Regulatory Guide 1.3

Assumptions Used for Evaluating the Potential Radiological Consequences of a Loss of Coolant Accident for Boiling Water Reactors

ML003739601
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Issue date:	06/30/1974
From:	Office of Nuclear Regulatory Research
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RG-1.3, Rev 2
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U.S. ATOMIC ENERGY COMMISSION

REGULATORY

DIRECTORATE OF REGULATORY STANDARDS

Revision 2 June 1974 GUIDE

REGULATORY GUIDE 1.3 ASSUMPTIONS USED FOR EVALUATING THE POTENTIAL RADIOLOGICAL CONSEQUENCES

OF A LOSS OF COOLANT ACCIDENT FOR BOILING WATER REACTORS

A. INTRODUCTION

Section 50.34 of 10 CFR Part 50 requires that each applicant for a construction permit or operating license provide an analysis and evaluation of the design and performance of structures, systems, and components of the facility with the objective of assessing the risk to public health and safety resulting from operation of the facility. The design basis loss of coolant accident (LOCA) is one of the postulated accidents used to evaluate the adequacy of these structures, systems, and components with respect to the public health and safety.

This guide gives acceptable assumptions that may be used in evaluating the radiological consequences of this accident for a boiling water reactor. In some cases, unusual site characteristics, plant design features, or other factors may require different assumptions which will be considered on an individual case basis. The Advisory Committee on Reactor Safeguards has been consulted concerning this guide and has concurred in the regulatory position.

B. DISCUSSION

After reviewing a number of applications for construction permits and operating licenses for boiling water power reactors, the AEC Regulatory staff has developed a number of appropriately conservative assumptions, based on engineering judgment and on applicable experimental results from safety research programs conducted by the AEC and the nuclear industry, that are used to evaluate calculations of the diological consequences of various postulated accidents.

This guide lists acceptable assumptions that may be used to evaluate the design basis LOCA of a Boiling Water Reactor (BWR). It should be shown that the offsite dose consequences will be within the guidelines of 10 CFR Part 100. (During the construction permit review, guideline, exposures of 20 rem whole body and

150 rem thyroid should be used rather than the values given in § 100.11 in order to allow for (a) uncertainties in final design details and meteorology or (b) new data and calculational techniques that might influence the final design of engineered safety features or the dose reduction factors allowed for these features.)

C. REGULATORY POSITION

1. The assumptions related to the release of radioactive material from the fuel and containment are as follows:

a.

Twenty-five percent of the equilibrium radioactive iodine inventory developed from maximum full power operation of the core should be assumed to be immediately available for leakage from the primary reactor containment. Ninety-one percent of this 25 percent is to be assumed to be in the form of elemental iodine, 5 percent of this 25 percent in the form of particulate iodine, and 4 percent of this 25 percent in the form of organic iodides.

b.

One hundred percent of the equilibrium radioactive noble gas inventory developed from maximum full power operation of the core should be assumed to be immediately available for leakage from the reactor containment.

c.

The effects of radiological decay during holdup in the containment or other buildings should be taken into account.

d.

The reduction in the amount of radioactive material available for leakage to the environment by containment sprays, recirculating filter systems, or other engineered safety features may be taken into account, but the amount of reduction in concentration of radioactive materials should be evaluated on an individual case basis.

e.

The primary containment should be assumed to leak at the leak rate incorporated or to be incorporated in the technical specifications for the duration of the USAEC REGULATORY GUIDES

Copies of published s nay be obtained by request Indicating the divisions desired to the US. Atomic Energy Commission, Washington, D.C. 20645, Regulatory Guides are issued to descobe and mal available to the Public Attention: Director of Regulatory Standrds. Comments and suggestions for methods acceptable to the AEC Regulatory staff of implementing specific parts of Improvements In thes guides we encouraged and should be sent to the Secretary ths Commission's regulations, to delineate techniques used by the staff in of the Commission, US. Atomic Energy Commission, Washington, D.C. 20645, eveluating specific problems or postulatedi accidents, or to provide guidance to Attention: Chief, Public Proceedings Staff.

applicants. Regulatory Guides are not substitutes for regulations end compliance with them is not required. Methods end solutions different from thorn set out in The auides are issued in the following ten broad divisions:

the guldes will be acceptable If they provide a basis for the findings requisite to the issuance or continuance of a permit or license by the Commission.

6. Products

2. Research and Test Reactors

7. Transportation

3. Fuels and Materials Facilities

8. Occupational Health Published guide will be revised periodically, as appropriate, to accommodate

4. Environmental and Siting

9. Antitrust Review comments to reflect new information or experience.

5. Materials and Plant Protection

1

0. General

accident. 1 The leakage should be assumed to pass directly to the emergency exhaust system without mixing_2 in the surrounding reactor building atmosphere and should then be assumed to be released as an elevated plume for those facilities with stacks. '

f.

No credit should be given for retention of iodine in the suppression pool.

2.

Acceptable assumptions for atmospheric diffusion and dose conversion are:

a.

