Regulatory Guide 1.4

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

ML13350A195
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Issue date:	06/30/1973
From:	US Atomic Energy Commission (AEC)
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References
RG-1.004, Rev. 1
Download: ML13350A195 (6)

Revision

1U.S. ATOMIC ENERGY COMMISSION

REGULATORY

DIRECTORATE

OF REGULATORY

STANDARDS

Revision

1June 1973GUIDEREGULATORY

GUIDE 1.4ASSUMPTIONS

USED FOR EVALUATING

THE POTENTIAL

RADIOLOGICAL

CONSEQUENCES

OF A LOSS OF COOLANT ACf',DENT

FOR PRESSURIZED

WATER REACTORS'

A. INTRODUCTION

Sect ion 50.34 o1f 10 CFR Pairl 50 requires that eachapplicant fir a c(nstruiction permit or operating licenseprovid,:

an analysis and cvalua3ion of the design and of structures.

systems, and components oftile facility with [he objective of assessing fhe risk topublic health and safety resulting froim operation of thefacility.

Tile design basis loss of" coolant accident(LOCA) is one of the postulated accidents Used toevaluate the adequacy of these structures, systems.

andcomiponents with respect to the public ltealth and safety.This guide gives acceptable assumptions that may beused in evaluating tIle radiologcal consequences of thisaccident for a pressurized water reactor.

In some cases.unusual site characteristics, platit design features.

orother factors may require different assumptions whichwill be considered on an individual case basis. TheAdvisory Committee on Reactor Safeguards has beenconsulted concerning this guide and has concurred in theregulatory position.

B. DISCUSSION

After reviewing a number of applications forconstruction permits and operating licenses forpressurized wateli power reactors, the AEC Regulatory staff has developed a number of appropriately conservative assumptions, based on engineering judgment and on applicable experimental results fromsafety research programs conducted by the AEC and thenuclear industry, that are used to evaluate calculations of the radioloocal consequences of various postulated acciden ts.This guide lists acceptable assumptions that may beused to evaluate the design basis LOCA of a Pressurized Water Reactor (PWR). It should be shown that thcoffsite dose consequences will be within thie guidelines of 10 CFR Part 100,'This guide is a revision of former Safety Guide 4.C. REGULATORY

POSITION1. The assuimptions related io the release of radioactive material from the fuel and containment are as Ibllows:a. T we n t y -five percent of the equilibriut radioactive iodine inventory developed from imlaximu ifull power operation of the core should be assumtned tobe immediately available for leakage from the prinmaryreactor containment.

Ninety-one percent of this 25percent is to be assumed ito he ill Ithe forma ofelenllelllal iodine. 5 percent of this 25 percent ill the form ofparticulate iodine. and 4 percent of this 25 percent inthe form of organic iodides.b. One hundred percent of the equilibrium radioactive noble gas inventory developed frontmaximum full power operation od the core should beassumed to be immediately available for leakage frontthe reactor containment.

c. The effects of radiological decay during holdupin the containment or other buildings should be takeninto account.d. The reduction in the amotunt of radioactive material available for leakage to tile environment bycontainment sprays, recirculating filter systems, or otherengineered safety features may be taken into account.but the amount of reduction in concentration ofradioactive materials should be evaluated on anindividual case basis.e. The primary reactor containment should beassumed to leak at the leak rate incorporated or to leincorporated as a technical specification requirement atpeak 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 50percent of this leak rate for the remaining duration ofthe accideint.

2 Peak accident pressure is the maximum1pressure defined in the technical specifications forcontainment leak testing.2Thte effect on coniainnmeni leakage tinder accidentconditions of features provided to reduce the leakage ot"radioactive materials from the containment will be evaluated onan individual case basi

s. USAEC REGULATORY

GUIDES Coples of published guldes may be obtained by request Indicating the divisions desired to the US. Atomic Energy Commission.

Washington.

0.1, 20545,Regulatory Guides are issued to describe and make avaliable to the public Attention:

Director of Regulatory Standards.

