 and those for components in Section 5.9.

The supporting structures and anchorages of these components are evaluated as per the criteria in Sections 5.1 and 5.2 for concrete and steel as applicable.

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12 San Onofre Nuclear Generating Station Unit 1 lil l

Document No. DC-85028-01, Rev. 0

In-line equipment such as pumps, valves and heat exchangers that are included in Table 2.3 are evaluated to ensure their operability and availability, as required, during and following postulated extreme wind and tornado events. The applicable acceptance criteria for these components are consistent with NRC's Seismic Criteria Reevaluation Guideline for SEP Group II Plants [27], as defined below.

Load combination:

D + Po + N + Wt where: D =

Dead load Po =

Design or maximum operating pressure loads and design mechanical loads N =

Nozzle loads Wt =

Tornado loads or extreme wind loads Stress criteria:

Heat exchangers, inactive pumps, valves and other mechanical components:

am < 2.0 S, and al + Ob < 2.4 S Active valves, pumps and other mechanical components:

am < 1.5 S, and a1 + ab < 1.8 S Southern California Edison Company Page 5 -

13 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

Bolt stresses are limited to:

Tension:

the smaller of S and 0.7 S Shear:

the smaller of 0.6S and 0.42 Su The following notes apply to the criteria for the in-line equipment

[27]:

a. Stress symbols:

am = General membrane stress a1 = Local membrane stress ab = Bending stress

b. Active pumps, valves and other mechanical components are defined as those that must perform a mechanical motion to accomplish a safety function

c. Nozzle loads include all piping loads transmitted to the component during the extreme wind or tornado event.

d. For active mechanical equipment contained in safe shutdown systems, it is assumed that deformation induced by the loading on these pumps, valves and other mechanical components does not introduce detrimental effects which preclude function of this equipment following a postulated event.

For valve operators integrally attached to valves, binding is considered precluded if stresses in the valve yoke or other operator supports are less than yield.

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5.8 Material Allowables and Design Strengths The basic materials used in the construction of structures mentioned in Section 2.0 as being part of the scope of the tornado resistance design review are listed below with their respective specified minimum design strengths [18].

Actual material strengths that are demonstrated by testing to be higher than the specified design strengths may be taken into account for determination of allowable stresses.

A.

Concrete (a)

1. Slabs on grade, building f'c (lb/in. 2) and equipment foundations

= 2,500

2. Supported floor slabs, beams, f'c (b/in.

2) walls, retaining walls, turbine 3,000 pedestal foundation, intake structure, shielding concrete

3. Prestressed decks, circulating f'c (lb/in. 2) water system gates, turbine 4,000 pedesta superstructure

4. Grout fic (b/in. 2)

= 2,000

5. Hollow concrete block UBC-63 f'm (lb/in. 2) masonry, Grade A ASTM C-90

= 1,50

6. Fully grouted, hollow block UBC-63 f'm lb/in.2) masonry, Grade A ASTM C-90 1,0

7. Mortar for concrete block ASTM 0270 fm (lb/in. 2)

-2,~000 B.

Reinforcing steel (b)

1. Intermediate Grade No.

2 ASTM A15 f (lb/in. 2) size round bars

=Y40,000

2. No. 3 thru 11 ASTM A15 f

(1b/in. 2)

ASTM A305

=Y4t=,000

__Sout ern California Edison Company Page 5 -15 fSan Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

3.

No.

14 and.18 ASTM A408 4 1 n.2

4. Welded Wire Mesh 10 gage and larger ASTM A185 f lb/in. 2) 6 A,000 11 gage and smaller ASTM A185 f (lb/in. 2) ty56,000

5.

Prestressed tendons ASTM fpu lb/in. 2)

A421-59T

=

40,000 Type BA C. Structural steel ASTM A36 f

lb/in.2)

= 36,000 D. Miscellaneous steel

1. Hilh-strength bolts

> -1/8 inch ASTM A325 f

1lb/in. 2) y81,000 2

< 1 inch ASTM A325 f

(lb/in.2)

= 2000

2. Hiah-strength anchor ASTM A193, f (lb/in.2) bo ts Grade B7

-105,000

3. Anchor bolts ASTM A307 f (lb/in. 2)

Grade A

=Y36,000

4. Stainless Steel plates ASTM'A167 f (lb/in.2)

Type 304

- 30,000 ASTM 240 (lb/in.2)

Type 304L tY2,000 ASTM A276 f

(1b/in. 2 Type 304

= 30,00

5.

