0 U.S. NUCLEAR REGULATORY COMMISSION March 1987 

)0C REGULATORY GUIDE 

r' OFFICE OF NUCLEAR REGULATORY RESEARCH 

REGULATORY GUIDE 3.59 

(Task WM 407-4) 

METHODS FOR ESTIMATING RADIOACTIVE AND 

TOXIC AIRBORNE SOURCE TERMS FOR URANIUM MILLING OPERATIONS

USNRC REGULATORY GUIDES 

Regulatory Guides are issued to describe and make available to the 

public methods acceptable to the NRC staff of Implementing specific parts of the Commission's regulations, to delineate tech

niques used by the staff In evaluating specific problems or postu lated accidents or to provide guidance to applicants. Regulatory Guides are not substitutes for regulations, and compliance with 

them is not required. Methods and solutions different from those set out in the guides 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. 

-This guide was issued after consideration of comments received from 

the public. Comments and suggestions for improvements in these 

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tion or experience. 

Written comments may be submitted to the Rules and Procedures 

Branch, DRR ADM, U.S. Nuclear Regulatory Commission, Washington, DC 20555.

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11-1 , ****41
TABLE OF CONTENTS 

SSection Page 

A. INTRODUCTION ...................................................... 3.59-1 

B. DISCUSSION ........................................................ 3.59-2 

1. Need for Source Terms ......................................... 3.59-2 

2. Identification and Description of Release Points .............. 3.59-4 

2.1 Ore Storage .............................................. 3.59-4 

2.2 Ore Crushing and Grinding ................................ 3.59-4 

2.3 Ore Processing ........................................... 3.59-6 2.4 Yellowcake Production, Drying, and Packaging ............. 3.59-6 

2.5 Tailings Impoundment ..................................... 3.59-6 

2.6 Heap Leaching ............................................ 3.59-6 

2.7 Ore Leaching in Situ ..................................... 3.59-7 

3. Use of This Guide ............................................. 3.59-7 

C. REGULATORY POSITION ............................................... 3.59-8 

1. Radioactive Particle Emission Source Terms .................... 3.59-8 

1.1 Process Emissions ........................................ 3.59-8 

1.2 Windblown Emissions ...................................... 3.59-11 

1.3 Parameter Selection ...................................... 3.59-14 

2. Radon Emission Source Term .................................... 3.59-14 

2.1 Run-of-Mine Ore Storage .................................. 3.59-15 

2.2 Hopper, Feeder, Crushing, and Grinding ................... 3.59-15 

2.3 Leaching and Extraction .................................. 3.59-15 

2.4 Yellowcake Drying and Packaging .......................... 3.59-15 

2.5 Tailings Disposal ........................................ 3.59-15 

2.6 Radon Release During in Situ Operations .................. 3.59-16 

3. Nonradioactive Emission Source Terms .......................... 3.59-20 

3.1 Nonradioactive Particulate Emission Source Terms ......... 3.59-21 

3.2 Windblown Emissions ...................................... 3.59-21 

3.3 Nonradioactive Gas Emission Source Terms ................ 3.59-22 

D. IMPLEMENTATION .................................................... 3.59-24 

APPENDIX A Principal Primary Parameters Needed to Estimate Source 

Terms for Uranium Mill Operations ......................... 3.59-25 

APPENDIX B Emission Factors ..................................... 3.59-29 

APPENDIX C Particulate Emission Reduction Factors for Ore Processing 3.59-30 

APPENDIX D Emission Factors from Fuel Combustion Without Emission 

Control ................................................... 3.59-31

iii
TABLE OF CONTENTS (Continued)

Section 

REFERENCES ............................................................ 

BIBLIOGRAPHY .......................................................... 

VALUE/IMPACT STATEMENT ................................................ 

LIST OF FIGURES 

Figure 

1 Decay Scheme for Uranium-238 ...................................... 

2 Block Flow Diagram for Uranium Milling Processes ..................

LIST OF TABLES

Table

Parameters for Calculating Annual Dusting Rate for Exposed 

Tailings Sands .................................................... 

Parameters for Calculating Example Tailings Emission Factor ....... 

Parameters for Determining Radon Release from in Situ Mining ...... 

Nonradioactive Emissions Generated by Uranium Milling ............. 

Chemical Airborne Release Factors for Acid Leach Mill .............

3.59-11 

3.59-12 

3.59-17 

3.59-20 

3.59-23

iv

Page 

3.59-32 

3.59-34 

3.59-36

3.59-3 

3.59-5

1

2 

3 

4 

5
A. INTRODUCTION 

Each licensee who processes or refines uranium ores in a milling operation 

is required by § 20.1 of 10 CFR Part 20, "Standards for Protection Against 

Radiation," to make every reasonable effort to maintain radiation exposures and 

releases of radioactive materials in effluents to unrestricted areas as low as 

is reasonably achievable, taking into account the state of technology and the 

economics of improvements in relationship to benefits to the public health and 

safety. In accordance with 10 CFR Part 40, "Domestic Licensing of Source 

Material," mill operations are to be conducted so that all airborne effluent 

releases are reduced to levels as low as is reasonably achievable. In addition, 

40 CFR Part 190, "Environmental Radiation Standards for Nuclear Power Operations," 

requires that the maximum annual radiation dose to individual members of the 

public resulting from fuel cycle operations be limited to 25 millirems to the 

whole body (radium and its daughters excepted) and to all organs except the 

thyroid, for which the dose must be limited to 75 millirems. 

40 CFR Part 192, "Health and Environmental Protection Standards for Uranium 

and Thorium Mill Tailings," is also pertinent to this guide. Subpart D of 40 CFR 

Part 192 governs the management of uranium byproduct materials under Section 84 

of the Atomic Energy Act of 1954, as amended, during and following the processing 

of uranium ore. After the closure period, this regulation limits releases of 

radon-222 from uranium byproduct materials to the atmosphere so as not to exceed 

an average release rate of 20 picocuries per square meter per second (para

graph 192.32b(ii)). In addition, 40 CFR Part 61, "National Emission Standards 

for Hazardous Air Pollutants (NESHAPs); Standards for Radon-222 Emissions from 

Licensed Uranium Mill Tailings," establishes work practices that limit the 

total size and area of new impoundments. Conditions are also provided for 

continued operation of existing impoundments. 

This regulatory guide provides guidance to applicants and licensees in 

preparing environmental reports and environmental impact statements and to the 

NRC staff in reviewing those reports. The guide addresses methods, models, 

data, and assumptions acceptable to the NRC staff for estimating airborne emis

sions of radioactive and toxic materials from various steps in uranium milling. 

The emissions and the methods for estimating the source terms for these emis

sions were identified from NRC licensing actions on uranium mills, evaluations 

and monitoring of mill operations, research programs conducted to identify and 

improve on methods for retention and stabilization of mill tailings, and methods 

and practices used by the NRC staff to generate the estimates. If alternative 

methods, models, data, or assumptions are used for estimating source terms, such 

alternatives will be reviewed by the NRC staff to determine their acceptability. 

Separate guidance provides direction on radiological effluent and environ

mental monitoring (Ref. 1), compliance with radiation protection standards 

(Ref. 2), and calculation of radiation doses from airborne materials (Ref. 3). 

Other related guides such as those for evaluating air pollution control devices 

and designing radon cover systems are being prepared. 

Any information collection activities mentioned in this regulatory guide 

are contained as requirements in 10 CFR Part 40, which provides the regulatory 

basis for this guide. The information collection requirements in 10 CFR Part 

40 have been approved under OMB Clearance No. 3150-0020.

3.59-1
B. DISCUSSION 

The milling of uranium ores involves the handling of large quantities of 

ore containing as little as a few hundredths of a percent of U308 . These ores, 

however, contain radionuclides in concentrations well above average background. 

Dusts and gas emissions result from ore handling, processing, and tailings (ore 

residues). Processing operations produce a uranium concentrate, "yellowcake," 

which when dried and packaged for shipment is a source term contributor. 

Residual wastes, including liquid and solid (tailings) wastes, are stored 

within manmade retaining structures where they are allowed to dry. Without 

proper planning and control, releases from each of these operations create the 

potential for doses to the public in excess of the applicable standards (e.g., 

40 CFR Part 190), and compliance with the standards can be achieved only by 

strict emission controls at the mill (Ref. 4). 

When environmental monitoring data are not yet available (as in the case 

of the licensing of new facilities or authorizing of significant modifications 

to existing ones), predictive models are used to evaluate the potential impacts 

of the prospective new operations (Ref. 2). Estimating radionuclide concen

trations to which nearby individuals may be exposed involves making numerous 

assumptions. In some cases, simplifications are made about important but fre

quently uncertain factors such as mill releases and atmospheric transport. 

Nevertheless, potential problem areas can be identified, and this information 

can be used to establish or modify environmental monitoring programs and 

locations. 

1. NEED FOR SOURCE TERMS 

Estimates of the quantities of radionuclides and toxic substances released 

in the airborne effluents of a uranium mill are needed for use in the licensing 

decisions by the NRC staff to predict (1) radiation doses to the public, (2) the 

extent or degree of effluent control, (3) the environmental impact of milling 

operations, and (4) the degree to which mill operations meet the as low as is 

reasonably achievable (ALARA) concept. With these predictions, the NRC staff 

can judge whether the mill operation meets Federal, State, and local criteria 

for environmental release of these materials. 

