TABLE OF CONTENTS

Acronyms and Abbreviations ....................................................................................................................... 6

1.0 Purpose and Scope.............................................................................................................................. 9

2.0 Site Description ................................................................................................................................ 11

2.1 PROCESS DESCRIPTIONS .................................................................................................. 11

2.1.1 Extrusion .................................................................................................................... 11

2.1.2 Rolling........................................................................................................................ 11

2.1.3 Forging ....................................................................................................................... 12

2.1.4 Uranium Metal Machining ......................................................................................... 12

2.1.5 Uranium Slug Production and Canning...................................................................... 13

2.1.6 Uranium Scrap Recovery and Casting ....................................................................... 13

2.2 SITE ACTIVITIES.................................................................................................................. 14

2.3 SOURCE TERMS................................................................................................................... 14

2.4 SAFETY.................................................................................................................................. 15

2.4.1 Available Mitigation Measures during Extrusion ...................................................... 15

2.4.2 Available Mitigation Measures during Uranium Rolling........................................... 15

2.4.3 Available Mitigation Measures during Uranium Forging .......................................... 16

2.4.4 Available Mitigation Measures during Uranium Metal Machining ........................... 16

2.4.5 Available Mitigation Measures during Uranium Slug Production and Canning........ 17

2.4.6 Available Mitigation Measures during Uranium Scrap Recovery and Casting ......... 17

3.0 Uranium Dosimetry.......................................................................................................................... 18

3.1 Characteristics of Uranium...................................................................................................... 18

3.2 Radiation Emissions................................................................................................................ 19

3.3 External Dosimetry.................................................................................................................. 20

Division of Compensation Analysis and Support

Site Profiles for Atomic Weapons Employers that Worked 

Uranium Metals

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Subject Expert: David Allen

Approval: Signature on file Date: 06/17/2011

Supersedes:

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James W. Neton, Associate Director for Rev. 0

Science
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3.3.1 Electron Dosimetry..................................................................................................... 20

3.3.2 Other Non-Penetrating Radiation............................................................................... 22

3.3.3 Photon Dosimetry....................................................................................................... 22

3.3.4 Neutron Radiation ...................................................................................................... 23

3.4 Dose Conversion Factors for External Doses.......................................................................... 25

3.4.1 Submersion in Contaminated Air............................................................................... 25

3.4.2 Exposures from Contaminated Surfaces .................................................................... 25

3.5 Internal Dosimetry................................................................................................................... 26

3.5.1 Inhalation.................................................................................................................... 28

3.5.2 Ingestion..................................................................................................................... 28

4.0 Occupational Medical Dose.............................................................................................................. 29

4.1 Chest X-Rays........................................................................................................................... 29

4.2 Pelvic X-Rays.......................................................................................................................... 29

5.0 Occupational Environmental Dose................................................................................................... 30

5.1 Environmental External Irradiation......................................................................................... 30

5.1.1 Environmental Doses During Operations................................................................... 30

5.1.2 After Operations and Initial Decontamination and Before FUSRAP Remediation ... 31

5.1.3 After FUSRAP Remediation ...................................................................................... 31

5.2 Environmental Internal Dose Due to Inhalation of Radioactive Material............................... 31

5.2.1 During Operations...................................................................................................... 31

5.2.2 After Operations and Initial Decontamination and Before FUSRAP Remediation ... 32

5.2.3 After FUSRAP Remediation ...................................................................................... 32

5.3 Summary of Occupational Environmental Doses ................................................................... 32

6.0 Occupational External Dose ............................................................................................................. 33

6.1 Submersion in Contaminated Air and Exposure to Contaminated Surfaces........................... 33

6.1.1 Exposures from Submersion in a Dust Cloud ............................................................ 33

6.1.2 Exposures from a Contaminated Surface ................................................................... 34

6.2 Whole Body Radiation Emitted from Metal Surfaces............................................................. 34

6.3 Nonpenetrating Radiation Emitted from Uranium Metal Surfaces......................................... 36

6.4 Summary of External Radiation Doses During Operation ...................................................... 37

7.0 Occupational Internal Dose .............................................................................................................. 42

7.1 Uranium................................................................................................................................... 43

7.1.1 Uranium Bioassay ...................................................................................................... 43

7.1.2 Uranium Air Sampling ............................................................................................... 43

7.1.3 Additional Assumptions for Assessing Internal Dose from Inhalation...................... 47

7.1.4 Uranium Intakes by Inhalation................................................................................... 48
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7.1.5 Resuspension During Periods with no Uranium Operations...................................... 49

7.1.6 Ingestion..................................................................................................................... 50

8.0 References........................................................................................................................................ 53
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LIST OF TABLES

Table 3.1. Isotopic composition of uranium at different enrichments 18

Table 3.2. Activity fraction (Bq contaminant/Bq uranium) of contaminants in recycled uranium 19

Table 3.3. Principal radiation emissions from natural uranium and its short-lived decay products that are 

of concern for external irradiation (not including bremsstrahlung) 20

Table 3.4 Beta Surface Exposure Rates from Equilibrium Thickness of Uranium Metal and Compounds 

(DOE-STD-1136) 21

Table 3.5. Neutron yields from spontaneous fission and (,n) reactions for oxides and fluorides 23

Table 3.6. Neutron yields for trace impurities in uranium 23

Table 3.7. Neutron dose rates from (,n) sources in uranium oxides 24

Table 3.8. Measured beta/gamma dose rates from containers of pitchblende ore 24

Table 3.9. Dose conversion factors for external dose due to submersion in uranium-contaminated air 25

Table 3.10 Dose conversion factors from natural uranium surface contamination 26

Table 3.11. Some internal dosimetry related characteristics of uranium 27

Table 4.1. Organ analogues for diagnostic chest X-ray 29

Table 5.1. Environmental external annual exposure to workers in non-operational areas of a facility. 31

Table 5.2. Environmental internal daily intakes to workers in non-operational areas of a facility. 32

Table 5.3. External doses and intakes for occupational exposure to environmental levels of radiation 32

Table 6.1. Dose rates from standard shapes of uranium metal 35

Table 6.2. Annual doses from penetrating photon radiation to a worker near bare uranium metal 35

Table 6.3. Annual doses from non-penetrating radiation to a worker’s skin near bare uranium metal 36

Table 6.4. Estimated annual doses, external exposure pathways, for metal-working processes. 38

Table 7.1. Some Internal Dosimetry Related Characteristics of Uranium Oxides 42

Table 7.2 Air sampling data for facilities extruding uranium rods 44

Table 7.3 Air sampling data for facilities rolling uranium rods 45

Table 7.4 Air sampling data for facilities forging uranium 45

Table 7.5 Air sampling data for facilities machining uranium 46

Table 7.6 Air sampling data for uranium slug production and canning 46

Table 7.7 Air sampling data for uranium scrap recovery 47

Table 7.8. Daily uranium intakes from uranium inhalation by process and job category 48

Table 7.9. Daily uranium intakes from uranium ingestion by process and job category 51
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RECORD OF ISSUE/REVISIONS

ISSUE

AUTHORIZATION

DATE

EFFECTIVE

DATE REV. NO. DESCRIPTION

12/13/2006 12/13/2006 0 New document to establish the technical 

basis for an exposure matrix for uranium 

metal sites.

06/16/2011 06/17/2011 1 Revision initiated to incorporate review 

comments. Added external beta dose from 

surface contamination. Expanded discussion 

in section 3.3.1. Additional editorial changes 

and typographical error corrections.
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Acronyms and Abbreviations

 alpha

 beta

γ gamma

μR microroentgen (0.000 001 roentgen)

μg microgram (0.000 001 gram)

(α,n) alpha-neutron (alpha particle absorbed, neutron emitted)

ABRWH Advisory Board on Radiation and Worker Health

ADU ammonium diuranate

AMAD activity median aerodynamic diameter

AP anterior-posterior

AWE Atomic Weapons Employer

BZ breathing zone

CATI Computer-Assisted Telephone Interview

Ci curie

CV coefficient of variation

d/m/m3disintegrations per minute per cubic meter

DCF dose conversion factor

DOL Department of Labor

dpm disintegrations per minute

d day

DR dose reconstruction

Dx diagnosis

DWA daily weighted average

E, E+, E 10 raised to the power, e.g., 2.37E4 = 2.37  104; 2.73E06 = 2.73  106

EEOICPA Energy Employees Occupational Illness Compensation Program Act

ESE entrance skin exposure

f1 fraction of radionuclide activity taken up into systemic circulation from the 

gastrointestinal (GI) tract

F ICRP Respiratory Tract Transportability Type Fast

FGR-12 Federal Guidance Report 12

FUSRAP Formerly Utilized Sites Remedial Action Program

g gram

GA general area

GSD geometric standard deviation

h hour

HASL [AEC] Health and Safety Laboratory

HLW high-level [radioactive] waste

HP health physicist

HRTM Human Respiratory Tract Model

ICD-9 International Classification of Diseases Revision 9

ICRP International Commission on Radiological Protection

IH industrial hygienist
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IMBA Integrated Modules for Bioassay Analysis

IREP Interactive Radioepidemiological Program

ISO isotropic

keV kiloelectronvolt

LAT lateral

LLW low-level [radioactive] waste

LOD limit of detection

LOGNORM4 computer program

m, m2, m3 meter, square meter, cubic meter

mg milligram (0.001 gram)

mR milliroentgen (0.001 roentgen)

mrem millirem (0.001 rem)

mrep millirep (0.001 rep)

M ICRP Respiratory Tract Transportability Type Moderate

MAC maximum allowable concentration

Max maximum

MCNP Monte Carlo N-Particle [computer code]

MED Manhattan Engineer District

MeV megaelectronvolt

Min minimum

MMAD mass median aerodynamic diameter

N/A not applicable

NIOSH National Institute for Occupational Safety and Health

NOCTS NIOSH Occupational Claims Tracking System

NORMSDIST() standard Normal distribution function in Microsoft Excel

NORMSINV() inverse standard Normal distribution function in Microsoft Excel

OCAS Office of Compensation Analysis and Support

PA posterior-anterior

pCi picocurie (0.000 000 000 001 Ci or 1012 Ci)

POC probability of causation

Q quality factor

R roentgen

ROT rotational

s second

S ICRP Respiratory Tract Transportability Type S

SD standard deviation (arithmetic)

SEC Special Exposure Cohort

SQRI Site Query Research Interface

TBD Technical Basis Document

TIB Technical Information Bulletin

TLD thermoluminescent dosimeter

TLV Threshold Limit Value ( American Conference of Governmental Industrial 

Hygienists)

Tn thoron (220Rn)
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TRU transuranic (i.e., elements with Z > 92, Np, Pu, Am, ...)

TWA time-weighted average

UMTRCA Uranium Mill Tailings Radiation Control Act

WL working level (a unit of potential alpha energy concentration)

WLM working level month (a unit of potential alpha energy exposure)

wR ICRP radiation weighting factor
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1.0 Purpose and Scope

Technical basis documents and site profile documents are not official determinations made by the 

National Institute for Occupational Safety and Health (NIOSH) but are rather general working documents 

that provide historic background information and guidance to assist in the preparation of dose 

reconstructions at particular sites or categories of sites. They will be revised in the event additional 

relevant information is obtained about the affected site(s). These documents may be used to assist 

NIOSH staff in the completion of the individual work required for each dose reconstruction.

In this document the word “facility” is used as a general term for an area, building, or group of buildings 

that served a specific purpose at a site. It does not necessarily connote an “atomic weapons employer 

[AWE] facility” or a “Department of Energy [DOE] facility” as defined in the Energy Employees 

Occupational Illness Compensation Program Act of 2000 [EEOICPA; 42 U.S.C. § 7384I(5) and (12)]. 

EEOICPA, as amended, provides for employees who worked at an AWE facility during the contract 

period and/or during the residual period.

Under EEOICPA, employment at an AWE facility is categorized as either (1) during the DOE contract 

period (i.e., when the AWE was processing or producing material that emitted radiation and was used in 

the production of an atomic weapon), or (2) during the residual contamination period (i.e., periods that 

NIOSH has determined there is the potential for significant residual contamination after the period in 

which weapons-related production occurred). For contract period employment, all occupationally derived 

radiation exposures received at covered facilities must be included in dose reconstructions. This includes 

radiation exposure related to the Naval Nuclear Propulsion Program and any radiation exposure received 

from the production of commercial radioactive products that were concurrently manufactured by the 

AWE facility during the covered period. NIOSH does not consider the following exposures to be 

occupationally derived (NIOSH 2010):

 Background radiation, including radiation from naturally occurring radon present in conventional 

structures

 Radiation from X-rays received in the diagnosis of injuries or illnesses or for therapeutic reasons

For employment during the residual contamination period, only the radiation exposures defined in 42 

U.S.C. § 7384n(c)(4) [i.e., radiation doses received from DOE-related work] must be included in dose 

reconstructions. Doses from medical X-rays are not reconstructed during the residual contamination 

period (NIOSH 2010). It should be noted that under subparagraph A of 42 U.S.C. § 7384n(c)(4), 

radiation associated with the Naval Nuclear Propulsion Program is specifically excluded from the 

employee’s radiation dose. This exclusion only applies to those AWE employees who worked during the 

residual contamination period. Also, under subparagraph B of 42 U.S.C. § 7384n(c)(4), radiation from a 

source not covered by subparagraph A that is not distinguishable through reliable documentation from 

radiation that is covered by subparagraph A is considered part of the employee’s radiation dose. This site 

profile covers only exposures resulting from nuclear weapons-related work. Exposures resulting from 

non-weapons-related work, if applicable, will be covered elsewhere.

