NUREG/CR-2650

SAND82-0774

R4

Printed October 1982

Allowable Shipment Frequencies

for the Transport of Toxic Gases

Near Nuclear Power Plants

David E. Bennett, David C. Heath

Prepared by

Sandia National Laboratories

Albuquerque, New Mexico 87185 andrj1ermore, California 94550

for the United States Department f V'ipgy

under Contract DE-AC04-76DPQ080

/( : I j-., :

,,. .... .:,-,~~~~' ,•,••, i, a:.) ,

; '; ':' • = :,: , : =• , . .. •: :• : .,= !t• "A , 1.--:, ' :

•. !:,,.!•,', , .; ;,. .,2.,";;.': :,• .•;: ; d:~i ,• , I I 2'41 

ii I"

'I.' 1'~-

J i

O4'

COMMISSION

h. 4..',

Prpre o

REGULATORY
NOTICE

This report was prepared as an account of work sponsored by an

agency of the United States Government. Neither the United

States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any

legal liability or responsibility for any third party's use, or the

results of such use, of any information, apparatus product or

process disclosed in this report, or represents that its use by such

third party would not infringe privately owned rights.

Available from

GPO Sales Program

Division of Technical Information and Document Control

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555

and

National Technical Information Service

Springfield, Virginia 22161
NOREG/CR-2650

SAND82-0774

R-4

Allowable Shipment Frequencies for the Transport

of Toxic Gases Near Nuclear Power Plants

David E. Bennett

Nuclear Facility Analysis Division 9415

David C. Heath*

Fuel Cycle Risk Analysis Division 9413

Sandia National Laboratories

Albuquerque, NM 87185

Date Published: October 1982

Sandia National Laboratories

Albuquerque, New Mexico 87185

operated by

Sandia Corporation

for the

U. S. Department of Energy

Prepared for

Division of Systems and Reliability Research

Office of Nuclear Regulatory Research

U. S. Nuclear Regulatory Commission

Washington, DC 20555

Under Memorandum of Understanding DOE-40-550-75

NRC FIN No. A1214

*Permanent Address:

School of Operations Research and Industrial Engineering

College of Engineering

Cornell University

Ithaca, NY 14853

i-ii

Abstract

One part of the safety analysis of offsite hazards for a

nuclear power plant is consideration of accidents which could

release toxic gases or vapors and thus jeopardize plant safety

through incapacitation of the control room operators. The purpose

of this work is to provide generic, bounding estimates of the

maximum allowable shipping frequencies for the transport of a

chemical near the plant, such that the regulatory criteria for the

protection of the operators are met. A probabilistic methodology

was developed and then applied to the truck and rail transport of

an example chemical, chlorine. The current regulatory criteria

are discussed in detail. For this study, a maximum allowable

probability of occurrence of operator incapacitation of 10-5 per

year was used in the example calculation for each mode of transport.

Comprehensive tables of conditional probabilities are presented.

Maximum allowable shipping frequencies are then derived. These

frequencies could be used as part of a generic, bounding criterion

for the screening of toxic hazards safety analyses.

Unless a transport survey assures shipping frequencies within

8 km of the plant on the order of or lower than 4/week for rail or

35/week for truck, the control room should be isolatable and the

shipping frequency then determines the degree of isolation needed.

The need for isolation implies the need for toxic chemical detection

at the air intake.

For a self-detection case in which the smell threshold is significantly lower than the incapacitation threshold and the control

room is isolatable, the corresponding shipping frequencies are

11/week for rail or 115/week for truck. Self-contained breathing

equipment is assumed to be used after 5 minutes.

iii-iV

TABLE OF CONTENTS

I n trod u ct ion ........................... .

Background ..................... ......... 1

Study Approach ......... ......... •......... 5

Transportation and Accident Statistics ....................... 8

Atmospheric Modeling ................. . ......... .............. 10

Control Room Ventilation System .............................. 13

Incapacitation Thresholds ...... ............................. 14

Meteorological Conditions . ...... ......... g..... 15

Model Implementation ........... .......... 16

Results ............................. ... . 17

Summary..........,......................................pk..e. 26

References ................................................... 28

V
LIST OF TABLES

Table Page

1. Examples of Weights of Hazardous Chemicals that

Require Consideration in Control Room Evaluations

(for a 50 mg/m 3 Toxic Limit and Stable Meteorological

Conditions) ............................................. 2

2. Probability of Control Room Operator Incapacitation

Given a Toxic Gas Release Along a 16 Kn Route (Rail).... 19

3. Probability of Control Room Operator Incapacitation

Given a Toxic Gas Release Along a 16 Ion Route (Truck)... 20

4. Probability of Control Room Operator Incapacitation

Given a Toxic Gas Release Along a 16 Rn Route.

Maximum of Probability Values for Four Road Directions

(Rail) .................................................. I.1

5. Probability of Control Room Operator Incapacitation

Given a Toxic Gas Release Along a 16 Rn Route.

Maximum of Probability Values for Four Road Directions

(Truck) .................. ................................ 21

6. Probability of Control Room Operator Incapacitation

Given a Toxic Gas Release Along a 16 Mn Route.

Self Detection Case with Two Minute Delay.. .............. 23

7. Probability of Control Room Operator Incapacitation

Given a Toxic Gas Release Along a 16 ift Route.

Maximum of Probability Values for Four Road Directions.

Self Detection Case with Two Minute Delay ............... 24

8. Maximum Allowable Annual Shipping Frequencies for Rail

and Truck Tank Cars of Toxic Gases .......... ........ * 25

vi
Introduction

As part of the safety analysis for a nuclear power plant,

offsite hazards which could threaten the safe operation or safe

shutdown capability of the plant are considered. One of these

hazards arising from the transport of hazardous materials in the

vicinity of the plant is a transportation accident involving toxic

gases (or volatile liquids). The release to the atmosphere of a

significant quantity of a toxic material could endanger the plant

through incapacitation of the control room operators.

The purpose of this report is to estimate, in a generic'manner,

an allowable shipping frequency for transport of a chemical in the

vicinity of the plant such that the regulatory criteria for the

protection of control room operators are met. A probabilistic

methodology was developed and then applied to the truck and rail

transport of an example chemical, chlorine.

Background

Several NRC documents describe the requisite safety analyses

for accidents involving toxic materials. The broadest guidance is

contained in Design Criterion 19 in 10 CFR Part 50, Appendix A,[1 1

which requires that a control room be provided from which the plant

can be operated safely under normal conditions and maintained in a

safe condition under accident conditions.

Regulatory Guide (RG) 1.70,[21 "Standard Format and Content

of Safety Analysis Reports for Nuclear Power. Plants," defines

Design Basis Events (DBE's) as those accidents external to the

nuclear power plant which have a probability of occurrence of 10-7

per year or greater and which "have potential consequences serious

enough to affect the safety of the plant to the extent that Part

100 guidelines could be exceeded." The guide then specifies that

the licensee protect against the effects of these DBE's. Accidents

involving the storage or transportation of toxic gases or volatile

liquids, either on site or off site, would be DBE's and would be

considered in evaluating control room habitability.

RG 1.78,[3] "Assumptions for Evaluating the Habitability of

a Nuclear Power Plant Control Room During a Postulated Hazardous

Chemical Release," provides detailed guidance for the safety analyses

of toxic gas transport hazards. According to RG 1.78, a shipment

frequency criterion may exclude a chemical from further consideration. Shipments are defined to be frequent if the number per year

equals or exceeds 10 for truck traffic, 30 for rail traffic, and

50 for barge traffic. The quantity of the chemical per shipment

is specified for a range of distances from the control room to the

accident and for three different types of control room ventilation

systems. This information is summarized in Table 1. For a given

distance of closest approach along the route and control room

type, only shipments whose size exceeds the values in Table 1

-1-
Table 1.. Examples of Weights of Hazardous Chemicals that Require

Consideration in Control Room Evaluations (for a 50 mg/

m3 Toxic Limit and Stable Meteorological Conditions)

Weight in Metric Tons

Distance from ______

Control Room Type A Type B Type C

(Kilometers) Control Room Control Room Control Room

<0.5 0.05 0.05 0.05

0.5 to 0.8 4.1 1.0 0.05

0.8 to 1.1 16 4.0 0.18

1.1 to 1.6 54 9.1 0.45

1.6 to 3.2 122 24 1.1

3.2 to 4.8 590 127 5.9

4.8 to 6.4 1680 354 15

6.4 to 8.0 4000 635 27

Control room* types:

Type A -

Type B -

Type C -

A tight control room having low leakage construction

features and the capability of detecting at the fresh air

intake those hazardous chemicals stored or transported

near the site. Detection of the chemical and automatic

isolation of the control room are assumed to have occurred.