The source terms for a uranium mill vary over its lifetime. Predictions 

are made under varying operational conditions: 

Maximum throughput -- representing maximum releases from ore pads 

and mill operations. 

Year prior to tailings impoundment reclamation -- representing 

particulate and radon releases as the tailings dry out. 

Postreclamation of the tailings impoundment -- representing the 

long-term impacts. 

The radionuclides in the uranium ore are generally assumed to be in secular 

equilibrium with uranium-238. Figure 1 depicts the decay scheme for uranium-238. 

After the uranium has been leached from the ore, long-lived daughter product 

isotopes are controlling factors in the tailings. Radon is considered separately 

since it emanates both from the ore and from the tailings and is therefore

3.59-2
- 238 U 234U UUI 

92 (Ulf (Uli) 4 510•09Y t2-380lO, 

i~/ "234Pa(UX2) •, 99.85% 

Pa 1.14m 2 10 %I 

91 2 'Pa46UZ) IT a 

I 1A 6.7h ý13 

Th 2 2hTh 

90 (UX1 ) (DO Ionium 

24 5d 8 3x0 4y 

Ac a 

89__ 

2 2 6Ra 

Ra C"Radium" 

881622y 

Fr 

87 a 

Rn 2 2 2Rn 

86 (Radon) 

3.825d 

2 18At 

At a 

85 1.3s. 

21Bp o03 214P 21°Ph 

P84 (Ra A) a (Ra C*) (Ra F) 

3.05m I I I5ops 140d 

2 14B, f399.96% 210 8, 1'OO O 

83 99-97% (Ra C) a (Ra E) a 

19.7m SOd 

i 21op2 1 O; , 3 206pb 

Pb (Ra B) 0.04% (Ra D) 5 K 10.5% (Ra G) 

82 26.8m 22y Stable 

TI 

210TI ( 

81 (Ra C") (Ra E" 

81 1.32m 4 23m

Figure 1. Decay Scheme for Uranium-238

3.59-3
released to the environment independently from other radioisotopes of the 

uranium decay chain. Thus, since models used in predicting radiological and 

environmental impact include the impacts of the short-lived decay products 

from longer-lived radionuclides, source term estimates for natural uranium, 

uranium-238, thorium-230, radium-226, lead-210, and radon-222 provide a suffi

cient base. Since the uranium-235 in natural uranium represents only about 0.7 

percent of natural uranium, radionuclides from its decay chain contribute only 

a small fraction of the total radioactivity for natural uranium and thus are 

not included in the source term estimates. 

Uranium ores usually contain small amounts of toxic elements such as arsenic, 

barium, cadmium, chromium, lead, mercury, selenium, and silver. The release of 

these elements is also included in source term estimates. 

2. IDENTIFICATION AND DESCRIPTION OF RELEASE POINTS 

Radioactive and nonradioactive dusts and gases are released from several 

steps in uranium mill processes. Figure 2 shows the major processing steps and 

the airborne release sources for a typical uranium mill. These steps and sources 

are described in the following sections. Methods for estimating quantities 

released are discussed in the regulatory position of this guide. 

2.1 Ore Storage 

Information needed by the NRC staff to estimate source terms depends in part 

on operational procedures that determine the quantity of ores stored at the 

mill, climatic conditions, need for blending widely varying ore compositions, 

and general requirements for backlogging. In addition, moisture content, which 

is a function of mine source, age in storage, and climatic conditions, con

tributes to the degree to which ore dust is dispersed. The ore may dry out in 

the stockpile, making it more susceptible to dispersion. The quantity of dust 

that may be dispersed may be controlled by keeping the stockpile wet or spraying 

it with chemical suppressants as an interim measure. This will have little 

effect on radon release from the ore storage unless the ore is kept saturated 

and not allowed to dry out. 

2.2 Ore Crushing and Grinding 

Detailed information on the steps and controls used in ore crushing and 

grinding is needed by the NRC staff because ore dust containing radioactivity 

can be released to the environment during these operations. Ore received from 

the mine is blended and successively reduced in size by, for example, jaw 

crushers, cone crushers, and ball mills, to permit ready leaching of the 

uranium. Dust generated during these process steps is not generally confined 

within the equipment, although offgases from the smaller-sized reduction equip

ment are usually scrubbed. The ore is transferred between stations by belt 

conveyors, usually canopied, in enclosed structures where entrained particles 

are filtered out before the air is discharged from stacks. The last stages of 

grinding are usually done wet to eliminate the free flow of airborne particu

lates from the finely ground product. 

Some of the radon from decay of radium-226 in the ore is released during 

the ore handling and crushing activities. The fraction of radon released varies, 

depending on the physical characteristics and chemical composition of the

3.59-4
Ore Raffinate Decanted Pond Water 

Decanted Pond Water From Solvent Floeculant to Evaporation, Pond 

to Evaporation Pond Extraction Water and/or Process Rfch"l 

and/or Process Recycle 

Flocclantre 

Sto age Countercurrent 

Filtration Decantation Fili 

TT(CCD) Fi t 

TalnsSodium Ami ne 

SadSime. S 'yd ,nd iHydroxide Kerosene Tailings. 

Liqidas ton , Alcohol Sand, Slime, 

Liquid Wastes to 

Flue Precipitation C rSolvent Tailings Pond 

Crasin Extraction 

0 

Recarbonator Filtration 0 Rn u G 

Carbonated Liquor D Grinding Stripping 

to Grinding/Leaching P 

Drying and Packaging Leachant 

of Yellowcake 1 Amoi Pr 

Product ' Leaching Precipitation 

Alkaline Leanch 4 I. Sulfuric Acid Leach 

Circuit Circuit 

G Major Sources of Dust Contamination 

Major Sources of Nonradioactive Gaseous Pollutants 

- Major Sources of Radon Release

Figure 2. Block Flow Diagram for Uranium Milling Processes

/
ore. Although radon-222 (the primary radon isotope released from uranium ores) 

is chemically inert and has a short half-life (3.8 days), its decay products 

reach secular equilibrium quickly and are dispersed and are therefore subject 

to being breathed in by man and animals. 

2.3 Ore Processing 

For ore processing operations conducted in solutions or slurries, particu

late emissions are negligible and therefore present little hazard. However, 

nonradioactive gaseous effluents consisting of carbon dioxide, sulfur dioxide, 

water vapor, and sulfuric acid mist from the leaching step, some of which are 

toxic, could be released. Organic chemical vapors consisting of kerosene with 

small amounts of amine and alcohol are released from the open solvent extrac

tion settling chambers. Ion exchange processes are enclosed and chemical vapor 

releases are negligible. 

2.4 Yellowcake Production, Drying, and Packaging 

The potential for particulate releases during uranium concentrate (yellow

cake) production depends on the degree to which the product is dried or cal

cined and on the effectiveness of offgas filtration. Particulate releases 

from the drying, calcination, and packaging steps are dependent on the control 

used to prevent release of excessive amounts of uranium in the offgases. Off

gases are scrubbed or filtered prior to release via a stack. 

Since the ore processing steps reject nearly all the radium to the tailings, 

very little radon is released during the production of yellowcake. However, 

yellowcake drying and packaging present a potential for particulate release 

and are therefore of concern in terms of this guide. 

2.5 Tailings Impoundment 

The processing of ore in uranium mills generates radioactive and nonradio

active waste generally referred to as tailings, which consist of the majority 

of the ore solids, process additives, and water. The industry uses different 

methods for storage of these tailings. The tailings together with the earthen 

dams or cells that contain these wastes are referred to as impoundments, and 

the impounded liquids are called tailings ponds. Depending on the procedure 

for disposing of the tailings in the impoundments, the significant airborne 

releases consist of the coarse sand solids, the finer slime solids, and the 

radon gas. Fugitive dust can be reduced by frequent wetting, application of 

chemical suppressants, or other physical strategies. Radon releases are more 

difficult to control because of the nature of radon gas. Interim reclamation, 

increased water cover, and below-grade design are some of the means by which 

radon release can be attenuated. 

2.6 Heap Leaching 

Heap leaching involves leaching low-grade ore (<0.04% U308) either by 

gravitational flow of the leachant through an open pile or by flooding a 

confined ore pile (Ref. 4). The leachate is treated on site by ion exchange 

or solvent extraction, and a crude yellowcake that may be shipped to a nearby 

mill for refinement is precipitated. When the ore dumps are reasonably near 

a mill, acid solutions from the mill may be used for the heap leaching and 

returned to the mill circuit for processing (Ref. 5).

3.59-6
Heap leaching has little impact on airborne environmental impacts. 

Radon-222 and its decay products are released and dispersed. The leached ore 

may be mixed with mill tailings. If the tailings are maintained as an isolated 

leached ore pile, control of fugitive dust is required. 

2.7 Ore Leaching in Situ 

Low-grade. ores can be leached in situ by using a network of wells to 

inject a leach solution into the ore formation, mobilizing the uranium through 

formation of a soluble complex uranium salt, and removing the pregnant solution 

from the ore body through production wells. The uranium that has been made 

soluble is recovered by uranium mill processing operations producing yellowcake. 

Radioactive airborne releases from in situ leaching are primarily limited 

to radon emanations from the solution resulting from the leaching of the ore. 