The two principal purposes of this technical basis document are (1) to provide information sufficient to 

enable dose reconstructors to estimate doses for these workers on an individual basis under the provisions 

of EEOICPA and (2) to allow claimants, federal assessors, and others to understand the information 

sources and assumptions on which the dose estimations are based.
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This document provides an exposure matrix for workers at AWE facilities that performed metal-working 

operations with uranium metal. Over 110 facilities performed these operations, and this document intends 

to provide guidance for dose reconstruction at any of these facilities. The main body of this document, in 

Sections 2-6, includes general discussions of operations and exposure conditions at these facilities. 

Following the main body of this document is a collection of appendices, with one appendix for each AWE 

site that performed metal-working operations. Each appendix contains site-specific information that can 

be used for dose reconstruction. For those sites where this information is insufficient or totally lacking, 

the dose reconstructor must use information in the main body of the TBD.
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2.0 Site Description

2.1 PROCESS DESCRIPTIONS

The processes covered in this TBD all involve working with uranium metal. 

2.1.1 Extrusion

Extrusion was a common method to change the dimensions of a large-diameter ingot of uranium metal 

into a long small-diameter rod. The original billets and the resulted rods had diameters that varied 

depending on the process and the desired product. In one case, a 11⁄4-in. diameter billet was extruded into 

a 3/8-in diameter rod. In another case the billet was 41⁄4-in. and 10-to-12 in. long. A variety of extrusion 

techniques were tested: extrusions were tested in the high-temperature range of the alpha phase of 

uranium and at temperatures throughout the gamma phase.

Harris and Kingsley (1959) describe the following steps for a typical commercial uranium metal extrusion

in the alpha phase:

 The ingot is heated in a salt bath furnace to a temperature of 1170F.

 The ingot is conveyed to a press, and extruded through a die block into a long, thin rod. About 12 

extrusions per hour can usually be performed.

 The extruded rod is passed through a quenching jacket onto a run-out trough.

 The butt-end of the extruded piece is cut off and thrown into a drum.

 The cut-end of the rod is reamed with an abrasive material mounted on a portable drill.

 The extruded rod is dragged using a grappling wire onto a run-out table, where it is stamped for 

identification and accountability.

 The die-block is deburred using abrasive material on the end of a portable drill.

 The rods are cut to a desired length.

 The rods are weighed, packed in shipping containers, and moved to the shipping area.

Several steps in this operation have the potential to release uranium oxide into the air, particularly after 

the actual extrusion. Section 2.4.1 describes measures that are used to reduce worker exposure in an 

extrusion plant.

2.1.2 Rolling

Rolling was another common method in the metal-working industry to change the dimensions of a largediameter billet of uranium metal into a long small-diameter rod. AWE sites tested a variety of rolling 

methods, including cold rolling and hot rolling in both the alpha and beta phases. 

Harris and Kingsley (1959) describe the following steps for uranium metal rolling in the alpha range, a 

common commercial practice:

 A uranium billet or slab is heated in a furnace to a temperature of about 1170F. The furnace 

may be a gas-fired, induction furnace, or a salt-bath or lead-bath. The salt- and lead-bath 

furnaces significantly reduced oxidation at the metal surface, reducing workplace air 

concentrations.

 The heated billet is removed from the furnace and conveyed to a roughing mill (also called a 

blooming mill) for lengthening into shapes (rods or slabs) of rough dimensions. Several passes in 

the roughing mill may be utilized.
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 After roughing, the rod or slab is sent to one or more finishing mills, for reducing to the final 

dimension.

 The finished item is conveyed to shears for cutting to the desired length.

 The item is then conveyed to an area where it is quenched or air cooled and stamped.

 After stamping, the items may be descaled, and straightened, bundled, weighed, recorded, 

packed, stored and shipped.

All of these operations may have been performed manually, or many may have been automated.

Most of these operations were capable of releasing large quantities of uranium dust to the atmosphere. 

Uranium readily oxidizes when exposed to air at temperatures above 600 F. The oxide scale formed on 

the surface spontaneously flakes off at elevated temperatures and is easily disturbed upon handling. The 

oxide formation and flaking produces high air concentrations and dust collection on the workplace floor 

and other surfaces. Any worker movement on a dusty floor will resuspend dust into the air, so that 

elevated air concentrations can be produced after the rolling has stopped. Safety measures to mitigate the 

air concentrations are discussed in Section 2.4.2.

2.1.3 Forging

Forging was another method for re-shaping uranium metal ingots. Two types were employed at AWE 

facilities, hot press forging and hammer forging.

In hot press forging, the ingot was heated in a salt bath to a working temperature of about 1170F. It was 

then conveyed on a monorail or conveyor to the flat die forge press. There were three pressings, with the 

pressed uranium returned to the salt bath after each of the pressings. After pressing, the lengthened 

uranium slab was quenched in a water tank, packaged and stored for shipment. Hot press forging 

produced low air concentrations of uranium because the metal was covered with a protective layer from 

the salt bath for most of the operations.

In hammer forging, the ingot was heated to the working temperature in an oil-fired air furnace, then 

moved to the forging die, where it was hammered to the desired dimensions. Upon completion of 

forging, the hammered metal was marked for identity, then moved to an area where it cooled in air. It 

was subsequently conveyed to a rolling mill for further working. The average cycle time for forging one 

ingot was about 10 minutes, with about 200 hammer blows administered to the ingot.

Hammer forging produced much higher air concentrations than hot press forging. The metal oxidized in 

the furnace, and the oxide fell off the metal as it was moved from the furnace to the die. Then each 

hammer blow knocked much of the scale from the metal surface, exposing more hot metal to air where it 

quickly oxidized to provide more scale for the next hammer blow. 

2.1.4 Uranium Metal Machining

After uranium metal rods were rolled or extruded, and before they were encased in cans as reactor fuel 

slugs, many machining steps were typically performed. In many ways these operations were similar to 

standard machine shop operations, but they needed to take into account the unique metallurgical 

properties of uranium. They also required more care to minimize the generation of oxide scale, which 

was an inhalation hazard to workers in the shop, and they needed to account for the pyrophoric nature of 

uranium metal.
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Machining processes commonly employed at AWE facilities include lathe operations, centerless grinder, 

abrasive cut-off wheel, sawing, milling, shaping, surface grinding, belt sanding, planning, and drilling.

2.1.5 Uranium Slug Production and Canning

Uranium slugs are segments of uranium metal rods used as basic elements of fuel rods in the production 

reactors. They are canned in a protective cladding. The earliest slugs were solid, but some later designs 

had a hole drilled through the cylindrical axis.

Typically, a rod 5 or 6 feet long, 1.425 to 1.475-in diameter, was used after it had been straightened, 

outgassed and finished to remove surface imperfections. A machinist began by finishing one end of the 

long rod, which was then put on a lathe to reduce the diameter to 1.36-in, and an 8-in length was cut off 

(for some reactor applications the lengths were 8.5-in). Both the length and diameter required tight 

tolerances. The cut end of the slug was then finished and all corners were rounded.

Another option for producing a slug is powder metallurgy, where powdered uranium metal is produced, 

and hot-pressed in a die to form a uranium slug. This process was less common than cutting sections 

from rolled or extruded rods.

Early attempts to encase the slugs in a protective can placed the slugs in aluminum cans without bonding 

the uranium to the can. This method was sufficient for early test reactors like the X-10 at Oak Ridge but 

was found to be unsuitable for the Hanford production reactors because of poor heat transfer. A “tripledip” slug coating process was developed at Hanford in 1944. Later Hanford developed a coextrusion 

process that installed a protective jacket as part of the extrusion process.

2.1.6 Uranium Scrap Recovery and Casting

Uranium is a sufficiently valuable material that scrap recovery is a cost-effective process. A plant that 

practices metal-working operations will collect all the chips, shavings and turnings, along with butt-ends 

from extrusions and similar cast-off pieces for melting and subsequent re-use. Most plants will compress 

the small pieces into a “briquette,” which can be stored and later melted and cast into ingots.

The uranium metal scraps were collected at the machining sites in 30- or 55-gallon drums, usually with 

the pieces kept under water or oil to avoid oxidation. The drums were brought to the collection site for 

cleaning, sorting, and pressing into a briquette. The pieces that are pressed into a briquette must be pure 

uranium metal, with minimal inclusion of uranium oxides or other material such as dust or steel. The 

metal in the briquette should be free of grease and cutting fluid. During the Manhattan Project, 

preparation of the material was done by hand sorting and cleaning, using hand tools such as small rakes. 

In later years the preparation was automated. Pieces were dumped into a crusher, washed, degreased and 

finely divided before loading into the pressing machine.

During pressing of the briquette, heat was generated inside the pressing machine, and the edges of the 

briquette could be ignited by this heat. When the briquette was unloaded, uranium oxide fumes could be 

released to the air.

For uranium oxide scrap, the scrap is collected and sent back to a refining plant to be converted to UF4

and then reduced and cast.

Uranium metal scrap, either in the form of a briquette or larger chunks such as billet butt-ends or rejected 

slugs, are placed in a graphite crucible and reheated to melt the metal. At the proper temperature for 
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pouring, a plug is removed from the crucible and the liquid metal drains into a form for new ingots or 

billets.

2.2 SITE ACTIVITIES

Uranium metal working was almost non-existent before 1942. In 1942-43, the first major studies of 

metallurgical properties were performed at the University of Chicago’s Metallurgical Laboratory and in 

several other universities and industrial research centers. These early research sites are AWE facilities.

The first large-scale requirements for uranium metallic products was fuel for Oak Ridge’s X-10 research 

reactor and the Hanford plutonium production reactors in 1943. In this year more than a dozen industrial 

facilities were contracted to roll and extrude uranium rods, and then produce fuel slugs. These and many 

other industrial AWE sites continued to develop metal-working techniques and produced production 

quantities of uranium metal products over the next two decades.

Hanford also developed uranium metal-working capabilities and operated fabrication facilities that 

provided much of the fuel needed for the Hanford production reactors from 1944 through 1971.

The Feed Materials Production Center was opened near the village of Fernald, Ohio in 1951, and by 1954 

it was fully operational. This facility had extensive capabilities in all areas of uranium metalworking and 

was a major producer for the AEC in the mid- and late-1950s and the 1960s. The Weldon Spring Plant in 

Missouri was a backup to the Fernald facility, operating from 1957 – 1967.

While Hanford, Fernald and Weldon Spring supplied a large volume of uranium metal products for the 

weapons complex, many AWE sites contributed to this effort in the decades following 1943. The AWE 

sites developed and tested new metal-working techniques, such as doing an experimental rolling of billets 

into rods. During some years, AWE sites were major providers of uranium metal to AEC facilities; 

during other years they did small production runs to supplement the work performed at Hanford, Fernald, 

or Weldon Spring. They also performed specialty functions not handled by the big AEC facilities.

The appendices to this TBD give detailed descriptions of the activities performed at each AWE facility 

that performed uranium metal-work.

2.3 SOURCE TERMS

Fuel for the production reactors during the Manhattan Project used uranium with no enrichment (“natural 

uranium”). Natural uranium continued to be used exclusively until the early 1950s, when some lowenriched uranium was used in reactor fuel. Most metal work at AWE sites used natural uranium. When 

enriched uranium was required, the metal working was usually performed at Hanford, Fernald or Weldon 

Springs, although some of these operations were developed at AWE sites, so some enriched uranium 

work occurred at these sites. Also several specialty applications with enriched uranium were performed 

at AWE sites. Recycled uranium may have appeared at some AWE sites after 1952, but before 1952 

there was no recycled uranium.

Most uranium at these sites was in the metallic form, but oxidation occurred readily during many 

operations. Thus oxides of uranium were present, and most of the internal exposure to uranium, by 

inhalation or ingestion, involved uranium oxides.
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2.4 SAFETY

Since uranium metal oxidizes readily, particularly at elevated temperatures, airborne uranium dust 

concentrations far exceeded accepted limits and guidance levels if no mitigation measures were 

employed. At AWE metalworking sites, a variety of safety measures were employed. Dust mitigation 

technologies continually improved from the mid-1940’s onward, so the earliest metal-working plants 

typically had primitive safety measures, or none at all, while sites operating in later years had more 

effective technologies. Even with the more effective technologies, however, hazardous dust levels could 

be observed in AWE facilities. A number of AWE facilities also were involved in only limited-duration 

operations and did not employ all available safety technologies for these operations. 

This section presents a summary of the types of mitigation measures that were available and sometimes 

employed. The description is based on (Harris and Kingsley 1959) so it is most closely representative of 

late-1950s technology. Some of the mitigation measures described here were not employed in the 1940s 

or early 1950s. As an example, salt baths are described for extrusion and rolling but they were not 

commonly employed for either process before 1951.

2.4.1 Available Mitigation Measures during Extrusion

If the ingot was heated in a salt bath, the resulting coating prevented uranium oxidation up to the point 

where it passed through the die block (the actual extrusion). However, the extrusion removed the 

protective coating and oxidation then became a problem. The major sources of contamination were 

(Harris and Kingsley, 1959):

 Fumes released when cutting off the butt end, tossing the end into a drum, and deburring the die 

block.

 Suspension of surface oxides at the run-off table and weigh area. Handling of the rods at these 

locations released the oxides into the air.

 Release of oxides at the discharge of the extrusion press, during extrusion and cut-off. 

 Poor housekeeping, particularly from dust accumulations at the conveyors and run-out table 

during material and personnel movement.

The following mitigation measures have been employed in plants performing uranium metal extrusions:

 Quenching: various rates of quenching were tested and it was found that the largest quench rate, 

immediately after extrusion, was most effective in minimizing oxide production.

 Ventilation at the extrusion press discharge: a hood that was carefully designed would limit dust 

generation after extrusion, and during cropping of the rod and during deburring of the die block.

 A hood surrounding the drum that holds the cropped butt-ends would limit dust.

 Dust catch pans positioned under roller conveyors would contain dust dropped from the 

conveyor.

