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Radiation Exposure for Uranium Industry Workers

(work in progress - last updated 1 May 2021)

Contents:

Standards
Mine
Mill
HWR Fuel Plant
Magnox Fuel Plant
Conversion and Enrichment Plant
Depleted Uranium Storage Buildings
LWR Fuel Plant
Summary
References

> see also:

Workers: Standards

The applicable radiation dose standard for workers is 20 mSv/a (averaged over 5 years), and the fatal cancer risk is 0.04 per Sv, according to [ICRP60].

Exposure to 20 mSv/a over a work life of 40 years results in an excess lifetime fatal cancer risk of 3.2% (1 : 31).

The radon emanation rate from the Jabiluka ore deposit in Australia was determined at 15 Bq/m²·s per %U₃O₈ (18 Bq/m²·s per %U) ore grade [Sonter2000]. For secular equilibrium of the uranium series nuclides, this corresponds to 0.142 Bq/m²·s per Bq_Ra-226/g.

Exposure of Miners

Data according to [UNSCEAR1993]

Inhalation of radon / radon progeny
(typ. 69% of total dose for underground miners, and 34% for open pit miners [UNSCEAR1993] for 1985-1989)
See also: Uranium Miner Health Risk Calculator · Radon Individual Dose Calculator
External radiation
For underground positions totally within ore, a gamma dose rate factor of 70 µSv/h per %U₃O₈ (83 µSv/h per %U) ore grade was determined for the Jabiluka mine in Australia [Sonter2000].
External radiation represents typ. 28% of total dose for underground miners, and 60% for open pit miners. [UNSCEAR1993] for 1985-1989
Inhalation of uranium ore dust
The effective dose from inhalation of 1 mg uranium ore of an ore grade of 0.1% U is 0.42 µSv (for higher ore grades, the dose increases correspondingly). The 20 mSv annual standard is equivalent to 47.6 g. This corresponds to a uranium ore concentration in air of 16.5 mg/m³. (See also: Uranium Radiation Individual Dose Calculator )
(based on ICRP68 dose factors for insoluble compounds, breathing rate of 1.6 m³/h, working time of 1800 h/a, U-238 in equilibrium with progeny)
Inhalation of uranium ore dust represents typ. 3.2% of the total dose for underground miners, and 6.2% for open pit miners. [UNSCEAR1993] for 1985-1989

Typical individual doses vary within the range of 3 - 20 mSv/a (avg. 4.45 mSv/a) for underground miners, and within the range of 1 - 5 mSv/a (avg. 1.56 mSv/a) for open pit miners, with an average of 4.4 mSv/a over all uranium miners.
The collective dose for all 260,000 underground uranium miners worldwide is estimated at 1140 man-Sv/a, and for all 2500 open pit uranium miners at 3.76 man-Sv/a. This corresponds to 25.9 man-Sv per 1000 t uranium mined underground, and to 0.258 man-Sv per 1000 t uranium mined in open pits, with an average of 20 man-Sv per 1000 t for all uranium mined. [UNSCEAR1993] for 1985-1989
The expected number of fatal cancers in all uranium miners is 44 per year, or 0.8 per 1000 t uranium mined.

Data according to [IAEA2020]

In April 2020, IAEA published the results of a survey held among world uranium producers in 2012 [IAEA2020]. The data is only given in a bar chart (average annual individual doses to workers):

RDP: inhalation of radon decay products
LLRD: inhalation of long lived radionuclide dust
Gamma: external gamma radiation
ISL: in situ leaching

According to this survey, the average individual doses to underground uranium mine workers (approx. 1.8 mSv/a) are much lower now than reported in the [UNSCEAR1993] report, while the doses remain unchanged for open cut miners (approx. 1.5 mSv/a).
Most remarkably, the average individual doses to workers at uranium in situ leach mines (approx. 3.9 mSv/a) are at least twice those reported for conventional (underground and open cut) mines.

Workers at Uranium mill

Source Term

...

