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Uranium Mine and Mill Resident Individual Dose Calculator - HELP

(last updated 15 Feb 2016)

Contents:


Introduction

This calculator performs individual dose and health risk calculations from inhalation of radon and dust for an individual living near a uranium mine and mill or an uranium in-situ leach facility.

The uranium production used for the risk calculations is presented in the Material Balance table. Upon entry of one value into any of the table's input fields, all other fields are calculated accordingly. So, it is possible to enter the uranium production in terms of annual production or cumulative production, or the total amount of ore processed, among others.
(For more detailed material balance calculations, see the Nuclear Fuel Material Balance Calculator).

The results of the risk calculations are presented in the Lifetime Dose and Health Risk Summary table in terms of cumulative individual dose in mSv, and expected excess lifetime risk of contracting fatal cancer resulting from this dose. It is assumed that the individual first is exposed to the emissions from the operating mine, mill and the bare tailings, and, after shutdown and (hopefully) subsequent reclamation of the tailings, to the emissions from the covered tailings. The calculator assumes continuous exposure in open air, there is no account for periods of indoor stay or absence.
Some intermediate results are shown in the Source Term, Average Air Concentration at Resident's Location, and Annual Dose Summary tables. Total annual doses above 1 mSv/a are marked with a red signal.
EEC stands for Equilibrium Equivalent Concentration, MBq stands for Mega-Becquerels (106 Bq), TBq stands for Tera-Becquerels (1012 Bq).

You can also enter a value into any of the Dose Summary or Source Term table fields, instead of entering one into the Material Balance table. This facilitates comparison.

The Radon-222 Release Rate from Tailings table shows the radon-222 releases per unit area, to allow for a comparison to current standards. These values are for display only and are not for change. Release rates above the U.S. EPA standard are marked with a red signal.

The contributions to Lifetime Dose are presented in a pie chart, and the Lifetime Dose depending on distance from the source is presented for the current sector in a line chart; if the default wind table is used, also a chart showing the Lifetime Dose depending on the sector is presented for the current distance.

The parameters used for the calculation can be set in the Health Risk Parameters and Process Parameters tables. These parameters show reasonable initial values which can be modified as needed. There are no other hidden parameters used in the calculation. Any assumptions made for the calculations are described on this page.

The calculator considers only the major aerial-pathway sources of health hazards to the resident:

 ConsideredNeglected
MineRadon and dust release during operationRelease of liquids
Releases after shutdown
Releases from waste rock piles
MillRadon and dust release during operationRelease of liquids
Releases from plant decommissioning
Mill TailingsRadon and dust release during operation
Radon release after decommissioning
Dust release after decommissioning (if not covered)
Seepage
Loss of integrity from erosion etc.
Risk of dam failure

See special instructions for offline use of this calculator.

Users who need a more sophisticated analysis than is possible with this calculator should have a look at Dose Modeling Software.

Dose calculations for individuals exposed to known concentrations of various forms of uranium can be performed with the Uranium Radiation Individual Dose Calculator, and individual doses from known concentrations of radon can be calculated with the Radon Individual Dose Calculator.
Dose calculations for individuals living on uranium-contaminated soil can be done with the Uranium in Soil and Building Material Individual Dose Calculator.
Collective dose calculations for the front end of the nuclear fuel cycle can be performed with the Nuclear Fuel Population Health Risk Calculator.

 

Health Risk Parameters

Select a sample parameter set from the drop-down list, and/or modify any parameter as required.
Mine: Operational Life of Mine (and Mill) [years]
Period during which the mine and mill operate at the given annual production rate.

Mine: Specific Radon Emission [GBq/t U3O8]
Release of Radon-222 from the mine per tonne U3O8 produced in the mill. GBq stands for 109 Becquerels.
The following table shows the extremely high variations for this figure (UNSCEAR1993, all for 1989):
Ranger Mine (Australia)OP22
former Panel Mine (Canada)UG110
former Thuringian mines (Germany)UG210
former Denison Mine (Canada)UG540
Rabbit Lake Mine (Canada)OP760
former Aue Mine (Germany)UG2000
OP = open pit   ·   UG = underground

The estimate for the proposed Husab open pit mine in Namibia is 72 GBq/t U3O8, and the estimated value for the Honeymoon uranium in-situ leach project in South Australia is 141 GBq/t U3O8.