 Steel grating on the floor would prevent workers from resuspending dust from the floor. Frequent 

vacuuming of the dust from the spaces in the grating was required to maintain effectiveness.

2.4.2 Available Mitigation Measures during Uranium Rolling

Harris and Kingsley (1959) describes the following recommended measures for controlling airborne dust 

in a uranium metal-rolling plant:

Oxidation of uranium metal occurred in the furnace when bringing the metal up to a temperature suitable 

for rolling. Two methods were developed for controlling this oxidation: a lead bath and a salt bath. Both 

of these methods excluded oxygen from contacting the metal surface during heating, and left a protective 
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coating on the heated metal that would reduce oxidation during rolling operations. The salt bath, utilizing 

a mixture of lithium and potassium salts, was more effective than the lead bath.

Ventilation was another measure employed to reduce dust loadings in the air at rolling sites. Ventilation 

over the roughing rolls was effective, particularly when a canopy hood with side shields was in place. 

Similar ventilation and hoods over other rolls was also effective. Man-cooling fans were sometimes 

positioned to blow the dust clouds away from the rolls, but while this method reduced the exposure of the 

roll operators, it increased the exposure of other workers and spread contamination around the plant. 

Ventilation utilizing hoods was also effective at other operations in the rolling plant, such as shearing, 

quenching, stamping, descaling and straightening.

Aggressive housekeeping practices, including the use of floor grates and vacuuming, also was helpful in 

controlling airborne dust. Workers walking on grating resuspended much less dust than walking on a 

smooth dust-laden floor. Frequent vacuuming of the dust from the openings in the grating was required 

to maintain effectiveness. Maintenance of the grating was also required to correct the flattening when 

heavy equipment drove over it. Frequent cleaning of the furnace to remove the scale that collects on the 

furnace floor is another measure that was necessary to keep dust loading low.

Experience showed that deliberately dripping water onto the rolls when they were hot increased air 

concentrations. Steam clouds formed from this operation, carrying fine particles of uranium oxide into 

the air. Air concentrations increased by a factor of 30 when water was dripped onto metal on the 

roughing rolls.

2.4.3 Available Mitigation Measures during Uranium Forging

The salt bath used in hot press forging was an effective method of uranium dust control. Well-designed 

ventilation control in hammer forging would be an effective method to control dust production. The 

housekeeping-related methods of dust control, such as using grating on the floor and frequent vacuuming, 

would also be effective mitigation methods.

2.4.4 Available Mitigation Measures during Uranium Metal Machining

Surface oxides are not formed or loosened during machining to the extent that they are during rolling and 

extrusion, because the metal is typically near room temperature for machining. The biggest generator of 

uranium dust is probably the ignition of small chips and turnings that are generated during machine 

operations. Mitigation measures typically focused on the control of these small metal pieces.

The most common mitigation measure was to flood the operation with coolant, which entrained the metal 

chips and prevented them from igniting. Machining technique was also critical – typically a low machine 

speed with a deep cut was best for reducing the generation of chips. The blade should also be kept sharp. 

For basic cutting operations, local ventilation was not necessary when sufficient coolant was supplied to 

the operation and optimal machining technique was followed. Major dust-generating operations such as 

grinding and sanding would require local ventilation, including enclosures around the machine, to 

minimize dust generation. In actual practice, application of ventilation was not always applied to the 

machining operations which needed it.
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2.4.5 Available Mitigation Measures during Uranium Slug Production and Canning

Safety measures employed during uranium slug production were very similar to measures employed 

during machining. A heavy coolant flow was directed over the metal as it was worked in the lathe to 

prevent oxidation, and to entrain the metal chips, preventing them from igniting.

2.4.6 Available Mitigation Measures during Uranium Scrap Recovery and Casting

The biggest opportunity for exposing a worker to uranium dust during scrap recovery was during the 

pressing of uranium scraps into a briquette, especially when opening the press. Heat generated inside the 

press often ignited the edges of the briquette, emitting fumes.

Local ventilation is usually the most effective means of limiting uranium dust concentrations in the air. 

Good ventilation has been shown to reduce air concentrations in the vicinity of briquetting by a factor of 

4.
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3.0 Uranium Dosimetry

This TBD discusses the radiation doses that could result from work at AWE uranium metal-working sites. 

This section describes the dosimetry of uranium. 

3.1 Characteristics of Uranium

Uranium is a heavy metal. There are several isotopes of uranium and, depending on the process in 

question, uranium may have been enriched in some of the isotopes. Most AWE uranium metal-working

sites were concerned with natural uranium.

All isotopes of uranium are radioactive and the decay progeny of uranium are also radioactive, forming a 

long decay chain. For the most part, the radioactive progeny of uranium were separated from uranium 

during refining. After those processes were completed, only the uranium isotopes were present. But 

some ingrowth of uranium progeny does occur even after a short time (~100 days) with a dose rate that 

exceeds the dose rate from pure uranium.

Uranium consists of four isotopes, 234U, 

235U, 236U, and 238U. The term enrichment refers to the extent to 

which the amount of 235U has been increased relative to naturally occurring uranium. The relative 

amounts of each isotope for different enrichments were obtained from IMBA Expert – OCAS Edition and 

are listed in Table 3.1.

Table 3.1. Isotopic composition of uranium at different enrichments

Enrichment Isotope

Weight 

Fraction

Specific Activity

Bq/mg pCi/mg dpm/mg

Depleted 234U 0.000010 2.31×1000 6.24×10+01 1.39×10+02

235U 0.001991 1.59×10-01 4.30×10

+00 9.55×10+00

236U 0.000003 7.44×10-03 2.01×10-01 4.46×10-01

238U 0.997996 1.24×10+01 3.35×10+02 7.45×10+02

Total 1.49×10+01 4.02×10+02 8.93×10+02

Natural 234U 0.000054 1.24×10+01 3.35×10+02 7.44×10+02

235U 0.007204 5.76×10-01 1.56×10+01 3.46×10+01

236U 0.000000 0.00×10+00 0.00×10+00 0.00×10+00

238U 0.992742 1.23×10+01 3.33×10+02 7.41×10+02

Total 2.53×10+01 6.84×10+02 1.52×10+03

Low 

Enrichment

234U 0.000290 6.70×10+01 1.81×10+03 4.02×10+03

235U 0.034989 2.80×10+00 7.56×10+01 1.68×10+02

236U 0.000000 0.00×10+00 0.00×10+00 0.00×10+00

238U 0.964722 1.20×10+01 3.24×10+02 7.20×10+02

Total 8.18×10+01 2.21×10+03 4.91×10+03

High 

Enrichment

234U 0.010606 2.45×10+03 6.62×10+04 1.47×10+05

235U 0.934636 7.47×10+01 2.02×10+03 4.48×10+03

236U 0.002075 4.97×10+00 1.34×10+02 2.98×10+02

238U 0.052683 6.55×10-01 1.77×10+01 3.93×10+01

Total 2.53×10+03 6.84×10+04 1.52×10+05

234U 0.000082 1.90×10+01 5.13×10+02 1.14×10+03
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Enrichment Isotope

Weight 

Fraction

Specific Activity

Bq/mg pCi/mg dpm/mg

Recycled

235U 0.009700 7.76×10-01 2.10×10+01 4.65×10+01

236U 0.000680 1.63×10+00 4.40×10+01 9.77×10+01

238U 0.989500 1.23×10+01 3.33×10+02 7.38×10+02

Total 3.37×10+01 9.10×10+02 5.03×10+03

Table 3.1 includes a reference to recycled uranium. Recycled uranium is uranium that has been irradiated 

in a reactor and from which the plutonium has been extracted. Recycled uranium will contain 236U, 

sparingly found in naturally occurring uranium, due to the processes in a reactor. Note that high 

enrichment uranium contains appreciable amounts of 236U while low enriched uranium contains virtually 

no 236U. The reason for this apparent discrepancy is that high enriched uranium is generally derived from 

recycled uranium and is commonly associated with weapons development whereas low enriched uranium 

is generally associated with the commercial fuel cycle where the feed material for enrichment is natural 

uranium. 

For the time period from 1944 until 1952, all uranium used by the DOE (and predecessor agencies) was 

derived from natural sources because processes that recover uranium from spent fuel were not available 

(DOE 2003, p 14). There is the possibility that uranium processed in refineries after 1953 was recycled 

uranium or contained recycled uranium, so for these time periods, in the absence of definitive information 

about the origin of the processed uranium, it should be assumed that the uranium contains the 

contaminants listed in Table 3.2 (ORAUT 2006). The appendices for each site should contain

information concerning whether recycled uranium was present at the site.

Table 3.2. Activity fraction (Bq contaminant/Bq uranium) of contaminants in recycled uranium

Recycled Uranium Contaminant 239Pu 237Np 99Tc 232Th 228Th 

Activity fraction of contaminant in uranium 0.00246 0.00182 0.379 2.73E-06 2.73E-06

Contaminant in ppb of uranium 10 1,040 9,000 10,888 *

* assumes same activity as Th-232

3.2 Radiation Emissions

Natural uranium emits both beta particles (electrons) and photons (x ray and gamma photons), as shown 

in Table 3.3, derived from Kocher (1981). The two primordial components of natural uranium are 238U

and 235U, but some of their decay products grow into equilibrium quickly enough to be hazardous in 

processing metal.

Uranium-238 transitions by alpha decay to 234Th, emitting traces of weakly penetrating ~ 13 keV L x rays. 

However, 234Th transitions primarily to 1.17-minute 234mPa, the metastable state of protactinium-234, 

which in turn transitions to 234U with the emission of a 2.28-MeV beta particle in 98.6% of transitions 

(Kocher 1981). This relatively high-energy beta particle accounts for significant external dose rates to 

skin, lens of the eye, and to a certain extent to shallow portions of other tissues. It also produces 

significant bremsstrahlung X-rays, primarily in the 30-250 keV energy range. Dose rates from uranium 

metals are presented in Sections 6.2 and 6.3.

Uranium-235 emits alpha particles and gamma photons in about 70% of its transitions, but occurs as 

0.7200 atom % in natural uranium. 

Like 238U, 

234U emits alpha particles and traces of weakly penetrating L x rays.
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Table 3.3. Principal radiation emissions from natural uranium and its short-lived decay products that are 

of concern for external irradiation (not including bremsstrahlung)

Radionuclide Half-life Beta Energy (MeV Max)

Photon (x or ) Energy 

(MeV)

238U 4.468E+9 years None x: 0.013 (8.8%)

234Th 24.1 days 0.096 (25%) x: 0.013 (9.6%)

0.189 (73%)  0.063 (3.8%)

 0.093 (5.4%)

234mPa 1.17 minutes 2.28 (98.6%)  0.765 (0.2%)

~1.4 (1.4%)  1.001 (0.6%)

235U 7.038E+8 years None x: 0.013 (31%)

x: 0.090-0.105 (9.3%)

 0.144 (10.5%)

 0.163 (4.7%)

 0.186 (54%)

 0.205 (4.7%)

231Th 25.5 hours 0.206 (15%) x: 0.013 (71%)

0.288 (49%)  0.026 (14.7%)

0.305 (35%)  0.084 (6.4%)

234U 244,500 years None x: 0.013 (10.5%)

 0.053 (0.2%)

3.3 External Dosimetry

External dosimetry refers to the radiation dose received from radioactive material that is outside the body. 

External doses can be associated with immersion in airborne radioactive material, accumulations of 

radioactive material associated with a particular process and radioactive material that contaminates the 

floor or other surfaces.

For consistent presentation, exposure or dose is reported as:

 penetrating, assumed to be associated with photons of energies 30 keV or greater, and

 nonpenetrating, assumed to be associated with photons of energies less than 30 keV or with 

electrons. 

Nonpenetrating dose from natural uranium consists primarily of electrons with energies >15 keV. 

3.3.1 Electron Dosimetry

Uranium metal and compounds emit beta and electron radiation that can irradiate the skin, and to a more 

limited extent, the shallow organs of the body. Table 3.4, taken from DOE-STD-1136 (DOE 2004) 

shows the measured beta surface dose rates from uranium metal and selected uranium compounds.
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Table 3.4 Beta Surface Exposure Rates from Equilibrium Thickness of Uranium Metal and Compounds 

(DOE-STD-1136)

Source

Beta Surface Exposure

Rate, mrad/ha

U-Nat metal slab 233

UO2 207

UF4 179

UO2(NO3)26H20 111

UO3 204

U3O8 203

UO2F2 176

Na2U2O7 167

a. Beta surface exposure rate in air through a polystyrene 

filter 7mg/cm2thick.

The data shown in Table 3.4 show that the dose rates from uranium metal exceed the dose rates from 

other uranium compounds. However, the dose rates from uranium oxides and UF4 are sufficiently similar 

in magnitude to the dose rates from uranium metal so that uranium metal dose rates can be assumed to be 

representative of the dose rates from all uranium compounds.

When uranium metal is melted, impurities can separate from the metal matrix. Differences in densities 

and melting points can then cause impurities to separate from the molten uranium metal and concentrate 

on the surfaces. This can cause a concentration of beta emitting isotopes near the surface and increase the 

beta dose rate. The two processes that routinely involve molten uranium metal are the metal reduction 

process and the remelting process. 

The metal reduction process involves mixing uranium tetrafluoride (UF4) with magnesium chips and 

loading the mixture into a lined reduction vessel. The sealed vessel is heated to initiate the exothermic 

reaction. The reaction results in the formation of magnesium fluoride (MgF2) and free uranium metal. 

The temperature inside the vessel exceeds the melting point of uranium and, due to the high specific 

gravity, the uranium collects in the bottom of the vessel forming a “derby”. The MgF2 is collected above 

the derby as a slag. After it cooled, the derby is “broken out” of the vessel. The MgF2 slag had to be 

broken and chipped away to dislodge it from the derby (Chrisofano and Harris 1960).