An air exchange rate of 0.015 per hour is assumed (0.015

of the control room air by volume is replaced with outside

air in one hour). The control volume is defined as the

volume of the entire zone serviced by the control room

ventilation system. The assumption that the air exchange

rate is less than 0.06 per hour requires verification by

field testing.

Same as Type A, but with an air exchange rate of 0.06 per

hour. This value is typical of a control room with normal

leakage construction features. The assumption that the

air exchange rate is less than 0.06 per hour requires

verification by field testing.

A control room that has not been isolated, has no provision

for detecting hazardous chemicals, and has an air exchange

rat~e of 1.2 per hour.

Ref.: Reproduced from Regulatory Guide 1.78, June 1974 [31.

-2-
need be counted. If this count for a chemical exceeds the above

frequency criterion, the licensee must provide protection against

accidents involving this chemical. If the frequency criterion is

not met, then shipment of this chemical need not be considered.

In summary, RG 1.78 specifies size and frequency cutoffs which are

used to eliminate chemicals from further consideration. The licensee

then provides adequate protection only for those chemicals which

exceed both the size and frequency criteria.

RG 1.95,[41 "Protection of Nuclear Power Plant Control Room

Operators Against an Accidental Chlorine Release," provides

specific safety analysis guidance for onsite or offsite releases

of chlorine. Maximum single-container inventory quantities are

specified for various standoff distances for six different types

of control room. The requirements for control room ventilation

system performance, emergency planning, and self contained breathing

equipment are also specified.

Section 2.2.3, "Evaluation of Potential Accidents," of the

Standard Review Plan (SRP),[5] describes the acceptance criteria and

review procedures to be used in reviewing a safety analysis. The

criteria require that "the design basis events include each postulated type of accident for which a realistic estimate of the

probability of occurrence of potential exposures in excess of

the 10 CFR Part 100 guidelines exceeds the NRC staff objective of

approximately 10-7 per year." The estimates are allowed to

be as realistic as is practicable due to the low probability of

occurrence of the events. Further, "a conservative calculation

showing that the probability of occurrence of potential exposures

in excess of the 10 CFR Part 100 guidelines is approximately 10-6

per year is acceptable if, when combined with reasonable qualitative arguments, the realistic probability can be shown to be lower."

Then the criteria stipulate that the effects of the DBE's on the

safety related features of the plant be analyzed and that appropriate mitigation measures be taken. The above quotations are

from the 1975 version of the SRP. The wording in the 1981

version[ 1 31 is somewhat less clear.

Concerning a quantitative measure that an analyst would use to

judge the sufficiency of a safety analysis, Design Criterion 19111

requires a habitable control room, with the unstated implication

that (functioning) operators would be present to take necessary

actions. RG 1.70 states the requirement in terms of DBE's whose

probability of occurrence exceeds 10-7 per year and which could

lead to releases in excess of the 10 CFR Part 100 guidelines. The

SRP states the requirement in terms of probability of occurrence

of potential exposures in excess of 10 CFR Part 100 guidelines.

To meet this latter criterion, it would seem that a necessary

ingredient of the probabilistic analysis would be the (conditional)

probability of exceeding 10 CFR Part 100 radioactive release guide-

-3-
lines given incapacitation of the control room operators and given

the plant in a stable condition. Estimating such a probability

is usually well beyond the scope of a toxic hazards analysis.

RG 1.70 separates the probability of occurrence of the

DBE and the consideration of exceeding 10 CFR Part 100 guidelines,

while the SRP simply uses the probability of occurrence of potential

exposures in excess of 10 CFR Part 100 guidelines. Conceptually

the methods that might be used to implement these criteria are

quite different. Since probabilistic phenomena like meteorology

affect only the probability of exceeding 10 CFR Part 100 guidelines,

given a toxic chemical release (the DBE), and do not affect the

probability of occurrence of the DBE, the results of analyses using

the two different criteria could be significantly different.

With reference to the 10- 7 /year probability, the 1975 version

of the SRP uses the term "realistic estimate" in the statement of

the criterion. RG 1.70, by the use of the phrase "Part 100 guidelines could be exceeded" implies a much more cautious and conservative approach.

RG 1.78 does not explicitly cover a probabilistic methodology

which clearly meets the requirements of RG 1.70 and the SRP.

Rather, a prescriptive method is presented and there is no discussion

of how a safety analysis performed according to RG 1.78 would adequately meet the requirements of RG 1.70 and the SRP.

Prior to July 1981 the question of aggregation of accident

frequencies in determining whether the'probabilistic criteria are

met was not explicitly addressed. The various guides use phrases

like "each postulated type of accident" and "for the type of accident

under consideration." Considering only toxic hazards, several

levels of aggregation might be:

1) Each mode of transport or storage of each chemical, or

2) all modes of transport or storage of each chemical, or

3) all modes of transport or storage of all chemicals.

The choice for level of aggregation will have a significant effect

on meeting the regulatory criteria. NRC has been using the last one,

all modes for all chemicals, in their license reviews.

The 1981 version[ 1 3 ] of the SRP stipulated that the

aggregate risk from all external man-made hazards should also meet

the previously quoted probability criteria. The adequacy of the

safety analysis of the control room ventilation (habitability)

system is then dependent upon the safety analyses of all other

external man-made hazards (explosions, fires, etc.). The design

-4-
requirements for the control room ventilation system for toxic

hazards protection could be more stringent due to unrelated hazards.

The question that prompted this study was to what extent the

shipment frequencies specified in RG 1.78 were overly conservative.

Considerable resources might be spent on extensive safety analyses

for a multitude of toxic gas shipments, rather than in a focused

effort on those chemicals which pose the greatest risk of incapacitating the control room operators. Allocation of resources is an

important consideration for both the licensee and the NRC.

The purpose of this report is to provide realistic, but still

conservative, estimates of allowable shipping frequencies of toxic

gases. The principal concern is truck and rail traffic. Barge

traffic was not explicitly considered, although the methodology

developed would be applicable. The goal is to relate the allowable

shipping frequency for a chemical directly to the regulatory criteria.

These more realistic shipping frequencies could be used as screening

criteria as part of toxic hazards safety analyses. Current NRC

research efforts involving quantitative safety goals and risk allocation may further clarify the application of screening criteria to

such safety analyses.

In the following Study Approach section, a clear and simple

criterion is presented. Then a probabilistic methodology is

developed that includes the effects of meteorology, control room

design and standoff distance. As an example, the method is

applied to the case of chlorine shipments along a straight route.

The question of determining the aggregate risk of operator incapacitation due to "all" toxic materials transportation is addressed

only to the extent of suggesting a method for allocating the risk

among different chemicals and modes of transport.

Study Approach

The simplest criterion for evaluating toxic gas hazards

analyses is a specification of an acceptable probability per year

of operator incapacitation. If the analysis shows a value below

the standard, no further protection measures are needed. If the

value is higher, various protection measures and strategies would

then peed to be implemented so as to reduce the probability to at

least the level of the criterion. The direct use of a probability

of operator incapacitation then separates from any toxic hazards

analysis the consideration of exceeding the 10 CFR Part 100 radioactive release guidelines as specified in RG 1.70 and the SRP.

Such an analysis for exceeding Part 100 guidelines would be quite

extensive and would not materially contribute to protection against

accidental exposures to toxic gases and vapors.

-5--
. .However, some allowance should be made in a toxic hazards

analysis when using a probability of operator incapacitation

derived from a probability of exceeding the Part 100 radioactive

release guidelines. That is, it would be overly conservative to

use a value of one for the probability of exceeding Part 100

guidelines given incapacitation of operators (P 1 0 0 / 0 1 ). Based

on discussions with NRC personnel,[ 1 /] a value of 0.1 will be

used in this study for P1 0 0 / 0 I. If further studies or analyses

suggest a different value, the maximum allowable shipping frequencies developed in this work can be simply scaled.

Following the philosophy of the SRP, a higher probability

could be used for the criterion in a conservative analysis as

compared to a realistic analysis. The use of a factor of 10

difference in the criterion for these two types of analyses would

not seem inappropriate.