Insert plates ASTM A36 3 lb/in. 2 )

a.

f'c = compressive strength of concrete as used in the BOP Structures Reevaluation [35]

f'm = specified compressive strength of masonry block at 28 days f'm= specified compressive strength of mortar at 28 days 0

b.

fy

= specified yield strength of steel fpu = ultimate strength of prestressed tendons Southern California Edison Company Page 5 -

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5.9 Component Evaluation Components required to place and maintain the plant in a safe shutdown condition are evaluated to the criteria outlined in Table 2.5 and as described below.

5.9.1 Boundary Perforation To determine if perforation will occur in steel barriers two equations developed by Stanford Research Institute (SRI) and Ballistics Research Laboratory (BRL) are used to study the perforation of steel shell by solid, non-deformable missiles; E

S (16,000 T2 +

1,500 ---

T) (SRI Equation)

D 46,000 Ws where: E = Critical kinetic energy required for perforation (ft-lb)

D = diameter of missile (in)

S = ultimate tensile strength of the target steel (psi)

T = steel thickness just to be perforated W = length of a square side between rigid supports (in)

Ws = length of a standard width (4 inches)

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DC-85028-01, Rev. 0

0.5 M V2 T1.5 m

s1.

(BRL Equation) 17,400 K 20 where: T = steel thickness just to be perforated Mm = mass of missile (lb.sec 2/ft)

Vs = Stricking velocity of the missile normal to the target surface (ft/sec)

K = constant depending on the grade of steel (usually K=1) 0 = diameter of missile (in) 5.9.2 Loss of Operability In determining the loss of operability to a component, missile impacts and wind loads are assumed to occur normal to the eccentric center of mass (i.e., valve operator, pump and pump driver C.G.).

This provides a conservative load to the component when evaluated for potential failure.

To determine the missile impact and wind load required to cause the loss of operability seismic qualification calculations are evaluated. These calculations are used to extrapolate seismic loads to acceptable wind/impact loads.

Based on these loads the maximum missile velocities, for the two NRC missiles and each of the site specific missiles outlined in Table 2.4, are determined. These velocities are then used as input results in the deterministic evaluation and as parameters in the TORMIS code for the probabilistic evaluation.

When these loads are exceeded, failure of the component is noted.

Southern California Edison Company Page 5 - 18 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

5.9.3 Structural Failure Missile impacts are also assumed to occur at the most critical location affecting the structural aspect of operability.

For example in pumps this may occur at the bearing supports or the drive shaft.

A review of these critical locations is performed to determine the maximum force that could cause failure.

This force is determined using the criteria outlined in Section 5.7.

Once these forces have been obtained, the critical force is used to determine if failure will occur.

Southern California Edison Company Page 5 -

19 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

Table 5.1 Masonry Allowable Stress Increase Factors (10].

Axial or flexural compresion 2.5 Bearing 2.5 Reinforcement stress except shear 2.0 (< 0.9 f )

Shear reinforcement and/or bolts 1.5 Masonry tension parallel to bed joint 1.5 Shear carried by masonry 1.3 Masonry tension perpendicular to bed joint:

for reinforced masonry 0

for unreinforced masonry 1.3 Southern California Edison Company Page 5 -20 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

Table 5.2 Allowable Design Loads for Concrete Expansion Anchors (1)

Allowable (2)

Design Load Min.

Anchor Shear or Min.

c/c Edge Diameter Tension Spacing Distance (Inches)

(Kips)

(Inches)

(Inches)l 1/4 0.30 3

3 3/8 0.60 4-1/2 4

1/2 1.0 5

6 5/8 2.0 6

6 3/4 3.0 7-1/2 6

1 4.0 10 6

(1) For 3000 psi (f ') or higher concrete.

(2) Subject to appropriate reductions due to dynamic shock or violation of center-to-center spacing, edge distances, or embedment length.