Some releases may occur from yellowcake dryers and packaging if such operations 

are present on site. Airborne releases from the chemical processing steps are 

comparable to those encountered during conventional mill operations. 

Solid wastes that require controlled disposal are generated; however, the 

volume produced is much less than that created by conventional uranium mining 

and milling. Dried evaporative ponds can contain residual radionuclides and 

toxic minerals leached along with the uranium. If disposed to the tailings 

pond at a conventional mill, the waste solutions will be only a minor increment 

to the tailings impoundment system. 

3. USE OF THIS GUIDE 

Present NRC staff practice for estimating radioactive airborne release 

rates (source terms) from uranium milling facilities involves the characteriza

tion of such releases by radionuclide, particle size, and density (Ref. 4). 

These data, when combined with a meteorological dispersion model representing 

the annual average meteorological conditions of the mill site, provide a basis 

by which the NRC staff can estimate concentrations, which in turn are used to 

calculate radiation doses as described in Reference 3. 

The primary calculational tool used by the NRC staff in evaluating the 

radiological impact of uranium milling operations is the MILDOS code (Ref. 6). 

As used by the NRC staff, the MILDOS code has only five primary radionuclides 

in the uranium-238 decay chain that are treated explicitly as source terms. 

These radionuclides are uranium-238, thorium-230, radium-226, lead-210, and 

radon-222. Release rates are required for these radionuclides for each poten

tial release source. The code accounts for releases and ingrowth of other 

radionuclides, assuming secular equilibrium. For radon-222 decay products, which grow in during transport of radon-222 from the site, the code calculates 

the resulting ingrowth. These radon-222 daughters include polonium-218, 

lead-214, bismuth-214, lead-210, and polonium-210. 

This guide provides technical guidance concerning methods, models, data, 

and assumptions acceptable to the NRC staff for estimating airborne emissions 

of radioactive and toxic materials from various steps in uranium milling. If 

alternative methods, models, data, or assumptions are used in estimating source 

terms, such alternatives will be reviewed by the NRC staff to determine their 

acceptability.

3.59-7
C. REGULATORY POSITION 

Methods described below for estimating radioactive and nonradioactive 

source terms from uranium milling operations and tailings disposal reflect the 

approaches used by the NRC staff. Certain bases and assumptions used in making 

acceptable calculations are identified and explained. Nonradioactive particulate emission source terms may be estimated in the same way as radioactive particulate emissions, with an estimate of the toxic element composition of the ore (or 

tailings). Estimates of nonradioactive gas emissions from process operations 

are based on raw material and fuel uses. Principal parameters needed to estimate 

source terms are listed in Appendix A to this guide. 

1. RADIOACTIVE PARTICLE EMISSION SOURCE TERMS 

The major particle emission sources at a uranium mill include ore handling, 

ore storage, crushing and grinding, yellowcake production (especially drying and 

packaging), and tailings piles. Much of the data useful in calculating source 

terms is enumerated in Appendix A to Reference 3 and in Appendices A, B, and C 

to Regulatory Guide 3.8, "Preparation of Environmental Reports for Uranium Mills." 

Information from the applicant needed by the NRC staff to estimate source terms 

is listed in Appendix A to this guide. The general method for calculating 

source terms is to multiply together the normalized emission rate, contaminant 

content, emission control factor, and processing rate for each process being 

evaluated. The following discussion shows typical equations and example calcula

tions used by the NRC staff for process and windblown emissions typical of 

uranium mills. 

1.1 Process Emissions 

Processes releasing particles include ore handling, grinding and crushing, 

conveying, and yellowcake drying and packaging. 

The basic equation is: 

S = MCEN(1 - R) (1) 

where 

S is the source term, quantity/time, e.g., kg 2 38U/hr; Ci 238 U/yr; 

M is the process rate, mass/time, e.g., metric ton ore/d; 

C is the contaminate concentration, percent, pCi/g uranium, or 

ppm of toxic elements in ore; 

E is the emission factor for process, dust released per metric ton 

of ore dumped to the grizzly; 

N is the unitless activity enrichment ratio; and 

R is the unitless emission control factor. 

The unitless activity enrichment ratio, N, expresses the extent to which 

the contaminant concentration is higher in the suspended airborne particles that 

are larger than 20 pm in diameter than in the bulk material. The NRC staff uses

3.59-8
N = 2.5, conservatively based on measured values (Refs. 7 and 8) in which the 

content of uranium-238 and its progeny in fines* was found to be up to 2.5 times 

higher than the content in the bulk ore. The emission factor, E, is tabulated 

for various common operations in Appendix B to this guide. The unitless reduc

tion factor, R, is tabulated in Appendix C for various control measures. Examples 

of calculating particle source terms follow. 

1.1.1 Example Calculation: Crushing 

The source terms for radionuclides in the chain for uranium-238 decay are 

the same as that for uranium-238 since they are in secular equilibrium. The 

following parameters are supplied by the applicant: 

M = 145,000 MT processed/yr 

C = 420 pCi 2 3 8U/g bulk ore 

N = 2.5 times greater 2 3 8U content in dust than in bulk ore 

The emission control device is a baghouse with an expected efficiency of about 

80 percent for the dust produced by the operation. The applicant has determined 

that the moisture content of the stored ore at the time of crushing is 7 wt-%. 

Because tertiary crushing is not used, the estimated uncontrolled emission factor, 

E, from Appendix B is 0.16 lb/ton. The estimated uranium-238 source term, using 

Equatioh (1), is: 

S = 145,000 MT/yr x 420 pCi/g x 0.16 lb/ton x 2.5 x (1 - 0.80) 

x 1.1025 ton/MT x 454 g/lb x l0-12 Ci/pCi 

= 2.4 x 10-3 Ci/yr 

1.1.2 Example Calculation: Truck Unloading to Ore Pad 

The ore processing rate, M, is 193,000 MT/yr. The bulk ore content, C, of 

uranium-238 and progeny in secular equilibrium is 435 pCi/g. The ore is end

dumped from a truck. No control measures are used. Thus, the emission factor, 

E, is 0.04 lb/yd3 , based on Appendix B. The bulk density of the ore is 1.5 ton/yd3 . The dust/ore specific activity ratio, N, is 2.5, and the source term for uranium-238 

and progeny, using Equation (1), is: 

S = 193,000 MT/yr x 435 pCi/g x 0.04 lb/yd3 x 1 yd3/1.5 ton 

x 1.1025 ton/MT x 454 g/lb x 2.5 x 10-12 Ci/pCi 

= 2.8 x 10-3 Ci/yr 

1.1.3 Example Calculation: Fine Ore Storage 

In this case, the fine ore is conveyed to and from the fine ore storage area 

for a total of four conveyor transfers. Ore is handled at a rate of 135,000 MT/yr, 

and the bulk uranium-238 and progeny content is 350 pCi/g. The 2.5 dust/ore 

activity ratio is applied. The operation occurs in an enclosed structure with 

a reduction factor of 75 percent based on engineering judgment (Appendix C). The 

emission factor for each transfer is 0.023 lb/ton (Appendix B). The combined 

emission factor for the fine ore storage conveying is: 

*<100 pm in diameter.

3.59-9
E = 4 transfers x 0.023 lb/ton per transfer = 0.092 lb/ton

The uranium-238 and progeny source term is then: 

S = 135,000 MT/yr x 350 pCi/g x 0.092 lb/ton x 1.1025 ton/MT 

x 454 g/lb x 10-12 Ci/pCi x (1 - 0.75) x 1 = 5.4 x 10-2 Ci/yr 

1.1.4 Example Calculation: Yellowcake Drying and Packaging 

Releases from the stack for offgases from the yellowcake drying and pack aging operations are quite variable (Ref. 9). Variability among mills and uniqueness of each mill are important factors. Also, changes in operating parameters can change emission rates over a period of time. Maintenance and repair work, malfunction of the exhaust air cleanup systems, and intermittent shutdown and startup are among other variables that can have an impact on the emissions from this operation. The NRC staff bases its estimates on measure

ments made at operating mills (Ref. 9) and the release assumed for the model mill in the GEIS on uranium milling (Ref. 4), which in turn were based on recommendations found in Reference 10. Accordingly, the staff estimates that 0.1 percent of yellowcake produced is released from the stack in the drying and packaging operations based on EPA-measured releases at six mills. 

For a mill with a yellowcake production of 200 MT/yr, of which 90 percent is U3 08 , the estimated release from the yellowcake stacks would therefore be: 

S = 200 MT/yr x 0.90 x 106 g/MT x 3.33 x 10-7 Ci/g 2 38 U 

x 0.85 g U/g U3 08 x 0.001 

= 5.1 x 10-2 Ci 2 3 8U/yr 

In the absence of firm data, the NRC staff assumes that 0.5 percent thorium and 0.1 percent lead and radium are processed along with the yellowcake. Since the decay products of uranium in the ore are in secular equilibrium with the uranium, the radioactivity of thorium-230 released from the stack is estimated to be 0.005 of the radioactivity of the uranium released. Thus, the thorium release for the example mill is calculated to be: 

S = 5 x 10-2 Ci 2 3 8U/yr x 0.005 

= 2.5 x 10-4 Ci 2 3 °Th/yr 

The lead and radium release is: 

S = 5 x 10-2 Ci 2 3 8 U/yr x 0.001 = 5 x 10-5 Ci/yr of either 2 1°Pb or 226Ra 

The NRC staff prefers reliable monitoring data when available. Renewal of licenses or modification of licenses are examples of when such data may be submitted by the licensee. 