Comments and tuggrsilons formethods acceptable to the AEC Regulatory staff of Implementing specific parts of impfrovements In these guides ere encouraged end should be sent to the Secretary the Commission's regulations, to delineate techniques used by the staff in of the Commission, US. Atomic Energy Commission, Washington.

O.C. 20545.evaluating specific problems or postulated accid3nts.

or to provide guidance to Attention:

Chief, Public Proceedings Staff.applicants.

Regulatory Guides are not substitutes for regulations and compliance with them is not required.

Methods and solutlons different from those set out in The guides are issued In the following ten broad divliions:

the guides will be acceptable if they provide a basis for the findings requisite tothe issuance or continuance of a permit or license by the Comrrssion.

1. Power Reactors

8. Products2. Researcha nd Tast Reactors

7. Transportation

3. Fuels and Materials Facilities

8. Occupational HealthPublished guides will be revised periodically, as appropriate, to accommodate

4. Environmental end Siting 9. Antlitrust Reviewcomments and to reflect new informatio"

or experience.

5. Materials and Plant Protection

1

0. General

.12. Acceptable assumptions for atmospheric diffusion and dose conversion are:a. The 0-8 hour ground level releaseconcentrations may be reduced by a factor ranging fromone to a maximum of three (.see Figure I) for additional dispersion produced by the turbulent wake of thereactor building in calculating potential exposures.

Thevolumetric building wake correction, as defined insection 3.3.5.2 of Meteorology and Atomic Energy1968. should be used only in the 0-8 hour period: it isused with a shape factor of 112 and the minimumcross-sectional area of the reactor building only.b. No correction should be made for depletion of'the effluent plume of radioactive iodine due todeposition on the ground, or for the radiological decayof 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 ofpersons offsite should be assumed to be 3.47 x 10'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 be1.75 x 104 cubic meters per second. After that until theend of the accident, the rate should be assumed to be2.32 x 104 cubic meters per second. (These values weredeveloped from the average daily breathing rate [2 x 107cnv'/dayJ

assumed in the report of ICRP, Committee

11-1959.)

d. The iodine dose conversion factors are given inICRP Publication

2, Report of Committee

11,"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 thedistance that the gamma rays and beta particles travel."Such a cloud would be considered an infinite cloud fora receptor at the center because any additional

[gammaand] beta emitting material beyond the clouddimensions would not alter the flux of [gamma raysand] beta particles to the receptor"

(Meteorology andAtomic Energy, Section 7.4. .1.-editorial additions made so that gamma and beta emitting material could beconsidered).

Under these conditions the rate of energyabsorption per unit volume is equal to the rate of energyreleased per unit volume. For an infinite uniform cloudcontaining X curies of beta radioactivity per cubic meterthe beta dose in air at the cloud center is:From a semi-infinite cloud, the gamma dose rate in airis:,D = 0,25EWherebeta dose rate from an infinite cloud (rad/sec)

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

EO3 = average beta energy per disintegration (Mev/dis)

E = average gamma energy per disintegration (Mev/dis)

X = concentration of beta or gamma emillingisotope in the cloud (curie/m3)

f. The following specific assumptions areacceptable with respect to the radioactive cloud dosecalculations:

(1) The dose at any distance from the reactorshould be calculated based on the maximumconcentration in the plume at that distance taking intoaccount specific meteorological, topographical, andother characteristics which may affect the maximumplume concentration.

These site related characteristics must be evaluated on an individual case basis. In the caseof beta radiation, the receptor is assumed to be exposedto an infinite cloud at the maximum ground levelconcentration at that distance from the reactor.