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Table 5.3 Allowable Design Loads for Rock Bolt Expansion Anchors (1)

Allowable Min.

Anchor Design Load (2)

Min. c/c Edge Diameter Tension Shear Spacing Distance (Inches)

(Kips)

(Inches)

(Inches) 1 25 33(3) 8(4)12(5) 10 6

1-3/8 50 66(3) 16(4)24(5) 14 8

2 100 133(3) 33(4)48(5) 20 10 (1) For 4000 psi (fic) or higher concrete.

(2) Subject to reductions per Note (2) of Table 5.2.

(3) These increased allowable loads are applicable only for "Abnormal/Extreme Environmental" or "Faulted" loading combinations.

They are based on 0.9 times Manufacturer's maximum working load to elastic limit.

(4) Preferred design load based on AISC limits using manufacturer's ultimate strength values.

(5) Design loads increased by 1.5 applicable only for "Abnormal/Extreme Environmental" (DBE) or "Faulted" loading combinations.

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Table 5.4 Allowable Stresses for Complete and Partial Penetration Groove Welds (SA36 Material)

TYPE OF STRESS ALLOWABLE STRESS Tension Normal to Effective Area 34.56 ksi Compression Normal to Effective Area Same as Base Metal Tension or Compression Parallel to Same as Base Axis of the Weld Metal Shear on Effective Area 23.04 ksi Southern California Edison Company Page 5 - 23 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

Table 5.5 Allowable Stresses for Complete and Partial Penetration Groove Welds (SA36 Material)

TYPE OF STRESS ALLOWABLE STRESS Stress on Effective Area 28.8 ksi Tension or Compression Parallel to Same as Base Axis of the Weld Metal Tension Stress on Leg 20.37 ksi Southern California Edison Company Page 5 -

24 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

TABLE 5.6 [34]

Allowable Design Loads for Through Bolts IN MASONRY WALLS Bolt Allowable Tension Allowable Shear Diameter Load (lbs)

Load (lbs) 1/2" 600 800 (1) The backup plate will be a minimum of 25 square inches.

(2) No interaction formula is required.

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Table 5.7 [34]

Allowable Design Load for Conduit Clamps Condition Conduit Pullout Slip Transverse Slip Longitudinal Size (1bs)

(1bs)

(1bs) 3/4" 1,170 170 180 1"

1,310 310 300 2"

1,890 400 400 3"

1,920 480 450 411 2,700 870 770 511 2,200 420 310 Southern California Edison Company Page 5 -

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San Onofre Nuclear Generating Station Unit 1 IIlIlII Document No. 0C-85028-01, Rev. 0

Table 5.8 [34]

Allowable Design Loads for 2-Bolt Conduit Straps UNKNURLED STRAPS:

Slip Slip Conduit Torque Pullout Transverse Longitudinal Size Bolt (Ft-Lb)

(Lbs)

(Lbs) 3/4" 1/4" 6

1340 568 337 1"

1/4" 6

1150 560 166 1-1/2" 1/4" 6

1280 495 315 2"

3/8" 19 2220 2440 462 3"

3/8" 19 3710 3150 1017 4"

3/8" 19 3710 3110 566 5"

3/8" 19 4200 2950 488 6"

3/8" 19 4000 3150 595 KNURLED STRAPS:

Slip Slip Conduit Torque Pullout Transverse Longitudinal Size Bolt (Ft-Lb)

(Lbs)

(Lbs) 3" 3/8" 30 3710 3150 1370 4"

3/8" 30 3710 3110 977

_Southern California Edison Company Page 5 -

27 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

Table 5.9 [34]

U-Bolt Conduit Tiedown Allowables U-Bolt Pullout Slip Transverse Slip Longitudinal Diameter (1bs)

(lbs)

(lbs) 1/4" 929 232 232 3/8" 2298 574 574 The above values have a 2.25 factor of safety against ultimate, therefore, no interaction is necessary.