The derby resulting from the reduction step contained impurities that made it unsuitable for reactor fuel. 

The metal was both purified and altered in shape in the remelt process. In this process, the derbies are 

melted in a vacuum furnace and molten uranium metal poured into a graphite mold (Chrisofano and 

Harris 1960). The vacuum casting removes volatile contaminants and allows other impurities to float to 

the surface concentrating impurities near the top. Impurities can also be concentrated where the molten 

uranium metal cools rapidly preventing (or minimizing) the time necessary for the impurities to separate. 

This can cause impurities to also concentrate near other surfaces of the casting. The separation can be 

improved by controlling the cooling of the cast uranium. If the mold is insulated near the top, a steep 

temperature gradient is formed causing the ingot to solidify from the bottom to the top. This allows 

impurities to separate and migrate to the top of the ingot without being trapped in solidifying metal. The 

“hot-top” that is formed is then cut off (cropped) to eliminate the impurities (Fleishman-Hillard 1967).

A third process worth mentioning is the dingot (direct ingot) process developed at Mallinckrodt. That 

process produced a finish ingot directly in the metal reduction step. This eliminated the remelting step by 

increasing the size of the metal reduction vessel and carefully controlling the temperature and ingredients. 

After separation, the dingot was “scalped” by machining all the surfaces (Fleishman-Hillard 1967).
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Some of the impurities in the uranium include Th-234 and Pa-234m, decay products of U-238 (as well as 

residual magnesium, some slag, hydrogen, and others). These isotopes are beta emitters with relatively 

short half-lives. The process then causes a high concentration of these beta emitters in the top and other 

surfaces of the cast ingot. This concentration can produce higher than normal beta dose rates that then 

decay to a normal dose rate with a half-life of 24.1 days. 

The concentrating of decay products during the reduction process does not appear to occur. When the 

uranium metal is first formed in the reduction process, it exists as molten droplets of uranium intermixed 

with MgF2, and unreacted UF4 and magnesium. These droplets of molten uranium settle to the bottom of 

the reduction vessel. The droplets are small enough that no appreciable separation can occur within the 

drop. Separation would be possible once the metal collects in the bottom of the vessel. There is some 

indication that these decay products are actually collected by the MgF2 before the derby is formed 

resulting in a decrease in beta radiation levels on the derby (Briggs 1986). Even if separation were to 

occur in the derby, the solidified MgF2 has to be broken or chipped away from the derby (Chrisofano and 

Harris 1960). This likely would remove appreciable amounts of any material concentrated in the surface 

layer. 

The concentrated beta emitters near the surface of castings cause elevated beta radiation levels from the 

uranium casting with little effect on gamma dose rates. This can cause beta to gamma dose rate ratios to 

be significantly higher than uranium metal in equilibrium with its decay products. This elevated ratio 

may not be limited to facilities where recasting of uranium metal is performed. Several months are 

required for the beta radiation levels decrease to normal levels and castings could be shipped to other sites 

in that time. 

Film badge readings at various sites indicate those sites engaged in remelting exhibit the highest ratio of 

whole body beta dose to whole body gamma dose. The ratio for those sites can approach 10. Therefore, 

a ratio of 10 is used in this document to account for this effect. 

3.3.2 Other Non-Penetrating Radiation

After 1952, small quantities of primarily alpha (239Pu, 237Np, and Th-232/228) and beta (99Tc) emitting 

radionuclides found their way into uranium metal via recycling (see Table 3.2). Because of their 

primarily non-penetrating radiation types, relatively low activities, and relatively low external radiation 

hazard when compared to that of their uranium matrix, their contribution to dose is considered adequately 

addressed by the uranium external dose estimates. A quick check of the relative penetrating dose from an 

overestimate of recycled uranium contaminants in ground surface contamination shows that they 

contribute less than 1% to penetrating dose. The assumed non-penetrating doses from uranium in this 

document are sufficiently large to bound any small contribution from 99Tc.

3.3.3 Photon Dosimetry

The majority of penetrating photons from natural uranium are in the 30 to 250 keV energy range. 

Uranium, even when present as chemical compounds, provides considerable shielding of the lower energy 

photons and will tend to harden the spectrum, causing the majority of photons emitted from uranium to 

have energies greater than 250 keV. While it is recognized that uranium sources will have a hardened 

photon spectrum, exposure to a thin layer of uranium on a surface will result in a larger fraction of 

exposure to lower energy photons. This analysis assumed workers were exposed to photon energies in the 

30 to 250 keV range, which is favorable to claimants when considering both organ dose conversion 

factors and radiation effectiveness factors.
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3.3.4 Neutron Radiation

There are two sources of neutrons. First, neutrons arise from (α,n) reactions, where the reactant is a light 

element, such as beryllium, oxygen or fluorine. In metal-working facilities, uranium oxides would be the 

most common generators of (,n) neutrons, but there may also be fluorine compounds. Second, there is a 

small amount of spontaneous fission by uranium. Table 3.5 shows spontaneous fission and (α,n) yields 

for various uranium isotopes.

Table 3.5. Neutron yields from spontaneous fission and (,n) reactions for oxides and fluorides

The production of neutrons by (,n) interactions in uranium compounds will vary according to the light 

element involved in the interaction. Table 3.6, obtained from DOE-STD-1136-2000, shows the neutron 

yields for various light elements. The data in this table show that the greatest yield is from fluorine and

the yield from oxygen compounds, which are more likely to be found in metal-working facilities, is two 

orders of magnitude less.

Table 3.6. Neutron yields for trace impurities in uranium

Element

Neutron Yield

per 106 Alphas

at 4.7 MeV (234U)

Li 0.16 ± 0.04

Be 44. ± 4

B 12.4 ± 0.6

C 0.051 ± 0.002

O 0.040 ± 0.001

F 3.1 ± 0.3

Na 0.5 ± 0.5

Mg 0.42 ± 0.03

Al 0.13 ± 0.01

Si 0.028 ± 0.002

Cl 0.01 ± 0.01

(DOE, 2004)

An analysis of neutron dose rates from uranium oxides and fluorides was performed for the Mallinckrodt 

site (ORAUT 2010). The calculated neutron dose rates are shown in Table 3.7. The calculated neutron 

dose rates can then be compared to the measured dose rates from pitchblende ore, shown in Table 3.8. 

Pitchblende ore contains a very high concentration of U3O8. The measured dose rates from pitchblende 

Isotope

Spontaneous

Fission Yield,

n/s-gram

(,n) Yield in

Oxides,

n/s-g

(,n) Yield in

Fluorides,

n/s-g

232U 1.3 1.49E4 2.6E+6

233U 8.6E-4 4.8 7.0E+2

234U 5.02E-3 3 5.8E+2

235U 2.99E-4 7.1E-4 0.08

236U 5.49E-3 2.4E-2 2.9

238U 1.36E-2 8.3E-5 0.028

(DOE-STD-1136)
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ore were divided by 4.43 so that the measured and calculated dose rates would represent the dose rate 

from the same amount of U3O8. Comparison of the measured beta/photon dose rates and the calculated 

neutron dose rates show that the neutron dose rate is about 0.07% of the beta/photon dose rate and need 

not be included in dose rate calculations. For uranium metal, the neutron dose rate is even less important. 

The data in Table 3.5 show that the neutron emission rate due to spontaneous fission is much less than the 

neutron emission rate due to (, n) reactions.

Table 3.7. Neutron dose rates from (,n) sources in uranium oxides

Form Source Target 

element(s)

Weight in 

container

Dose rate at

1 ft, rem/h

Dose Rate at

3 ft, rem/h

U3O8 U natural mix O 100 lb 1.29E-07 1.44E-08

U natural mix + 

daughters

O 100 lb 1.10E-07 1.22E-07

UO3, 

UO2

U natural mix O 75 lb 9.71E-08 1.08E-08

U natural mix + 

daughters

O 75 lb 8.27E-07 9.19E-08

Data taken from Table A-34 of (ORAUT 2010).

In the (,n) case, the neutron energy was taken as 1.5 MeV because it is the approximate maximum energy 

for 232Th; the other isotopes also emit neutrons in the range 1.0-2.0, and the flux-to-dose conversion factor 

varies slowly in this range.

Table 3.8. Measured beta/gamma dose rates from containers of pitchblende ore

Source Material

Exposure

mrep/h or mR/h

443 lb 100 lb Reference

High-grade pitchblende ore, 15-gal drum, 443 lbs 

ore: 60”

2.4 0.55 Rochester 1945

High-grade pitchblende ore, 15-gal drum, 443 lbs 

ore: 60”

3.6 0.81 Rochester 1945

High-grade pitchblende ore, 15-gal drum, 443 lbs 

ore: 60”

7.1 1.6 Rochester 1945

High-grade pitchblende ore, 15-gal drum, 443 lbs 

ore: 60”

90 20 Rochester 1945

The column labeled “443 lb” contains the actual measured dose rates. The column labeled “100 lb” 

contains dose rates that have been reduced by a factor of 4.43 so they can be compared with the neutron 

dose rates shown in Table 3.7.

The data shown in Table 3.7 and Table 3.8 indicate that, for U3O8, the neutron dose rate is about 0.07% of 

the beta/gamma dose rate. This fraction is small enough to be neglected in dose calculations. The data in 

Table 3.5 indicate that, for uranium metal, the neutron dose rate will be an even smaller fraction of the 

total dose rate.
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3.4 Dose Conversion Factors for External Doses

External doses in uranium metal-working facilities typically arise from six different modes of exposure:

 Submersion in air contaminated with uranium dust,

 Exposure to electrons from contaminated surfaces,

 Exposure to photons from contaminated surfaces,

 Exposure to electrons from the surface of the uranium, particularly if the uranium is metal,

 Exposure to photons from the surface of uranium, and

 Exposure to an annual diagnostic X-ray.

Exposures to diagnostic X-rays are discussed in Section 4.0. The other components of external dose are 

discussed in Section 5.0.

3.4.1 Submersion in Contaminated Air

When workers are enveloped in a cloud of radioactive dust, they will receive a small amount of external 

dose. External exposure rates from uranium and its radioactive progeny are shown in Table 3.9. The 

doses were calculated using the computer code MiroShield version 6.02 (Grove Engineering 2003). The 

calculated dose rates are for natural uranium and include the dose contribution from the radioactive 

progeny of 238U, 

235U, and 234U. In accordance with (ORAUT 2006) 100 days of radioactive progeny 

ingrowth was assumed for these calculations. 

Table 3.9. Dose conversion factors for external dose due to submersion in uranium-contaminated air

External Dose Conversion factor

Time since separation (mR/h per dpm(α)/m3) (mR/d per dpm(α)/m3)

100 d 2.46E-09 1.97E-08

Notice that the dose quantity calculated for this conversion factor is exposure, in units of milliRoentgen. 

For this particular conversion factor, 50.5% of the exposure is associated with photons with energies 

below 30 keV; 28.5% is from photons with energies between 30 keV and 250 keV, and the remaining 

21.0% is for photons with energies greater than 250 keV.

The dose reconstructor should refer to Appendix A of OCAS-IG-001 (NIOSH 2007) to determine which 

of the tabulated organ dose rates should be used for any particular ICD code.

3.4.2 Exposures from Contaminated Surfaces

When workers are working on a contaminated surface, they will receive a small amount of external dose. 

External exposure rates from uranium and its radioactive progeny are shown in Table 3.10. The exposure 

rates were calculated using the computer code MCNP (LANL 2009). Surface contamination uniformly 

deposited in a 100 m radius circle was assumed. For short lived uranium progeny, 100 days of ingrowth 

was assumed. Since the conversion factors are intended to be used for a range of contamination values, 

the source was assumed to be infinitely thin to avoid self-absorption of beta radiation. Exposure rates 

were determined 1 m above the floor. Photon exposure rates from both direct photon exposure and 

bremsstrahlung x-rays were determined utilizing Table A.1 of ICRP Publication 74 (ICRP 1996) and 

converting to Roentgen. The beta dose rate in Table 3.10 was determined for the skin utilizing the dose 

conversion factors in Table A.43 of ICRP Publication 74. Beta dose rates for other organs exposed to

shallow dose can be calculated from this conversation factor.
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Table 3.10 Dose conversion factors from natural uranium surface contamination

Surface contamination dose conversion factors

Time since separation

Photon Exposure Rate 

(mR/h per dpm(α)/m2)

Beta dose rate

(mRad/h per dpm(α)/m2)

100 d 3.94E-10 3.82E-08

Notice that the quantity calculated for the photon conversion factor is exposure, in units of milliRoentgen. 

For this particular conversion factor, 71.8% of the exposure is associated with photons with energies 

below 30 keV; 17.8% is from photons with energies between 30 keV and 250 keV, and the remaining 

10.4% is for photons with energies greater than 250 keV.

The dose reconstructor should refer to Appendix A of OCAS-IG-001 (NIOSH 2007) to determine which 

of the tabulated organ dose rates should be used for any particular ICD code.

The quantity of uranium on the floor surface can be obtained from floor survey (wipe) sample 

measurements. Most survey samples were based on a 100 cm2sample rather than a 1 meter squared 

sample. When measured floor contamination rates are not available the contamination on the floor may 

be estimated from measured air concentrations. The level of surface contamination is determined by first 

calculating a terminal settling velocity for 5-m activity mean aerodynamic diameter (AMAD) particles. 