In thecase of gamma radiation, the receptor is assumed to beexposed to only one-half the cloud owing to thepresence of the ground. The maximum cloudconcentration always should be assumed to be at groundlevel.(2) The appropriate average beta and gammaenergies emitted per disintegration, as given in the Tableof Isotopes, Sixth Edition, by C. M. Lederer, J. M.Hollander, I. Perlman;

University of California, Berkeley, Lawrence Radiation Laboratory;

should be used.g. The atmospheric diffusion model should be asfollows:(1) The basic equation for atmospheric diffusion from a ground level point source is:X/Q= ruayaWhereX = the short term average centerline value of theground level concentration (curie/meter3)

Q = amount of material released (curie/see)

u = windspeed (meter/see)

y = the horizontal standard deviation of theplume (meters)

[See Figure V-I. Page 48.Nuclear Safety, June 1961, Volume 2.D! = 0.457 EOXThe surface body dose rate from beta emitters in theinfinite cloud can be approximated as being one-half thisamount (i.e., 0DD' = 0.23 E'X).For gamma emitting material the dose rate in air at theuloud center is:7.D = 0.507 Ey(1.4-2 Number 4, "Use of Routine Meteorolo-ical Observations for Estimating Atmospcheric Dispersion,"

F. A. Gifford.

Jrj..o" = the vertical standard deviation cf the pluii.e(meters)

ISee Figure V-2, Page 48, NuclearSafqev',

June 19(1. Volume 2. Number 4."Use of Routlinc Me leorological Oh,'ervations for Estimating Atmospheric Dispersion,"

F. A. G;ifford.

Jr.I(.2) For lime periods of greater than 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />sthe plume shouid hI assumed to meander and spread ovcr a 22.i" sector. The resultlant e'quaition is:2.032x/Q = lx\Vhicrcx distance from point of release to the receptor;.

other variables are as given in g( 1).(3) Tlhe at mospheric diffusion model" forground level releases is based on the information in thefollowing lable.-' 'This niIdo.l'

%liould be useud until adequate sitemetcorologic'al d:ta are obtained.

In some ,-uses. available information.

such u,;

topography and geovaphicut.

tocalion.

may dictate Itic use of a more restrictive model toinsurc a conscrvative eltimuie of potentla oflfsitc exposures.

TimeFollowing AccidentAtmospheric Conditions

0.8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Pasquill Type F. wiudspeed I meter/sec.

uniform direction

8-24 hours Pasquill Type F, windspced I metcr/s.c.

variable direction within a 22.5" sector1-4 days (a) 4(Y,,%( Pasquill Type D.rilel r/sec(b) 600,, Pasquill Type F.leter/sec (W' wind direction v: riabiesectorwindspeed

3windspeed

2within a 22._.4-30 days (a) 33.35, Pasquill Type C, windspeed

3meter/sec (N) 33.3%'. Pasquill Type D. windspeed

3ineter/sec (c) 33.3%; Pasquill Type F, wirdspeed

2viieter/sec (d) Wind direction

33.3,:, frequency in a22.50 sector(4) Figures 2A and 213 give the groud levelrelease atmospheric diffusion factors based on theparameters given in g( 3).1.4-3 bI .1-GiAKbuPRIP IOýAO2.5 FIGURE 1O.SA-SO meters20 P'mtr2 4.0 .5A-1000

-nws O.SA-2500atr

2 meti2 O.BA-1500

motors 0.5A-3000meru p. O.5A-2000

metonus ýwccI0zIw1.54 IuIII I i ..I *10wDistance from Structure (metars)

I3 LFIGLS1i .. ._10-A7----4--Ia -... *---- -- ......0 0\44sanc 4m St .tu. ... tes1 o .* '1 %Ditne rmSrut- (eesI II _ .III1.4-5

10-II I A ... ; I .... 1 1I.", .---I.-- I--,- -.-*" i ... v -.1 -1 %ýFIGURE 2(81 -_____0-8 hours7~..,D LIUE0.1.N.. I I ' I%, ...:.7 :::::'Vt~rV~'IF-W0 * ,p -I *.X1 ,-,I- --7I..~.i... I_... ... -101631 1 .ý 10.5 b 7 1Distance from Structure (maters)1.4-6