Mine: Specific Ore Dust Emission [g/t ore mined]
Release of dust from the mine per tonne ore mined.
EPA1976 gives 1.8 g/t for an underground mine and 12.6 g/t for on open pit mine. The estimate for the proposed Husab open pit mine in Namibia is 1347 g/t without mitigation measures, and 165 g/t with mitigation measures.
Note: set this value to 0 for in-situ leach facilities.

Mine: Effective Release Height [m]
effective height above ground for radon emission source

Mill: Specific Radon Emission [GBq/t U3O8]
Release of Radon-222 from the mill per tonne U3O8 produced. GBq stands for 109 Becquerels. This value shows small variations around 13, according to UNSCEAR1993. NUREG-0706 uses 4.8 for the NRC model mill.
Note: set this value to 0 for in-situ leach facilities.

Mill: Specific Ore Dust Emission [g/t ore milled]
Release of dust from the mill per tonne ore milled.
This parameter applies to dust from the crushing and milling operations of the plant, where the progeny still is attached to the uranium.
NUREG-0706 gives a value of 3.5 g/t for the NRC model mill. The estimate for the proposed Husab open pit mine in Namibia is 20 g/t without mitigation measures, and 3.33 g/t with mitigation measures.
For the dose calculations, all isotopes of the U-238- and U-235-series and their decay products are considered, assuming secular equilibrium for each of the series.
Note: set this value to 0 for in-situ leach facilities.

Mill: Specific U3O8 Dust Emission [g/t U3O8 produced]
Release of U3O8 dust from the mill per tonne U3O8 produced.
This parameter applies to dust from the final product recovery plant, where the progeny is no longer attached to the uranium.
NUREG-0706 uses a value of 982.7 g/t for the NRC model mill. The Ranger mill (Australia) releases 47.4 g/t, and the Olympic Dam mill (Australia) 3.7 g/t.
For the dose calculations, all uranium isotopes (U-238, U-234, U-235) are considered, assuming their fractions contained in natural uranium.

Mill: Effective Release Height [m]
effective height above ground for radon emission source

Mill Tailings: Tailings Thickness [m]
Thickness of the tailings in the deposit, typically in the range of 10 to 50 meters (used for calculation of surface area, square shape assumed)

Mill Tailings: Tailings Density [g/cm3]
typically 1.6

Mill Tailings: Specific Radon Exhalation Rate [Bq/m2s per BqRa-226/g]
Release of radon-222 from the bare surface of the tailings deposit, normalized per square meter and concentration of radium-226 in the tailings.
Radium-226 is the precursor of radon-222 in the decay chain. It is assumed that radium-226 in the ore is in secular equilibrium with uranium-238, and that all radium-226 contained in the ore ends up in the tailings. Often, a rule-of-thumb value of 1 is used for unsaturated tailings (EPA1986); this applies for "infinite" (in terms of radon exhalation) thickness of the tailings, that is more than 4 meters. In case of a smaller tailings thickness, the value has to be corrected appropriately.
For a given situation, the Uranium Mill Tailings Cover Calculator can be used to calculate the specific radon exhalation rate ("Specific Bare Source Flux from Layer 1").
Note: set this value to 0 for in-situ leach facilities.

Mill Tailings: Specific Tailings Dust Emission Rate [g/(m2d)]
Release of tailings dust from the surface of the bare tailings deposit per square meter and day.
NUREG-0706 gives a value of 1.08 g/(m2d).
For the dose calculations, all nuclides of the U-238- and U-235-series are considered, according to their concentrations given by ore grade and mill loss.

Mill Tailings: Effective Release Height [m]
effective height above ground for radon emission source

Mill Tailings: Percentage of tailings area exposed during mill operation [%]
Percentage of the final tailings area that is not covered by ponding water (1 m at least), or, in case of phased disposal, that is in use and has not been covered with some interim cover.
It is simplistically assumed that the ponding water and/or interim cover blocks radon emission completely; if this is not the case, increase the percentage figure accordingly.