The selection of numerical values for the criterion depends

on the range of accidents to be included. That is, should the

criterion cover transportation and storage of a single chemical

or all chemicals? Since the transportation and accident data

are not available at this time to definitely support aggregate

risk estimates, a criterion for a single chemical will be used

for this study. As the following methodology and example calculation would be judged conservative, as compared to a realistic

or best estimate calculation, a value of 10-5 per year will be

used in the example calculation for an acceptable probability of

control room operator incapacitation, based on a value of 10-6 per

year for the maximum allowed probability of exceeding Part 100

guidelines. Since the maximum allowable shipping frequencies are

directly proportional to this probability, the results can easily

be scaled should a different value for the acceptable incapacitation

probability be desired.

A very simple method was used to decompose the overall probability of operator incapacitation (01) into several constituent

parts, one of which is the shipment frequency FS. For the transport

of a single chemical near the plant, the overall probability POI

can be written as:

-POI = FS x PA x PR x PI

where

POI = Probability of operator incapacitation

FS = Frequency of shipments (shipments/year)

PA = Probability that a given shipment will

yield an accident over a specified

stretch of road (accidents/shipment)

-6-
PR = Probability that a large release will

occur from a given accident (release/ accident)

P, = Probability that operators will be incapacitated given that a large release

occurs along a specified stretch of

road (Poi/release).

The probability POI actually represents the expected number of

instances of operator incapacitation in a year. Since the expected

number of instances is small, it is essentially the same as the

probability of an instance. For this study, we restricted the

range of the accidents to those which produced a large puff releases; i.e., a sudden, massive release of the entire contents of

a tank car. This assumption avoids the complexities of a distribution of release quantities and durations and the dependency of

the incapacitation estimate on this distribution.

A simple transportation route geometry was selected. A

straight route was assumed to have an offset distance or distance

of closest approach D. RG 1.78 requires that accidents which

could occur within five miles of the plant be considered in the

Road Direction

D-D Plant

safety analysis. For accidents beyond this distance, a very

restricted range of meteorological conditions would be necessary

for incapacitation to occur (very stable atmospheric conditions,

constant wind direction for the duration of the accident, exact

wind direction from accident to the plant, etc.). Therefore, the

length of the route was taken to be 16 km (twice the five mile

radius).

-7-
Assuming a constant accident frequency, PA can be written as

PA = PAK(accidents/km) x L(km exposed/shipment)

The overall equation becomes:

POI = Fs(shipments/year) x

PAK(accidents/km) x

L(km exposed/shipment) x

PR(large release/accident) x

PI(OI/large release)

The last term is actually the probability of 01 given a large

release anywhere along the 16 km route.

Transportation and Accident Statistics

Transportation data and accident data that are sufficient to

perform risk analyses are generally not available for a wide variety

of toxic chemicals. Even for a chemical which has been studied

extensively, like chlorine, only summary production and transport

data are available. Local data which could be used to support

site specific analyses are gathered at relatively high cost and

may not predict future trends in shipping rates.

In terms of the previous probability equation, P0 1 can be

calculated given FS, or vice versa. Since one cannot a priori

develop a "generic" shipping rate for an individual route, the

maximum acceptable value for P0 I will be used to estimate the maximum allowable shipping frequency. If the analysis is sufficiently

conservative, this frequency is site independent and hence can be

used as a generic screening criteria. That is, if a local transport survey showed a higher shipping frequency, a site specific

analysis should be performed to assess the level of protection

needed.

Several studies [8,14,15,161 have considered tank car accidents,

their expected frequency of occurrence, and their severity. Overall

accident rates for truck and rail tank cars were compiled as part

of a detailed study[ 1 4 ] of accident dynamics:

-8-
Accident Rate

(per tank car-km)

Truck 1.6 x 10-6

Rail 1.0 x 10-6

These numbers are comparable to those quoted in NUREG-0170,[6]

which studied the shipment of radioactive materials in urban environs. In NUREG-0170, the quoted truck rate was slightly lower:

1 x 10-6 per car-km.

Several studies of dynamic accident analyses for tank cars

have included the full range of potential failure mechanisms:

fire, crush, impact and puncture.J 1 4 ,

1 5] The results are summarized

in terms of general accident categories: minor, moderate, severe,

extra severe and extreme. Since this study and the example calculation for chlorine use only a two box model for characterizing potential releases (no release and a large release), the risk from small

releases must be lumped into the probability of the large release.

This resulting probability will be somewhat larger than a realistic

estimate of just a massive release. The probabilities for a severe

or worse accident were estimated by Sandia to be:[141

Accident Rate

(per tank car-km)

Truck 8 x 10-9

Rail 9 x 10-8

These values would be about a factor of 4 to 6 higher for moderate

or worse accidents.

Simmons, Erdmann and Naft studied the risk of catastrophic

spills of toxic chemicals, more specifically chlorine.[ 8 ] Their

rail accident data leads to a probability for a large release of

5 x 1 0 -8 per tank car-km, based on data for all hazardous cargo and

assuming an average shipment distance of 450 km.[16] For a projected 55,000 shipments per year,[ 1 6] this accident probability

corresponds to slightly more than one large release per year. In

comparison, the rate from the Battelle report is about the same,

while the Sandia accident rate leads to just over two per year.

The authors[ 8 ] point out that the historical data for chlorine

suggests a large release rate about 10 times lower (0.1 releases

per year versus about 1 per year). The Battelle report [161 also

discusses this historical discrepancy.

For use in the example calculation, the accident rate for

truck transport from the Sandia study will be used. For rail transport, the slightly lower accident rate from the Simmons, Erdman and

-9-
Naft, and Battelle studies will be used, as the historical data on

chlorine would tend to support a lower value. The values for PR,

the probability of a large release, given an accident, are:

Truck .005

Rail .05

indicating that severe accidents for trains are an order of magnitude more frequent than for trucks. This is supported in a general

sense by rail accident data; for instance, that over 80% of all

train accidents involve derailments.[15]

One heuristic way of checking the estimate of the probability

of a large release is to consider the total quantity of hazardous

materials (HM) shipments per year. The National Transportation

Safety Board estimates about 218 billion ton-miles of HM/year.[ 7 1

Using about 50 tons per shipment yields an annual shipping distance

of seven billion km/year. Using an estimate of about 100 major

accidents per year which involve large releases (based on one

author's rough but conservative recollection of current events)

yields an annual probability of a large release of 1.4 x 10-8

large releases/km, which is comparable to the rates suggested

earlier from other sources.

Atmospheric Modeling

For this work, a relatively detailed analysis was made of the

probability of operator incapacitation given a large release on

the 16 km route. The location of the accident along the route was

assumed to be uniformly distributed; that is, no preferential

accident sites were assumed.

A Gaussian puff was used to describe the atmospheric transpqrt

of the toxic gas after release from the tran?9rt container. The

initial size of the release is characterizedL=* by ao:

1 1/2 Ml1/3

aO (meters) = 2M3

where M is the mass released and p is the gas density.

For tank cars of pressurized liquid which flash to vapor upon

rupture of the tank, the mass released is proportional to the

flashing fraction. Theremainder, which did not flash to vapor,

is a supercooled liquid and will boil off over some period of

time. For chlorine, the flashing fraction ranges from about 17% at

20 0 C (70 0 F) to about 35% at 70 0 C (160 0 F). These fractions are

-10-
based on the adiabatic decompression of the pressurized liquid. 1 81

Further liquid will flash to vapor as the spilled liquid contacts

the terrain surrounding the accident site; this contribution to the

initial puff is highly dependent on the accident scenario. The

boiloff will form a plume, which follows the initial puff. For

this study, it is assumed that the entire inventory of the tank

car is contained in the initial puff and that there is no plume.

This conservative assumption will maximize the peak concentration

seen in the control room. For truck and rail tank cars of chlorine,

the values for co are 9.25 m and 15 m, corresponding to 20 and 90

tons/tank car, respectively.

The formulation for a neutrally bouyant Gaussian puff is

given in terms of a unit concentration (C = 1 corresponds to a

100% concentration):

ex{-1 ,(X - Ut)2 + y2 Z2__-

C = o exp -.. +

2 02 +0C2 02

where:

a2-1/2 02 -1

X2 1 +.

