Regulatory Guide 1.98
| ML003740259 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/1976 |
| From: | Office of Nuclear Regulatory Research |
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| RG-1.98 | |
| Download: ML003740259 (6) | |
U.S. NUCLEAR REGULATORY COMMISSION 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
A. INTRODUCTION
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. of neutr Pý o nuch 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 decompoconditions. 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 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 syste 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 perused to evaluate the adequacy of thes ste with formed to assess the radiological consequences of an offrespect 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 shortuse 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 accimaY 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 Sectio 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 S. Products with them Is not required. Methods and solutions differant from those set out n 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 & Occupational Health the issuance or continuance of apermit or 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 eamments 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. titcularly useful in evaluating the need for an early revision 2O55. Attention: ODiector. Office of Standards Development.March 1976/
fractional release of the particulate matter on the filter under upset conditions involving explosion or fir Although WASH-1338, in some cases, postulates total release of the material trapped on the HEPA filter located at the end of the delay line, this guide does not specify the fractional release of particulates to be used and the applicant should substantiate his selection of a specified fractional release. This fractional release will be evaluated on a case-by-case basis. When more information pertaining to the fractional release of particulate matter from HEPA filters under upset conditions Is available, this guide will be revised to include a specific particulate release fractio
C. REGULATORY POSITION
I. The assumptions related to the release of radioactive material from the fuel are: a. A noble gas release rate at the SJAE such that it would equal 350,000 pCi/sec after 30-min delay, for a period of 30 days preceding the postulated accident and of 100,000 ACi/sec (at 30-min delay) for times earlier than 30 days for a 3500 MWt reactor. The release rate should be scaled linearly for reactors of higher and lower power b. The isotopic composition of the noble gases may be determined from Table TABLE 1 NOBLE GAS SOURCE TERM Source Term, pCi/secApprox.30-Min.Isotope Half-Life 0 Decay Decay Xe-140 13.7s 1.1 x 106 Kr-90 33s 9.8 x Ios Xe-139 41.Os 9.8 x 105 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 Xe-138 14.0 m 3.1 x 10 7.0 x 104 Xe-135m 15.6m 9.1 x104 2.4 x 10W Kr-87 76 m 7.0 x 104 5.3 x 104 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 Kr-85m 4.4 hr 1.1 x104 1.0 x 10l Xe-135 9.2 hr 7.7 x 10' 7.4x 104 Xe-133m 2.3d 1.0x lop 1.0x 103 Xe-133 5.27 d 2.9 x 104 2.9 x 104 Xe-131m 11.9 d 5.2 x 015.2 x 101Kr-8510.76 y Total7.0 x 10' 7.0 x 10' ,4.7 x 106 -3.4 x 1052. The assumptions related to the release of radioactive material from the processing equipment are:a. The release from the SJAE is assumed to occur from a break in the delay line just downstream of 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 (automatic isolation) is provided to limit the release from this source. The release from the SJAE is assumed to be at ground level, and a delay of 5 minutes is assumed to account for transit from the SJAE to the break in the delay lin b. Activation gases and iodine are neglecte c. It is assumed that there is no deposition or decay during downwind transpor d. The total radioactive content (neglecting activation gases and iodine) of the delay line is assumed to be released over a period of 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> e. The total noble gas content of the charcoal delay beds is assumed to be released over a period of 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> f. The assumed absorption coefficients for ambient temperature systems are K(Xe) = 1000 cm3 /g and K(Kr) = 65 cm3/g and, for chilled temperature systems, are K(Xe) = 8000 cm3 g and K(Kr) = 333 cm3/ g. Condenser air inleakage is assumed to be 6 scf . The atmospheric diffusion assumptions* for ground-level releases are: a. The basic equation for atmospheric diffusion from a ground-level point source is: 1 X/Q= I Where X = the short-term average centerline value of the ground-level concentration (curies/meter3) Q = amount of material released (curies/sec) u = windspeed (meters/sec) Oy = the horizontal standard deviation of the plume (meters) [See Figure V-1, Page 48, of Ref. 21 *These diffusion assumptions should be used until adequate site meteorological data are obtained. In some cases, available information on such site conditions as meteorology, topography, and geographical location may dictate the use of more restrictive* parameters to ensure a conservative estimate of potential offsite exposures.1.98-2 oz = the vertical standard deviation of the plume (meters) [See Figure V-2, Page 48, of Re ] b. For ground-level releases, atmospheric diffusion factors used in evaluating the radiological consequences of the accident addressed in this guide are based on the following assumptions: (1) windspeed of I meter/sec; (2) uniform wind direction; (3) Pasquill diffusion category c. Figure 1 is a plot of atmospheric diffusion factors (x/Q) versus distance derived by use of the equation for a ground-level release given in regulatory position 3.a. above under the meteorological conditions given in regulatory position 3.b. abov d. Atmospheric diffusion factors for groundlevel releases 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. The volumetric building wake correction as defined in Subdivision 3-3.5.2 of Reference 3 is used with a shape factor of 1/2 and the minimum cross-sectional area of the building from which the release emanate . The following assumptions and equations may be used to obtain conservative approximations of external whole body dose from radioactive clouds: a. External whole body doses are calculated using "Infinite Cloud" assumptions; i.e., the dimensions of the cloud are assumed to be large compared to the distances that the gamma rays and beta particles trave The dose at any distance from the reactor is calculated based on the maximum ground-level concentration at that distanc For an infinite uniform cloud containing X curies of beta radioactivity per cubic meter, the beta dose rate in air at the cloud center is (Chapter 7 of Re ): P D,= 0.457Epx Where = beta dose rate from an infinite cloud (rad/ sec) EP average beta energy per disintegration (Mev/ dis) X = concentration of beta or gamma emitting isotope in the cloud (curie/m3) Because of the limited range of beta particles in tissue, the surface body dose rate from betaemitters in the infinite cloud can be approximated as being one-half this amount or: D.' = 0.23 fox For gamma-emitting material, the dose rate in air at the cloud center is:D. = 0.507EyxWhere=D: gamma dose rate from an infinite cloud (rad/sec) Eff = average gamma energy per disintegration (Mev/dis) However, because of the presence of the ground, the receptor is assumed to be exposed to only one-half of the cloud (semi-infinite) and the equation becomes: ,yD'= 0.25 EYX Thus the total beta or gamma dose to an individual located at the center of the cloud path may be approximated as:orR_ fi 0.23 EO 0.25Where 0 is the concentration time integral for the cloud (curies-sec/m3). b. The beta and gamma energies emitted per disintegration, as given in Reference 4, are averaged and used according to the methods described in Reference
D. IMPLEMENTATION
The purpose of this section is to provide information to applicants regarding the NRC staff's plans for using this regulatory guid This guide reflects current NRC staff practic Therefore, except in those cases in which the applicant proposes an acceptable alternative method for complying with the specified portions of the Commission's regulations, the method described herein is being and will continue to be used in the evaluation of submittals for operating license or construction permit applications until this guide is revised as a result of suggestions from the public or additional staff review.1.98-3 10-3 l 0 10 io : 10-5 io2io 102 1 103 104 105 Distance from Release Point (Meters) Figure 1 GROUND LEVEL RELEASE, ATMOSPHERIC DIFFUSION FACTORS1984 Building Wake Dispersion Correction Factor C" C" M I > 0~ ai '1 m CD wP oC I-b o a8-6 Q A REFERENCES1. WASH-1338, "BWR Waste Gas Treatment System Dose Evaluation Under Upset Conditions," available from Superintendent* of Documents, US. Government Printing Office, Washington, D.C. 2040 . Gifford, F. A., Jr., "Use of Routine Meteorological Observations for Estimating Atmospheric Dispersion,"Nuclear Safety, June 1961, Vol. 2, No. . TID-24190, "Meteorology and Atomic Energy -1968,' available from National Technical Information Service, Springfield, Va. 2215 . Lederer, C. M., J. J. Hollander, and I. Perman, Table of Isotopes, Sixth Edition, New York: John Wiley and Sons, Inc., 196 . International Commission on Radiation Protection, Report of Committee II on Permissible Dose for Internal Radiation, New York: Pergamon Press, 1959..198-6