_Southern California Edison Company Page 5 -28 Z

San Onofre Nuclear Generating Station Unit I Document No. DC-85028-01, Rev. 0

6.0 STRUCTLRAL EVALUATION METHODS The structural evaluations performed in the tornado resistance design review include explicit, detailed structural analyses to account for tornado loads as well as comparisons of loads and characteristic responses with existing, structural analyses to qualify structures and structural elements for the various types and intensity levels of wind and tornado loads.

Additional detailed analysis may be performed as required in cases where the acceptance criteria of Section 5.0 are not satisfied.

Structures and components which have been determined to require protection from, or to have the ability to resist, the effects of tornado events are evaluated for tornado wind speeds corresponding to probabilities of occurrence ranging from 10-4 to 10-7 per year.

6.1 Tornado Wind Load Evaluation The structural loads caused by wind velocity pressure during a tornado are idealized as a static equivalent pressure load acting on exposed surfaces of the structures in the most adverse of the probable wind directions.

The wind pressure intensities are determined in accordance with the methods outlined in Section 3.1.1.

The pressure intensity is proportional to the square of the wind velocity for the occurrence probability being considered and is also a function of the shape of the exposed structure.

For the structural evaluation a screening approach is used, in which comparisons of load intensities and response characteristics are made with existing structural analyses involving lateral loads.

The recent seismic reevaluations were performed using methods and acceptance criteria consistent with the tornado resistance design Southern California Edison Company Page 6 - 1 San Onofre Nuclear Generating Station Unit 1 Document No.

DC-85028-01, Rev. 0 hu IIIIIhIIhIlhillIhIhI

review and are appropriate for such comparisons. Typically the seismic structural response is characterized by a lateral inertia force distribution that increases with elevation of the structure.

This means that a comparison of the total horizontal shear and overturning moment at any structural elevation, between the horizontal seismic load case and the lateral wind pressure load case is conservative with respect to the wind pressure case; i.e., if the total shear and moment magnitudes for the wind load case are less or equal to to the same quantities for the horizontal seismic load case, then the global wind load effects are enveloped by the seismic case.

Additionally, to keep the evaluation method within a manageable effort, selective members and connections representing the worst anticipated cases are evaluated first.

If these cases satisfy the qualification criteria, remaining members and connections are considered qualified by comparison. Otherwise, applying a similar logic, a second-cut qualification is attempted on items less limiting than those chosen for the worst case.

In this manner, a matrix is formed relating each tornado occurrence probability and the number of items passing or failing for that occurrence probability. This matrix is used to determine the cost/risk relation for different possible upgrade schemes as a function of different tornado occurrence probabilities.

When employing this method of qualification by comparison,-the assumptions of applicability and load distribution are verified on an individual structure basis.

The structural surfaces that are subjected directly to the wind pressure and the structural components that transfer the lateral wind pressure forces to the main load resisting structural elements Southern California Edison Company Page 6 - 2 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

are evaluated using traditional structural methods.

Here, also, a screening approach is used in the sense that "the weakest link" or the components subjected to the highest intensity loads are evaluated and qualified first.

Elements and components that are stronger or are subjected to lower intensity loads are then qualified generically in groups.

6.2 Differential Pressure Evaluation The maximum internal pressure a structure can sustain as a result of the atmospheric pressure drop is a function of the ratio between the total vent area (doors, windows, etc.) and the total volume.

If this ratio exceeds certain critical values the structure can be considered fully vented and the internal pressure is neglected

[9].

For SONGS 1 the criteria for a fully vented condition are based on the vent area requirements listed in Table 6.1 [17].

For structures that have openings less than that required by Table 6.1, differential pressures due to atmospheric pressure drop tend to force external surfaces outward.

The magnitude of the differential pressure loading is calculated using the pressure drops and associated rates of pressure change shown in Table 3.1.

The methodology descri.bed in Appendix D of [9], or equivalent, is used for the determination of air flow rates and differential pressures between compartments of a structure and across exterior surfaces of buildings subjected to the tornado-induced pressure drop.

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6.3 Tornado Missil.e Loads The evaluation of structures for the effects from tornado-propelled missiles consists of two main considerations:

(1) a highly localized damage or penetration evaluation, and (2) a global structural response evaluation. These two considerations, which in general can be decoupled from each other, are discussed below in Subsections 6.3.1 and 6.3.2. The evaluation of tornado missile loads on masonry block walls is addressed in the alternate criteria of Appendix A to this document.