Exposure of mill workers

Data according to [UNSCEAR1993]

Inhalation of radon / radon progeny
(typ. 37% of total dose [UNSCEAR1993] for 1985-1989)
See also: Radon Individual Dose Calculator
inhalation of uranium ore dust
The effective dose from inhalation of 1 mg uranium ore of an ore grade of 0.1% U is 0.42 µSv (for higher ore grades, the dose increases correspondingly). The 20 mSv annual standard is equivalent to 47.6 g. This corresponds to a uranium ore concentration in air of 16.5 mg/m³. (See also: Uranium Radiation Individual Dose Calculator )
(based on ICRP68 dose factors for insoluble compounds, breathing rate of 1.6 m³/h, working time of 1800 h/a, U-238 in equilibrium with progeny)
> See also Uranium Biokinetics Calculator
> See also Internal Dosimetry Model for Applications to Bioassay at Uranium Mills, NUREG-0874 , U.S. NRC, 1986
inhalation of uranium concentrate dust
The effective dose from inhalation of 1 mg pure natural uranium is 0.2 mSv. The 20 mSv annual standard is equivalent to 100 mg. This corresponds to a uranium concentration in air of 34.7 µg/m³. (See also: Uranium Radiation Individual Dose Calculator )
(based on ICRP68 dose factors for insoluble compounds, breathing rate of 1.6 m³/h, working time of 1800 h/a)
> See also Uranium Biokinetics Calculator
> See also Internal Dosimetry Model for Applications to Bioassay at Uranium Mills, NUREG-0874 , U.S. NRC, 1986
Inhalation of uranium dust represents typ. 47% of the total dose for uranium mill workers. [UNSCEAR1993] for 1985-1989
external radiation
(typ. 16% of total dose [UNSCEAR1993] for 1985-1989)

Typical individual doses for uranium mill workers vary within the range of 0.1 - 13 mSv/a (avg. 6.3 mSv/a).
The collective dose for all 18,000 uranium mill workers worldwide is estimated at 116 man-Sv/a; this corresponds to 2.01 man-Sv per 1000 t uranium extracted. [UNSCEAR1993] for 1985-1989
The expected number of fatal cancers in all uranium mill workers is 4.64 per year, or 0.08 per 1000 t uranium extracted.

Data according to [IAEA2020]

In April 2020, IAEA published the results of a survey held among world uranium producers in 2012 [IAEA2020]. The data is only given in a bar chart (average annual individual doses to workers) - see above.
According to this survey, the average individual doses to uranium mill workers are now much lower than reported in the [UNSCEAR1993] report: approx. 0.5 mSv/a for processing at underground mines and approx. 1.5 mSv/a for processing at open cut mines.

Workers at Heavy Water Reactor Fuel Plant

For use in heavy water reactors (HWR), the uranium ore concentrate is refined (purified) and converted to UO₂. Then it is formed into pellets and filled into fuel rods. The fuel rods are bundeled into fuel elements.

Source Term

...

Exposure of HWR fuel fabrication workers

external radiation
inhalation of uranium dust
The effective dose from inhalation of 1 mg pure natural uranium (as contained in uranium ore concentrate or heavy water reactor fuel) is 0.2 mSv. The 20 mSv annual standard is equivalent to 100 mg. This corresponds to a uranium concentration in air of 34.7 µg/m³. (See also: Uranium Radiation Individual Dose Calculator )
(based on ICRP68 dose factors for insoluble compounds, breathing rate of 1.6 m³/h, working time of 1800 h/a)

The average individual dose for a heavy water reactor fuel fabrication worker is 1.67 mSv/a. The collective dose for all 1140 HWR fuel fabrication workers worldwide is estimated at 1.9 man-Sv/a; this corresponds to 1.21 man-Sv per 1000 t fuel fabricated. [UNSCEAR1993] for 1985-1989
The expected number of fatal cancers in all HWR fuel workers is 0.076 per year, or 0.048 per 1000 t fuel fabricated.

Workers at Magnox Reactor Fuel Plant

For use in Magnox reactors, the uranium ore concentrate is refined (purified) and converted to uranium metal. This is formed into fuel rods. The fuel rods are cladded and bundeled into fuel elements.

Source Term

...

Exposure of Magnox fuel fabrication workers

external radiation
inhalation of uranium dust
The effective dose from inhalation of 1 mg pure natural uranium (as contained in uranium ore concentrate or Magnox reactor fuel) is 0.2 mSv. The 20 mSv annual standard is equivalent to 100 mg. This corresponds to a uranium concentration in air of 34.7 µg/m³. (See also: Uranium Radiation Individual Dose Calculator )
(based on ICRP68 dose factors for insoluble compounds, breathing rate of 1.6 m³/h, working time of 1800 h/a)
pyrophoricity hazard from uranium metal
Finely divided particles of uranium metal can ignite and require special precautions.