The distances X, Y, Z are measured from the release point. The

time t is measured from the start of the release and U is the wind

speed in kn/s.[ 31 The wiOd direction is assumed constant during

and after an accident and in the X direction.

The dispersion parameters a, and a3 are defined by[81

al = Cl(Ut)

P3

a3 = C3 (Ut)

The parameters C1 , C3 , 01, and 03 for the three stablility categories are summarized below:[81

-11-
Dispersion Parameters

Cl

Unstable

Neutral

Stable

0.27

0.13

0.078

0.91

0.91

0.91

0.11

0.11

0.1]

1.0

0.80

0.72

The geometry of the route and plant locations, accident

site, and wind direction is shown below:

ROAD

DIRECTION

PLANT ORIGIN OF L

-L

ITE ACCIDENT SI

The along-wind distance X and the cross wind distance Y can be

expressed in terms of the distance along the route L, the offset

distance D and the angle between the road and wind direction:

X = -L cos e + D sin 9

Y = D cos e + L sin O

-12-
For this study, six offset distances D (distance of closest approach)

were considered: 500, 750, 1000, 1500, 2000, and 3000 m. The specification of wind speed and direction, road direction, stability class,

offset distance, and accident location is sufficient to calculate

the concentration profile at the plant site as a function of time.

Control Room Ventilation System

The control room ventilation system draws in contaminated air,

which leads to the exposure of the operators. The concentration

inside the control room, CI, can be expressed by means of a differential equation involving the Qutside concentration Co and

the ventilation system air exchange rate R:19]

dC1

- = R(Co - CI)

dt

where R is in units of control room volumes/time unit.

As described in the notes in Table 1, there are different

types of control room ventilation systems. For an unisolated

control room, no provision is made for detection of toxic chemicals

in the intake and thus a constant air exchange rate is maintained

throughout an accident sequence. For an isolatable control room,

the outside air intake is closed upon detection of a toxic chemical

in the intake and remains-closed as the cloud passes the plant.

The intake reopens when the outside concentration is reduced to a

negligible level.

To perform the calculation, the times of arrival and departure

of the outside cloud are needed:

Time Event

T1 Outside concentration reaches a threshold

level (0.1 ppm)

T2 Outside concentration reaches the detector

level (1.0 ppm)

T3 Outside concentration falls below the

detector level

T4 Outside concentration falls below the

threshold level

-13-
A simple function for the air exchange rate was chosen:

Time Air Exchange Rate

t < T2 R = R1 open rate

T2 i t < T3 R = R2 isolated rate

t > T3 + A R = R3 exhaust rate

The open rate is typically one volume per hour. The closing and

opening of the intake were modeled as a ramp of one second duration.

A delay A of 30 seconds was assumed for opening of the system to an

exhaust rate, which could be larger than the normal rate. Five

cases were considered in this study to cover the range of control

room ventilation system designs:

Case R1 R2 R3

i1 . 1. I.

2. 1. .06 1.

3. 1. .06 2.

4. 1. .015 1.

5. 1. .015 2.

The increased exhaust rate. does not affect the peak concentration

in the control room, but reduces the total dose to which the

operator is exposed.

Incapacitation Thresholds

While a multitude of toxic chemicals are shipped in bulk

by truck and train, a few, like chlorine and ammonia, stand out

as suspected dominant contributors to the overall risk. Note that

local transport and chemical manufacturing activities could result

in other chemicals being the principal hazards at a particular site.

Since chlorine has a much lower incapacitation level (10 ppm) than ammoni~lf5 ppm), it was chosen as the "example" chemical for this study.n Thus P, (OI/large release), mentioned earlier, is the

probability of the concentration in the control room equaling or

exceeding 10 ppm.

The physiological and toxicological effects[1 0] of chlorine

are concentration dependent. That is, incapacitation is assumed

to have occurred when the exposure concentration reaches the specified level, independent of the dose or integrated exposure. Ammonia

and many other chemicals fall into this concentration dependent

-14-
class of effects. The other broad class of toxicological effects

is dose dependency. Carbon monoxide, vinyl chloride, nitrogen

dioxide and acetophenone are gases with dose-dependent incapacitation

effects. In this study, the data needed for the probability of

exceeding a dose threshold were also collected. A dose of 105

ppm-seconds was chosen, as it is somewhat conservative. A few

chemicals have lower dose thresholds for immediate incapacitation,

but most have higher thresholds (_106 ppm-sec).

Meteorological Conditions

Since the shipment frequency estimates calculated in this

study are to be used to screen safety analyses for adequacy and to

determine whether further analysis is required, a conservative set

of meteorological conditions were assumed.

The meteorological data for the site are given in terms of the

probabilities of wind direction, wind speed and stability class.

The wind roses for all U. S. reactor sites were examined and the

one with largest peak for a single direction was used:[II]

Direction Probability

Toward N .048

NNE

NE

ENE

E

ESE

SE

SSE

.046

.043

.038

.070

.160

.265

.052

Direction

S

SSW

SW

WSW

W

WNW

NW

NNW

Probability

.013

.006

.009

.013

.035

.092

.055

.055

This rose also has the feature that about 72%

wind blows into the east half plane.

of the time the

The combined probabilities for wind speed and atmospheric

stability class were obtained from several such distributions in

WASH-1400.[ 1 2] Some sites had a high probability of neutral and

stable conditions and others had a predominance of low wind speeds.

Since no one site had both features, a composite site with a

predominance of both neutral and stable atmospheric conditions

and low wind speeds was constructed:

-15-
Probability

Wind Speed (m/s)

1 Stability Class

Range Value Used Unstable Neutral Stable Total

0-1 0.5 .0051 .1231 .3594 .4876

1-2 1.5 .0072 .0775 .1481 .2328

2-3 2.5 .0046 .0341 .0582 .0969

3-4 3.5 .0045 .0260 .0485 .0790

4-5 4.5 .0026 .0119 .0202 .0347

5-6 5.5 .0024 .0106 .0133 .0263

6-7 6.5 .0009 .0055 .0046 .0110

>7 8.0 .0014 .0173 .0130 .0317

Total .0287 .3060 .6653 1.000

Model Implementation

The methodology and data needed to calculate PI and hence FS

have been described above. A computer program was written to

perform the calculations and prepare concentration and dose

histograms. From these histograms, values for P, were obtained.

In the following tables, both the probability that the peak inside

concentration equals or exceeds 10 ppm and the probability that

the exposure dose equals or exceeds 105 ppm-seconds are presented.

The one remaining factor in the analysis is the direction

of the road with respect to the assumed wind rose. Several

trial computations were made for 16 possible road directions,

equally spaced. For a given road direction, the plant lies to

the right of the road (refer to previous figure showing wind-road

geometry). In general ENE or NNW gave the highest probabilities

and SSE the lowest, for the assumed wind rose. For the final

calculations four representative road directions were used: ENE,

ESE, SSE, and NNW.

In the methodology described above, specific properties of

the example chemical (in our case, chlorine) are needed in only

two places. First, the shipment size and the ambient density of

the initial gas cloud fix the variable ao, the initial size of

the puff. Second, the incapacitating exposure concentration for

chlorine is used to determine whether incapacitation occurred for

each individual case or combination of conditions. The transport

of the gas cloud through the atmosphere (Gaussian puff) and through

-16-
the ventilation system treats the toxic material as a neutrally

bouyant ideal gas, which is independent of specific physical or

chemical properties.

Note that refinements in atmospheric transport modeling like

negative or positive cloud bouyancy, or site specific terrain

features like wooded areas were not included in this analysis

methodology. Inclusion of these latter phenomena is unlikely to

significantly affect the results.

The assumption of constant wind direction allows the differential equations to be solved using a simple integrating routine. A

far more complex finite element formulation for the mass and momentum distributions and a finite difference solution technique would

be required if varying wind directions were included.

The air intake (or intakes) for the ventilation system are

modeled as a single point receptor, as this is the minimum requirement for any plant. Some plants have two widely separated,

independent inlets, with uncontaminated air (hopefully) being

generally available at one of them. Since the purpose of this

work is to develop generic or site independent allowable shipping

frequencies, dual inlet systems were not considered. If they were,

an additional modeling complexity would be introduced that would

not materially enhance the applicability of the results. It should

be pointed out that larger accident-plant distances, less stable

atmospheric conditions, and to a lesser extent slow wind speeds

all contribute to lateral dispersion of the cloud. Hence many of

the individual cases (combinations of conditions) might still lead

to incapacitation for a dual inlet system. While the specific

calculations for dual inlet systems were not performed, it would

probably require a considerable separation (more than a few hundred

meters)-to significantly reduce the probability of operator

incapacitation.