6.3.1 Local Impact Effects The deterministic evaluation of local impact effects addressed in this criteria is limited to reinforced concrete walls.

The failure criteria for the reinforced concrete walls for the missile impact are the total penetration or severe spalling of the inside of the wall (scabbing). The equations for the reinforced concrete walls are shown as follows:

0.4 0.5 Tss

= 15.5

'U.b D0.2 c

W0.4 V

0.65 T

=5.42 sp uf 00.2 c

where: Tss

= thickness for threshold of spalling for low velocity solid steel missiles (in)

Tsp thickness for threshold of spalling for low velocity steel pipe missiles (in)

W

= missile weight (lbs)

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Vs

= missile striking velocity (ft/sec) fc = concrete compressive strength (psi)

D

= missile diameter (in)

In the probabilistic evaluation of local impact effects the TORMIS missile impact methodology distinguishes impacts for penetration-type missiles from those for soft-type missiles, such as vehicles.

The local effects damage assessment is based upon threshold scabbing or perforation for concrete barriers and perforation for steel barriers.

The modified NDRC formula is used for concrete barriers and the BRL formula is used for steel barriers.

The main features of this methodology are summarized below:

(a) Use of equivalent velocity relation to account for conditions of oblique, noncollinear, and rotating missile impact of slender body type missiles.

The impulse model accounts for general orientations and for angular motions in 3-D space and is used in conjunction with the missile time history data to compute effective impact velocity for each barrier impact.

(b) A procedure that accounts for the effects of missile size on the prediction of the impact probability for small targets and the development of a simplified geometric rule to account for offset hits.

(c) Updated coefficients for the NDRC model that reflect all available data on reinforced concrete impact.

The data has been statistically analyzed and parameters updated to produce unbiased estimations with minimum variance in the error term.

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(d)

Development of a velocity exceedance option to evaluate the effects of overall response failure modes for each missile type.

For the automobile missile, a distribution of impact velocities (based on 4 input exceedance velocities) is generated.

In TORMIS methodology, the time history of each missile is predicted and hence for each impact the following information is generated:

(a) The position of impact on the target (b) Whether or not the impact would damage the target (c) The instantaneous velocity of the missile after impact.

These results are used in a Monte Carlo procedure to estimate local effects damage probabilities for each plant target.

6.3.2 Global, Structural Effects In the deterministic evaluation, hand calculations or the computer program IMPACT (Cygna Corp. Proprietary) is used for structural response evaluations of hard missile impact.

IMPACT performs a complete impact analysis calculation for the overall collapse margins of typical structural members.

The impact can be located anywhere along the span of various types of structural members acting either by themselves or in combination with other members.

The analytical method used in the program is based on the energy balance concept.

The member types considered include the following:

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1. Rectangular concrete beam

2.

One-way concrete slab

3. Symmetric concrete T-beam

4. Asymmetric concrete T-beam

5. Two-way concrete slab

6.

Steel beam

7. Any parallel combination of members 1 through 6 The output of IMPACT will quantify the global effects of tornado missile loads, Wm, for use in the structural evaluation load combination equations listed in Section 4.0.

Yield line analyses may also be performed for the structural response evaluation of primarily concrete slabs and walls.

In the probabilistic evaluation, following the local impact evaluation, the global, structural response is determined using traditional structural analysis methods.

The size and boundary locations of the local area considered initially in the impact analysis is arbitrary within a reasonable range determined by the total size of the structural element being evaluated and by the locations of stiffening elements, beams, columns, etc.

The reactions on the chosen boundary resulting from the missile impact form the input load, with directions reversed, on the structure as a whole. These reaction loads are in general applied as equivalent static loads without excessive conservatism.

Undeformable missiles with low mass are of design concern primarily for their potential ability to penetrate and otherwise locally damage the target as discussed in the Southern California Edison Company Page 6 -

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previous subsection.

Soft but massive missiles on the other hand are subjected to substantial deformation or disintegration upon impact.

The dynamic interaction between missile and target may also be significant for large mass missiles.