The average individual dose for a Magnox fuel fabrication worker is 3.12 mSv/a. The collective dose for all 1,110 Magnox fuel fabrication workers in the United Kingdom is estimated at 3.48 man-Sv/a; this corresponds to 4.29 man-Sv per 1000 t fuel fabricated. [UNSCEAR1993] for 1985-1989
The expected number of fatal cancers in all UK Magnox fuel workers is 0.14 per year, or 0.17 per 1000 t fuel fabricated.

Workers at Uranium Conversion and Enrichment Plant

For use in light water reactors, the uranium ore concentrate is refined (purified) and converted to uranium hexafluoride (UF₆) in a conversion plant.
At the enrichment plant, the concentration of the fissile uranium isotope U-235 in the uranium hexafluoride is raised from its natural grade of 0.711% to the range of 3 - 5%.

Source Term

Additional hazards exist, if not only uranium of natural origin is processed, but also uranium recovered from reprocessing of spent nuclear fuel. The latter uranium is contaminated with radioactive transuranics and fission products.
The Paducah (Kentucky) uranium enrichment plant, for example, processed recycled uranium between 1953 and 1976. Paducah received approximately 90,000 metric tonnes of recycled uranium containing an estimated 3.6 ppb of plutonium-239, 0.2 ppm of neptunium-237 and 7.3 ppm of technetium-99. The majority of the plutonium and neptunium was separated out as waste during the initial chemical conversion to uranium hexafluoride. Because of this, only a fraction (0.03%) of the plutonium contamination was actually introduced to the gaseous diffusion cascade. (DOE Press Release Sep 29, 1999

)
Moreover, uranium recycled from spent fuel contains several artificial uranium isotopes, such as U-232, U-233, U-236, and U-237. Uranium-232 is of special concern, since some of its decay products are strong gamma emitters (in particular thallium-208).

Exposure of conversion and enrichment workers

inhalation of uranium concentrate dust
The effective dose from inhalation of 1 mg pure natural uranium is 0.2 mSv. The 20 mSv annual standard is equivalent to 100 mg. This corresponds to a uranium concentration in air of 34.7 µg/m³. (See also: Uranium Radiation Individual Dose Calculator )
If the uranium was recycled from spent fuel, the inhalation dose from 1 mg is 0.66 mSv. The 20 mSv annual standard is equivalent to 30.3 mg. This corresponds to a uranium concentration in air of 10.5 µg/m³.
(based on ICRP68 dose factors for insoluble compounds, breathing rate of 1.6 m³/h, working time of 1800 h/a, initial enrichment to 3.5%, burnup of 39 GWd/tHM, storage time of 5 years after unload)

external radiation from UF₆
The gamma dose rates measured at the surface of a uranium hexafluoride storage cylinder filled with depleted uranium hexafluoride are typically about 2 - 3 mrem/h (20 - 30 µSv/h), decreasing to about 1 mrem/h (10 µSv/h) at a distance of 30 cm [DOE1999] p.1-2.

For cylinders containing uranium recycled from spent fuel, gamma dose rates are 10 - 100 times higher than for uranium from natural sources:

Gamma dose rate at UF₆ cylinder of type 30B
(for initial enrichment to 3.2% and burnup of 33 GWd/tHM)
U-235 conc.
[wt_%] Storage time
[years] Dose rate [µSv/h]

surface 1 m 2 m

enriched natural U 3.2% - 4 1 0.4

recycled U 0.93% 0.25 40 10 4

2 90 22 9

enriched recycled U 3.44% 0.25 90 22 9

2 400 100 40

The type 30B cylinder has a nominal diameter of 30 inches (76.2 cm) and contains max. 2277 kg of UF₆
Source: [Neghabian1991] p.168 - 186

**Gamma dose rate at UF₆ cylinder of type 30B**
(for initial enrichment to 3.2% and burnup of 33 GWd/tHM)
	U-235 conc. [wt_%]	Storage time [years]	Dose rate [µSv/h]
surface	1 m	2 m
enriched natural U	3.2%	-	4	1	0.4
recycled U	0.93%	0.25	40	10	4
2	90	22	9
enriched recycled U	3.44%	0.25	90	22	9
2	400	100	40

For higher burnups, dose rates rise considerably, in particular after longer storage times:

Gamma dose rate at UF₆ cylinder of type 30B
(for initial enrichment to 4.4% and burnup of 50 GWd/tHM)
U-235 conc.
[wt_%] Storage time
[years] Dose rate [µSv/h]

surface 1 m 2 m

enriched natural U 4.4% - 5 1.5 0.6

recycled U 0.86% 0.25 50 13 5

2 160 40 16

enriched recycled U 4.93% 0.25 220 55 22

2 1200 300 120

The type 30B cylinder has a nominal diameter of 30 inches (76.2 cm) and contains max. 2277 kg of UF₆
Source: [Neghabian1991] p.168 - 186