It is noteworthy that particulate releases from the yellowcake production step occur almost entirely in drying and calcining operations. If the yellow cake product were to be packaged as a slurry or as a damp filter-cake product, particulate emissions from this operation would be negligible.

3.59-10
1.2 Windblown Emissions 

Fugitive dust varies significantly from mill to mill. Meteorological 

- conditions (wind, rainfall, temperatures), exposed surfaces, ore compositions 

and physical characteristics, particle size distributions, site characteris

tics, and operational procedures are among the factors that affect the degree 

to which dust is blown about. 

1.2.1 Example Calculations: Tailings Pile 

The NRC staff estimates windblown particle emissions using the method 

described in MILDOS (Appendix A to Ref. 6). In using this approach, the 

emission factor, Ew, is calculated as follows: 

Ew 3.156 x 10 (2) 

= 0.5 x RsF( s 

where 

Ew is the annual dust loss per unit area, g/m 2 -yr; 

F is the annual average frequency of occurrence of wind speed 

group s, dimensionless, obtained from joint relative frequency 

wind distribution for the site; 

R s is the resuspension rate for tailings sands at the average wind 

speed for wind speed group s, for particles ! 20 pm in diameter, 

g/m 2.sec; 

3.156 x 107 is the number of seconds per year; and 

0.5 is the fraction of the total dust loss constituted by particles 

• 20 pm in diameter. 

The MILDOS-calculated resuspension rates for tailings sands are tabulated in 

Table 1 for each wind speed group, s. 

Table 1 

Parameters for Calculating Annual Dusting Rate for Exposed Tailings Sands 

Wind Speed Average Wind Dusting Rate 

Group, knots Speed, mph (Rs), g/m 2 "sec 

0-3 1.5 0 

4-6 5.5 0 

7-10 10.0 3.92 x 10-7 

11-16 15.5 9.68 x 10-6 

17-21 21.5 5.71 x 10-5 

21+ 28.0 2.08 x 10-4

3.59-11
The source term for each tailings beach area is then calculated as: 

S = E w ACfN(1 - R) 

where

(3)

E w is the emission factor in g/m2 .yr, as calculated above; 

A is the exposed surface area (of the beach at the tailings 

impoundment or of the ore pad, for example) in mi2 ; 

C is the contaminant concentration in percent, pCi/g of 

uranium, or ppm for toxic elements in the initial ore; 

N is the unitless activity enrichment ratio of concentration 

in dust/bulk material; 

R is a unitless control factor depending on the degree of control 

applied (see Appendix C); and 

f is the fraction of a particular contaminant present. 

The first example below estimates the radium-226 release from an abandoned 

tailings pile temporarily stabilized with a synthetic polymer coating sprayed 

onto the sand (R = 0.85, from Appendix C). The pile area, A, is 53 acres and 

contains 99.5 percent of the 300 pCi 2 2 6Ra/g originally in the ore. The annual 

average frequency of occurrence of each wind speed group, resuspension factor, 

and their product are shown in Table 2. 

Table 2 

Parameters for Calculating Example Tailings Emission Factor 

Wind Speed Resuspension Ratea FrequencYbof Product 

Group, knots Rs, g/m 2 -s Occurrence, Fs Rs x F g/m 2 -s

0 

0 

3.92 x I0-7 

9.68 x 10-6 

5.71 x I0-5 

2.08 x I0-4

0.4035 

0.1942 

0.0501 

0.0089

0 

0 

1.58 x I0-7 

1.88 x 10-6 

2.86 x 10-6 

1.85 x 10-6 

= 6.75 x 10-9

aDusting rate of a function of wind speed is computed by the MILDOS code 

(Ref. 6). 

bWind speed frequencies obtained from annual joint frequency data for the 

site.

3.59-12

0-3 

4-6 

7-10 

11-16 

17-21 

21+
The calculated emission factor (annual average dust loss rate) is: 

Ew = 3.156 x 107 s/yr x 6.75 x 10-6 g/m 2 .s/(0.5) = 4.3 x 102 g/m 2 -yr 

The radium-226 source term, using Equation (3), is therefore: 

S = 4.3 x 102 g/m 2 .yr x 53 acres x 4047 m2 /acre x 300 pCi 2 2 6Ra/g x 10-12 Ci/pCi x 0.995 x 2.5 x (1_- 0.85) = 1.0 x 10-2 Ci 2 2 6Ra/yr 

The second example considers an active tailings impoundment at the same site (same wind frequency occurrence, as above). Beaches are maintained wet, 

as needed (R = 25%, Appendix C), and are approximately 50 percent of the total impoundment area of 45 acres. Using Equation (3) and a specific activity con centration ratio of N = 2.5, the radium-226 source term is estimated to be: 

S = 4.3 x 102 g/m 2 -yr x 45 acres x 0.50 x 4047 m2 /acre 

x 300 pCi 26Ra/g x 10-12 Ci/pCi x 0.995 x 2.5 x (1 - 0.25) 

= 2.2 x 10-2 Ci 2 2 6Ra/yr 

For an active below-grade impoundment system, the NRC staff usually estimates that particulate releases during operation are negligible since solid tailings material is covered by tailings solution. Therefore, few, if any, exposed solids are subject to wind erosion. 

1.2.2 Example Calculations: Ore Pad 

Particulates on the ore pad subject to wind erosion are less than those from tailings piles since the ore has not yet been ground. The NRC staff's approach is to base the fugitive dust release from the ore pad on an.emission factor estimated to be 10 percent of that calculated for the tailings pile. Equation (2) for ore pads is thus modified to read: 

Ew= 0.1 x 3.156 x 107 (4) = ~0.5 x Rs(4 

Thus, for the site with the wind frequency occurrence described above, the annual average dust loss rate is estimated to be: 

Ew = 0.1 x 3.156 x 107 s/yr x 6.75 x 10-6 g/m 2 -s/(0.5) = 43 g/m 2 .yr 

The source term for an ore pad of 10 acres containing ore with 300 pCi 2 3 8U/g, using Equation (3) and a specific activity concentration ratio of N = 2.5 and without any control (R = 0), is thus estimated to be: 

S = 43 g/m 2 .yr x 10 acres x 4047 m2 /acre x 300 pCi/g x 10-12 Ci/pCi x 2.5 

= 1.3 x 10-3 Ci 2 3 8U/yr 

Since the progeny from uranium-238 are in secular equilibrium in the ore, the 

source terms for uranium-234, thorium-230, radium-226, lead-210, and polonium-210 would also be 1.3 x 10-3 Ci/yr. Any control such as keeping the ore pile wet would reduce fugitive dust by the appropriate factor as shown in Appendix C.

3.59-13
1.3 Parameter Selection 

Production rate, pile areas, description of operation, and contaminant 

specie contents are reasonably well-identified parameters used in particle 

source term measurements. Emission factors and emission control reduction 

factors are less certain parameters. The NRC staff realizes that many of these 

factors are difficult to measure, e.g., the tailings resuspension factor and 

the control factor for chemical dust suppressants. Factors measured by the 

applicant or by others in the regulatory and emission control fields may be 

used. Examples of such measured values include the efficiency of emission con

trol devices installed in stacks and the historical emission measurements at an 

applicant's yellowcake dryer stack. The NRC staff prefers to use reliably meas

ured values for these parameters. Design parameters are generally chosen only when other data are unavailable. An adjustment should be made for expected 

performance, and minimum performance should be noted. The following informa

tion sources are used in source term estimates: 

1. Applicant's measurements, 

2. Default values listed in this regulatory guide, 

3. Other measurements or estimates shown by the applicant to be 

acceptable, 

4. Manufacturers' specifications, and 

5. Best engineering judgment. 

Section 9 of the GEIS for uranium mills (Ref. 4) indicates that tailings surface control and an efficient yellowcake dust collection system are the major 

factors necessary to maintain acceptable airborne emissions. 

Alternative methods for treating mill tailings in ways to reduce the potential of fugitive dust are discussed in Sections 8 and 9 of Reference 4. Various 

strategies can be used for controlling dust, including vegetative cover; gravel, crushed rock, or riprap cover; manmade covers and sealants; and combinations of 

the above. Some of these are also useful in reducing radon emissions, as 

discussed below. Progressive reclamation, i.e., the practice of drying up and 

covering tailings piles in sections as they are filled, is an effective method 

for reducing airborne particulates from the tailings and is used by several 

mills in the United States. 

2. RADON EMISSION SOURCE TERM 

Processing of uranium ore and subsequent tailings disposal presents pathways for release of radon to the environment. The major pathways for radon release 

occur from ore storage, ore crushing and grinding, and the mill tailings disposal site. The amount of radon released through each of the pathways depends on the 

ore type, ore storage procedures, crushing or grinding operations, and tailings 

disposal practices. The factors affecting radon common to all the source path

ways are (1) radium content of ore, (2) emanating power (coefficient) of ore or 

tailings, (3) radon diffusion coefficient in ore stockpiled, ground ore, and 

tailings, and (4) physical characteristics, including configuration of ore

3.59-14
storage and tailings pile. The following sections describe methods used to 

estimate the release of radon from ore storage, crushing and grinding, leaching 

and extraction, and the tailings impoundment. Example calculations illustrate 

the calculation procedures. 