Mill Tailings: Time to Final Cover Installation [years]
Time in years during which the surface of the bare tailings is exposed, usually during active operation of the mill plus some delay until the cover is completed.

Mill Tailings: Cover: Radon Retention [%]
Percentage of radon-222 release retained by cover on top of tailings.
Note: If a value is entered here, the Cover Radon Release Rate Limit entry (see below) is deleted.
Set this value to zero for bare tailings; in this case, the dust emission from the tailings will be taken into account for the period after shutdown. Otherwise it is assumed that the cover will prevent any dust releases from the tailings surface.
Engineered covers (whether from clay or synthetic materials) show high radon retention rates immediately after installation, while their long-term performance is a matter of discussion. Water covers of more than 1 meter have high radon retention rates, if undisturbed.
The following table shows some examples for earth covers (EPA1986):
Earth TypeMoistureRadon Reduction
Cover Depth
0.5m1m2m3m
sandy soil3.4%29%50%75%88%
soil7.5%37%60%84%94%
soil12.6%50%75%94%98%
compacted moist soil17%68%90%99%>99%
clay21.5%94%>99%>99%>99%
For a given situation, the Cover Radon Retention can be calculated with the Uranium Mill Tailings Cover Calculator.

Cover: Radon Release Rate Limit [Bq/m2s]
Maximum radon-222 release rate from the covered tailings.
The U.S. EPA standard (40 CFR 192) is 20 pCi/m2s, which is equivalent to 0.74 Bq/m2s.
Note 1: If a value is entered here, the Cover Radon Retention entry (see above) is deleted.
Note 2: This value comes into effect only, if it is lower than the radon release rate from the bare tailings.

Common Data (Mine, Mill, Tailings): Distance of Resident from Mine/Mill/Tailings [km]
There is only one distance figure, since all three sources are modeled together as one point source. This introduces errors for low distances.

Common Data (Mine, Mill, Tailings): Mixing Layer Height [m]
The troposheric mixing layer height is the maximum height above ground the radon plume can reach. It highly depends on the climatic conditions, day-night cycle etc. The value used for NRC's model mill in NUREG-0706 is 850 meters.

Common Data (Mine, Mill, Tailings): Annual precipitation [cm]
Precipitation washes some of the radon out from the plume. This value is only taken into account in the "precise" mode (see below). The value used for NRC's model mill in NUREG-0706 is 31 cm.

Common Data (Mine, Mill, Tailings): Radon Progeny Equilibrium Fraction (used in fast mode only)
Describes the ratio of the short-lived decay products of radon-222 compared to radon-222 itself in the air. A typical value for distances of single kilometers is 0.4, and for longer distances is 0.7. In the "Fast" mode, the calculator uses this single value, while, in "Precise" mode it automatically takes radon progeny ingrowth during travel time (resp. travel distance) into account.

Common Data (Mine, Mill, Tailings): Air Dispersion Calculation Mode
The calculation of radon dispersion in the air is the most time-consuming step in the calculation. Therefore, two options are provided:
In the "Fast" mode, the calculator does not take into account radon progeny ingrowth and plume depletion during its travel time. This mode thus overestimates the risk, in particular for very short and for very long distances (see also Air Dispersion Modeling).
In the "Precise" mode, radon progeny ingrowth during travelling time is considered automatically, and two effects responsible for plume depletion are taken into account: precipitation scavenging and the decay of radon (with its half-life of 3.8 days). On slow machines, it may take some seconds for the results to appear. For the user's convenience, the air dispersion calculation is only performed during the first run, and otherwise only if any parameters affecting air dispersion have been changed.