**Gamma dose rate at UF₆ cylinder of type 30B**
(for initial enrichment to 4.4% and burnup of 50 GWd/tHM)
	U-235 conc. [wt_%]	Storage time [years]	Dose rate [µSv/h]
surface	1 m	2 m
enriched natural U	4.4%	-	5	1.5	0.6
recycled U	0.86%	0.25	50	13	5
2	160	40	16
enriched recycled U	4.93%	0.25	220	55	22
2	1200	300	120

In addition to gamma radiation, UF₆ cylinders also emit neutron radiation. The neutron radiation results from an (Alpha,n)-reaction of the uranium's alpha radiation with fluorine, and from spontaneous fission of U-238 (see: Alpha-Neutron Reaction Calculator ). Near cylinders carrying enriched uranium, up to 70% of the radiation exposure can be due to the neutron radiation. Near cylinders carrying depleted uranium, up to 20% of the radiation exposure can be due to the neutron radiation. [Urenco2002]

external radiation from "empty" cylinders containing heels
After unloading of UF₆ by heating in an autoclave, the non-volatile residue remaining in a cylinder (called "heels") emits gamma radiation (mainly from Pa-234m). As, in an "empty" cylinder, the gamma radiation is no longer shielded by the uranium, it can reach the cylinder surface nearly unhindered.
While the gamma radiation dose rate at 30 cm from a full cylinder carrying natural UF₆ reaches a few µSv/h, the dose rate rises approx. one-hundred-fold to 500 µSv/h at 30 cm from the bottom of the cylinder after unloading, making the "empty" feed cylinders the source of the highest gamma radiation fields in an enrichment plant [Bailey1975]!
For cylinders carrying recycled UF₆, the strong gamma emitter thallium-208 (Tl-208) remains with the heels in the cylinder, causing even higher gamma dose rates: such cylinders may not be suitable for transport and must be cleaned first. [IAEA1994]
inhalation of toxics during accidents
If the whole contents of a UF₆ cylinder is released during a fire, lethal air concentrations of toxic substances can occur within distances of 500 to 1,000 meters.
irradiation from criticality accidents
Persons standing nearby a criticality excursion may be exposed to lethal radiation doses of tens of Sieverts (see for example: Criticality accident at Tokai nuclear fuel plant).

The average individual dose for an uranium enrichment worker is 0.08 mSv/a. The collective dose for the 5,000 enrichment workers for whom data is reported is estimated at 0.43 man-Sv/a. [UNSCEAR1993] for 1985-1989
The average individual dose for cylinder yard workers at three U.S. enrichment plants ranged between 0.16 - 1.96 mSv/a during the years 1990-1995 [DOE1999] p.3-15/32/51.

Workers at Depleted Uranium Storage Buildings

Inside Areva's storage buildings for depleted uranium in the form of U₃O₈ at Bessines-sur-Gartempe in France, the dose rate (gamma only?) is measured as 30 - 35 µSv/h. [DRIRE2009]

Workers at Light Water Reactor Fuel Fabrication Facilities

In the fabrication plant for light water reactor fuel, the enriched uranium hexafluoride is converted to UO₂. Then it is formed into pellets and filled into fuel rods. The fuel rods are bundeled into fuel elements.

Source Term

Exposure of LWR fuel fabrication workers

external radiation
For external exposure from type 30B cylinders filled with enriched UF₆ or heels, see under Exposure of conversion and enrichment workers above
inhalation of uranium dust
The effective dose from inhalation of 1 mg natural uranium enriched to 3.5% is 0.676 mSv. The 20 mSv annual standard is equivalent to 29.6 mg. This corresponds to a uranium concentration in air of 10.3 µg/m³. (See also: Uranium Radiation Individual Dose Calculator )
If the uranium was recycled from spent fuel, the inhalation dose from 1 mg is 2.86 mSv. The 20 mSv annual standard is equivalent to 7.0 mg. This corresponds to a uranium concentration in air of 2.4 µg/m³.
(based on ICRP68 dose factors for insoluble compounds, breathing rate of 1.6 m³/h, working time of 1800 h/a, burnup of 39 GWd/tHM, storage time of 5 years after unload)
criticality accidents
Persons standing nearby a criticality excursion may be exposed to lethal radiation doses of tens of Sieverts.