Potential soft missiles are primarily those of wood and concrete. The characteristics of soft missile impact is taken into account by the development of impulsive load time histories based on the stiffness and strength properties of the missile and the target [24].

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Table 6.1 Venting Area Necessary to Alleviate Atmospheric Pressure Change Forces [17]

Atmospheric Required Venting Area Pressure Drop per 1000 cu ft Volume

[psi]

[sq. ft]

0.28 0.177 0.63 0.407 1.12 0.750 1.75 1.229 Southern California Edison Company Page 6 -

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7.0 ALTERNATE TORNADO SHUTDOWN SYSTEM SELECTION CRITERIA 7.1 General Criteria The criteria for selecting an acceptable set of equipment to comprise a system required for safe shutdown of SONGS 1 after a tornado is based on several factors.

First of all, the tornado does not occur coincident with or immediately after a design basis event (LOCA). In addition, no ruptures of the reactor coolant system are assumed to occur as a result of this tornado event.

Seismic and tornado events are separate and diverse such that they are not considered to occur simultaneously.

Second, sufficient time exists after the tornado event for operator action to realign fluid flow paths and electrical power for an orderly shutdown.

Third, because tornado damage to safe shutdown equipment already represents a low probability event, no arbitrary single failures will be assumed in shutdown equipment not directly affected by the tornado.

Based on the foregoing, the tornado shutdown system design is not required to be safety related.

7.2 Existing Systems Systems and equipment available to bring the reactor to safe shutdown status are determined by a review of the normal, abnormal and emergency shutdown procedures and the proposed dedicated shutdown system developed for compliance with 10CFR50, Appendix R.

Individual shutdown system trains are identified without Southern California Edison Company Page 7 -

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consideration of safety classification or the single failure criterion.

The single failure criterion is only used in the case where parallel trains required for shutdown employ a single' common system or component. For example if multiple cooling water supply systems share a common header, this header is evaluated against the single failure criterion. When evaluating systems and components against the single failure criteron, only tornado induced failures are considered.

No arbitrary failure is postulated.

While the safety classification of the systems and components is not a primary criterion, if safety related systems are available and protected, they are selected in lieu of non-safety related systems.

When reactor protection or accident mitigation systems are considered, only the shutdown capability is considered. No accident mitigation functions are deemed necessary. System control from the main control room, auxiliary control panels or local control is considered acceptable.

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8.0 BIBLIOGRAPHY

1.

"Design Basis Tornado for Nuclear Power Plants," Regulatory Guide 1.76, USNRC April 1974.

2.

"Tornado Design Classification," Regulatory Guide 1.117, Revision 1, USNRC, April 1978.

3.

"Safety-Related Concrete Structures for Nuclear Power Plants (other than Reactor Vessels and Containment)", Regulatory Guide 1.142, Revision 1 USNRC, October 1981.

4.

"SEP Topic 111-2, Wind and Tornado Loadings San Onofre Nuclear Generating Station, Unit 1", Docket No. 50-206, LS05-82-02-006 USNRC, February 1, 1983.

5.

"SEP Topic III-4.A, Tornado Missiles San Onofre Nuclear Generating Station, Unit 1", Docket No. 50-206, LS05-82-11-065 USNRC, November 19, 1982.

6.

USNRC Standard Review Plan, NUREG-0800, Section 3.3.2 "Tornado Loadings" Rev. 2, July 1981.

7.

USNRC Standard Review Plan, NUREG-0800, Section 3.5.1.4 "Missiles Generated by Natural Phenomena," Rev. 2, July 1981.

8.

USNRC Standard Review Plan, NUREG-0800, Section 3.5.3 "Barrier Design Procedures."

Rev 1, July 1981.

9.

"Tornado and Extreme Wind Design Criteria for Nuclear Power Plants,"

BC-TOP-3-A, Rev. 3, August 1974, Bechtel Power Corporation.

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10.

USNRC Standard Review Plan, NUREG-0800 Section 3.8.4 "Other Seismic Category I Structures" Rev. 1, July 1981.

11.

"Development of Criteria for Seismic Review of Selected Nuclear Power Plants" N. M. Newmark, J. J. Hall, NUREG/CR-098 USNRC, May 1978.