2.1 Run-of-Mine Ore Storage 

Ore received at the mill is stockpiled on ore storage pads in sufficient 

quantity to provide for a continuous supply to the mill. Radon release from 

the ore storage area depends on (1) the characteristics of ore, (2) the area 

and thickness of the ore pads, and (3) the storage time. The quality of the 

ore received varies with respect to ore concentration, grade, and size. Selec

tion of ores from the stockpile is generally made to allow for a reasonably 

consistent composition as feed to the mill chemical processes. 

2.1.1 Estimation Using Flux Factor 

In the majority of cases, the NRC staff estimates radon release by using a 

specific radon flux factor of 1 pCi 2 2 2 Rn/m 2 -s per pCi/g of 2 26 Ra. Only the area 

of the ore stockpile and the average radium content need be known to make the 

calculation of yearly release. An example calculation for an ore pad covering 

3 hectares (7.5 acres) and containing an average radium-226 concentration of 

300 pCi/g is: 

(1 pCi 2 2 2 Rn/m 2 -s)/(pCi/g 2 2 6 Ra) x 300 pCi 2 2 6Ra/g x 3 ha 

x 104 m2 /ha x 3.156 x 10 s/yr x 10-12 Ci/pCi 

= 285 Ci 2 2 2Rn/yr 

2.2 Hopper, Feeder, Crushing, and Grinding 

Blended run-of-mine ore from the storage pile is fed to the crushing and 

grinding circuits. Because of the short residence time in the crushing and 

grinding circuits, only a small amount of radon will be released. It is esti

mated that less than 10 percent of the radon in the ore will be released during 

crushing and grinding (Ref. 7). The radon released during the ore crushing and 

grinding is estimated as follows: 

135,000 MT/yr x 350 pCi/g x 106 g/MT x 10-12 Ci/pCi x 10% = 4.73 Ci/yr 

2.3 Leaching and Extraction 

Leaching and extraction are wet processes and again require short residence 

times; therefore, radon-222 release is estimated not to be significant. 

2.4 Yellowcake Drying and Packaging 

No significant radon release occurs since only NO.1 percent of the original 

radium-226 in the ore is found in the yellowcake. 

2.5 Tailings Disposal 

The major waste discharged from a mill is the tailings slurry, which contains 

the barren ore plus process solutions. The tailings liquid contains residual 

acid or residual alkaline (depending on the leaching agent) and dissolved solids

3. 59-15
from the leaching steps. Some of the liquid (.1/3) may be returned to the mill 

for reuse. The tailings consist of sand, slimes, and a mixture of sand and 

slimes, which are the sources of radon. Estimates of radon release are based 

on about 99.9 percent of the radium-226 remaining with the tailings unless 

measurements that indicate lesser amounts of radium are available. 

Radon will be released from the exposed tailings. During the active period 

of the tailings pile, the impoundment is assumed to have areas of saturated 

tailings (slimes) mostly covered with raffinate solution and areas of relatively 

dry tailings (beach sands). The factors affecting the release of radon from the 

tailings pile are basically the same as those for the ore storage pads, including 

(1) emanating power, (2) diffusion coefficient, (3) moisture, (4) density, and 

(5) tailings thickness. The basic difference, however, is that during the active 

life of the tailings pile there are two areas on the tailings piles: the drier 

beach area and the saturated slimes area, which is generally covered with the 

raffinate pond. The tailings in the beach areas generally contain less radium 

than the tailings in the slimes areas (Ref. 4). The relative amounts of slimes 

and sands or mixtures on the surface of a tailings pile depend not only on the 

quantity of sands and slimes but also on the procedure used to distribute the 

tailings on the pile. The beach areas have tailings with a higher radon diffusion 

coefficient resulting from the larger particle sizes and lower moisture contents. 

The slimes areas have tailings with finer particle sizes and higher moisture 

content, which reduce the radon coefficient. 

2.5.1 Estimation Using Flux Factor 

The condition (slimes/sands distribution, moisture content, fraction 

covered by solution raffinate, etc.) of the tailings impoundment is variable and 

complex and difficult to accurately predict. In general, the NRC staff uses the 

specific flux factor of 1 pCi 2 22 Rn/m 2 -s per pCi Y26Ra/g to estimate the radon 

release from the tailings. Thus, for a hypothetical tailings pile containing 

an average of 300 pCi 2 2 6 Ra/g and covering 50 hectares (124 acres), the annual 

radon-222 release is: 

(1 pCi 2 2 2 Rn/m2.s)/(pCi 2 2 6Ra/g) x 300 pCi 2 2 6Ra/g x 50 ha x 104 m2 /ha 

x 3.165 x 107 s/yr x 10-12 Ci/pCi 

= 4750 Ci/yr 

2.6 Radon Release During in Situ Operations 

The major source of radon release during in situ mining operations is the 

lixiviant which, when exposed to the atmosphere, will release radon. The release 

will occur when the lixiviant arrives at the process recovery surge tanks, ion 

exchange tanks, or columns or evaporation ponds. 

Aquifer restoration, which includes ground-water sweeping and clean water 

circulation, is also a source of radon that must be considered. 

The key parameters used to determine the average annual radon release are 

listed in Table 3.

3.59-16
Table 3 

Parameters for Determining Radon Release 

from in Situ Mining 

Ore grade, % U3 08 

Concentration in ore 

Mined area per year, m2 

Average lixiviant flow rate, L/min 

Average restoration flow rate, L/min 

Number of operating days 

Formation thickness, m 

Formation porosity 

Rock density, g/cm3 

Residence time for lixiviant, d 

Residence time for restoration solution, d 

Emanating power of ore 

In order to determine a reasonably conservative annual radon release, it 

is assumed that one mining unit will be mined, one unit soaked, and one unit 

restored during the year. The radon release from these operations is discussed 

in the following paragraphs. 

2.6.1 Radon Release from Leaching 

If the radium-226 content of the ore has not been measured, it is assumed 

that the uranium-238 is in equilibrium with all its daughters. The radium-226 

and radon-222 concentration present in the ore would therefore be 2820 pCi/g 

per % U3 08 . The radon emanating power is assumed to average 0.2 unless other

wise determined. The radon release at equilibrium, G, in 1 m3 of rock may be 

calculated using Equation (4). 

G = RpE(1 - p)/p x 10-6 (4) 

where 

G is the radon release, Ci/m 3 ; 

R is the radium content, pCi/g; 

p is the rock density, g/cm3 ; 

E is the emanating power; and 

p is the formation porosity. 

The yearly radon release, Y (Ci/yr), may be calculated using Equation (5). 

Y = GM&D x 1.44 (5)

3.59-17
where 

G is the radon release at equilibrum, Ci/m 3 of rock; 

M is the lixiviant production rate, L/min; 

& is the equilibrium factor for radon; and 

D is the production days per year. 

The equilibrium factor, &, equals 1 - e-xt where X is the radon decay 

constant and t is the residence time. This is a conservative estimate since 

it assumes that the radon immediately goes into the lixiviant solution. 

2.6.2 Radon Release from Soaking 

In addition to the release of radon from the lixiviant dissolution, it is 

estimated that one pore volume of'nonproduction solution will be removed as each 

mining unit is put into service. The startup radon release, S, may be calculated 

using Equation (6). 

S = GATp (6) 

where 

G is the radon release at equilibrium, Ci/m 3 of rock; 

A is the area of mining unit, mi2 ; 

T is the thickness of ore, m; and 

p is the formation porosity. 

For a mining unit that will be soaked for 1 year, it is also assumed that 

one pore volume of mining solution will be removed when the lixiviant is added. 

Therefore, the release of radon would be the same as during the startup. 

2.6.3 Radon Release During Restoration 

The annual radon released during restoration, r (Ci/yr), is calculated 

using Equation (7). 

r = GN&D x 1.44 (7) 

where 

G is the radon release at equilibrium, Ci/m 3 of rock; 

N is the restoration solution rate, L/min; 

s is the equilibrium factor; and 

D is the restoration days per year.

3.59-18
In a similar manner to startup, it is assumed that one pore volume of solution 

will be removed before restoration begins. 

2.6.4 Example Calculation: Radon Release from an in Situ Mine 

The following is a sample calculation of the total release of radon from 

a hypothetical in situ uranium mining operation. 

Assumptions: 

Ore Grade 0.1% U3 08 

Average area to be mined 10 acres 

Average lixiviant flow 4000 L/min 

Average restoration flow 400 L/min 

Operating days per year 365 

Formation thickness 3 m 

Formation porosity 0.3 

Rock density 1.8 g/cm3 

Residence time for lixiviant 5 days 

Residence time for restora

tion solution 10 days 

Emanating power 0.2 

From mining and soaking, the radon release per cubic meter of the rock is esti

mated using Equation (4). 

The radium content, R, is first calculated assuming secular equilibrium between the uranium-238 and radium-226. 

R = 3.33 x 105 pCi U2 38/g U x 0.001 g U308/g ore x 0.85g U/g U3 08 

= 28.3 pCi/g ore 

Next the radon release, G, is calculated. 

