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Uranium Radiation Individual Dose Calculator - HELP

(last updated 12 Mar 2012)

Contents:


Introduction

This calculator performs radiation dose calculations for individuals exposed to uranium and/or its decay products. The calculator handles four different exposure situations: ingestion, inhalation, external from contaminated soil, and external from a point source.
The calculator considers the uranium-isotopes U-238, U-235, and U-234 and all their decay products. In case of uranium recycled from spent fuel, also U-236 and U-232 and their decay products are considered.
For an assessment of future exposure situations (waste management!), time delays can be selected, for taking decay and ingrowth of nuclides into account. The set of dose coefficients used can easily be switched between ICRP 60/61 and ICRP 68/72.

The calculator only determines exposure to radiation; the chemical toxicity of uranium is not covered (see Uranium Biokinetics Calculator and Uranium Toxicity).
The calculator only determines doses to exposed individuals. For collective dose calculations, see the Nuclear Fuel Population Health Risk Calculator.
The calculator only determines doses and dose rates for situations, where the pathway and the rate of exposure to a contaminant is known. Otherwise, some more sophisticated software has to be used (see Uranium in Soil and Building Material Individual Dose Calculator, Uranium Mine and Mill Resident Individual Dose Calculator and Dose modeling software).
The calculator only determines doses for adults. For age-specific dose calculations, see the Uranium Radiation Age-specific Dose Calculator.
The calculator only determines effective doses. For organ-specific dose calculations, see the Uranium Radiation Organ Dose Calculator.
For more sophisticated calculations of doses from external radiation, see the External Radiation Dose Calculator.

The parameters used for the calculation can be set in the Material Input and Exposure 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.

 

Material Input

Input
enter number (mandatory!) and select appropriate unit.

Type
select appropriate type

Parameters: ore grade [% U] (used for types "ore" and "mill tailings")
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).
Note: this parameter can also be used to assess the exposures to waste rock, by entering the appropriate uranium concentration.

Parameters: mill loss [%] (used for type "mill tailings")
Not all of the uranium contained in the ore is 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.

Parameters: natural uranium (used for types U ... U3O8)
uranium obtained from natural sources. The U-238 and U-235 decay series are considered.

in equilibrium with all progeny (used for natural uranium)
uranium of natural isotope composition, in secular equilibrium with all decay products (U-238 and U-235 series)
Note: to obtain results including just the short-lived progeny, rather use "pure" with Delay = "1 year".

pure (used for natural uranium)
pure uranium of natural isotope composition, without decay products. (0.711 weight-% U-235; U-234 in equilibrium with U-238).

enriched to ... wt% U-235 (used for natural uranium)
pure uranium with U-235 contents enriched to level higher than natural. Values for use in pressurized water reactors (PWR) range between 3.6% and 4.1 wt-% (weight-percent), and for use in boiling water reactors (BWR) between 3.0% and 3.2%.

depleted to ... wt% U-235 (used for natural uranium)
Pure uranium with U-235 contents depleted to lower than natural level. Typical values range between 0.2% and 0.3%. This tails assay can be selected according to economic feasibilty. Since the concentration of U-234 in depleted uranium is depending on the product assay obtained in the enrichment process, an input is also required for this figure.

Parameters: recycled uranium (used for types U ... U3O8)
uranium obtained from recycling of spent fuel. The U-236 and U-232 decay series are considered in addition to the U-238 and U-235 series. The U-237 and U-233 decay series are neglected for their insignificant dose contributions. Fission products and transuranics are not considered.
The composition of the uranium isotopes is determined according to the selection from the "burnup / initial enrichment" pick list, based on [Neghabian1991]. The burnup unit GWd/tHM stands for Giga-Watt-days per metric tonne heavy metal. A 5 year storage time after reactor unload is assumed.

as is (used for recycled uranium)
uranium as is recycled from spent fuel

re-enriched to initial U-235 equivalent (used for recycled uranium)
recycled uranium re-enriched to initial U-235 equivalent; the actual U-235 concentration is higher to compensate for the presence of U-236.

depleted to 0.2 wt% U-235 (used for recycled uranium)
recycled uranium depleted to 0.2 wt% U-235

 

Exposure Parameters

Exposure Situation
Select one.