An associated issue is the rescue of the plant operators by

other onsite personnel or by the operators from the second unit

of a two unit site. Due to the large cloud size (at the plant)

and the relatively low concentration needed for incapacitation,

personnel not in an isolated enclosure would have a very high

probability of incapacitation (-4) and thus not be available

for rescue or emergency work. Again, since the purpose of this

work is to provide generic and conservative shipping frequencies,

there does not appear to b6 a defensible generic method for allowing credit for emergency response.

Results

The results for rail tank cars are presented in Table 2 and

for truck tank cars in Table 3. The values for P, are shown for

the two incapacitation means, six offset distances, four road

directions, five control room types, and three exposure durations.

-17-
*The variation in road direction leads to a change by a factor

of two to (at most) four in-the probability values. The wide range

of probabilities in the assumed wind rose does not lead to a strong

dependence on road direction because of the large distances at

which the plant is vulnerable and the cross wind diffusion of the

cloud. Since the goal of this study is to provide generic shipping

frequencies which are independent of off-site features like road

direction, the appropriate probability is the maximum of the values

for the four road directions. *These reduced sets of probabilities

are presented in Table 4 for rail shipments and Table 5 for truck

shipments.

Increasing the offset distance of the plant from the road

does not greatly reduce the pr~obability. This arises because, for

the combinations of wind speed, stability class and accident location

along the route which produced concentrations above 10 ppm, the

level was significantly above the 10 ppm threshold.

Reducing the duration of the exposure significantly reduces

the probability of incapacitation. This is seen by comparing the

"2-MIN," "5-MIN," and "MAX" columns in the various tables. Cessation

of the exposure would require the use of self contained breathing

equipment with sufficient capacity for several hours of use.

Another interesting result concerns the distance (from the

accident site to the plant) beyond which no combination of wind

direction, wind speed or stability class produced incapacitating

levels in the control room. These distances are listed in Tables

4 and 5. Remember that the road considered extends in each direction only 8 km. The isolation of the control room and limiting

the exposure by the use of breathing equipment can significantly

reduce this maximum "distance of concern." For a given control

room type and exposure duration, increased standoff distance, in

many cases, has little effect. From a generic, site independent

point of view, there is not a reasonable standoff distance criterion

such that operator incapacitation is precluded;*that is, P, is

identically zero.

The above calculations are based on the use of an outside

detector and automatic isolation of the control room upon reaching

the set point of the detector (1 ppm). Another scenario for

operator protection involves detection by personnel and a delay

in isolating the control room. Detection (by smell) could occur

either by the control room operators or by other plant personnel.

Since outside personnel would detect the presence of the chemical

considerably before those inside, detection is assumed to occur

when the outside concentration reaches 2 ppm. A two minute

delay is then assumed before control room isolation occurs; this

represents the time needed for assessment and communication.

An additional five minute delay is assumed for the time required

for the control room operators to begin using self contained

breathing equipment. The probabilities of operator incapacitation

-18-
TABLE 2

RAIL

SIGMAO - 15.00

STANDOFF

MODE DISTANCE

PROBABILITY OF CONTROL ROO OPERATOR INCAPACITATION GIVEN A TOXIC GAS RELEASE ALONG A 16 KM ROUTE.

VENTILATION SYSTEM RATES/HOUR -- (ROVIROV2,ROV3]

[1.00,1.000,1.00] -1.00,0.060,1.001 11.00,0.060,2.00] [1.0010.015,1.00] 11.00O0.015,2.00)

ROAD

DIRECTION

EXPOSURE DURATION FOR DETERMINING INCAPACITATION

2-MIN 5-MIN MAX 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX

ICONC 500. ENE

ESE

SSE

NNW

750. ENE

ESE

SSE

NNW

1000. ENE

ESE

SSE

NNW

1500. ENE

ESE

SSE

NNW

2000. ENE

ESE

SSE

NNW

3000. ENE

ESE

SSE

NNW

DOSE 500. ENE

-ESE

SSE

NNW

750. ENE

ESE

SSE

NNW

1000. ENE

ESE

SSE

NNW

1500. ENE

ESE

SSE

NNW

2000. ENE

ESE

SSE

NNW

3U00. ENE

ESE

SSE

NNW

.009 .016 .025

.012 .029 .068

.005 ,V11 .025

.014 .030 055

.008 .017 .026

.008 .025 .060

,004 .010 .022

,011 .029 056

.007 .017 .028

.006 .020 .057

.003 .009 .021

.009 .026 .057

.006 .016 .031

.003 .014 051

.002 .007 .019

.006 .021 .058

.005 .014 .033

.002 .010 .043

.002 .006 .018

.004 .017 .055

.003 .011 *035

.001 .006 .030

.001 .004 .016

,002 .011 .047

,000 .004 ,020

.000 .002 .053

.000 .001 .020

.000 .004 .045

.000 .002 .022

.000 .001 .048

.000 .001 .018

.000 .002 .046

.000 .001 .023

.000 .000 .045

.000 .000 .017

.000 .001 .046

.000 .000 .025

.000 .000 .038

.000 .000 .015

.000 .000 .046

.000 .000 .026

.000 .000 .032

.000 .000 ,014

.000 .000 .042

.000 .000 .028

.000 .000 .023

.000 .000 .012

.000 .000 .037

,003 .007 .012

.002 .006 *024

,001 .003 .009

.004 .010 .023

,003 .006 .012

.001 .004 .022

.001 .003 .009

.002 .007 .023

.002 .006 .013

.000 .003 .020

.001 .002 .008

.001 .005 .022

.001 .003 .013

.000 .001 *014

.000 .001 .006

,000 .002 .019

.000 .002 .012

.000 .000 .011

.000 .001 .006

.000 .001 .017

.000 .000 .011

.000 .000 .007

.000 .000 .004

.000 .000 .012

.000 .000 .008

.000 .000 .014

.000 .000 .005

.000 o000 .015

.000 .000 .008

.000 .000 o012

.000 .000 .005

.000 .000 .014

,000 .000 .007

.000 .000 o008

.000 .000 .004

.000 .000 .011

,000 .000 .007

.000 .000 .007

.000 .000 .003

.000 .000 .010

.000 .000 .006

.000 .000 .004

.000 .000 .002

.000 .000 .007

.000 .000 .005

.000 .000 .002

.000 .000 .002

.000 .000 .005

.003 .007 .012

.002 o006 .024

.001 .003 .009

.004 .010 .023

.003 .006 .012

.001 .004 .022

.001 .003 .009

.002 .007 .023

.002 .006 013

.000 .003 .020

.001 .002 .008

.001 .005 .022

.001 .003 .013

.000 .001 .014

.000 .001 .006

.000 .002 .019

.000 .002 .012

.000 .000 .011

.000 .001 .006

.000 .001 .017

.000 .000 .011

.000 .000 .007

.000 .000 .004

.000 .000 .012

.000 .000 .006

.000 .000 .009

.000 .000 .004

.000 .000 .010

.000 ,000 .006

.000 .000 .006

.000 .000 .003

.000 .000 .009

.000 .000 .006

.000 .000 .005

.000 .000. .003

.000 .000 .008

.000 .000 .005

.000 .000 .003

.000 .000 .002

.000 .000 .006

.000 .000 .004

.000 .000 .001

.000 .000 .001

.000 .000 .003

.000 .000 .003

.000 .000 .000

.000 .000 .001

.000 .000 .002

.001 .004 .006

.000 .002 .008

.000 .001 .003

.001 .004 .010

.001 .002 .006

.000 .001 .006

.000 .001 .003

.000 .002 .009

.000 6001 .005

.000 .000 .004

.000 .000 .002

.000 .001 .007

.000 .000 .005

.000 .000 .003

.000 .000 .002

.000 .000 .005

.000 .000 .003

.000 .000 .001

.000 .000 .001

.000 .000 .003

.000 .000 .002

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .003

.000 .000 .003

.000 .000 .001

.000 .000 .004

.000 .000 .003

.000 .000 .002

.000 .000 .001

.000 .000 .003

.000 .000 .002

.000 .000 .001

.000 .000 .001

.000 .000 .002

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .000

.000 .000 .000

*.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.001 .004 .006

.000 .002 .008

.000 .001 .003

.001 .004 .010

.001 .002 .006

.000 .001 .006

.000 .001 .003

.000 .002 .009

.000 .001 .005

.000 .000 .004

.000 .000 .002

.000 .001 .007

.000 .000 .005

.000 .000 '.003

.000 .000 .002

.000 .000 .005

.000 .000 .003

.000 .000 .001

.000 .000 .001

.000 .000 .003

.000 .000 .002

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .002

.000 .000 .001

.000 .000 .001

.000 .000 .002

,000 .000 .002

.000 .000 .001

.000 .000 .001

.000 .000 .001

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000
TABLE 3

TRUCK

SIGMA0 = 9.25

STANDOFF

MODE DISTANCE

PROBABILITY OF CONTROL ROOM OPERATOR INCAPACITATION GIVEN A TOXIC GAS RELEASE ALONG A 16 KM ROUTE.