Common Data (Mine, Mill, Tailings): Fractional Frequency of Wind Speed Classes
The distribution of wind speed frequencies is the basic input data for the air dispersion calculations.
The table contains the fractional frequencies (in percent) of the wind speed fitting into any of six wind speed classes, for each of the stability classes A to F in each of 16 sectors. The wind speed classes are described by their average wind speed in meters per second. The stability classes are defined according to Pasquill, as follows: A - extremely unstable, B – moderately unstable, C – slightly unstable, D – neutral, E – moderately stable, F – very stable. The sectors are labeled according to the direction where the wind blows from (so, the "SW" sector is located NE of the plant, for example). The "<" and ">" buttons allow for toggling between the sectors. The DEFAULT data set is from NRC's model mill in NUREG-0706, located at a site with a semiarid climate in the Western U.S.
User input is possible for one sector (labeled "User"). If not all wind speed classes are needed, leave the fields for the average speed of the unused classes free (the unused classes must be at the end). The number of total sectors must be entered appropriately (often 12 or 16).

General Data: Radon Dose Factor [nSv/h per Bq/m3 EEC]
Effective dose coefficient for exposure to equilibrium equivalent concentration (EEC) of radon. UNSCEAR1993 uses a value of 9, ICRP65(1993) uses a value of 6.4. Based on the revised dose factor for the public of 9 mSv/WLM presented in J.W. Marsh et al: Dose conversion factors for radon, in: Health Physics Vol. 99, No. 4 (Oct. 2010), p. 511-516, the resulting value is 14.1 nSv/h per Bq/m3 EEC (with 1 WLM = 6.37·105 Bq·h/m3 of EEC of Rn-222).

Uranium Inhalation Dose Factor (natural uranium with progeny) [µSv/Bq U-238]
Effective Dose per unit activity Uranium-238 contained in natural uranium in secular equilibrium with its decay products inhaled. The dose is meant for the combination of all nuclides present. The value obtained from ICRP72 is 56.71 µSv/Bq U-238.

Uranium Inhalation Dose Factor (pure natural uranium) [µSv/Bq U-238]
Effective Dose per unit activity Uranium-238 contained in pure natural uranium inhaled. The dose is meant for the combination of all uranium nuclides present. The value obtained from ICRP72 is 17.79 µSv/Bq U-238.

Breathing rate (public) [m3/h]
(used for dose calculation from dust)

General Data: Radiation Risk Factor [1/Sv]
Fatal cancer risk for lifetime exposure of the general population at low doses and low dose rates per unit dose received. ICRP60(1991) uses a value of 0.05

 

Process Parameters

Ore Deposit: Waste/Ore Ratio
At conventional uranium mines, overburden and waste rock has to be removed to get access to the uranium ore. The waste-to-ore ratio can range between 1 and 5 for underground mines and between 1 and 60 for open pit mines.

Ore Deposit: Ore Grade [% U]
Weight-percent of uranium contained in the ore removed from the ore body for processing in the mill. Other units used are % U3O8, among others (see also Unit Conversion). Ore grades being processed at present cover a wide range of 0.026% U (Rössing, Namibia) to 1.1% U (Key Lake, Canada). New uranium mining projects under development even have ore grades of up to 12.7% U (McArthur River Project, Canada).

Mill: Extraction Losses [%]
Not all of the uranium contained in the ore can be recovered in the milling process. The extraction losses are depending on the grade of the ore processed. Upon entry of an Ore Grade value, the calculator presents an estimated value for the Mill Extraction Losses. If you want to use another value for the losses, you can overwrite it.

 

Air Dispersion Modeling

The calculator uses the sector-averaged Gaussian plume algorithm (for details, see NUREG-0706, or Parks1998). This algorithm is valid for flat land only.
The uranium mine, the mill and the tailings pile together are regarded as one point source, differing only by their effective release height. These simplifications produce some error in the near field.

In the "Fast" mode, there is no account for radon progeny ingrowth or plume depletion effects.
In the "Precise" mode, radon progeny ingrowth and plume depletion from precipitation scavenging and radon decay is taken into account. Precipitation is accounted for with a scavenging coefficient of 10-7 a/(cm s).
It is highly recommended to use the "Precise" mode.
There is no account for plume depletion from dry deposition.

For the graphs of lifetime dose vs. distance and wind direction, dispersion of dust is simplistically calculated together with radon. This introduces negligible errors.

 

Bibliography

 

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