G = RpE(1 - p)/p 

= 28.3 pCi/g x 0.1% U3 0 x1.8 g/cm3 x 106 cm3 /m3 x 0.2 

x (1 - 0.3)/0.3 x 10-12 Ci/pCi = 2.4 x 10-6 Ci/m 3 

Next the yearly release of radon is calculated using Equation (5). 

Y = GMeD x 1.44 

S= I - e"(O' 18 1 /d)(5d) - 0.6 

Y = 2.4 x 10-6 Ci/m 3 x 4000 L/min x 0.6 x 365 d/yr x 1.44 

= 3.0 Ci/yr 

The radon released from the startup solution and soaking is calculated 

using Equation (6). 

S = GATp 

= 2.4 x 10-6 Ci/m 3 x 10 acres x 4074 m2 /acre x 3 m x 0.3 

= 0.088 Ci/yr 

The total release of radon from the startup solution, production lixiviant, 

and soaking solution is: 

3.59-19
Startup solution 

Production 

Soaking solution

0. 09 Ci/yr 

3.0 Ci/yr 

0.09 Ci/yr 

3.18 Ci /yr

The radon release from the restoration operation is calculated using 

Equation (7). 

r = GN&D x 1.44 

1 

- e-(O '181/d)(lOd) = 0.84 

r =2.4 x 10-6 Ci/ml x 400 L/min x 0.84 x 365 d/yr x 1.44 

= 0.42 Ci/yr

The total radon release from restoration includes a small 

release similar to that from the startup solution. Therefore, 

would be:

increment of 

the total release

0.42 Ci/yr + 0.09 Ci/yr = 0.51 Ci/yr 

The total release from this 10-acre hypothetical in situ mining operation 

is then 3.18 + 0.51 = 3.69 Ci/yr. 

3. NONRADIOACTIVE EMISSION SOURCE TERMS 

During uranium milling, some nonradioactive contaminants and toxic elements 

are also released to the environment as shown in Table 4. In addition, combustion 

products are released from burning of fuel in the process and heating boilers. 

Table 4 

Nonradioactive Emissions Generated by Uranium Milling

Source 

Ore storage and 

crushing/grinding 

Leaching tanks vent 

Solvent extraction vent 

Burning of fuel oil 

Yellowcake precipitation 

Yellowcake centrifuge or 

filter and calciner 

Laboratory hood 

Tailings pile

Emission 

Ore dust 

Sulfuric acid mist 

Sulfur dioxide 

Organic solvent 

(kerosene) 

S02 , NO2 

Ammonia 

Ammonia 

Misc. vapors 

Tailings dust

3.59-20
3.1 Nonradioactive Particulate Emission Source Terms

The major sources of nonradioactive particulate emissions are the same as 

the sources for radioactive particulate emissions as previously described in 

Section C.1. The general method for calculating these source terms is the same 

as that for the radioactive source term discussed and illustrated in Sec

tions C.1.1 and C.1.2. Example calculations of nonradioactive particulate 

source terms follow. 

3.1.1 Example Calculation: Crushing 

Source terms for toxic elements in the ore are estimated in a parallel 

manner to the radioactive particulate emissions. For example, if the applicant 

has indicated that the manganese content of the above ore is 500 ppm (500 g/MT), 

the annual release of manganese from ore crushing for a uniform concentration of 

manganese in the ore, N = 1 (assuming 80 percent reduction), is estimated using 

Equation (1) in Section C.1 to be: 

S 145,000 MT/yr x 500 g Mn/MT x 0.16 lb/ton x 1 ton/2000 lb 

x (1 - 0.80) x 1 = 1.2 x 103 g Mn/yr 

3.1.2 Example Calculation: Truck Unloading to Ore Pad 

In this example, the ore contains 250 ppm (250 g/MT) of lead; again assuming 

uniform concentration of lead in the ore, N = 1, the estimate of annual lead 

release would be: 

S = 193,000 MT/yr x 250 g/MT x 0.04 lb/yd3 x 1 yd3 /1.5 ton 

x 1 ton/2000 lb x 1 

= 640 g Pb/yr 

3.1.3 Example Calculation: Fine Ore Storage 

In this example, the fine ore is conveyed to and from the fine ore storage 

area for a total of four conveyor transfers. Ore is handled at a rate of 

135,000 MT/yr. The operation occurs in an enclosed structure with a reduction 

factor of 75 percent based on engineering judgment (Appendix C). The emission 

factor for each transfer is 0.023 lb/ton (Appendix B). The combined emission 

factor for the fine ore storage conveying is: 

E = 4 transfers x 0.023 lb/ton per transfer = 0.092 lb/ton 

If, for example, the dust contained an arsenic content of 50 ppm (50 g/MT) and 

assuming N = 1, the estimate of annual arsenic release would be: 

S = 135,000 MT/yr x 0.092 lb/ton x 1 ton/2000 lb x 50 g/MT = 310 g As/yr 

3.2 Windblown Emissions 

Fugitive dust varies significantly from mill to mill. Meteorological condi

tions (wind, rainfall, temperatures), exposed surfaces, ore compositions and 

physical and chemical characteristics, particle size distributions, site charac

teristics, and operational procedures are among the factors that affect the

3.59-21
degree to which dust is dispersed into the atmosphere. The nonradioactive 

windblown particle emissions are estimated in a manner similar to that used for 

the radioactive particulate emissions described in Section C.1.2. 

3.2.1 Example Calculations: Tailings Pile 

Using the same assumptions presented in the example calculations in Sec

tion C.1.2.1 and Equations (2) and (3), the toxic element releases are estimated. 

For the ore with an initial lead concentration of 250 ppm (250 g/MT), with 

essentially all (99.9%) of the lead disposed to the tailings pile (assuming that 

the process conditions are identical to those in the crushing example, Sec

tion C.1.1.1), the source term for lead for the abandoned tailings pile example 

in Section C.1.2.1 is: 

S = 4.3 x 102 g/m 2 -yr x 53 acres x 4047 m2 /acre 

x 250 g Pb/MT x 1 MT/10 6 g x (1 - 0.85) 

= 3.5 x 101 g Pb/yr 

3.2.2 Example Calculations: Ore Pad 

Particulates on the ore pad subject to wind erosion are less than those 

from tailings piles since the ore has not yet been ground. The NRC staff has 

estimated the fugitive dust release from the ore pad by assuming an emission 

factor of 10 percent of that calculated for the tailings pile. The modified 

equations for ore pads are discussed and presented in Section C.1.2.2. Thus, 

for the site with a wind frequency occurrence as described in Section C.1.2.2, 

the annual average dust loss rate is estimated to be: 

Ew = 0.1 x 3.156 x i07 s/yr x 6.75 x 10-6 g/m 2 -s/(0.5) = 43 g/m 2 .yr 

The toxic source term for an ore pad of 10 acres containing ore with 200 ppm 

(200 g/MT) lead, no enrichment of lead in the fines,* N = 1, no emission control, 

R = 0, is estimated using Equation (3): 

S = 43 g/m 2 .yr x 10 acres x 4047 m2 /acre x 200 g Pb/MT x 1 MT/IO6 g x 1 

= 348 g Pb/yr 

Any control such as keeping the ore pile wet would reduce fugitive dust by the 

appropriate factor as shown in Appendix C. 

3.3 Nonradioactive Gas Emission Source Terms 

Milling operations will result in the release of nonradioactive gases and 

vapors to the atmosphere (see Table 4). The main sources of these emissions are 

the leach circuit, the solvent extraction circuit, yellowcake precipitator and 

dryer, the analytical laboratory, and the mill power plant and heating systems. 

The annual average concentrations off site are expected to be below background 

and in general are too low to be measured (Ref. 4). 

*<100 pm in diameter.

3.59-22
3.3.1 Leaching 

Small amounts of sulfuric acid mist can escape from the vent system. Carbon 

dioxide can also be produced as a result of acid reaction with carbonate materials 

present in the ore. Trace quantities of sulfur dioxide and free chlorine may also be released. A demister can remove more than 99 percent of the acid mist. 

Release of hydrides such as arsine, stibine, and hydrogen sulfide during leaching 

are considered negligible (Ref. 11). Release factors that may be used to 

estimate releases from an acid circuit are shown in Table 5. 

3.3.2 Solvent Extraction 

Solvent extraction and stripping result in some evaporation loss of exposed organic solvents. Kerosene represents about 92 percent of the organic, with the 

remaining 8 percent an organic acid such as alkyl phosphoric acid. A wet scrubber 

can be used to reduce emissions by more than 99 percent. A source term may be 

calculated using data in Table 5 as follows: 

Table 5 

Chemical Airborne Release Factors for Acid Leach Mill

Material Released Release Factor, kg/kg U 

Sulfur oxides 2 x 10-4 

Nitrogen oxides 2 x 10-3 

Ammonia 2 x 10-3 

Kerosene 2 x 10-4 

Organic acids 5 x 10-s 

Aldehydes 8 x 10-4 

Hydrocarbons 3 x 10-3 

Source: Reference 12.

For a mill processing 145,000 MT/yr with an average U3 08 content of 0.1 percent and a wet scrubber with 99 percent efficiency (organic acid plus kerosene), the 

emission source term from solvent extraction is calculated as shown below. 