VENTILATION SYSTEM RATES/HOUR -- (ROVI,ROV2,ROV3]

[1.00,1.000,1.001 [1.00,0.060,1.00] 11.00,0.060,2.001 [1.00,0.01501.001 [1.00,0.015,2.00J

ROAD

DIRECTION

EXPOSURE DURATION FOR DETERMINING INCAPACITATION

2-NIN S-NIN MAX 2-MIN 5-NIN MAX 2-NIN 5-MIN MAX 2-NIN 5-MIN MAX 2-MIN 5-NIN MAX ----------------------------------------------------------------------------------------------------------------------------------

CONC 500. ENE

ESE

SSE

NNW

750. ENE

ESE

SSE

NNW

1000. ENE

ESE

SSE

NNW

1500. ENE

ESE

SSE

NNW

2000. ENE

ESE

SSE

NNW

3000. ENE

ESE

SSE

NNW

I

.007

.007

.003

.010

.006

.005

.002

.007

.005

.003

.002

.005

.003

.001

.001

.003

.002

.000

.001

.001

.001

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.012 .017

.018 .040

.007 .015

.021 .037

.012 .019

.014 .041

.006 .015

.018 .040

.012 .021

.010 .038

.005 .015

.015 .040

.010 .021

.006 .029

.004 .012

.011 .036

.007 .023

.003 .026

.003 .011

.007 .035

.004 .022

.001 .017

.001 0010

.003 .028

.001 .013

.000 .028

.000 .010

.001 .027

.000 .015

.000 .029

.000 .011

.000 .029

.000 .015

.000 .024

.000 .009

.000 .027

.000 .015

.000 .018

.000 .008

.000 .023

.000 .015

.000 .015

.000 .007

.000 .022

.000 .014

.000 .009

.000 .006

.000 .016

.001 .004 .006

.000 .002 .008

.000 .002 .003

.001 .004 .010

.001 .003 .006

.000 .001 .006

.000 .001 .003

.000 .002 .008

.000 .001 .005

.000 .000 .004

.000 .000 .002

.000 .001 .006

.000 .000 .004

.000 .000 .002

.000 .000 .002

.000 .000 .005

.000 .000 .003

.000 .000 .001

.000 .000 .001

.000 .000 .002

.000 .000 .002

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .003

.000 .000 .003

.000 .000 .001

.000 .000 .004

.000 .000 .003

.000 .000 .001

.000 .000 .001

.000 .000 .003

.000 .000 .002

.000 .000 .001

.000 .000 .001

.000 .000 .002

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000. .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.001 .004 .006

.000 .002 .008

.000 .001 .003

.001 .004 .010

.001 .003 .006

.000 .001 .006

.000 .001 .003

.000 .002 .008

.000 .001 .005

.000 .000 .004

.000 .000 .002

.000 .001 .006

.000 .000 .004

.000 .000 .002

.000 .000 .002

.000 .000 .005

.000 .000 .003

.000 .000 .001

.000 .000 .001

.000 .000 .002

.000 .000 .002

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .002

.000 .000 .001

.000 .000 .001

.000 .000 .002

.000 .000 .002

.000 .000 .001

.000 .000 .001

.000 .000 .001

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .002 .002

.000 .000 .002

.000 .000 .001

.000 .001 .003

.000 .001 .002

.000 .000 .001

.000 .000 .001

.000 .000 .002

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 O00 .000

.000 .000 .000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.001

.000

.000

.001

.001

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.U00

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.002

.002

.001

.003

.002

.001

.001

.002

.001

.000

.000

.001

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.000

.0OU

.000

DOSE 500. ENE

ESE

SSE

NNW

750. ENE

ESE

SSE

NNW

1000. ENE

ESE

SSE

NNW

1500. ENE

ESE

SSE

NNW

2000. ENE

ESE

SSE

NNW

3000. ENE

ESE

SSE

NNW
RAT

SIG

MOD

CON

MAX

FOR

DoS

MAX

FOR

TABLE 4 PROBABILITY OF CONTROL ROOM OPERATOR INCAPACITATION GIVEN A TOXIC GAS RELEASE ALONG A 16 EM ROUTE.

MAXIMUM OF PROBABILITY VALUES FOR FOUR ROAD DIRECTIONS.

ALSO MAXIMUM ACCIDENT-PLANT DISTANCES(EM).

IL VENTILATION SYSTEM RATES/HOUR -- IROVIROV2,ROV3)

;MAO - 15.00 (1.00,1.000,1.00] [1.00,0.*060.1.00 11.00,0.060,2.00] 11.00,0.015,1.00| [1.00,0.015,2.001

STANDOFF EXPOSURE DURATION FOR DETERMINING INCAPACITATION

DE DISTANCE 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX 2-MIN $-MIN MAX

IC 500. .014 .030 .068 .004 .010 .024 .004. .010 .024 .001 .004 .010 .001 .004 .010

750. .011 .029 .060 .003 .007 .023 .003 .007 .023 .001 .002 .009 .001 .002 .009

1000. .009 .026 .057 .002 .006 .022 .002 .006 .022 .000 .001 .007 .000 .001 .007

1500. .006 .021 .058 .001 .003 .019 .001 .003 .019 .000 .000 .005 .000 .000 .005

2000. .005 .017 .055 .000 .002 .017 .000 ,002 .017 .000 .000 .003 .000 .000 .003

3000. .003 .011 .047 .000 .000 .012 .000 .000 .012 .000 .000 .002 .000 .000 .002

INUM DISTANCE(MM) 7.5 8.5 8.5 2.3 3.3 8.2 2.3 3.3 8.2 1.2 1.8 4.0 1.2 1.8 4.0

INCAPACITATION

E 500. .000 .004 .053 .000 .000 .015 .000 .000 .010 .000 .000 .004 .000 .000 .002

750. .000 .002 .048 .000 .000 .014 .000 .000 .009 .000 .000 .003 .000 .000 .002

1000. .000 .001 .046 .000 .000 .011 .000 .000 .008 .000 .000 .002 .000 .000 .001

1500. .000 .000 .046 .000 .000 .010 .000 .000 .006 .000 .000 .001 .000 .000 .000

2000. .000 .000 .042 .000 .000 .007 .000 .000 .004 .000 .000 .000 .000 .000 .000

3000. .OOu .000 .037 .000 .000 .005 .000 .000 .003 .000 .000 .000 .000 .000 .000

IMUM DISTANCE(KM) 0.5 1.6 8.5 6.3 - - 4.3 - - 2.2 - - 1.5

I INCAPACITATION

TRU

SIG

MOD

CON

MAX

FOR

DOS

MAX

FOR

TABLE 5 PROBABILITY OF CONTROL ROOM OPERATOR INCAPACITATION GIVEN A TOXIC GAS RELEASE ALONG A 16 KM ROUTE.

MAXIMUM OF PROBABILITY VALUES FOR FOUR ROAD DIRECTIONS.

ALSO MAXIMUM ACCIDENT-PLANT DISTANCES(KM).