The average individual dose for a light water reactor (LWR) fuel fabrication worker is 0.45 mSv/a. The collective dose for all 24,000 LWR fuel fabrication workers worldwide is estimated at 11 man-Sv/a; this corresponds to 1.6 man-Sv per 1000 t fuel fabricated. [UNSCEAR1993] for 1985-1989
The expected number of fatal cancers in all LWR fuel workers is 0.44 per year, or 0.064 per 1000 t fuel fabricated.

Workers: Summary

**Workers' Dose Summary**
	no. of workers	avg. individual dose [mSv/a]	collective dose [man-Sv/a]
all uranium miners	260,000	4.4	1,100
uranium mill workers	18,000	6.3	116
HWR fuel facility workers	1,140	1.67	1.9
Magnox fuel facility workers	1,110	3.12	3.48
enrichment workers	5,000	0.08	0.43
LWR fuel facility workers	24,000	0.45	11
AGR fuel facility workers	1,850	2.97	5.51
TOTAL	311,100	3.98	1,238

[UNSCEAR1993] for 1985-1989 (minor inconsistencies in ref.)

Workers' Risk Summary
no. of workers excess lifetime cancer risk* collective risk
[fatalities per year]

all uranium miners 260,000 0.7% 1 : 142 44

uranium mill workers 18,000 1.01% 1 : 99 4.64

HWR fuel facility workers 1,140 0.27% 1 : 374 0.076

Magnox fuel facility workers 1,110 0.5% 1 : 200 0.14

enrichment workers 5,000 0.013% 1 : 7812 0.017

LWR fuel facility workers 24,000 0.072% 1 : 1389 0.44

AGR fuel facility workers 1,850 0.48% 1 : 210 0.22

TOTAL 311,100 0.64% 1 : 156 49.5

* based on 40 working years
based on [UNSCEAR1993] for 1985-1989, using risk factor of 0.04 per Sv

**Workers' Risk Summary**
	no. of workers	excess lifetime cancer risk*	collective risk [fatalities per year]
all uranium miners	260,000	0.7%	1 : 142	44
uranium mill workers	18,000	1.01%	1 : 99	4.64
HWR fuel facility workers	1,140	0.27%	1 : 374	0.076
Magnox fuel facility workers	1,110	0.5%	1 : 200	0.14
enrichment workers	5,000	0.013%	1 : 7812	0.017
LWR fuel facility workers	24,000	0.072%	1 : 1389	0.44
AGR fuel facility workers	1,850	0.48%	1 : 210	0.22
TOTAL	311,100	0.64%	1 : 156	49.5

References

[Bailey1975] Uranium handling at the Oak Ridge gaseous diffusion plant , by J. C. Bailey, K-L-6346, 1975

[DOE1999] Final Programmatic Environmental Impact Statement for Alternative Strategies for the Long-Term Management and Use of Depleted Uranium Hexafluoride, DOE-EIS-0269, U.S. DOE, Germantown MD, April 1999
> Download PEIS from ANL or DOE EH

[DRIRE2009] Rapport d'inspection - Entreposage d'uranium appauvri de Bessines-sur-Gartempe (87), Le 17 juin 2009, DRIRE Limousin

[IAEA1994] Interim Guidance for the Safe Transport of Reprocessed Uranium , IAEA-TECDOC-750, IAEA, Vienna, June 1994, 68 pages (3.2M PDF)

[IAEA2020] Occupational Radiation Protection in the Uranium Mining and Processing Industry , Safety Reports Series No. 100, IAEA, April 2020 (6.1MB PDF)

[ICRP60] 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60, Oxford 1991

[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.

[NUREG-0713] Occupational Radiation Exposure at Commercial Nuclear Power Reactors and Other Facilities , Annual Reports, NUREG-0713, U.S. Nuclear Regulatory Commission

[NUREG/CR-4884] Interpretation of Bioassay Measurements , NUREG/CR-4884, July 1987 (38.6MB PDF)

[Sonter2000] Underground Radiation Studies and Observations in the Jabiluka Ore Access Drive, by Mark J Sonter, Australian Radiation Protection Society, ARPS25 Abstracts , 2000

[UNSCEAR1993] Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR 1993 Report to the General Assembly, with Scientific Annexes, United Nations , New York, 1993, 922 p.

[Urenco2002] Urananreicherungsanlage Gronau. Kurzbeschreibung des Endausbaus und der voraussichtlichen Auswirkungen auf die Umgebung. Stand: Dezember 2002, Urenco Deutschland

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