S = 145,000 MT ore/yr x 0.1 kg U30 /MT ore 

x 0.85 kg U/kg U308 x (5 x 10-1 kg/kg U + 0.2 x 10-3 kg/kg U) 

x (1 - 0.99) 

= 640 g organic acid plus kerosene/yr 

3.3.3 Analytical Laboratory 

Various process reagents and products will be analyzed. The fume hoods 

will collect air and a mixture of chemical fumes and mists. A wet scrubber 

could be used to reduce the emission by more than 99 percent.

3.59-23
3.3.4 Mill Power Plant and Building Heat Boiler

The source term for mill electrical power and process heat will depend on 

the systems and fuel used. For example, if a diesel-generator unit were used 

with number 2 diesel fuel (maximum 1% sulfur), several gaseous emissions would 

result: CO, hydrocarbons, NOx, and S0 2. If an oil-fired boiler were used for 

process and building heat, similar emissions would occur. Emission factors for 

fuel combustion have been developed by EPA (Ref. .13). For convenience, the NRC 

staff has abstracted conservative values from the compilation and summarized 

them in Appendix D. Data from this appendix can be used to calculate appropriate 

combustion source terms. 

To illustrate how the NRC staff would calculate the source term for a heat 

boiler, the following example is provided. Assume that the boiler will be used 

to supply supplementary heat during cold weather and that it will burn an average 

of 23 L/hr fuel oil distillate with a 0.1 percent sulfur content. The unit will 

operate for 120 days during the year. Based on the emission factors from fuel 

combustion presented in Appendix D, the following average estimated emissions 

would result: 

kg/103 L L/hr hr/d d/yr kg/yr 

Sulfur dioxide 17 x 0.001* x 23 x 24 x 120 = 1.1 

Carbon monoxide 0.63 x 23 x 24 x 120 = 41.7 

Hydrocarbons 0.12 x 23 x 24 x 120 = 7.9 

Nitrogen oxides 2.8 x 23 x 24 x 120 = 185 

*Sulfur content in fuel oil. 

D. IMPLEMENTATION 

The purpose of this section is to provide information to applicants and 

licensees regarding the NRC staff's plans for using this regulatory guide. 

The methods presented in this guide are acceptable to the NRC staff for 

complying with the Commission's regulations. Therefore, except in those cases 

in which the applicant or licensee proposes acceptable alternative methods for 

complying with the specified portions of the Commission's regulations, the 

methods described in the guide are being and will continue to be used in the 

evaluation of applications for or amendments to licenses for uranium milling 

operations to estimate radioactive and toxic airborne source terms for such 

operations.

3.59-24
APPENDIX A 

Principal Primary Parameters Needed to Estimate 

Source Terms for Uranium Mill Operationsa 

Ore Quality 

Concentration of U3 08 in ore (including ranges), % by weight 

Processing rate, MT/d 

Radionuclide content (2 3 8U and daughter products), pCi/g 

Concentration of nonradioactive toxic elements, g/MT (ppm) 

Dust/ore activity ratio, 2 . 5 b 

Moisture content, % by weight 

Bulk density, g/cm3 

Diffusion coefficient (D) for radon in ore piles (if availablec'd), cm2 /s 

Emanating power for radon (E) (if availablee) 

Ore Unloading Stov'age Dataf 

Area of each pile or bin complex and total area, m2 

Average depth of pile, m 

Average annual quantity of ore in storage, MT 

Average porosity of the ore pile, % 

Receipt (truck or rail unloading) rates, MT/d 

Operational period, d/yr 

Description of dusting controlg 

Quantity of each range of ore quality 

Radon emission,c Ci/yr 

Vehicle requirements 

"- type 

"• number 

"* capacity, MT or m3 /vehicle 

"• frequency of operation (deliveries/d, MT/delivery)

3.59-25
Crushing/Grinding 

Description of ventilation air treatment, including 

* design efficiency of scrubbers and filters 

• expected efficiency of scrubbers and filters 

• minimum efficiency of scrubbers and filters 

Uncontrolled emission factorsh 

Description of emission controls 

Leaching/Extraction 

Ratio of leachant to ore, L/kg 

Composition of leachant, M 

Composition of solvent (if used) 

Ion exchange medium (if used) 

Residence time of ore in mill, d 

Yellowcake Drying and Packaging 

Yellowcake characteristics 

"* bulk density, g/cm3 

"* purity, % U308 

Production rates, MT/yr 

* drying 

• packaging 

Processing times, hr/d and d/yr 

Description of air ventilation controls 

"* design efficiencies 

"* expected efficiencies 

"* minimum efficiencies 

Tailings Impoundment Systems 

Tailings characteristics 

• radionuclide content ( 2 38 U, 2 30Th, 22 6 Ra, 2 10 Pb), pCi/g 

* average radionuclides 

* beach sands 

• slimes b 

* dust/bulk solids activity ratio of tailings sands

3.59-26
* bulk density, g/cm3 

* moisture content, % by weight d 2/s 

* diffusion coefficients for radon (if availabled), cm 

* emanating powercfor radon (E) (if available ) - radon emission, Ci/yr 

Impoundment Area,i m2 

Total 

Beach sands 

Under water 

Exposed wet slimes 

Dried slimes 

Description of dust control 

Estimated drying time required prior to initiation of reclamation 

procedures and basis 

Estimated time required to stabilize and reclaim after drying and basis 

Energy Requirements 

Electricity, kWh/yr 

Diesel oil and gasoline, L/yr 

Fuel oil, gal/yr 

Fuel gas, m3/yr 

Coal, tons/yr 

Process Chemical Requirements 

Sulfuric acid (including concentration), MT/yr 

Sodium carbonate, MT/yr 

Solvent (including composition), MT/yr 

Oxidant, kg/yr 

Ammonia, kg/yr 

Others, annual use

3.59-27
Footnotes for Appendix A 

a. Default values listed in these footnotes or in the text can be used 

unless measured values are provided. 

b. The dust/ore activity ratio used by the NRC staff is 2.5 unless there 

is specific, convincing evidence that the enrichment factor should be 

another ratio, either lower or higher. The dust/bulk activity ratio used 

for tailings sands is also 2.5 (used for radioactivity releases only). 

c. The NRC staff normally calculates the operation radon emission from ore 

stockpiles and tailings impoundments using the flux ratio: 

(1.0 pCi/m 2 -s of 2 2 2 Rn)/(pCi/g of 2 26 Ra) 

d. If no data are available, the following diffusion coefficients, D, for 

radon may be considered: 

2x10- 2 cm2/s for ores and beach sands (tailings) 

• 5x10- 3 cm2 /s for wet slimes (tailings) 

* lx1O- 2 cm2 /s for dry slimes (tailings) 

As new data are obtained, these values will be changed as appropriate. 

e. If specific data are not otherwise available, the NRC staff uses 0.2 as 

the emanating power of radon. 

f. Information should be distinguished as to specific ore pad activity--front

end loaders, unloading, and storage. 

g. Various emission reduction factors used by the NRC are listed in 

Appendix C. 

h. If not available from onsite operations, uncontrolled emission factors 

used by the NRC staff are shown in Appendix B. 

i. The indicated information is needed for varying operational periods, 

for example: 

"* last year of mill operations 

"• period just prior to pond drying up 

"* period just prior to reclamation 

"• period of maximum generation, if different from above

3.59-28
APPENDIX B 

Emission Factors

Uncontrolled Emission

1. Ore loadout to grizzly, 

or raw, or finished 

stockpile 

2. Transfer point such as 

conveyor loading 

3. Primary crushing, secondary 

crushing, and screening 

combined. The addition 

of tertiary crushing will 

double the chosen factor. 

4. Yellowcake drying and 

packaging

0.002 lb/yd3 truck bottom gumpa 

0.04 lb/yd3 truck end dump 

0.023 lb/ton conveyor transfer pointa 

0.023 lb/tona 

0.002 lb/ton (moisture 2 9% a 

0.04 lb/ton (moisture 8-9%)a 

0.16 lb/ton (moisture < 8%)a 

0.1,%b

aReference 14. 

bBased on EPA-measured releases at six mills, the NRC staff estimates 

controlled releases from yellowcake facilities at 0.1 percent.

