tornado resistance design review criteria for

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

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,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. OC-85028-01, Rev. 0

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.

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

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


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.

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

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.

Southern California Edison Company Page 2 - 4

- - - cSan Onofre Nuclear Generating Station Unit 1 - EE ?-1Document No. DC-85028-01, Rev. O

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.


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

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.

_ _ Southern California Edison Company Page 2 - 6 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

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 -San Onofre Nuclear Generating Station Unit 1

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

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

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 -. San Onofre Nuclear Generating Station Unit 1

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

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.


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

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- 2 - 12 - - San Onofre Nuclear Generating Station Unit 1

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

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


0


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


- _ . - 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].

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

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


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.

Southern California Edison Company Page 3 - 4 San Onofre Nuclear Generating Station Unit 1

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

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].

Southern California Edison Company Page 3-5

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

lilillIllIIIIIIIIIIIIIIIIIIIi

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.

Southern California Edison Company Page 3- 6 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

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.


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.


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. DC-85028-01, Rev. 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]


San Onofre Nuclear Generating Station Unit 1

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

HiiItIIIIIIuIIIIIIIIIIIlII

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



- - 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.


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

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

IIIIIIIIIIIIIIIIIIliIIIIII111

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.




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



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



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


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

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].


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].




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


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:


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. DC-85028-01, Rev. 0

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


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.

Southern California Edison Company Pyae 5 - 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



- - - - 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.

*_ Southern California Edison Company Page 5 - 14



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 - 16



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)

*_ Southern California Edison Company Page 5 - 17


- - - 1 Document No. 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.


- - - - - 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.



- - 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.



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

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) (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.


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

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




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


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.

*_ Southern California Edison Company Page 5 - 25 San Onofre Nuclear Generating Station Unit 1

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

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


Y - 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) (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) (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


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



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


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.

*_Southern California Edison Company Page 6 - 3



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)




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

(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:


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

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


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

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].

Southern California Edison Company Page 6- 8 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

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




. 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



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.

_ o Southern California Edison Company Page 7 - 2 San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

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.


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.



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.


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

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.

Southern California Edison Company Page 8 - 4 . -San Onofre Nuclear Generating Station Unit 1


APPENDIX A

Alternate Tornado Resistance Criteria

for Reinforced Masonry Walls

Computech Engineering Services

Report No. R573.01

Dated August, 1985

* _Southern California Edison Company San Onofre Nuclear Generating Station Unit 1 Document No. DC-85028-01, Rev. 0

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tornado resistance design review criteria for

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