Regulatory Guide 1.98

Assumptions Used for Evaluating Potential Radiological Consequences of Radioactive Offgas System Failure in Boiling Water Reactor,For Comment

ML003740259
Person / Time
Issue date:	03/31/1976
From:	Office of Nuclear Regulatory Research
To:
References
RG-1.98
Download: ML003740259 (6)

U.S. NUCLEAR REGULATORY COMMISSION

March 1976 REGULATORY GUIDE

OFFICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 1.98 ASSUMPTIONS USED FOR EVALUATING THE POTENTIAL

RADIOLOGICAL CONSEQUENCES OF A

RADIOACTIVE OFFGAS SYSTEM FAILURE

IN A BOILING WATER REACTOR

B. DISCUSSION

Section 5034, "Contents of Applications: Techni- Offgas systems of boiling water reactors are cal Information," of 10 CFR Part 50, "Licensing of designed to reduce the release of radioactive materials to Production and Utilization Facilities," requires that each the atmosphere. Both radioactive and nonradioactive applicant for a construction permit or operating license gases are dissolved in the reactor coolant of boiling water provide an analysis and evaluation of the design and reactors and are released to the steam In boiling performance of structures, systems, and components of process. The radioactive gases are activatl es such as the facility with the objective of assessing the risk to N-13, N.16, and 0-19 that are 1or d ro lements public health and safety resilting from operation of the which become radioactive in p e ugh actor facility. General Design Criterion 61, "Fuel Storage and core from the effect. oof nuch neutr Pý as

/ Handling and Radioactivity Control,t of Appendix A, the noble gases krypt xe se from the

"General Design Criteria for Nuclear Power Plants," to burnup of fuel. no ti ses are air that is

10 CFR Part 50 requires, in part, that systems which introduced into eac c with the makeup may contain radioactivity be designed to ensure ade- feedwater I in turbine condenser and quate safety under normal and postulated accident hydr n duced by radiolytic decompo conditions. sito e e nonradioactive gases are by far p tituents of gases in the coolant. Gases Radioactive offgas systems of boiling water nuc :o from the condensing steam in the main power reactors are used to permit decay of radi*r y the steam jet air ejectors (SJAE) and then gases as a means of reducing the release o di 'tive te by the radioactive offgas system.

materials to the atmosphere. The accid le o the contents from this system is a ated ' i A series of parametric studies (Ref. 1) has been per used to evaluate the adequacy of thes ste with formed to assess the radiological consequences of an off respect to the public health and safet . guide gas system accident based on the dose that an individual provides assumptions ble to the NRC staff for located at the site boundary would receive from short use in evaluating the t ological consequences of term release of the noble gases and their daughters, this postulattin i e me cases, unusual site activation gases, iodine, and particulate matter on the dharacte ti p1 de features, or other factors high-efficiency particulate air (HEPA) filters. The acci maY re ereg assumptions which will be con- dent postulated by the staff assumes release of 100% of dei ,e basis. the noble gas inventory stored in the system and a'

USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission. U.S. Nuclear Regulatory Guides ae issued to describe and make available to the pubtic Regulatory Commission. Washington. D.C. 2055. Attention: Docketing and methods acceptable to the NRC staff of implementing specific parts of the Service Section.

Commission's regulations, to delineate techniques used by the staff in evslu- The guides pie issued I the following ten broad divisions:

sting specific problems or postulated accidents. or to provide guidance to applig cents. Regulatory Guides are not substitutes tar regulations, and compliance 1. Power Reactors with them Is not required. Methods and solutions differant from those set out n S. Products

2. Research and Teat Reactors 7. Transporation the guides win be acceptable it they provide a basis for the findings requisite to 2. Fuels and Materials acUtom the issuance or continuance ofapermit or & Occupational Health fcense by the Commission. 4, Environmental and Siting se.le . Antitrust Review Comments and suggestions for improvements in these guides are encouraged S Materials and Plant Protection 10. General at all times, and guides will be revised, es appropriate, to accommodate eam ments and to reflect new information or experience. However. comments on Copies of published guides may be obtained by written request indicating the this guide, if received within about two months after Its issuance, will be per. divisions desired to the U.S. Nuclear Ragulatory Commission. Washington. D.C.