------ ----------------------------------------------------------------------------------------------------

ICE VENTILATION SYSTEM RATES/HOUR -- IROVIROV2,ROV3]

MAO - 9.25 11.00,1.000,1.00] 11.00,0.060.itn0] 11.00,0.060,2.001 [1.0000.015,1.00] 11.00,0.015,2.001

------ ------------------------------ ------------------------------------------------------------------

STANDOFF EXPOSURE DURATION FOR DETERMINING INCAPACITATION

E DISTANCE 2-MIN 5-NIN MAX 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX

------------------------------------------------------------------------------------------------------------

C 500. .010 .021 .040 .001 .004 .010 .001 .004 .010 .000 .002 .003 .000 .001 .003

750. .007 .018 .041 .001 .003 .008 .001 .003 .008 .000 .001 .002 .000 .001 .002

1000. .005 .015 .040 .000 .001 .006 .000 .001 .006 .000 .000 .001 .000 .000 .001

1500. .003 .011 .036 .000 .000 .005 .000 .000 .005 .000 .000 .uuO .000 .000 .000

2000. .002 .007 .035 .000 .000 .003 .000 .000 .003 .000 .000 .000 .000 .000 .000

3000. .001 .004 .028 .000 .000 .002 .000 .000 .002 .000 .000 .000 .000 .000 .000

IMUM DISTANCE(EM) 4.3 6.3 8.5 1.3 1.9 3.9 1.3 1.9 3.9 0.5 0.8 1.6 0.5 0.8 1.6

INCAPACITATION

E 500. .000 .001 .028 .000 .000 .004 .000 .000 .002 .000 .000 .001 .000 .000 .000

750. .000 .000 .029 .000 .000 .003 .000 .000 .002 .000 .000 .000 .000 .000 .000

1000. .000 .000 .027 .000 .000 .002 .000 .000 .001 .000 .000 .000 .000 .000 .000

1500. .000 .000 .023 .000 .000 .001 .000 .000 .000 .000 .000 .000 .000 .000 .000

2000. .000 .000 .022 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000

3000. .000 .000 .016 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .OUO .000

IMUM DISTANCEEM) - 0.8 8.5 - - 2.2 - - 1.5 - - 0.8 - - 0.5

INCAPACITATION
for this scenario for a ventilation system with normal isolation

(infiltration rate of 0.06 volumes/hour) are listed in Table 6

in the columns labeled "5-MIN" * These probabilities are higher

than the corresponding values in the previous tables. Table 7

lists the maximum probability values independent of road direction

and the maximum distances for incapacitating accidents.

A comment should be made about values in the probability

tables reported as zero. No distinction is made between a value

smaller than 0.0005 (which rounds to zero) and a value which

is identically zero. The relative error in P, increases as P1

decreases, due to the small number of cases which lead to incapacitation. The probabilities reported are believed to be accurate

to within a few~ digjits in the last place, due to computational

accuracies.

The maximum probability values from Tables 4, 5 and 7 were

used to estimate the maximum allowable shipping frequencies for

truck and rail transport. In Table 8, the frequencies are given

for the five control room types and for two exposure durations

(five minutes and maximum). For each combination, the range of

values reflects the dependence on standoff distance. These maximum

allowable shipping frequencies are based on a criterion of 10-5

per. year as the maximum acceptable probability of operator incapacitat ion.

The principal result is that the frequencies are lower for

rail than truck, contrary to RG 1.78. This follows directly from

the accident frequency and severity data, which indicates that the

probability of a large release is larger for rail than truck.

A second result is that for unisolated control rooms, the

allowable shipping frequency would appear to be below the licensee's

ability to assuredly exclude the chemical on the basis of his

traffic survey (e.g., about 4 per week for rail). To do so the

survey would have to extend out to 8 km for both rail and truck

transport.

A critical assumption in using these transport frequencies

for plants with isolated control rooms is that there. is a detector

for the chemical under consideration. But what was the reason for

analyzing an isolatable control room prior to showing the need for

isolation? It would seem that unless the licensee's survey shows

assuredly a frequency below that adequatfe for an unisolated control

room, then detection is required and the traffic frequency sets

the degree of isolation needed. This type of a protection strategy

is markedly different from that in RG 1.78.

-22-
TABLE 6 PROBABILITY OF CONTROL ROOM OPERATOR INCAPACITATION GIVEN A

TOXIC GAS RELEASE ALONG A 16 KM ROUTE.

SELF DETECTION CASE WITH TWO MINUTE DELAY. -----------------------------------------------------------------------------

TRUCK

SIGMAO - 9.25

RAIL

SIGMAO - 15.00

STANDOFF ROAD EXPOSURE DURATION FOR DETERMINING INCAPACITATION

MODE DISTANCE DIRECTION 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX

CONC 500.

750.

1000.

1500.

2000.

3000.

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

ENE

ESE

SSE

NNW

.008 .009 .010

.008 .009 .015

.004 .004 .006

.011 .013 .018

.007 .008 .010

.005 .006 .011

.003 .004 .005

.008 .010 .015

.006 .008 .010

.003 .004 .008

.002 .003 .004

.006 .008 .012

.004 .005 .008

.002 .002 .004

.001 .002 .003

.004 .004 .008

.002 .003 .006

.001 .001 .001

.001 .001 .002

.002 .002 .004

.001 .001 .003

.000 .000 .000

.000 .000 .001

.001 .000 .001

.000 .001 .007

.000 .000 .006

.000 .000 .003

.000 .001 .009

.000 .000 °006

.000 .000 .004

.000 .000 .002

.000 .000 .007

.000 .000 .005

.000 .000 .002

.000 .000 .002

.000 -. 000 .004

.000 .000 .003

.000 .000 .001

.000 .000 .001

.000 .000 .002

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .001

.000 .000 .000

.000 .000 .000

.000 .000 .000

.000 .000 .000

.011 .012 .016

.014 .019 .032

.006 .008 .012

.017 .022 .032

.010 .013 .017

.011 .014 .030

.005 .007 .012

.015 .019 .032

.009 .013 .017

.008 .011 .026

.004 .006 .011

.012 .016 .030

.007 .010 .017

.005 .006 .018

.003 .004 .008

.008 .011 .025

.006 .008 .017

.003 .003 .014

.002 .003 .008

.006 .007 .022

.003 .004 .014

.001 .001 .008

.001 .001 .005

.003 .003 .015

.002 .003 .012

.001 .001 .020

.001 .001 .008

.001 .003 .022

.001 .002 .012

.000 .000 .017

.000 .001 .007

.000 .001 .021

.000 .001 .012

.000 .000 .012

.000 .000 .006

.000 .001 .017

.000 .000 .011

.000 .000 .009

.000 .000 .005

.000 .000 .014

.000 .000 .009

.000 .000 .005

.000 .000 .003

.000 .000 .010

.000 -. 000 .006

.000 .000 .002

.000 .000 .002

.000 .000 .005

DOSE 500.

750.

1000.

1500.

2000.

3000.

-23-
TABLE 7 PROBABILITY'OF CONTROL ROOM OPERATOR INCAPACITATION GIVEN A

TOXIC GAS RELEASE ALONG A 16 KM ROUTE*

MAXIMUM OF PROBABILITY VALUES FOR FOUR ROAD DIRECTIONS.

SELF DETECTION CASE WITH TWO MINUTE DELAY.

ALSO MAXIMUM ACCIDENT-PLANT DISTANCES(KM).

TRUCK

SIGMA0 = 9.25

RAIL

SIGMAO = 15.00

STANDOFF EXPOSURE DURATION FOR DETERMINING INCAPACITATION

MObE DISTANCE 2-MIN 5-MIN MAX 2-MIN 5-MIN MAX

CONC

I

t-j

500.

750.

1000.

1500.

2000.

3000.

.011

.008

.006

.004

.002

.001

.013

.010

.008

.005

.003

.001

.018

.015

.012

.008

.006

.003

.017

.015

.012

.008

.006

.003

.022

.019

.016

.011

.008

,004

.032

.032

.030

.025

.022

.015

MAXIMUM DISTANCE(KM)

FOR INCAPACITATION

DOSE 500.

750.

1000.

1500.

2000.

3000.

4.3

.000

.000

.000

.000

.000

.000

0.7

4.3 A3 7.8 7.8 8.2

.001

.000

.000

.000

.000

.000

.009

.007

.005

.003

.001

.000

,002

.001

.000

.000

.000

.000

.003

.002

.001

.000

.000

.000

.022

.021

.017

.014

.010

.006

MAXIMUM DISTANCE(KM)

FOR INCAPACITATION

1.0 2.8 1.2 1.6 6.3
Table 8. Maximum Allowable Annual Shipping Frequencies for

Rail and Truck Tank Cars of Toxic Gases.