The calculated terminal settling velocity was 0.00075 meters per second. Next the amount of time 

necessary for the surface contamination to build up to an equilibrium value is needed. In order to 

determine this time, surface contamination values from Adley (Adley, Gill and Scott, 1952) and from

Simonds Saw and Steel (AEC 1949) were used. Also, the inhalation values from Table 7.8 were 

converted to airborne activity and used in this analysis. The geometric mean of the Table 7.8 airborne 

activity was compared to the geometric mean of the Adley surface contamination values. It was 

determined that with a settling rate of 0.00075 m/s, a 27 days settling period was necessary to match the 

Adley surface contamination values. The analysis indicated a settling time of 15 days was necessary to 

match the Simonds Saw and Steel contamination values. Both values are within a factor of two indicating 

reasonable agreement. Based on this analysis, the higher value was rounded up to 30 days and used in 

this document. Using a 30 day deposition time and a 0.00075 m/s settling rate, a deposition factor of 

1944 meters can be calculated. The floor contamination level is then estimated as Floor Concentration 

(dpm/m2) = Air Concentration (dpm/m3) × 1944 meters.

3.5 Internal Dosimetry

Internal dosimetry refers to the radiation dose received from radioactive material that is inside the body. 

Radioactive material can enter the body via inhalation of radioactive dusts, ingestion of radioactive dusts 

as may happen due to incidental hand to mouth transfers, and contaminated wounds. Internal doses for 

individuals can be estimated based on airborne concentrations of radioactive materials by using the 

computer code IMBA Expert OCAS Edition that implements the biokinetic models that have been 

developed by the International Commission on Radiological Protection (ICRP).

IMBA Expert also provides mechanisms for interpretation of bioassay data. Bioassay data can be of two 

kinds: in vivo bioassay and in vitro bioassay. In vivo bioassay consists of placing the person near 

radiation detectors that measure the amount of radiation that exits the body and based on the efficiency of 

the counting process the quantity of radioactive material in the body can be determined. In vitro bioassay 

consists of collecting the excreta (urine and feces) or breath of an individual who has had an intake of 

radioactive material and, by comparing the measured results with the results predicted by biokinetic 
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models, the quantity of radioactive material that would be required to be in the body to produce the 

observed excretion is calculated.

Internal doses are influenced by several properties of the material that is taken into the body. Pertinent 

quantities include the particle size of the aerosol, the shape of individual particles in the aerosol, the 

density of the airborne material, and the solubility of the material.

During the metal-working operations, several different oxides of uranium are formed and may become 

airborne. The impact of uranium-forming compounds is that the specific activity of uranium metal, 

shown in Table 3.1, will be different than the specific activity of the compound. The specific activities of 

the oxides of natural uranium are shown in Table 3.11.

Table 3.11. Some internal dosimetry related characteristics of uranium

Material

U weight 

Fraction

Density Solubility Data Specific Activity

g/cm3 Type f1 Bq/mg pCi/mg dpm/mg

UO2 0.881498 10.96 S 0.002 2.23E+01 6.03E+02 1.34E+03

UO3 0.832190 7.29 M 0.02 2.11E+01 5.69E+02 1.26E+03

U3O8 0.848001 8.3 S 0.002 2.15E+01 5.80E+02 1.29E+03

Unless specified otherwise, the characteristics of aerosols are:

 Particle Size is 5 micron AMAD

 Shape Factor is 1.5

 Density is 3

 Lung Solubility Type as given in Table 3.11

 Absorption factor f1 as given in Table 3.11

The dose reconstructor should use the default values shown above. The default values of ICRP-66 (ICRP 

1994) should be used. The density values in Table 3.11 are for reference only.

The intake of radioactive material via inhalation depends on the characteristics of the worker, that is their 

breathing rate and the extent to which they breath through the mouth. IMBA does not calculate intakes 

based on air concentrations, rather the dose reconstructor is required to calculate the intake from the

breathing rate and the air concentration. Unless specified otherwise in the site specific guidance, the 

following worker characteristics should be assumed:

 Worker type: Light Worker

 Breathing Characteristics: Nasal Augmentor

 Breathing Rate: 1.2 m3/h or 9.6 m3/day (for an 8 h day)

The intake is the product of the breathing rate, shown above, and the air concentration. The generic air 

concentrations are listed in Section 7.0. For some processes, the air concentration tables show a daily 

weighted average (DWA) and in those cases the DWA is the air concentration to use. If a DWA air 

concentration is not available then use the average daily exposure air concentration.
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3.5.1 Inhalation

Inhaled uranium can have two sources:

 Uranium dust generated by plant operations. This source will dominate while the plant is operating.

 Uranium dust generated by resuspension of material on contaminated floors by casual foot traffic.

Specific information concerning these two sources is discussed in the internal dosimetry section.

3.5.2 Ingestion

In the case where inhalation intakes are calculated from air concentrations, ingestion intakes are also to be 

considered. NIOSH (2004) indicates that the ingestion rate, in terms of dpm for an 8-hour workday, can 

be estimated by multiplying the air concentration in dpm per cubic meter by a factor of 0.2. NIOSH 

(2004) also indicates adjustments must be made to account for workdays of duration other than 8 hours. 
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4.0 Occupational Medical Dose

In most AWE facilities, workers received a pre-employment X-ray examination, and in many of these 

facilities, the X-ray was also administered annually to employees who worked with uranium metal. The 

“pre-employment” X-ray was often administered at the start of AEC operations. In the absence of sitespecific information about medical X-rays required for employment, the assumption should be made that 

it was administered at the beginning of AEC operations (or at the beginning of a worker’s employment) 

and annually during uranium metal-working operations. This follows the practice at Simonds Saw & 

Steel (Simonds, 1948). The exposure geometry was assumed to be posterior-anterior (PA) (NIOSH,

2007).

4.1 Chest X-Rays

Information to be used in dose reconstruction for the early years for which no specific information is 

available is provided in ORAUT-OTIB-0006, the dose reconstruction project technical information 

bulletin covering diagnostic X-ray procedures (ORAUT 2005c). ORAUT (2005c) should be referred to 

regarding the underlying bases, interpretation details, and a sample of a summary data table where actual 

beam data are known.

Doses for organs not listed in ICRP Publication 34 (ICRP 1982) but specified in the IREP code should be 

determined by analogy with anatomical location as indicated below. Analogues for IREP organs not 

included in ICRP 34 are given in Table 4.1.

Table 4.1. Organ analogues for diagnostic chest X-ray

Anatomical location ICRP 34 reference organ IREP organ analogues

Thorax Lung Thymus

Esophagus

Stomach

Bone surface

Liver/gall bladder/spleen

Remainder organs

Abdomen Ovaries Urinary/bladder

Colon/rectum

Head and neck Thyroid Eye/Brain

As ORAUT (2005c) notes, for any individual entrance skin exposure (ESE) or derived organ dose, an 

uncertainty of ± 30% at the one sigma confidence level may be assumed; for further conservatism it may 

be appropriate to assume that errors are all positive and thus only the + 30% should be used.

4.2 Pelvic X-Rays

Pelvic X-rays were administered to workers who handled fluoride compounds, so they may not have been 

administered to workers at uranium metal-working facilities. If workers at any of these facilities received 

pelvic X-rays as conditions of employment, the dose can be estimated using the guidance provided in 

Appendix A of ORAU-OTIB-0006 (ORAUT 2005c).
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5.0 Occupational Environmental Dose

In the context of reconstructing doses for Atomic Weapons employees, the occupational environmental 

dose includes doses due to 

 direct, external irradiation from material in process, in storage, in transit, and from radioactive 

contamination on surfaces, in soil and water, and in plumes of radioactive material

 internal irradiation due to intakes of residual radioactive material through inhalation, ingestion, 

dermal contact with radioactive material, and through wounds. Generally, dermal contact and 

wound entry are assumed to be negligible in the absence of information to the contrary.

5.1 Environmental External Irradiation

Typically, atomic weapons employees who were not categorized as radiation workers were not monitored 

using personal dosimeters. However, the work environment for these employees was sometimes routinely 

monitored using area dosimeters or periodically monitored using survey instrumentation to measure the 

“background” environmental radiation levels. At many of these facilities, routine monitoring stations have 

recorded the average photon dose in a general area or at the plant boundaries. At several DOE facilities, 

radioactive emissions from plant stacks have been known to significantly increase the “background” 

radiation levels on the plant site. In general the dose from increased background is rather low.

5.1.1 Environmental Doses During Operations

Direct, external irradiation of people on site can occur from material in process, in storage, in transit, and 

from radioactive contamination on surfaces, in soil and water, and in plumes of radioactive material.

Uranium metal emits beta particles (electrons) and to a lesser extent, photon radiation primarily in the 

form of bremsstrahlung X-rays but with some gamma emissions (e.g., the 186 keV photon from 235U).

Neutron radiation (from spontaneous fission) is negligible, even for massive quantities of uranium (based 

on neutron production calculated by SOURCES-4 (Wilson et al. 1999)).

During operations, environmental doses were much smaller than those occurring in the metal-working 

portions of the facility, so these doses would be significant only for workers who spent little time in the 

high-dose portions of the facility. For these workers, the exposure scenario is spending eight hours per 

working day in an area with a low level of airborne contamination and a low level of contamination 

deposited on the floor. To estimate external doses resulting from these two pathways, dose factors are 

provided in 3.4.

The environmental external dose received by a worker exposed to contaminated air and walking on 

contaminated ground can be found by multiplying the dose factors by the contamination levels, assuming 

a number of hours of exposure per workday. This analysis assumes that during plant operation, the 

worker away from the main operation area is exposed to a uranium concentration in air of 7 dpm/m3. 

This level corresponds to 0.1 MAC, and is consistent with general area air sampling results for positions 

on the factory floor away from operations. Air sampling results for three plants, American Machine and 

Foundry, Medart, and Allegheny Ludlum were examined, comparing air samples at the highest 

concentration areas to air samples at the lowest concentration areas during the same operation. For 11 

different cases, the ratio of the low to high concentration ranged from 0.002 to 0.029, with all but two of 

those ratios below 0.01. Thus it would be reasonable to use a ratio of 0.01 for areas that are further away 
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from the heavy operations, which non-operational areas of the facility would be. We can assume that a 

heavy operation would produce a daily-weighted air concentration of 10 MAC at the operator’s position, 

so ratioing this by 0.01 gives a value of 0.1 MAC or 7 dpm/m3in the non-operational areas of the plant.

For the surface contamination, it is assumed that the uranium deposited on the floor with a deposition 

velocity of 0.00075 m/s for a period of 30 days without cleanup, then remained at that level of 

contamination for the duration of operations. This would be a contamination level of 1.36104dpm/m2. 

The worker exposure is estimated as annual doses for 40-, 44-, and 48-hour workweeks. Using these 

assumptions, the annual doses can be calculated, and they are presented in Table 5.1. 

Table 5.1. Environmental external annual exposure to workers in non-operational areas of a facility.

Hours worked 

per week

Submersion 

Exposure

(mR/yr)

Contaminated 

Surface Exposure

Photon

(mR/yr)

Contaminated 

Surface Exposure

Beta

(mrad/yr)

40 3.44E-05 1.07E-02 1.04

44 3.79E-05 1.18E-02 1.14

48 4.13E-05 1.29E-02 1.25

Since the total exposure is dominated by the surface contamination pathway, 71.8% of the exposure is 

associated with photons with energies below 30 keV; 17.8% is from photons with energies between 30 

keV and 250 keV, and the remaining 10.4% is for photons with energies greater than 250 keV.

5.1.2 After Operations and Initial Decontamination and Before FUSRAP Remediation

Workers at a facility that is no longer performing AWE work will also be exposed to radiation from 

residual contamination. If measurements of the contamination are not available for this time period, the 

doses presented in Table 5.1 can be used as an estimate of the external doses from this dose pathway.

5.1.3 After FUSRAP Remediation

At the conclusion of remediation, exit surveys should be available to base dose calculations on. If no exit 

surveys are available, external doses can be estimated using the doses presented in Table 5.1.

5.2 Environmental Internal Dose Due to Inhalation of Radioactive Material

At several DOE facilities, radioactive emissions from plant stacks have been known to significantly 

increase the “background” radiation levels on the plant site. In general the dose from increased 

background is rather low.

5.2.1 During Operations

Radioactive material aerosolized by various industrial processes in uranium metalworking can be released 

deliberately or inadvertently to the environment, producing uranium aerosols in the environs of the site. 

An estimate of the intake from the inhalation pathway can be estimated assuming an airborne 

contamination level, a breathing rate, and daily exposure period. The estimate of 7 dpm/m3used in 

Section 5.1.1 can be assumed for the contamination level. A breathing rate of 1.2 m

3

/h can be used, and 

the conversion factor of 2.22 dpm/pCi must also be employed, to give intakes in units of pCi/d of 

uranium. Ingestion intakes were found using the equation 

I

I Ah 5MBA 3.062 10

 

as discussed in 
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Section 7.1.6. Table 5.2 gives the intakes, both from inhalation and ingestion, for these conditions. The 

intake values are assumed to be the geometric means of lognormal distributions with GSD=5.

Table 5.2. Environmental internal daily intakes to workers in non-operational areas of a facility.

Hours worked 

per week

Daily Intake from 

Inhalation

(pCi/d)

Daily Intake from 

Ingestion

(pCi/d)

40 20.7 0.429

44 22.8 0.472

48 24.9 0.514

To account for the uncertainty in the estimation of doses, it is recognized that any estimate of an intake is 

actually a best estimate chosen from the range of all possible values. The distribution of possible values 

is assumed to follow a lognormal distribution, as discussed in (Battelle Team 2006). The best estimate 

chosen from this distribution is the geometric mean of the lognormal. The lognormal distribution is 

further described by its geometric standard deviation (GSD). In some cases the GSD can be determined 

from a set of data associated with the site. In many cases, however, the GSD cannot be derived, and in 

these cases a GSD of 5 will be assigned, as discussed in (Battelle Team 2006).

5.2.2 After Operations and Initial Decontamination and Before FUSRAP Remediation

Workers at a facility that is no longer performing AWE work may also be inhaling uranium from residual 

contamination. If measurements of the contamination are not available for this time period, the intake 

presented in the previous section can be used as an estimate of the internal doses from this dose pathway.

