Regulatory Guide 1.4

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

ML003739614
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Issue date:	06/30/1974
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RG-1.4, Rev 2
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Revision 2 June 1974 U.S. ATOMIC ENERGY COMMISSION

REGULATORY GUIDE

DIRECTORATE OF REGULATORY STANDARDS

REGULATORY GUIDE 1.4 ASSUMPTIONS USED FOR EVALUATING THE POTENTIAL RADIOLOGICAL CONSEQUENCES

OF A LOSS OF COOLANT ACCIDENT FOR PRESSURIZED WATER REACTORS

A. INTRODUCTION

given in § 100.11 in order to allow for (a) uncertainties in final design details and meteorology or (b) new data Section 50.34 of 10 CFR Part 50 requires that each and calculational techniques that might influence the applicant for a construction permit or operating license final design of engineered safety features or the dose provide an analysis and evaluation of the design and reduction factors allowed for these features.)

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

C. REGULATORY POSITION

facility. The design basis loss of coolant accident (LOCA) is one of the postulated accidents used to 1. The assumptions related to the release of radioactive evaluate the adequacy of these structures, systems, and material from the fuel and containment are as follows:

components with respect to the public health and safety. a. Twenty-five percent of the equilibrium This guide gives acceptable assumptions that may be radioactive iodine inventory developed from maximum used in evaluating the radiological consequences of this full power operation of the core should be assumed to accident for a pressurized water reactor. In some cases, be immediately available for leakage from the primary unusual site characteristics, plant design features, or reactor containment. Ninety-one percent of this 25 other factors may require different assumptions which percent is to be assumed to be in the form of elemental will be considered on an individual case basis. The iodine, 5 percent of this 25 percent in the form of Advisory Committee on Reactor Safeguards has been particulate iodine, and 4 percent of this 25 percent in consulted concerning this guide and has concurred in the the form of organic iodides.

regulatory position. b. One hundred percent of the equilibrium

B. DISCUSSION

radioactive noble gas inventory developed from maximum full power operation of the core should be After reviewing a number of applications for assumed to be immediately available for leakage from construction permits and operating licenses for the reactor containment.

pressurized water power reactors, the AEC Regulatory c. The effects of radiological decay during holdup staff has developed a number of appropriately in the containment or other buildings should be taken conservative assumptions, based on engineering into account.

judgment and on applicable experimental results from d. The reduction in the amount of radioactive safety research programs conducted by the AEC and the material available for leakage to the environment by nuclear industry, that are used to evaluate calculations containment sprays, recirculating filter systems, or other of the radiological consequences of various postulated engineered safety features may be taken into account, accidents. but the amount of reduction in concentration of radioactive materials should be evaluated on an This guide lists acceptable assumptions that may be individual case basis.

used to evaluate the design basis LOCA of a Pressurized e. The primary reactor containment should be Water Reactor (PWR). It should be shown that the assumed to leak at the leak rate incorporated or to be offsite dose consequences will be within the guidelines incorporated as a technical specification requirement at of 10 CFR Part 100. (During the construction permit peak accident pressure for the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, and at 50

review, guideline exposures of 20 rem whole body and percent of this leak rate for the remaining duration of

150 rem thyroid should be used rather than the values USAEC REGULATORY GUIDES Copies of published guide may. be obtained by request the divisions indicating D.C. 20646, desired to the US. Atomic Enemgy Commilss*o, Washlngton.

Attention: Director of Regulatory Standards. Comments and suggestions for Regulatory Guides we issuad to describe and make available to the parts public methods acceptable to the AEC Regulatory staff of implementing specific of Impr° ments In theose uldes we encouraged and should be sent to the Secretary by the staff in of the Commislion, U.S. Atomic Energy Commission, Washington, D.C. 20645, the Commission's regulations, to delineate techniques used Attention: Chief, Public ProcoedlnglStaff.

eanluating specific problems or postulated accidents, or to provide guidance to applicants. Regulatory Guides are not substitutes for regulations and compliance setout in The guides are issued in the following ten broad divisions:

with them is not required. Methods and solutions different from thoserequisite to the guides will be acceptable if they provide a basis for the findings 1. PeOWrdReactors 6. Products the Issuance or continuance of a permit or )iconse by the Commissio

7. Transportation

2. Research end Test Reactors

3. Fuels end Materials Facilities EL Occupatlonal Health

4. Environmental and Siting 9. Antitrust Review Published guides will be revised periodically, asappropriate, to accommodate 5. Materials and Plant Protection 10. General comments and to reflect new information or experienca.

the accident., Peak accident pressure is the maximum The surface body dose rate from beta emitters in the pressure defined in the technical specifications for infinite cloud can be approximated as being one-half this containment leak testing. amount (i.e., PD-1 = 0.23 Eox).