12.

American Institute of Steel Construction (AISC) "Steel Construction Manual," Eighth Edition, 1980.

13.

ACI 349-80 "Code Requirements for Nuclear Safety-Related Structures," American Concrete Institute.

14.

"Tornado Hazard Analysis Relating to SEP Topic 111-2 at San Onofre Unit 1," Cygna Energy Services, July 1984.

15.

"Tornado-Resistant Design of Nuclear Power Plant Structures," By J.R. McDonald, K.C. Mehta, J.E. Minor; Nuclear Safety, Vol 15, No.

4, July-August 1974.

16.

"Wind Forces on Structures," American Society of Civil Engineers (ASCE) Paper No. 3269. Transaction of the American Society of Civil Engineers, Vol. 126, Part II (1961).

17.

"Tornadic Loads on Structures," by K. C. Mehta, J. R. McDonald, and J. E. Minor.

From "Wind Effects on Structures," Proceedings of the Second USA-Japan Research Seminar on Wind Effects on Structures, University of Tokyo Press.

18.

"Balance of Plant Structures Seismic Reevaluation Criteria, San Onofre Nuclear Generating Station Unit 1," Bechtel Power Corporation, February 17, 1981.

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19.

"U.S.

Reactor Containment Technology," ORNL-NSIC-5, Vol 1, Chapter

6. Oak Ridge National Laboratory.

20.

"Reactor Safeguards," C.R. Russel.

MacMillan, New York, 1962

21.

"Full-Scale Tornado-Missile Impact Tests" A.E. Stephenson, G.E.

Sliter.

(Sandia Laboratories/EPRI).

22.

"A Review of Procedures for the Analysis and Design of Concrete Structures to resist Missile Impact Effects," R.P. Kennedy; Holmes and Narver, Inc., September 1975.

23.

ASME Boiler and Pressure Vessel Code,Section III, Division 1, 1980 Edition.

24.

Twisdale, L.A., Dunn, W.L., Chu, J., Lew, S.T., Davis, T.L., Hsu, J.C., and Lee, S.T., "Tornado Missile Risk Analysis," NP-768 and NP-769, Electric Power Research Institute, Palo Alto, California, May 1978.

25.

Twisdale, L.A., and Dunn, W.L., "Tornado Missile Simulation and Design Methodology," NP-2005, Electric Power Research Institute, Palo Alto, California, August 1981.

26.

"Building Code Requirements for Minimum Design Loads in Buildings and other Structures," Committee A58.1, American National Standards Institute (ANSI A58.1-1982).

27.

"Reevaluation Guideline Seismic Crite'ria for SEP Group II Plants (Excluding Structures)" Revision 1. USNRC LS05-82-09-058.

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28.

"Tornado Resistance Criteria for Reinforced Masonry Walls,"

Computech Engineering Services, Inc., Berkeley, California, August, 1985. Report No. R573.01.

29.

Memorandum from Frank J. Miraglia to L.S. Rubenstein dated October 26, 1983, subject Safety Evaluation Report - EPRI Topical Report Concerning Probabilistic Missile Assessment Approach (EPRI-NP-768, NP-769, NP-2005 Vol. 1 and 2).

30.

"Design Criteria for SONGS 1, Project Design Criteria Manual, Vol.

I, Seismic Upgrade General Design Criteria," SONGS-1 Document No. M 86018, Revision 3, November 1984.

31.

American Iron and Steel Institute, "Cold Formed Steel Design Manual," 1980 Edition.

32.

American Welding Society, "Structural Welding Code," AWS D.1.1, 3rd Edition, 1979.

33.

ACI 531-79, "Building Code Requirements for Concrete Masonry Structures", American Concrete Institute, 1979.

34.

"Design of Raceway Support Modifications", SONGS-1 Document No. M 37452, Revision 1, September 1984.

35.

Letter from M.O. Medford (SCE) to D.M. Crutchfield (NRC), dated November 21, 1983.

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APPENDIX A Alternate Tornado Resistance Criteria for Reinforced Masonry Walls Computech Engineering Services Report No.

R573.01 Dated August, 1985

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ML13333B091

Text

1.0 INTRODUCTION

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