5.2.3 After FUSRAP Remediation

At the conclusion of remediation, exit surveys should be available to base intakes on. If no exit surveys 

are available, intakes can be estimated as identical to that given in Section 5.2.1.

5.3 Summary of Occupational Environmental Doses

The external doses and internal intakes of uranium at environmental levels are summarized in Table 5.3.

Table 5.3. External doses and intakes for occupational exposure to environmental levels of radiation

Workweek, 

hours

External Photon 

(mr/yr)

External Beta 

(mrad/yr)

Inhalation 

(pCi/day)

Ingestion 

(pCi/day)

40 1.08E-02 1.04E+00 20.7 0.429

44 1.18E-02 1.14E+00 22.8 0.472

48 1.29E-02 1.25E+00 24.9 0.514
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6.0 Occupational External Dose

Film badge usage at AWE sites varied from plant to plant and over time. When film badge data for 

workers are available, these readings are the preferred indicator of the worker’s whole body dose. In 

some cases there may be coworker dosimetry results available that can be used to estimate an unbadged 

worker’s dose. When film badges were not issued, the worker’s dose must be determined from plant 

conditions. The estimation of doses in this section will assume that no dosimetry results were available, 

and will assume typical conditions for the type of workplace addressed in this document, but will use

worst case exposure conditions as assumptions favorable to a claimant. The appendices to this document 

will present site-specific information to provide more appropriate estimates where available. If site 

information is insufficient to estimate a dose to a worker, the information in this section can be used.

The majority of photons from natural uranium metals are in the 30 to 250 keV energy range. Solid 

uranium objects provide considerable shielding of the lower energy photons and harden the spectrum, 

causing the majority of photons emitted from a solid uranium object, such as a billet or a rod, to have 

energies greater than 250 keV. While it is recognized that solid uranium sources will have a hardened 

photon spectrum, exposure to a thin layer of uranium on a surface will result in a larger fraction of 

exposure to lower energy photons. This analysis assumed workers were exposed to photon energies in the 

30 to 250 keV range, which is favorable to claimants. Nonpenetrating dose from natural uranium consists 

primarily of electrons with energies above 15 keV. For consistent presentation, exposure or dose is 

reported as:

 penetrating, assumed to be associated with photons of energies 30 keV or greater, and

 nonpenetrating, assumed to be associated with photons of energies less than 30 keV or with 

electrons.

External doses in uranium metal-handling facilities typically arise from six different modes of exposure:

 Submersion in air contaminated with uranium dust (whole body exposure from penetrating 

radiation),

 Exposure to photons from contaminated surfaces (whole body exposure),

 Exposure to non-penetrating radiation from contaminated surfaces (whole body exposure),

 Exposure to photons from uranium metal (whole body exposure),

 Exposure to non-penetrating radiation from uranium metal (skin of hands and forearms)

 Exposure to non-penetrating radiation from uranium metal (skin other than hands and forearms).

6.1 Submersion in Contaminated Air and Exposure to Contaminated 

Surfaces

Clouds of radioactive dust were frequently present in uranium metal-working facilities. The dust material 

consisted of uranium oxide, usually originating in the oxidation of uranium that occurred on hot metal 

surfaces as the uranium metal was processed. This dust cloud produced two types of external exposure: 

exposure to radiation emitted by the dust cloud, and exposure emitted by uranium oxide that settled on 

horizontal surfaces in the shop.

6.1.1 Exposures from Submersion in a Dust Cloud

When workers are enveloped in a cloud of radioactive dust, they will receive a small amount of external 

dose. External dose rates from uranium and its radioactive progeny are calculated using the dose factor in 

Section 3.4.1. 
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A worker’s external dose due to submersion in a dust cloud can be found by taking the air concentration 

appropriate for the job title and multiplying it by the dose factor. Air concentrations appropriate for job 

categories for the metal-working processes are given in Section 7.1 and they are converted to annual 

doses in Section 6.4.

6.1.2 Exposures from a Contaminated Surface

When workers are working on a contaminated surface, they will receive a small amount of external dose. 

External dose rates from uranium and its radioactive progeny are calculated using the dose factor in 

Section 3.4.2. These dose rates assume that a worker is standing on a contaminated floor, with the 

contamination level uniform to infinity in all directions. 

Surface contamination levels can be found in one of two ways: measurement of surface contamination or 

calculation of surface contamination based on air concentrations. If surface measurements are used, the 

dose reconstructor should be sure that the measurement units are converted to alpha dpm per m

2

(notice 

that most measurements are based on a probe area of 100 cm2, so conversion is required) when using 

values in this table.

When measured floor contamination rates are not available the contamination on the floor may be 

estimated from measured air concentrations. The level of surface contamination was determined by first 

calculating a terminal settling velocity for 5-μm activity mean aerodynamic diameter (AMAD) particles. 

The calculated terminal settling velocity was 0.00075 meters per second. The surface contamination can 

be found by multiplying the air concentration by the deposition velocity and then by the assumed time 

that the deposition occurs. As discussed in Section 3.4.2, for metal sites, an assumption can be made that 

surface contamination can be characterized by a 30 day deposition time. In other words, the 

contamination level is the result of deposition occurring for 30 days, and then additional deposition and 

cleanup balancing each other so that this level is constant for the remainder of the operating period. With 

this assumption the deposition factor would be 1944 (= 0.00075 m/s × 2592000 s) to convert the air 

concentration, in units of dpm/m3to surface concentration in units of dpm/m2.

A worker’s external dose due to exposure from a contaminated surface can be found by taking the air 

concentration appropriate for the job title, converting that to a corresponding surface concentration, and 

multiplying it by the dose factor. This calculation will give a dose rate in mr/h, so multiplying that value 

by the number of hours worked per day will give the dose per workday. Air concentrations appropriate 

for job categories for the metal-working processes are given in Section 7.1 and they are converted to 

annual doses in Section 6.4.

6.2 Whole Body Radiation Emitted from Metal Surfaces

For estimating external dose rates due to penetrating radiation emitted from the surface of uranium metal, 

MCNP calculations were performed for a number of basic shapes representative of those that are used in 

AWE metal-working facilities (Anderson and Hertel 2005). Table 6.1 shows these calculated dose rates 

for distances of 1 cm, 30.48 cm (equal to 1 foot) and 1 meter from the surface. The 1-cm dose position 

can be considered to give the “surface” dose rate.
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Table 6.1. Dose rates from standard shapes of uranium metal

Shape

Surface dose rate 

(mrem/h)

30.48-cm dose rate 

(mrem/h)

1-m dose rate

(mrem/h)

Long Rod 5.09 0.285 0.0883

Slug 7.63 0.0524 0.00519

Long Billet 7.74 0.703 0.108

Short Billet 7.36 0.469 0.0585

Cylindrical Ingot 8.44 1.15 0.185

Rectangular Ingot 8.26 2.08 0.373

Flat Plate 6.27 0.231 0.0278

The dose rates were calculated using ANSI/ANS 6.1.1-1977 (ANSI 1977) dose-equivalent conversion 

coefficients. These were calculated as the maximum dose deposited in a slab phantom, including a 

quality factor, so it is a measure of a whole-body dose equivalent.

These dose rates can be used to estimate the component of whole body dose that a worker would receive 

while handling or near uranium metal. For an individual site, there may be information on which shape 

applied to a site’s operations, what a representative distance from the source would be, and how many 

hours of exposure at that distance there would be per year. However, for the generic case, a worst-case 

assumption should be made, which is that all work was done with a uranium metal slab, and the following 

assumptions are made about a worker’s exposure conditions:

 Operator: 50% of the workday was spent at 1 foot from the surface of the metal

 General Laborer: 50% of the workday was spent at 1 meter from the metal surface

 Supervisor: exposure was equal to 50% of a general laborer’s exposure

 Clerical: exposure was equal to 10% of a supervisor’s exposure.

With these assumptions, Table 6.2 lists the annual exposures to four job categories in a metal plant. 

Exposures are whole body, assuming that the incident radiation is photons with energies between 30 and 

250 keV.

Table 6.2. Annual doses from penetrating photon radiation to a worker near bare uranium metal

Job Title

Annual dose 

for a 48-hr 

workweek

(mr/yr)

Annual dose 

for a 44-hr 

workweek

(mr/yr)

Annual dose 

for a 40-hr 

workweek

(mr/yr)

Operator 2496 2288 2080

General Laborer 447.6 410.3 373.0

Supervisor 223.80 205.15 186.50

Clerical 22.380 20.515 18.650
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6.3 Nonpenetrating Radiation Emitted from Uranium Metal Surfaces

Skin doses (7 mg/cm2) are estimated for two worker cases: the hands and forearms of a worker who 

handles uranium metal, and the other skin surfaces of a worker who handles the metal.

The 7 mg/cm2dose from non-penetrating radiation when the skin is in contact with an unshielded slab of 

uranium metal is 230 mrem/hour (Coleman, Hudson, and Plato, 1983; U.S. Army, 1989). Exposure 

assumptions for hands-on contact with uranium metal for the four job categories assumes:

 Operator: 50% of the workday was spent with hands in contact with the surface of the metal

 General Laborer: exposure would be 50% of the exposure of the operator

 Supervisor: exposure would be 10% of the exposure of the general laborer (assuming the 

supervisor seldom has a reason to touch metal)

 Clerical: 0 (assuming the clerical worker has no reason to touch metal)

These assumptions can be used with the contact dose rate of 230 mrem/h to estimate the dose of the skin 

of the hands and forearm. This dose estimate assumes that no gloves or protective clothing shielded the 

worker’s hands and forearms, which may have been true for some of the earliest years of uranium metalworking, and is an assumption favorable to the claimant for other workers.

For dose to other skin on the worker’s body that is not in direct contact with uranium metal, but is nearby 

(for example, a worker’s neck and face when the hands are in contact with metal), a dose relation can be 

used that estimates this dose to be 10 times the photon dose rate at 1-foot. This relation is based on the 

discussion in Section 3.3.1. In Table 6.1, the photon dose rate at 1 foot from a slab of uranium is 2.08 

mrem/h, which would give a non-penetrating dose rate of 20.8 mrem/h using this relation. Using this 

relation with the four assumptions given for time spent with hands in contact with metal gives the annual

doses for the four job categories for skin other than the hands and forearms.

The annual doses for non-penetrating radiation to skin of a worker in a metal-working facility are given in 

Table 6.3.

Table 6.3. Annual doses from non-penetrating radiation to a worker’s skin near bare uranium metal

Job Title

Annual dose for a 48-

hr workweek, rad/yr

Annual dose for a 44-

hr workweek, rad/yr

Annual dose for a 40-

hr workweek, rad/yr

Hands &

Forearm

Other 

Skin

Hands & 

Forearm

Other 

Skin

Hands & 

Forearm

Other 

Skin

Operator 276 25.0 253 22.9 230 20.8

General 

Laborer 138 12.5 127 11.4 115 10.4

Supervisor 13.8 1.25 12.7 1.14 11.5 1.04

Clerical 0 0 0 0 0 0
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6.4 Summary of External Radiation Doses During Operation

The annual doses received by workers at a plant that handled uranium, according to the six pathways 

described in this section, are given in Table 6.4.

For the air submersion and photons from contaminated floors, the dose quantity is exposure and doses 

should be evaluated using the fractional distributions in energy ranges that were given in Sections 3.4.1

and 3.4.2.

For the metal whole body dose, the dose quantity is dose equivalent, and the exposure geometry is an AP 

beam. For this geometry it is conservative to assume that all photons have energies in the range of 30-250 

keV.

The “hands and forearms” and “other skin” pathways are doses at a skin depth of 7 mg/cm2, caused by 

electrons with energies above 15 keV. 

Each annual dose value is assumed to be the geometric mean of a lognormal distribution with a GSD of 5.

Data in Table 6.4 can be used for a metal-working site that performed one of the six processes discussed 

in this section. If a site has more specific data describing exposures to workers, the exposure data will be 

listed in its appendix to this document. However, if exposure data were unavailable for a site, data from 

this table can be used for calculating worker doses. Data in this table are chosen for worst-case 

exposures, so they would be favorable to the claimant. Data presented here assumes that the facility 

operates full-time over the course of a year, while many metal-working sites worked with uranium for 

only small portions of a year. If it is known that the site operated with uranium for only a small fraction 

of a year but the exposure conditions were unknown, the data in this table could be scaled for the fraction 

of the year actually worked and used for worker exposure assessment.
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Table 6.4. Estimated annual doses, external exposure pathways, for metal-working processes.