titcularly useful in evaluating the need for an early revision 2O55. Attention: ODiector. Office of Standards Development.

a. The release from the SJAE is assumed to fractional release of the particulate matter on the filter occur from a break in the delay line just downstream of under upset conditions involving explosion or fire. the SJAE. The SJAE is assumed to operate for a period of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after the accident unless a positive means Although WASH-1338, in some cases, postulates (automatic isolation) is provided to limit the release total release of the material trapped on the HEPA filter from this source. The release from the SJAE is assumed located at the end of the delay line, this guide does not to be at ground level, and a delay of 5 minutes is specify the fractional release of particulates to be used assumed to account for transit from the SJAE to the and the applicant should substantiate his selection of a break in the delay line.

specified fractional release. This fractional release will be evaluated on a case-by-case basis. When more informa b. Activation gases and iodine are neglected.

tion pertaining to the fractional release of particulate matter from HEPA filters under upset conditions Is c. It is assumed that there is no deposition or available, this guide will be revised to include a specific decay during downwind transport.

particulate release fraction.

d. The total radioactive content (neglecting

C. REGULATORY POSITION

activation gases and iodine) of the delay line is assumed to be released over a period of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.

I. The assumptions related to the release of radioactive material from the fuel are: e. The total noble gas content of the charcoal delay beds is assumed to be released over a period of 2 a. A noble gas release rate at the SJAE such hours.

that it would equal 350,000 pCi/sec after 30-min delay, for a period of 30 days preceding the postulated f. The assumed absorption coefficients 3for accident and of 100,000 ACi/sec (at 30-min delay) for ambient temperature systems are K(Xe) = 1000 cm /g times earlier than 30 days for a 3500 MWt reactor. The 3 and K(Kr) = 65 cm /g and, for chilled temperature release rate should be scaled linearly for reactors of systems, are K(Xe) = 8000 cm 3 g and K(Kr) = 333 higher and lower powers. cm 3/g.

b. The isotopic composition of the noble g. Condenser air inleakage is assumed to be 6 gases may be determined from Table I. scfm.

TABLE 1

3. The atmospheric diffusion assumptions* for NOBLE GAS SOURCE TERM ground-level releases are:

Source Term, pCi/sec a. The basic equation for atmospheric diffu Approx. 30-Min. sion from a ground-level point source is:

Isotope Half-Life 0 Decay Decay

1 X/Q= I

Xe-140 13.7s 1.1 x 106 Kr-90 33s 9.8 x Ios

41.Os 9.8 x 105 Where Xe-139 Kr-89 3.2 m 4.6 x I0s 6.9 x 102 Xe-137 3.8 m 5.3 x 10s 2.2 x 103 X = the short-term average centerline value of

4 the ground-level concentration (curies/me

3.1 x 10 7.0 x 10

Xe-138 14.0 m ter3 )

Xe-135m 15.6m 9.1 x104 2.4 x 10W

76 m 7.0 x 10 4 5.3 x 10 4 Kr-87 Q = amount of material released (curies/sec)

Kr-83m 1.86 hr 1.2 x 1W 1.0 x 10W

Kr-88 2.8 hr 7.0 x 104 6.2 x 104 u = windspeed (meters/sec)

Kr-85m 4.4 hr 1.1 x1 04 1.0 x 10l Xe-135 9.2 hr 7.7 x 10' 7.4x 1 04 Oy = the horizontal standard deviation of the Xe-133m 2.3d 1.0x lop 1.0x 103 plume (meters) [See Figure V-1, Page 48, of Xe-133 5.27 d 2.9 x 1 04 2.9 x 104 Ref. 21 Xe-131m 11.9 d 5.2 x 01 5.2 x 101 Kr-85 10.76 y 7.0 x 10' 7.0 x 10' *These diffusion assumptions should be used until adequate site Total ,4.7 x 106 -3.4 x 105 meteorological data are obtained. In some cases, available information on such site conditions as meteorology, topog raphy, and geographical location may dictate the use of more restrictive* parameters to ensure a conservative estimate of

2. The assumptions related to the release of potential offsite exposures.

radioactive material from the processing equipment are:

1.98-2

oz = the vertical standard deviation of the plume emitters in the infinite cloud can be approximated as (meters) [See Figure V-2, Page 48, of Ref. being one-half this amount or:

2] D.' = 0.23 fox b. For ground-level releases, atmospheric diffusion factors used in evaluating the radiological For gamma-emitting material, the dose rate consequences of the accident addressed in this guide are in air at the cloud center is:

based on the following assumptions:

D. = 0.507Eyx

(1) windspeed of I meter/sec;

Where

(2) uniform wind direction;

=D: gamma dose rate from an infinite cloud

(3) Pasquill diffusion category F. (rad/sec)

c. Figure 1 is a plot of atmospheric diffusion Eff= average gamma energy per disintegration factors (x/Q) versus distance derived by use of the (Mev/dis)

equation for a ground-level release given in regulatory position 3.a. above under the meteorological conditions However, because of the presence of the given in regulatory position 3.b. above. ground, the receptor is assumed to be exposed to only one-half of the cloud (semi-infinite) and the equation d. Atmospheric diffusion factors for ground becomes:

level releases may be reduced by a factor ranging from ,yD'= 0.25 EYX

one to a maximum of three (see Figure 2) for additional dispersion produced by the turbulent wake of the Thus the total beta or gamma dose to an reactor building. The volumetric building wake correc individual located at the center of the cloud path may be tion as defined in Subdivision 3-3.5.2 of Reference 3 is approximated as:

used with a shape factor of 1/2 and the minimum R_ fi 0.23 EO

cross-sectional area of the building from which the release emanate

s. or

0.25

4. The following assumptions and equations may Where 0 is the concentration time integral for the cloud be used to obtain conservative approximations of exter (curies-sec/m 3 ).

nal whole body dose from radioactive clouds:

b. The beta and gamma energies emitted per a. External whole body doses are calculated disintegration, as given in Reference 4, are averaged and using "Infinite Cloud" assumptions; i.e., the dimensions used according to the methods described in Reference 5.

of the cloud are assumed to be large compared to the distances that the gamma rays and beta particles travel.

The dose at any distance from the reactor is calculated

D. IMPLEMENTATION

based on the maximum ground-level concentration at that distance. The purpose of this section is to provide infor mation to applicants regarding the NRC staff's plans for For an infinite uniform cloud containing X using this regulatory guide.

curies of beta radioactivity per cubic meter, the beta dose rate in air at the cloud center is (Chapter 7 of Ref.

3): This guide reflects current NRC staff practice.

Therefore, except in those cases in which the applicant PD,= 0.457Epx proposes an acceptable alternative method for comply Where ing with the specified portions of the Commission's regulations, the method described herein is being and

= beta dose rate from an infinite cloud (rad/

will continue to be used in the evaluation of submittals sec)

for operating license or construction permit applications EP average beta energy per disintegration (Mev/ until this guide is revised as a result of suggestions dis) from the public or additional staff review.

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

Because of the limited range of beta particles in tissue, the surface body dose rate from beta

1.98-3

10-3 l

0 10

io :

10-5

2 io io

102 1103 104 105 Distance from Release Point (Meters)

Figure 1 GROUND LEVEL RELEASE, ATMOSPHERIC DIFFUSION FACTORS

1984

Building Wake Dispersion Correction Factor C" C" M

I >

0~ ai

'1 m

CD

wP

oC

I-b o a8

-6A

Q

REFERENCES

1968,' available from National Technical Informa

1. WASH-1338, "BWR Waste Gas Treatment System tion Service, Springfield, Va. 22151.

Dose Evaluation Under Upset Conditions," available from Superintendent* of Documents, US. Govern 4. Lederer, C. M., J. J. Hollander, and I. Perman, John ment Printing Office, Washington, D.C. 20402. Table of Isotopes, Sixth Edition, New York:

Wiley and Sons, Inc., 1967.

2. Gifford, F. A., Jr., "Use of Routine Meteorological 5. International Commission on Radiation Protection, Observations for Estimating Atmospheric Disper Report of Committee II on Permissible Dose for sion,"NuclearSafety, June 1961, Vol. 2, No. 4. Internal Radiation, New York: Pergamon Press,

1959..

-

3. TID-24190, "Meteorology and Atomic Energy

198-6