2. Acceptable assumptions for atmospheric diffusion and dose conversion are:

a. The 0-8 hour ground level release For gamma emitting material the dose rate in air at the concentrations may be reduced by a factor ranging from cloud center is:

one to a maximum of three (see Figure 1) for additional dispersion produced by the turbulent wake of the ^/DL = 0.507 E&x reactor building in calculating potential exposures. The volumetric building wake correction, as defined in From a semi-infinite cloud, the gamma dose rate in air section 3-3.5.2 of Meteorology and Atomic Energy

1968, should be used only in the 0-8 hour period; it is is:

used with a shape factor of 1/2 and the minimum cross-sectional area of the reactor building only. 7D = 0.25EYx b. No correction should be made for depletion of the effluent plume of radioactive iodine due to Where deposition on the ground, or for the radiological decay of iodine in transit. 0 , = beta dose rate from an infinite cloudi(rad/sec)

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 DI= gamma dose rate from an infinite cloud persons offsite should be assumed to be 3.47 x 10"4 (rad/sec)

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 E3 average beta energy per disintegration the accident, the breathing rate should be assumed to be (Mev/dis)

1.75 x 104 cubic meters per second. After that until the EF"= average gamma energy per disintegration end of the accident, the rate should be assumed to be (Mev/dis)

1.75 x 10-4 cubic meters per second. After that until the X = concentration of beta or gamma emitting end of the accident, the rate should be assumed to be isotope in the cloud (curie/m 3 )

2.32 x 104 cubic meters per second. (These values were developed from the average daily breathing rate [2 x 107 f. The following specific 'assumptions are cm3 /day] assumed in the report of ICRP, Committee acceptable with respect to the radioactive cloud dose calculations:

11-1959.)

d. The iodine dose conversion factors are given in (1) The dose at any distance from the reactor ICRP Publication 2, Report of Committee II, should be calculated based on the maximum concentration in the plume at that distance taking into

"Permissible Dose for Internal Radiation," 1959.

account specific meteorological, topographical, and e. External whole body doses should be calculated other characteristics which may affect the maximum using "Infinite Cloud" assumptions, i.e., the dimensions of the cloud are assumed to be large compared to the plume concentration. These site related characteristics must be evaluated on an individual case basis. In the case distance that the gamma rays and beta particles travel.

of beta radiation, the receptor is assumed to be exposed

"Such a cloud would be considered an infinite cloud for to an infinite cloud at the maximum ground level a receptor at the center because any additional [gamma and] beta emitting material beyond the cloud concentration at that distance from the reactor. In the case of gamma radiation, the receptor is assumed to be dimensions would not alter the flux of [gamma rays and] beta particles to the receptor" (Meteorology and exposed to only one-half the cloud owing to the Atomic Energy, Section 7.4.1.1 -editorial additions presence of the ground. The maximum cloud made so that gamma and beta emitting material could be concentration always should be assumed to be at ground considered). Under these conditions the rate of energy level.

absorption per unit volume is equal to the rate of energy (2) The appropriate average beta and gamma released per unit volume. For an infinite uniform cloud energies emitted per disintegration, as given in the Table containing X curies of beta radioactivity per cubic meter of Isotopes, Sixth Edition, by C. M. Lederer, J. M.

the beta dose in air at the cloud center is: Hollander, I. Perlman; University of California, Berkeley;

Lawrence Radiation Laboratory; should be used.

SD4 = 0.457 fEX g. The atmospheric diffusion model should be as follows:

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

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

XIQ = SrUayoz

1.4-2

Time Where Following Accident Atmospheric Conditions X = the short term average centerline value of the 3 ground level concentration (curie/meter ) 0-8 hours Pasquill Type F, windspeed 1 meter/see, Q = amount of material released (curie/sec) uniform direction u = windspeed (meter/sec)

ay = the horizontal standard deviation of the

8.24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Pasquill Type F, windspeed 1 meter/sec, plume (meters) [See Figure V-i, Page 48, variable direction within a 22.50 sector Nuclear Safety, June 1961. Volume 2, Number 4, "Use of Routine Meteorological Observations for Estimating Atmospheric 1-4 days (a) 40% Pasquill Type D, windspeed 3 Dispersion," F. A. Gifford, Jr.] meter/sec z= the vertical standard deviation of the plume (b) 60% Pasquill Type F, windspeed 2 (meters) [See Figure V-2, Page 48, Nudear meter/sec Safety, June 1961, Volume 2, Number 4, (c) wind direction variable within a 22.50

"Use of Routine Meteorological sector Observations for Estimating Atmospheric Dispersion," F. A. Gifford, Jr.] 4-30 days (a) 33.3% Pasquill Type C, windspeed 3 meter/sec

(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 /> (b) 33.3% Pasquill Type D, windspeed 3 the plume should be assumed to meander and spread meter/sec uniformly over a 22.50 sector. The resultant equation is: (c) 33.3% Pasquill Type F, windspeed 2 meter/sec x/Q = 2.032 uu (d) Wind direction 33.3% frequency in a OzU 22.50 sector Where

(4) Figures 2A and 2B give the ground level x = distance from point of release to the receptor; release atmospheric diffusion factors based on the other variables are as given in g(l). parameters given in g(3).

2

(3) The atmospheric diffusion model for ground level releases is based on the information in the following tabl

D. IMPLEMENTATION

2 This model should be used until adequate site The revision to this guide (indicated by a line in the meteorological data are obtained. In some cases, available margin) reflects current Regulatory staff practice in the information, such as meteorology, topography and geographical review of construction permit applications; therefore, location, may dictate the use of a more restrictive model to this revision is effective immediately.

insure a conservative estimate of potential offsite exposures.

1.4-3

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