3.59-29

Process
APPENDIX C 

Particulate Emission Reduction Factorsa 

for Ore Processing

Emission Control

Ore pads, heap leach piles, or tailings piles 

Chemical suppressant 

(synthetic polymer usually) 

Mulch 

Rapid revegetation 

Wind breaks = mature forest 

Wind breaks = height of pile 

Wind breaks < height of pile 

Frequent water (twice daily) 

Water sprinkle as needed 

Chemical and vegetation stabilization 

Water cover 

Soil cover 

Rip rap + soil cover 

Oiling 

Complete enclosure (includes silos) 

Partial enclosure 

Canvas covers

Ore loadout to grizzly, or raw, or finished 

Negative pressure with fabric filter 

Chemical suppressants 

Enclosed structure 

Telescopic chute 

Stacker - water spray 

Water spray 

Wind guard 

Stacker - height adjustable 

Stone ladder

stockpile

Ore crushing and grinding 

Bag filter 

Semiautogenous grinding 

Yellowcake drying and packaging 

Venture scrubber and demister 

Slurry product

% Reduction

80 

85 

75 

75 

50 

20 

50 

50 

93 

99 

100 

100 

80 

99 

50 

80 

85 

85 

75 

75 

75 

50 

50 

25 

80 

33 

100 

90 

100

3.59-30

aMost from Reference 14; others based on staff's engineering 

judgment and Reference 4.
(

APPENDIX D 

Emission Factors from Fuel Combustion Without Emission Controla

Sulfur Carbon Nitrogen 

Sourse of Emissions Particulates Oxides Hydrocarbons Monoxide Oxides Aldehydes 

Coal, kg/MT 8 .5Ab c Neg. d 0.5 d 

Anthracite (1.25) (45) 

Bituminous 8.5A(l0)d 0.5 ( 10 )d 5 ( 4 5 )d 28 0.0025 

Fuel oil, kg/103 L 

Distillate oil 0.25 17S 0.12 0.63 2.8 

Natural gas, kg/lO6 m3 240 9.6 128 320 3680 

Liquid petroleum gas 

S(LPG), kg/103 L 0.23 0.09S 0.096 0.24 1.5 

Ue 

Vehicles, g/km 

Gasoline-powered 

Light-duty truck 2.1 26.6 3.3 

Heavy-duty truck 8.4 117 7.8 

Diesel-powered 

Heavy-duty truck 0.81 1.7 2.9 18 21 0.2 

Off-highway, stationary sources 

Gas-fired, kg/106 m3 220 83 670 1800 6600 

Oil-fired, kg/1O3 L 0.60 0.4 0.7 1.9 8.1 

Gasoline-powered, kg/103 L 0.78 0.64 16 470 12 0.52 

Diesel-powered, kg/lO3 L 4.0 3.7 4.5 12 56 0.84 

a Emission factors are abstracted on a conservative basis (higher values) from Reference 13. "b "A" represents the weight percentage of ash in the fuel. 

c "S" represents the weight percentage of sulfur in the fuel. 

d For hand-fired units. 

e Data are for 1972 model year and for emissions at either high or low altitudes, depending on which value is higher. 

For earlier model years, consult Reference 13.
REFERENCES

1. U.S. Nuclear Regulatory Commission (USNRC), Regulatory Guide 4.14, 

"Radiological Effluent and Environmental Monitoring at Uranium Mills," 

Washington, DC, 1980. 

2. USNRC, "Compliance Determination Procedures for Environmental Radiation 

Protection Standards for Uranium Recovery Facilities - 40 CFR Part 190," 

NUREG-0859, Washington, DC, 1982. 

3. USNRC, Regulatory Guide 3.51, "Calculational Models for Estimating Radia

tion Doses to Man from Airborne Radioactive Materials Resulting from 

Uranium Milling Operations," Washington, DC, 1982. 

4. USNRC, "Final Generic Environmental Impact Statement on Uranium Milling," 

NUREG-0706, Vols. 1-3, Washington, DC, 1980. 

5. R. C. Merritt, The Extractive Metallurgy of Uranium, Colorado School of 

Mines Research Institute, Golden, CO, 1971. 

6. USNRC, "MILDOS - A Computer Program for Calculating Environmental Radia

tion Doses from Uranium Recovery Operations," NUREG/CR-2011, PNL-3767, pre

pared by R. L. Strenge and T. J. Bander, Pacific Northwest Laboratory, 

Richland, WA, for the USNRC, Washington, DC, 1981. 

7. M. G. Sears et al., "Correlation of Radioactive Waste Treatment Costs and 

the Environmental Impact of Waste Effluents in the Nuclear Fuel Cycle for 

Use in Establishing "As Low As Practicable" Guides - Milling of Uranium 

Ores," ORNL-TM-4903, Vol. 1, Oak Ridge National Laboratory, Oak Ridge, 

TN, 1975. 

8. L. C. Schwendiman et al., "A Field and Modeling Study of Windblown 

Particles from a Uranium Mill Tailings Pile," NUREG/CR-1407, PNL-3345, 

prepared by Pacific Northwest Laboratory, Richland, WA, for the USNRC, 

Washington, DC, 1980. 

9. C. W. Fort, Jr., R. L. Douglas, and W. E. Moore, "Radioactive Emissions 

from Yellowcake Processing Stacks at Uranium Mills," Technical Note ORP 

LV-80-3, Environmental Protection Agency, Las Vegas, NV, 1980. 

10. M. H. Momeni et al., "Radioisotopic Composition of Yellowcake. An Estima

tion of Stack Release Rates," NUREG/CR-1216, ANL/ES-84, prepared by Argonne 

National Laboratory, Argonne, IL, for the USNRC, Washington, DC, 1979. 

11. USNRC, "Nuclear Fuel Cycle Risk Assessment: Descriptions of Representative 

Non-Reactor Facilities," coordinated by K. G. Schneider, Pacific Northwest 

Laboratory, Richland, WA, 1982. 

12. K. G. Schneider and T. G. Kabele, "Descriptions of Reference LWR Facilities 

for Analysis of Nuclear Fuel Cycles," Pacific Northwest Laboratory, 

Richland, WA, 1979.

3.59-32
13. U.S. Environmental Protection Agency, "Compilation of Air Pollution 

Factors," and Supplements, Third Edition, PB-275-525, Office of Air and 

Waste Management, Office of Air Quality Planning and Standards, Research 

Triangle Park, NC, 1977. 

14. I. Tistinic, "Fugitive Dust Emissions," interoffice communication of the 

Colorado Department of Health, APCD, 1981.

3.59-33
BIBLIOGRAPHY 

Austin, S. R., and D. F. Droullard, "Radon Emanation From Domestic Uranium Ores 

Determined by Modifications of the Close-Can Gamma-Only Assay Method," Bureau 

of Mines Report of Investigation 8264, 1978. 

Freeman, H. D., and J. N. Hartley, "Predicting Radon Flux from Uranium Mill 

Tailings," Proceedings from Sixth Symposium on Management of Uranium Mill Tail

ings, Low-Level Waste and Hazardous Waste, Colorado State University, Fort 

Collins, CO, 1984. 

Hartley, J. N., et al., "1981 Radon Barrier Field Test at Grand Junction 

Uranium Mill Tailings Pile," UMT-0213/PNL-4539, Pacific Northwest Laboratory, 

Richland, WA, 1982. 

Nielson, K. K., et al., "Radon Emanation Characteristics of Uranium Mill 

Tailings," Fifth Symposium on Management of Uranium Mill Tailings, Fort Collins, 

CO, 1982. 

Rogers, V. C., et al., "Characterization of Uranium Tailings Cover Materials 

for Radon Flux Reduction," NUREG/CR-1081, FBDU-218-2, U.S. Nuclear Regulatory 

Commission, Washington, DC, 1980. 

Rogers, V. C., and K. K. Nielson, "A Handbook for the Determination of Radon 

Attenuation Through Cover Materials," NUREG/CR-2340, U.S. Nuclear Regulatory 

Commission, Washington, DC, 1981. 

Rogers, V. C., et al., "Measurements and Calculations of Radon Flux Attenuation 

by Western U.S. Soils," Fifth Symposium on Management of Uranium Mill Tailings, 

Fort Collins, CO, 1982. 

Rogers, V. C., et al., "Radon Attenuation with Earthen Covers - 1983 Annual 

Report," RAE-36-3, Rogers and Associates Engineering Corp., Salt Lake City, 

UT, 1983. 

Silker, W. B., and P. C. Heasler, "Diffusion and Exhalation of Radon From 

Uranium Mill Tailings," NUREG/CR-1138, U.S. Nuclear Regulatory Commission, 

Washington, DC, 1979. 

Strong, K. P., et al., "Radon Diffusion Through Uranium Tailings and Earth 

Covers," International Conference on Radiation Hazards in Mining: Control 

Measurement and Medical Aspects, Golden, Colorado, published by AIME, New York, 

NY, pp. 713-719, 1981. 

Strong, K. P., and D. M. Levins, "Effect of Moisture Content on Radon Emanation 

from Uranium Ore and Tailings," Health Physics, Vol. 42, No. 1, pp. 27-32, 1982. 

U.S. Environmental Protection Agency, "Environmental Standards for Uranium and 

Thorium Mill Tailings at Licensed Commercial Processing Sites; Final Rule," 

Federal Register, October 7, 1983.

3.59-34
U.S. Nuclear Regulatory Commission, "The Uranium Dispersion and Dosimetry 

(UDAD) Code," NUREG/CR-0553, ANL/ES-72, prepared.by M. H. Momeni, Y. Yuan, and 

A. J. Zielen, Argonne National Laboratory, Argonne, IL, for the USNRC, 

Washington, DC, 1979.

3.59-35
VALUE/IMPACT STATEMENT

A draft value/impact statement was published with the draft version of 

this guide, task WM 407-4, when the draft guide was published for public 

comment in April 1986. No changes were necessary, so a separate value/impact 

statement for the final guide has not been prepared. A copy of the draft 

value/impact statement is available for inspection and copying for a fee at 

the Commission's Public Document Room at 1717 H Street NW., Washington, DC, 

under Task WM 407-4.

UNITED STATES 

NUCLEAR REGULATORY COMMISSION 

WASHINGTON, D.C. 20555 

OFFICIAL BUSINESS 

PENALTY FOR PRIVATE USE, $300

FIRST CLASS MAIL 

POSTAGE & FEES PAID 

USNRC 

PERMIT No. 0-47

3.59-36