(1,1(1)

Transport

Mode

Rail

Incapacitation

mode

Conc

Truck

Dose

Conc

Dose

5-Min

420-

1100

3100-

UNL

3700-

20000

78000-

UNL

Max

180-

270

240-

340

1900-

2800

2800-

4900

5

5

Se

Ventilation System Rates

(I, 06, ) . . ..(10,.06,2) .. .(1,.015,1) (1,.015t2}

Exposure Duration for Determining Incapacitation

-Min Max 5-Min Max 5-Min Max 5-Min Max

1250- 520- 1250- 520- 3100- 1250- 3100- 1250-

UNL 1000 UNL 1000 UNL 6300 UNL 6300

UNL 830- UNL 1250- UNL 3100- UNL 6300-

2500 4200 UNL UNL

0000- 7800- 20000- 7800- 39000- 26000- 39000- 26000-

UNL 39000 UNL 39000 UNL UNL UNL UNL

UNL 20000- UNL 39000- UNL 78000- UNL UNL

UNL UNL UNL

lf Detection Case

2 Minute Delay

(1,.06,1)

5-Min

570-

3100

4200-

UNL

6000-

78000

78000-

UNL

VI

Max

390-

830

570-

2100

4300-

26000

8700-

UNL

2

Notes: 1. UNL - Unlimited.

2. Ranges of values are for standoff distances of 500 m to 3000 m.
As the licensee develops a map of projected route locations

and directions and a meteorological data base for his site, the

allowable transport frequencies could be based on detailed values

similar to those in Tables 2 through 5, rather than on the maximum

1screening or global" values used to construct Table 8. For example,

a more uniform wind rose would decrease P, by about a factor of

two from the maximum.

This report addresses the rail and truck transport of a

chemical as if they were independent. That is, a separate

assessment is made for each mode to assure compliance with the

probabilistic criterion on operator protection. One method for

allocating allowable shipping frequencies among the various modes

of transport is to use fractional-frequencies. Define FT, FR,

and FB as the actual shipping frequencies for truck rail, and

barge transport, respectively. Similarly, define NT, NR and NB

as the maximum allowable shipping frequencies. An acceptance

criterion for all transport of a single chemical might be:

FT FR FB - + - + - <1

NT NR NB

Such a measure properly allocates the risk among the various modes

of transport. A similar extension would allow consideration of

more than one chemical.

Summary

This report presents a methodology for estimating allowable

shipping frequencies for the truck and rail transport of toxic

gases near a nuclear power plant. The resulting frequencies are

based on a criterion that the probability of incapacitating the

control room operators be less than 10-5 /year for each chemical.

Using conservative accident and meteorological data, calculations

were done for an example chemical, chlorine. Because of these

conservative assumptions, the allowable shipping frequencies could

be used to screen safety analyses of nuclear plants to determine

whether a more detailed analysis-of toxic gas hazards is warranted.

The principal conclusions are that:

1. Rail transport is more hazardous than truck transport.

2. offset distance from the route to the plant is generally

of minor significance for offset distances less than 2

to 3 km.

-26-
3. For unisolated control rooms, rail and truck accidents at

8 km can lead to operator incapacitation.

4. Unless a transport survey assures shipping frequencies on

the order of or lower than 4/week for rail or 35/week for

truck, the control room should be isolatable and the

shipping frequency then determines the degree of isolation

needed.

5. For a self-detection case in which the smell threshold is

significantly lower than the incapacitation threshold and

the control room is isolatable, the corresponding shipping

frequencies are li/week for rail or 115/week for truck.

Self-contained breathing equipment is assumed to be used

after 5 minutes.

Except when detection by smell is adequate, the need for control

room isolation implies the need for chemical detection in the

control room air intake. The protection strategy of first determining the need for control room isolation and then the degree of

isolation is markedly different from that.in RG 1.78.

-27-
References

1. U. S. Code of Federal Regulations, Title 10, Part 50, Appendix

A, General Design Criteria 19; Office of the Federal Register,

General Services Administration, Washington, DC, 1981

2. Standard Format and Content of Safety Analysis Reports for

Nuclear Power Plants, LWR Edition, U.S. Nuclear Regulatory

Commission (USNRC), Office of Standards Development (SD),

Regulatory Guide 1.70, Revision 3, November 1978

3. Assumptions for Evaluating the Habitability of a Nuclear Power

Plant Control Room During a Postulated Hazardous Chemical

Release, USNRC/SD, Regulatory Guide 1.78, June 1974.

4. Protection of Nuclear Power Plant Control Room Operators

Against An Accidental Chlorine Release, USNRC/SD, Regulatory

Guide 1.95, Revision 1, January 1977.

5. Standard Review Plan for the Review of Safety Analysis Reports

for Nuclear Power Plants, USNRC, Office of Nuclear Reactor

Regulation (NRR), Washington, DC, NUREG-75/087, 1975.

6. Final Environmental Statement on the Transportation of Radioactive Materials by Air and Other Modes, USNRC/SD, NUREG-0170,

Vol. 1, December 1977.

7. Safety Effectiveness Evaluation - Federal and State Enforcement

Efforts in Hazardous Materials Transportation by Truck, National

Transportation Safety Board, NTSB-SEE-81-2, February 1981.

8. Simmons, J. A., Erdmann, R. C., Naft, D. N., Risk of Catastrophic

Spills of Toxic Chemicals, California University, Los Angeles,

CA, UCLA-ENG-7425, May 1974.

9. Bennett, D. E., and Finley, N. C., Hazards to Nuclear Power

Plants from Nearby Accidents Involving Hazardous Materials - A Preliminary Assessment, Sandia National Laboratories,

Albuquerque, NM, NUREG/CR-1748, SAND80-2334, April 1981.

10. Smith, G. J., and Bennett, D. E., Models for the Estimation

of Incapacitation Times Following Exposures to Toxic Gases

or Vapors, Sandia National Laboratories, Albuquerque, NM,

NUREG/CR-1741, SAND80-2226, December 1980.

11. Sprung, J. L., Steck, G. P., and Frazier, A. W., Correlations

Between Wind Flow and Population Location at 67 Light Water

Nuclear Power Plant Sites, Sandia National Laboratories,

Albuquerque, NM, SAND78-0557, October 1978.
12. Reactor Safety Study, WASH-1400, USNRC, October 1975.

13. Standard Review Plan for the Review of Safety Analysis Reports

for Nuclear Power Plants, USNRC/NRR, Washington, DC, NUREG-0800,

July 1981.

14. Clarke, R. K., Foley, J. T., Hartman, W. F., Larson, D. W.,

Severities of Transportation Accidents, Sandia National

Laboratories, Albuquerque, NM, SLA-74-001, July 1976.

15. Dennis, A. W., Foley, J. T., Hartman, W. F., Larson, D. W.,

Severities of Transportation Accidents Involving Large

Packages, Sandia National Laboratories, Albuquerque, NM,

SAND77-0001, May 1978.

16. Andrews, W. B., An Assessment of the Risk of Transporting

Liquid Chlorine By Rail, Battelle Pacific Northwest Laboratory,

Richland, WA, PNL-3376.

17. Private Communication from K. G. Murphy, Division of Systems

and Reliability Research, Office of Nuclear Regulatory Research,

U. S. Nuclear Regulatory Commission, Washington, DC.

-29-
Distribution

U. S. NRC Distribution Contractor (CDSI) (360)

7300 Pearl Street

Bethesda MD 20014

335 copies for R4

25 copies for NTIS

Professor David C. Heath (5)

School of Operations Research and Industrial Engineering

College of Engineering

Cornell University

Ithaca NY 14853

Kenneth G. Murphy (5)

Division of Systems and Reliability Research

U. S. Nuclear Regulatory Commission

Washington, DC 20555

3311 D. R. Parker

9400 A. W. Snyder

9410 D. J. McCloskey

9412 J. W. Hickman

9413 N. R. Ortiz

9413 N. C. Finley

9414 G. B. Varnado

9414 D. M. Ericson, Jr.

9415 D. C. Aldrich

9415 D. E. Bennett (25)

9440 D. A. Dahlgren

9443 D. C. Carlson

9780 R. M. Jefferson

9781 R. E. Luna

9781 J. M. Taylor

9782 R. T. Reese

8214 M. A. Pound

3141 L. J. Erickson (5)

3151 W. L. Garner (3)

*U.S. GOVERNMENT PRINTING OFFICE* 1982-0-576-021/621 .30