Elevated releases should be considered to be at a height equal to no more than the actual stack height.

Certain site dependent conditions may exist, such as surrounding elevated topography or nearby structures which will have the effect of reducing the actual stack height. The degree of stack height reduction should be evaluated on an individual case basis. Also, special meteorological and geographical conditions may exist which can contribute to greater ground level concentrations in the immediate neighborhood of a stack. For example, fumigation should always be assumed to occur; however, the length of time that a fumigation condition exists is strongly dependent on geographical and seasonal factors and should be evaluated on a case-by-case basis.4 (See Figures IA

through 1D for atmospheric diffusion factors for an elevated release with fumigation.)

b.

No correction should be made for depletion of the effluent plume of radioactive iodine due to deposition on the ground, or for the radiological decay of iodine in transit.

c.

For the first 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, the breathing rate of persons offsite should be assumed to be 3.47x 104 cubic meters per second. From 8 to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following the accident, the breathing rate should be assumed to be

1.75 x 10"4 cubic meters per second. After that until the end of the accident, the rate should be assumed to be

2.32 x 10-4 cubic meters per second. (These values were

1The effect on containment leakage under accident conditions of1 features provided to reduce the leakage of radioactive materials from the containment will be evaluated on an individual case basis.

"2 In some cases, credit for mixing will be allowed; however, the amount of credit allowed will be evaluated on an individual case basis.

' Credit for an elevated release should be given only if the point of release is (1) more than two and one-half times the height of any structure close enough to affect the dispersion of the plume, or (2) located far enough from any structure which could have an effect on the dispersion of the plume. For those BWR's without stacks the atmospheric diffusion factors assuming ground level release given in section 2.h. should be used to determine site acceptability.

4 For sites located more than 2 miles from large bodies of water such as oceans or one of the Great Lakes, a fumigation condition should be assumed to exist at the time of the accident and continue for one-half hour. For sites located less than 2 miles from large bodies of water, a fumigation condition should be assumed to exist at the time of the accident and continue for

4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

developed from the average daily breathing rate [2 x 107 cm3 /day] assumed in the report of ICRP, Committee

11-1959.).

d.

The iodine dose conversion factors are given in ICRP Publication

2, Report of Committee II,

"Permissible Dose for Internal Radiation," 1959.

e.

External whole body doses should be calculated using "Infinite Cloud" assumptions, i.e., the dimensions of the cloud are assumed to be large compared to the distance that the gamma rays and beta particles travel.

"Such a cloud would be considered an infinite cloud for a receptor at the center because any additional [gamma and]

beta emitting material beyond the cloud dimensions would not alter the flux of [gamma rays and] beta particles to the receptor" (Meteorology and Atomic Energy, Section 7.4.1.1-editorial additions made so that gamma and beta emitting material could be considered). Under these conditions the rate of energy absorption per unit volume is equal to the rate of energy released per unit volume. For an infinite uniform cloud containing X curies of beta radioactivity per cubic meter the beta dose in air at the cloud center is:

SD4g = 0.457 EX

The surface body dose rate from beta emitters in the infinite cloud can be approximated as being one-half this amount (i.e., 0D+/- = 0.23 ETX).

For gamma emitting material the dose rate in air at the cloud center is:

D

0.507 .EX

From a semi-infinite cloud, the gamma dose rate in air is:

S=

0.25 E~x Where

= beta dose rate from an infinite cloud (rad/sec)

gamma dose rate from an infinite cloud (rad/sec)

Eg =

average beta energy per disintegration (Mev/dis)

EB = average gamma energy per disintegration

"(Mev/dis)

X

= concentration of beta or gamma emitting isotope in the cloud (curie/m 3)

f.

The following specific assumptions are acceptable with respect to the radioactive cloud dose calculations:

(1) The dose at any distance fronthe reactor should be calculated based on the maximum concentration in the plume at that distance taking into account specific meteorological, topographical, and other characteristics which may affect the maximum plume concentration. These site related characteristics

1.3-2

must be evaluated on an individual case basis. In the case of beta radiation, the receptor is assumed to be exposed to an infinite cloud at the maximum ground level concentration at that distance from the reactor. In the case of gamma radiation, the receptor is assumed to be exposed to only one-half the cloud owing to the presence of the ground. The maximum cloud concentration always should be assumed to be at ground level.

(2) The appropriate average beta and gamma energies emitted per disintegration, as given in the Table of Isotopes, Sixth Edition, by C. M. Lederer, J. M.

Hollander, I. Perlman; University of California, Berkeley;

Lawrence Radiation Laboratory; should be used.

g.