Process Job Title Years

Air 

Submersion 

Exposure

(mR/yr)

Contaminated 

Floor Photon

(mR/yr)

Contaminated 

Floor Beta

(mrad/yr)

Metal WholeBody Dose

(mr/yr)

Hands & 

Forearms NonPenetrating 

dose (rad/yr)

Other Skin 

NonPenetrating 

dose (rad/yr)

Extrusion

Operator

up to 

12/31/1950 5.86E-03 1.82E+00 1.77E+02 2.50E+03 2.76E+02 2.50E+01

1951 – 55 5.37E-03 1.67E+00 1.62E+02 2.29E+03 2.53E+02 2.29E+01

1956 on 4.88E-03 1.52E+00 1.47E+02 2.08E+03 2.30E+02 2.08E+01

General 

Laborer

up to 

12/31/1950 8.64E-04 2.69E-01 2.61E+01 4.48E+02 1.38E+02 1.25E+01

1951 – 55 7.93E-04 2.47E-01 2.40E+01 4.10E+02 1.27E+02 1.14E+01

1956 on 7.21E-04 2.24E-01 2.18E+01 3.73E+02 1.15E+02 1.04E+01

Supervisor

up to 

12/31/1950 4.33E-04 1.35E-01 1.31E+01 2.24E+02 1.38E+01 1.25E+00

1951 – 55 3.97E-04 1.24E-01 1.20E+01 2.05E+02 1.27E+01 1.14E+00

1956 on 3.61E-04 1.12E-01 1.09E+01 1.87E+02 1.15E+01 1.04E+00

Clerical

up to 

12/31/1950 4.33E-05 1.35E-02 1.31E+00 2.24E+01 0.00E+00 0.00E+00

1951 – 55 3.97E-05 1.24E-02 1.20E+00 2.05E+01 0.00E+00 0.00E+00

1956 on 3.61E-05 1.12E-02 1.09E+00 1.87E+01 0.00E+00 0.00E+00

Rolling

Operator

up to 

12/31/1950 2.09E-02 6.49E+00 6.30E+02 2.50E+03 2.76E+02 2.50E+01

1951 – 55 1.91E-02 5.95E+00 5.77E+02 2.29E+03 2.53E+02 2.29E+01

1956 on 1.74E-02 5.41E+00 5.25E+02 2.08E+03 2.30E+02 2.08E+01

General Labor

up to 

12/31/1950 3.84E-03 1.20E+00 1.16E+02 4.48E+02 1.38E+02 1.25E+01

1951 – 55 3.52E-03 1.10E+00 1.06E+02 4.10E+02 1.27E+02 1.14E+01

1956 on 3.20E-03 9.97E-01 9.67E+01 3.73E+02 1.15E+02 1.04E+01

Supervisor

up to 

12/31/1950 1.92E-03 5.99E-01 5.81E+01 2.24E+02 1.38E+01 1.25E+00

1951 – 55 1.76E-03 5.49E-01 5.33E+01 2.05E+02 1.27E+01 1.14E+00

1956 on 1.60E-03 4.99E-01 4.84E+01 1.87E+02 1.15E+01 1.04E+00

Clerical up to 1.94E-04 6.05E-02 5.86E+00 2.24E+01 0.00E+00 0.00E+00
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Process Job Title Years

Air 

Submersion 

Exposure

(mR/yr)

Contaminated 

Floor Photon

(mR/yr)

Contaminated 

Floor Beta

(mrad/yr)

Metal WholeBody Dose

(mr/yr)

Hands & 

Forearms NonPenetrating 

dose (rad/yr)

Other Skin 

NonPenetrating 

dose (rad/yr)

12/31/1950

1951 – 55 1.78E-04 5.54E-02 5.37E+00 2.05E+01 0.00E+00 0.00E+00

1956 on 1.62E-04 5.05E-02 4.90E+00 1.87E+01 0.00E+00 0.00E+00

Forging

Operator

up to 

12/31/1950 6.91E-03 2.15E+00 2.09E+02 2.50E+03 2.76E+02 2.50E+01

1951 – 55 6.33E-03 1.97E+00 1.91E+02 2.29E+03 2.53E+02 2.29E+01

1956 on 5.76E-03 1.79E+00 1.74E+02 2.08E+03 2.30E+02 2.08E+01

General Labor

up to 

12/31/1950 2.14E-03 6.65E-01 6.45E+01 4.48E+02 1.38E+02 1.25E+01

1951 – 55 1.96E-03 6.10E-01 5.91E+01 4.10E+02 1.27E+02 1.14E+01

1956 on 1.78E-03 5.55E-01 5.38E+01 3.73E+02 1.15E+02 1.04E+01

Supervisor

up to 

12/31/1950 1.07E-03 3.33E-01 3.23E+01 2.24E+02 1.38E+01 1.25E+00

1951 – 55 9.79E-04 3.05E-01 2.96E+01 2.05E+02 1.27E+01 1.14E+00

1956 on 8.91E-04 2.77E-01 2.69E+01 1.87E+02 1.15E+01 1.04E+00

Clerical

up to 

12/31/1950 1.06E-04 3.31E-02 3.21E+00 2.24E+01 0.00E+00 0.00E+00

1951 – 55 9.75E-05 3.03E-02 2.94E+00 2.05E+01 0.00E+00 0.00E+00

1956 on 8.86E-05 2.76E-02 2.67E+00 1.87E+01 0.00E+00 0.00E+00

Machining

Operator

up to 

12/31/1950 3.24E-02 1.01E+01 9.77E+02 2.50E+03 2.76E+02 2.50E+01

1951 – 55 2.97E-02 9.23E+00 8.95E+02 2.29E+03 2.53E+02 2.29E+01

1956 on 2.70E-02 8.39E+00 8.14E+02 2.08E+03 2.30E+02 2.08E+01

General Labor

up to 

12/31/1950 1.62E-02 5.04E+00 4.88E+02 4.48E+02 1.38E+02 1.25E+01

1951 – 55 1.48E-02 4.62E+00 4.48E+02 4.10E+02 1.27E+02 1.14E+01

1956 on 1.35E-02 4.20E+00 4.07E+02 3.73E+02 1.15E+02 1.04E+01

Supervisor

Operator

up to 

12/31/1950 8.09E-03 2.52E+00 2.44E+02 2.24E+02 1.38E+01 1.25E+00

1951 – 55 7.41E-03 2.31E+00 2.24E+02 2.05E+02 1.27E+01 1.14E+00

1956 on 6.74E-03 2.10E+00 2.03E+02 1.87E+02 1.15E+01 1.04E+00
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Process Job Title Years

Air 

Submersion 

Exposure

(mR/yr)

Contaminated 

Floor Photon

(mR/yr)

Contaminated 

Floor Beta

(mrad/yr)

Metal WholeBody Dose

(mr/yr)

Hands & 

Forearms NonPenetrating 

dose (rad/yr)

Other Skin 

NonPenetrating 

dose (rad/yr)

Clerical

up to 

12/31/1950 8.08E-04 2.52E-01 2.44E+01 2.24E+01 0.00E+00 0.00E+00

up to 

12/31/1950 7.41E-04 2.31E-01 2.24E+01 2.05E+01 0.00E+00 0.00E+00

1951 – 55 6.73E-04 2.10E-01 2.03E+01 1.87E+01 0.00E+00 0.00E+00

Slug 

Production

Operator

up to 

12/31/1950 1.17E-03 3.64E-01 3.53E+01 2.50E+03 2.76E+02 2.50E+01

1951 – 55 1.07E-03 3.34E-01 3.24E+01 2.29E+03 2.53E+02 2.29E+01

1956 on 9.75E-04 3.03E-01 2.94E+01 2.08E+03 2.30E+02 2.08E+01

General Labor

up to 

12/31/1950 5.84E-04 1.82E-01 1.76E+01 4.48E+02 1.38E+02 1.25E+01

1951 – 55 5.35E-04 1.67E-01 1.62E+01 4.10E+02 1.27E+02 1.14E+01

1956 on 4.87E-04 1.52E-01 1.47E+01 3.73E+02 1.15E+02 1.04E+01

Supervisor

up to 

12/31/1950 2.95E-04 9.17E-02 8.90E+00 2.24E+02 1.38E+01 1.25E+00

1951 – 55 2.70E-04 8.41E-02 8.15E+00 2.05E+02 1.27E+01 1.14E+00

1956 on 2.45E-04 7.64E-02 7.40E+00 1.87E+02 1.15E+01 1.04E+00

Clerical

up to 

12/31/1950 2.95E-05 9.17E-03 8.90E-01 2.24E+01 0.00E+00 0.00E+00

1951 – 55 2.70E-05 8.41E-03 8.15E-01 2.05E+01 0.00E+00 0.00E+00

1956 on 2.45E-05 7.64E-03 7.40E-01 1.87E+01 0.00E+00 0.00E+00

Scrap 

Recovery

Operator

up to 

12/31/1950 9.98E-03 3.11E+00 3.01E+02 2.50E+03 2.76E+02 2.50E+01

1951 – 55 9.15E-03 2.85E+00 2.76E+02 2.29E+03 2.53E+02 2.29E+01

1956 on 8.31E-03 2.59E+00 2.51E+02 2.08E+03 2.30E+02 2.08E+01

General Labor

up to 

12/31/1950 4.99E-03 1.55E+00 1.51E+02 4.48E+02 1.38E+02 1.25E+01

1951 – 55 4.57E-03 1.42E+00 1.38E+02 4.10E+02 1.27E+02 1.14E+01

1956 on 4.16E-03 1.29E+00 1.26E+02 3.73E+02 1.15E+02 1.04E+01

Supervisor up to 

12/31/1950 2.49E-03 7.76E-01 7.53E+01 2.24E+02 1.38E+01 1.25E+00
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Process Job Title Years

Air 

Submersion 

Exposure

(mR/yr)

Contaminated 

Floor Photon

(mR/yr)

Contaminated 

Floor Beta

(mrad/yr)

Metal WholeBody Dose

(mr/yr)

Hands & 

Forearms NonPenetrating 

dose (rad/yr)

Other Skin 

NonPenetrating 

dose (rad/yr)

1951 – 55 2.29E-03 7.12E-01 6.90E+01 2.05E+02 1.27E+01 1.14E+00

1956 on 2.08E-03 6.47E-01 6.28E+01 1.87E+02 1.15E+01 1.04E+00

Clerical

up to 

12/31/1950 2.50E-04 7.79E-02 7.55E+00 2.24E+01 0.00E+00 0.00E+00

1951 – 55 2.29E-04 7.12E-02 6.91E+00 2.05E+01 0.00E+00 0.00E+00

1956 on 2.08E-04 6.47E-02 6.28E+00 1.87E+01 0.00E+00 0.00E+00
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7.0 Occupational Internal Dose

The primary sources of internal radiation exposure at the AWE metal-working sites was uranium dust 

produced during the manipulation of metal objects. At some sites, bioassays were performed on workers, 

and urinalysis was the most effective method of determining an individual worker’s intake. When 

bioassay data are available for individual workers, this should be the primary source of dose 

reconstruction for internal exposure. When no bioassay data are available, intakes can be derived from air 

sampling data. The appendices to this document present air sampling data, where available, for individual 

sites, and these data can be used for site-specific dose reconstruction where available. In the absence of 

site-specific air sampling data, the air sampling data presented in this section can be used for dose 

reconstruction.

In this section the internal dosimetry parameters are recommended for use in dose reconstruction. 

Subsequent subsections present tables of default dust air concentrations that can be used to estimate 

intakes when site specific information is lacking.

Internal doses are influenced by several properties of the material that is taken into the body. Pertinent 

quantities include the particle size of the aerosol, the shape of individual particles in the aerosol, the 

density of the airborne material, and the solubility of the material.

In metal-working facilities, airborne uranium exists as an oxide compound of uranium. The specific 

activities of various oxides of natural uranium are shown in Table 7.1.

In the text of this TBD the chemical compound associated with each process will be identified.

Table 7.1. Some Internal Dosimetry Related Characteristics of Uranium Oxides

Density Solubility Data Specific Activity

Material

U weight 

Fraction g/cm3 Type f1 Bq/mg pCi/mg dpm/mg

UO2 0.881498 10.96 S 0.002 2.23E+01 6.03E+02 1.34E+03

UO3 0.832190 7.29 M 0.02 2.11E+01 5.69E+02 1.26E+03

U3O8 0.848001 8.3 S 0.002 2.15E+01 5.80E+02 1.29E+03

Unless specified otherwise, the characteristics of aerosols are:

 Particle Size is 5 micron AMAD

 Shape Factor is 1.5

 Density as given in Table 7.1

 Lung Solubility Type as given in Table 7.1

 Absorption factor f1 as given in Table 7.1

When calculating intakes of uranium, the dose reconstructor should use the default values shown in Table 

7.1 unless site research indicates that these assumptions are not warranted. For all times, the materials 

should be assumed to have a particle size distribution of 5 micron AMAD with a shape factor of 1.5.
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Uranium oxides are formed in a variety of ways in metal-working plants, including scale formation on hot 

surfaces, oxidation enhanced by the presence of water, and fires involving chips and turnings. Thus all 

three of the compounds listed in Table 7.1 can be found in these facilities. The compounds are typically 

insoluble, primarily class S, but some class M material may be observed. The solubility rate and f1 should 

be chosen based on the organ of interest to be favorable to claimants.

The intake of radioactive material via inhalation depends on the characteristics of the worker, that is their 

breathing rate and the extent to which they breath through the mouth. IMBA does not calculate based on 

air concentrations, rather the dose reconstructor is required to calculate the intake from the breathing rate 

and the air concentration. Unless specified otherwise in the site specific guidance, the following worker 

characteristics should be assumed:

 Worker type: Light Worker

 Breathing Characteristics: Nasal Augmenter

 Breathing Rate: 1.2 m3/h or 9.6 m3/day

The intake is the product of the breathing rate, shown above, and the air concentration. Air 

concentrations are presented in the following sections.

7.1 Uranium

7.1.1 Uranium Bioassay

Bioassays were performed on workers at many sites, and urinalysis was the most effective method of 

determining an individual worker’s uranium intake. When bioassay data are available for individual 

workers, this should be the primary source of dose reconstruction for internal exposure.

7.1.2 Uranium Air Sampling

Air sampling was performed by the AEC at many of the AWE metal-working sites, and many of these 

results are presented in this document’s appendices. Harris and Kingsley (1959) summarized 

representative measurements for most of the processes performed by AWE metal-working facilities. 

These results are presented in this section and are available for use in dose reconstruction in situations 

where no site-specific information is available. These results are typical of the state of technology in the 

late 1950s, as surveyed by Harris and Kingsley. Results presented in this section always assumed the 

minimal use of mitigation technologies as published in Harris and Kingsley, so that for instance if results 

were presented for ventilated situations and non-ventilated, the non-ventilated are always presented here. 

In many cases the air concentrations are well above the MAC.

Some sites did not implement all the mitigation technologies represented in the survey and may have had 

higher air concentrations than those listed. If a site is found to have higher measured air concentrations, it 

would be appropriate to use the higher values for dose reconstruction.