Rate
determines the rate at which a person is exposed to the amount of material given in the Material Input section.
For ingestion and inhalation, there is the choice of a single exposure ("once") resulting in calculation of a dose (in Sv), and a variety of exposure rates, resulting in calculation of a dose rate (in Sv/h).
For external exposure on soil, the material input is used per gram of soil. If the person is standing on pure material, as may be the case for ore / waste rock, or mill tailings, then a mass of 1 g has to be entered in the material section, to obtain a correct result. Select contaminated surface area from Source area pick list.
For external exposure on plane, the material input is used per square meter of the surface on which the person is standing.
For external exposure to a point source, the distance in meters to the source must be entered. Note that the simplistic assumption of a point source introduces errors for real sources, in particular for small distances.

Occupancy (used for inhalation other than once, and for external exposure)
determines the time in a year a person is exposed at the given rate. The time can be entered in hours per year, or as percentage of total time, or continuous exposure can be selected.

Dose Factors
For ingestion and inhalation, there is a choice of three sets of ICRP dose coefficients. At present, the dose coefficients of ICRP60/61 (1990) are widely used, while revised dose coefficients have been presented for workers in ICRP68 (1995) and for the public in ICRP72 (1997). The new dose factors show significant differences from the old ones for the nuclides of interest.
The calculator simplistically uses only the committed effective dose coefficients, rather than the organ specific dose coefficients. It thus does not perform the exact calculations prescribed by ICRP; the results are approximations only.
All coefficients used are for adults. For inhalation, an activity median aerodynamic diameter (AMAD) of 1 m is assumed. The solubility class is selected according to the material type selected. For decay products, the calculator assumes the same solubility class as for the parent nuclide.
For external exposure on soil, the dose coefficients of [FGR12] for soil contaminated to infinite depth are used. These are based on ICRP 60/61 . It is assumed that the person is standing on a plane of soil contaminated to infinite depth. The dose is modified for source area by the area correction factors of [EPA2000].
For external exposure on plane, the dose coefficients of [FGR12] for exposure to contaminated ground surface are used. These are based on ICRP 60/61 . It is assumed that the person is standing on an infinite plane contaminated at the given specific surface activity.
For external exposure to a point source, only gamma radiation is considered. The calculator simplistically assumes an energy-independent mass absorbtion coefficient in air (en/rho) of 0.0028 m2/kg. The conversion factor from absorbed energy in air to effective dose is used as entered in the "Sv per Gy" field (UNSCEAR_2000 recommends 0.7 Sv/Gy for adults, 0.8 for children, and 0.9 for infants).

Delay
Delay in years, after which the dose assessment is performed.
The radiation from uranium and its decay products is not constant over time, although the half-lives of the natural uranium nuclides are extremely long (see uranium radiation properties). In cases, where disequilibrium obtains between uranium and its decay products, considerable increases of the radiation levels can occur over time, due to the ingrowth of decay products. This is of particular concern for the long-term management of uranium-bearing material as a waste, and for uranium recycled from spent fuel.
For Delay = "none" the isotopic composition as given by the parameters entered in the Material Input section is used for the calculation. However, this is not representative for most exposure situations, since short-lived decay products are growing in within a few months. So, a delay of "1 year" will best fit most actual exposure situations for natural uranium; "10 years" is of interest for situations involving recycled uranium, since there is a peak from the ingrowth of U-232 decay products.
For the management of uranium mill tailings and/or of radioactive waste dumps, design lives of 1000 or 10,000 years are of interest. For other delays, the time can be entered in the "other" field.
More than one delay can be checked to perform multiple calculations in a single run; this affects calculation time, however.
 

Bibliography

[EPA2000] Soil Screening Guidance for Radionuclides: Technical Background Document , EPA/540-R-00-006, U.S. Environmental Protection Agency, Washington, D.C., October 2000

[FGR12] U.S. EPA: Federal Guidance Report No. 12: External Exposures to Radionuclides in Air; Water; and Soil, EPA 402-R-93-081, September 1993
> download full text (1081k - PDF format)
> online lookup of FGR 12 dose factors for external exposure
> download database DFEXT of FGR 12 dose factors, contained in the DFACT package
[The FGR 12 dose factors are based on ICRP26. The DFEXT software also allows computing of the effective dose according to ICRP60: these values have been used here.]

[Neghabian1991] Verwendung von wiederaufgearbeitetem Uran und von abgereichertem Uran, von A.R. Neghabian, H.J. Becker, A. Baran, H.-W. Binzel, Der Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit (Hg.), Schriftenreihe Reaktorsicherheit und Strahlenschutz, BMU-1992-332, November 1991, 186 S.

[UNSCEAR_2000] Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes, Vol. I. United Nations, New York, 2000.

ICRP 60, ICRP 68, ICRP 72

 

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