For BWR's with stacks the atmospheric diffusion model should be as follows:

(1) The basic equation for atmospheric diffusion from an elevated release is:

exp(-h2 I2oz2)

X/Q

iu a Sy~z Where X

= the short term average centerline value of the ground level concentration (curie/meter 3)

Q

= amount of material released (curie/sec)

u

= windspeed (meter/sec)

y= the horizontal standard deviation of the plume (meters) [See Figure V-l, Page 48, Nuclear Safety, June 1961, Volume 2, Number 4, "Use of Routine Meteorological Observations for Estimating Atmospheric Dispersion," F. A. Gifford, Jr.]

oz= the vertical standard deviation of the plume (meters) [See Figure V-2, Page 48, Nuclear Safety, June 1961, Volume 2, Number 4,

"Use of Routine Meteorological Observations for Estimating Atmospheric Dispersion," F. A. Gifford, Jr.]

h

= effective height of release (meters)

(2) For time periods of greater than 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> the plume from an elevated release should be assumed to meander and spread uniformly over a 22.50 sector. The resultant equation is:

2.032 exp(-h2/2az 2)

x/Q

a=ux Where x

= distance from the release point (meters);

other variables are as given in g(l).

(3) The atmospheric diffusion model s for an elevated release as a function of the distance from the reactor, is based on the information in the table below.

Time Following Accident Atmospheric Conditions

0-8 hours See Figure I(A)

Envelope of Pasquill diffusion categories based on Figure A7 Meteorology and Atomic Energy-1968, assuming various stack heights; windspeed 1 meter/sec; uniform direction.

8-24 hours See Figure I(B)

Envelope of Pasquill diffusion categories; windspeed 1 meter/sec;

variable direction within a 22.50 sector.

14 days See Figure 1(C) Envelope of Pasquill diffusion categories with the following relationship used to represent maximum plume concentrations as a function of distance:

Atmospheric Condition Case 1

40% Pasquill A

60% Pasquill C

Atmospheric Condition Case 2

50% Pasquill C

50% Pasquill D

Atmospheric Condition Case 3

33.3% Pasquill C

33.3% Pasquill D

33.3% Pasquill E

Atmospheric Condition Case 4

33.3% Pasquill D

33.3% Pasquill E

33.3% Pasquill F

Atmospheric Condition Case 5

50% Pasquill D

50% Pasquill F

wind speed variable (Pasquill Types A, B, E,

and F windspeed 2 meter/sec; Pasquill Types C and D windspeed 3 meter/sec);

variable direction within a 22.50 sector.

4-30 days See Figure I(D) Same diffusion relations as given above; windspeed variable dependent on Pasquill Type used; wind direction 33.3%

frequency in a 22.50 sector.

This model should be used until adequate site meteorological data are obtained. In some cases, available information, such as meteorology, topography and geographical location, may dictate the use of a more restrictive model to insure a conservative estimate of potential offsite exposures.

1.3-3

h.

For BWR's without stacks the atmospheric diffusion model 6 should be as follows:

(1) The

0-8 hour ground level release concentrations may be reduced by a factor ranging from one to a maximum of three (see Figure 2) for additional dispersion produced by the turbulent wake of the reactor building in calculating potential exposures. The volumetric building wake correction factor, as defined in section 3-3.5.2 of Meteorology and Atomic Energy

1968, should be used only in the 0-8 hour period; it is used with a shape factor of 1/2 and the minimum cross-sectional area of the reactor building only.

(2) The basic equation for atmospheric diffusion from a ground level point source is:

1 x/Q = 7rUOryc"Z

Where

(4) The atmospheric diffusion model for ground level releases is based on the information in the table below.

Time Following Accident Atmospheric Conditions

0-8 hours Pasquill Type F, windspeed

1 meter/sec, uniform direction

8-24 hours Pasquill Type F, windspeed

1 meter/sec, variable direction within a 22.50 sector

14 days (a) 40% Pasquill Type D, windspeed

3 meter/sec (b) 60% Pasquill Type F,

meter/sec (c) wind direction variable sector windspeed

2 within a 22.50

x

= the short term average centerline value of the ground level concentration (curie/meter 3)

Q

= amount of material released (curie/sec)

u

= windspeed (meter/sec)

ay = the horizontal standard deviation of the plume (meters) [See Figure V-1, Page 48, Nuclear Safety, June 1961, Volume 2, Number 4, "Use of Routine Meteorological Observations for Estimating Atmospheric Dispersion," F. A. Gifford, Jr.]

z= the vertical standard deviation of the plume (meters) [See Figure V-2, Page 48, Nuclear Safety, June 1961, Volume 2, Number 4,

"Use of Routine Meteorological Observations for Estimating Atmospheric Dispersion," F. A. Gifford, Jr.]

(3) For time periods of greater than 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> the plume should be assumed to meander and spread unikormly over a 22.50 sector. The resultant equation is:

4-30 days (a) 33.3% Pasquill Type C, windspeed 3 meter/sec (b) 33.3% Pasquill Type D, windspeed 3 meter/sec (c) 33.3% Pasquill Type F, windspeed 2 meter/sec (d) Wind direction 33.3% frequency in a

22.50 sector

(5) Figures 3A and 3B give the ground level release atmospheric diffusion factors based on the parameters given in h(4).

D. IMPLEMENTATION

The purpose of the revision (indicated by a line in the margin) to this guide is to reflect current Regulatory staff practice in the review of construction permit appli cations, and the revised guide, therefore, is effective immediately.

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