For the air sampling data presented in this section, data are presented for individual worker positions, as 

listed in the Harris and Kingsley (1959) tables. When a claimant’s job category is known, the air 
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sampling data for the corresponding job category can be used for the dose reconstruction. Where the 

claimant’s job category is unknown or does not correspond to a listed category, the maximum air 

sampling data should be used.

For some of the measurements, the authors were not specific about the nature of the air concentrations, 

whether they were for a short time duration or a longer time-weighted average. It is assumed that they 

represent peak values that occurred during an operation. Thus they would need to be adjusted by the 

worker’s actual hours and proximity during a workday to estimate the actual time-weighted average 

exposure. Some values were daily-weighted averages, however, and could be used as DWA values for 

the worker exposure.

Air sampling data are presented as lognormal distributions. In the Harris and Kingsley (1959) tables, air 

concentrations were presented as either a single value or as a two-value range. If the air concentration 

was presented as a single value, this value was assumed to be the arithmetic mean, with an assumed 

geometric standard deviation (GSD) of 5 (Battelle Team 2006). The geometric mean can be calculated 

from the arithmetic mean and standard deviation. If the value was presented as a two-value range, the 

two values were assumed to be set about the geometric mean such that the geometric mean is equal to the 

square root of the product of the two values; this lognormal distribution is also assumed to have a GSD=5. 

Table 7.2 shows air sampling data for workers who were involved in extrusion processes at AWE 

facilities. The air concentrations in this table assume that there was no ventilation and minimal use of 

dust mitigation procedures, so the air concentrations are expected to be among the highest experienced in 

extrusion facilities. The data presented by Harris and Kingsley were daily weighted averages.

Table 7.2 Air sampling data for facilities extruding uranium rods

Job Category

Measured air 

concentrations 

(dpm/m3)

Geometric 

Mean

(dpm/m3)

Salt-Bath Operator, DWA 11-90 31.5

Extrusion Press Operator, 

DWA

29-180 72.2

Die-head operator, DWA 410-2400 992

Weigh man, DWA 58-370 147

Operator DWA --- 992

General Laborer DWA --- 147

Supervisor DWA --- 73

Clerical DWA --- 7

For extrusion, the air concentration for the operator was taken as the die-head operator, since this position 

had the highest tabulated exposure.. The assumption for the general laborer is exposure to the “Weigh 

Man” concentration. For the supervisor, the DWA was assumed to be 50% of the general laborer, and the 

clerical worker 10% of the supervisor.

Air concentrations for rolling operations are presented in Table 7.3. These concentrations are 

instantaneous measured concentrations. The daily weighted average for the operator’s is assumed to be 

the measured air concentration for the roughing roll operator, with a 75% weighting factor assuming that 

25% of the operator’s time was spent away from the high concentration. The general laborer’s DWA was 

derived from the stamper, applying a 75% time factor. The supervisor was assumed to be 50% of the 

general laborer, and the clerical worker 10% of the supervisor.
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Table 7.3 Air sampling data for facilities rolling uranium rods

Job Category

Measured air 

concentrations 

(dpm/m3)

Geometric 

Mean

(dpm/m3)

Furnace Operator 180 80.5

Roughing Roll Operator 1620-13700 4710

Finishing Roll Operator 800-8400 2590

Cooling 1470 657

Stamper 1940 868

Drag Down Operator 730 327

Shear Man 1500 671

Operator DWA --- 3533

General Laborer DWA --- 651

Supervisor DWA --- 326

Clerical DWA --- 33

Table 7.4 shows air sampling data for facilities where forging of uranium was practiced. For the press 

forging operations, the measurements were short-duration samples. However, for the hammer forging air 

samples, the measured air concentrations were already identified by Harris and Kingsley as daily 

weighted averages. So the operator DWA was identified as the backside operator of hammer forging and 

the general laborer was identified as the “furnace operator and helper,” while the supervisor DWA was 

taken to be 50% of the general laborer’s DWA, and the clerical 10% of the supervisor.

Table 7.4 Air sampling data for facilities forging uranium

Job Category

Measured air 

concentrations 

(dpm/m3)

Geometric 

Mean

(dpm/m3)

Press Forging – Salt bath 1.7 0.8

Press forging – Press 16 7.2

Press forging – Quench tank 6.2 2.8

Hammer Forging – Front 

hammer operator, DWA

2480 1110

Hammer Forging – Backside 

hammer operator, DWA

2610 1170

Hammer Forging – Furnace 

operator and helper, DWA

810 362

Operator DWA --- 1170

General Laborer DWA --- 362

Supervisor DWA --- 181

Clerical DWA --- 18

Table 7.5 shows air sampling data for facilities where machining of uranium was practiced. For these air 

concentrations, it was assumed that there was no ventilation or other dust mitigation practices. 

Operations with ventilation would have produced much lower air concentrations. Air concentrations 

listed for machining operations were daily weighted averages. The operator DWA was assumed to equal

the Centerless Grinder air concentration; with the general laborer having half of the operator’s DWA, the 

supervisor having half of the general laborer’s DWA, and the clerical worker 10% of the supervisor’s.
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Table 7.5 Air sampling data for facilities machining uranium

Job Category

Measured air 

concentrations 

(dpm/m3)

Geometric 

Mean

(dpm/m3)

Automatic lathe, DWA 200-300 245

Turret lathe, DWA 150 67

Facing, DWA 100 45

Cutoff, DWA 100 45

Milling, DWA 100 45

Slotting, DWA 100 45

Drill, DWA 20 9

Radius Cutting, DWA 100-300 173

Milling, DWA 40 18

Shaping, DWA <10 4

Planning, DWA <10 4

Surface Grinder, DWA 2000-5000 3160

Portable Grinder, DWA 400 179

Belt Sander, DWA 3000 134

Centerless Grinder, DWA 5000-6000 5480

Straightening, DWA 1500-1900 1690

Operator DWA --- 5480

General Laborer DWA --- 2740

Supervisor DWA --- 1370

Clerical DWA --- 137

For job categories where the air concentration was listed as “<10” or “nil,” this analysis assumed that the 

average air concentration was 10 dpm/m3, which would give a geometric mean value of 4 and 95th

percentile of 32.

Table 7.6 shows air sampling data for facilities where uranium slugs were produced and canned. For 

these air concentrations, it was assumed that there was no ventilation or other dust mitigation practices. 

Operations with ventilation would have produced much lower air concentrations. The concentrations 

were short-duration measurements, so the operator’s concentration was assumed to correspond to the 

stamping slug category, with a 75% exposure time, and the general laborer, supervisor, and clerical 

DWA’s found from the operator’s value with the same ratios applied previously.

Table 7.6 Air sampling data for uranium slug production and canning

Job Category

Measured air 

concentrations 

(dpm/m3)

Geometric 

Mean

(dpm/m3)

Stamping slug 590 264

Filing slug 440 197

Wire-brush cleaning die 

section 260

116

Cleaning end slugs 220 98

Cleaning die liners 220 98

Operator DWA --- 198

General Laborer DWA --- 99
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Job Category

Measured air 

concentrations 

(dpm/m3)

Geometric 

Mean

(dpm/m3)

Supervisor DWA --- 50

Clerical DWA --- 5

Table 7.7 shows air sampling data for facilities where uranium scrap recovery operations were practiced. 

For these air concentrations, it was assumed that there was no ventilation or other dust mitigation 

practices. Operations with ventilation would have produced much lower air concentrations. The 

concentrations listed here were daily weighted averages, so the operator’s air concentration was taken as 

the value for straightening, and the other three job categories ratioed as before.

Table 7.7 Air sampling data for uranium scrap recovery

Job Category

Measured air 

concentrations 

(dpm/m3)

Geometric 

Mean

(dpm/m3)

Straightening, DWA 1500-1900 1690

Drawing, DWA nil 4

Swaging, DWA <10 4

Degreasing, DWA 260 116

Briquetting, DWA 250 112

Briquette discharge, DWA 600 268

Operator DWA --- 1690

General Laborer DWA --- 845

Supervisor DWA --- 423

Clerical DWA --- 42

7.1.3 Additional Assumptions for Assessing Internal Dose from Inhalation

In addition to the assumptions specified in the previous section, the following assumptions may be used 

by dose reconstructors when assessing internal dose from the inhalation of air containing uranium dust:

 Radionuclide Constituents: Most uranium handled in AWE metal-working sites was natural 

uranium. There may have been some operations where the uranium was either depleted or lowenriched, but in any case any air measurements were reported in units of dpm/m3

, so the 

measurements were based on activity, not mass. So it is valid to assume that for all intakes, the 

uranium consists solely of 234U.

 Recycled Uranium: There is the possibility that uranium processed after 1953 was recycled 

uranium, so for these time periods, in the absence of definitive information about the origin of the 

processed uranium, it should be assumed that the uranium contains the contaminants listed in

Table 3.2.

 Operational Period, Workdays, Work hours: In most metal-working plants, AEC work with 

uranium was interspersed with similar work done with steel or other non-radioactive material, and 

in most plants only a small fraction of a year was devoted to AEC work. Each site should use its 

AWE operational history to estimate the number of hours worked each year on AWE-related 

work. However, a default assumption of 2000 hours per year, or 10 hours per day, could be made 
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in the absence of historical operational information. This assumption would overestimate the 

actual exposure period.

7.1.4 Uranium Intakes by Inhalation

Air sampling values can be converted to daily intakes by dividing by 2.2 dpm/pCi, multiplying by the 

breathing rate, multiplying by the number of work hours per week and then the number of workweeks per 

year, then dividing by 365. The air concentrations in this calculation are appropriately the short-duration 

air concentrations. The intakes for the metal-working operations are given in Table 7.8, using the 

geometric mean of the air samples and assuming that the intakes would follow the same lognormal 

distributions as the air sample data. The intake value listed in the table is therefore assumed to be the 

geometric mean of a lognormal distribution, and the GSDs for all intakes are assumed to be 5, the same as 

the GSDs for the air samples in Section 7.1.2.

Table 7.8. Daily uranium intakes from uranium inhalation by process and job category

Process Job Title Years Intake, 

pCi/d

Extrusion

Operator Up To 

12/31 

1950

3558

General Laborer 525

Supervisor 263

Clerical 26.3

Extrusion

Operator 1951 

to 

12/31 

1955

3261

General Laborer 482

Supervisor 241

Clerical 24.1

Extrusion

Operator 1/1 

1956 

onward

2965

General Laborer 438

Supervisor 219

Clerical 21.9

Rolling

Operator Up To 

12/31 

1950

12671

General Laborer 2335

Supervisor 1169

Clerical 118

Rolling

Operator 1951 

to 

12/31 

1955

11615

General Laborer 2140

Supervisor 1072

Clerical 108

Rolling

Operator 1/1 

1956 

onward

10559

General Laborer 1946

Supervisor 974

Clerical 98.6

Forging

Operator Up To 

12/31 

1950

4196

General Laborer 1298

Supervisor 649

Clerical 64.6

Forging

Operator 1951 

to 

12/31 

3847

General Laborer 1190

Supervisor 595
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Process Job Title Years Intake, 

pCi/d

Clerical 1955 59.2

Forging

Operator 1/1 

1956 

onward

3497

General Laborer 1082

Supervisor 541

Clerical 53.8

Machining

Operator Up To 

12/31 

1950

19654

General Laborer 9827

Supervisor 4914

Clerical 491

Machining

Operator 1951 

to 

12/31 

1955

18016

General Laborer 9008

Supervisor 4504

Clerical 450

Machining

Operator 1/1 

1956 

onward

16379

General Laborer 8189

Supervisor 4095

Clerical 409

Slug Production

Operator Up To 

12/31 

1950

710

General Laborer 355

Supervisor 179

Clerical 17.9

Slug Production

Operator 1951 

to 

12/31 

1955

651

General Laborer 325

Supervisor 164

Clerical 16.4

Slug Production

Operator 1/1 

1956 

onward

592

General Laborer 296

Supervisor 149

Clerical 14.9

Scrap Recovery

Operator Up To 

12/31 

1950

6061

General Laborer 3031

Supervisor 1515

Clerical 152

Scrap Recovery

Operator 1951 

to 

12/31 

1955

5556

General Laborer 2778

Supervisor 1389

Clerical 139

Scrap Recovery

Operator 1/1 

1956 

onward

5051

General Laborer 2526

Supervisor 1263

Clerical 126.3

7.1.5 Resuspension During Periods with no Uranium Operations

There was a potential for internal exposure to resuspended material from the AEC work during non-AEC 

operations following soon after the actual operations. To estimate exposure from resuspended materials, 
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this analysis assumed that surfaces in the building became contaminated by deposition of uranium dust 

during metal-working operations. (ORAUT 2006) estimates that for uranium metal-working operations, 

a reasonable maximum time-weighted average air concentration would be 7000 dpm/m3(equal to 100 

MAC) during AEC operations. 

The level of contamination was determined by multiplying the air concentration of 7000 dpm/m3by the 

indoor deposition velocity and the assumed deposition time of 30 days (Section 3.4.2). The calculated 

terminal settling velocity was 7.5 × 10-4 m/s, which is within the range of deposition velocities (2.7 × 10-6

to 2.7 × 10-3 m/s) measured in various studies (NRC 2002a).

The calculated surface contamination level created from airborne dusts during a 30 day period of uranium 

metal-working operations would be 1.47×108pCi/m2. This level of surface contamination assumes that 

all uranium deposited on the floor was present for the entire period of AEC operations. Therefore, using a 

resuspension factor of 1×10-6/m (NRC 2002b), the air concentration due to resuspension would be 147

pCi/m3. 

The annual inhalation intake received from resuspension of deposited material, assuming 10-hour 

workdays and the worst-case air concentrations for a one-year metal-working operation, would be 1161

pCi/day.

7.1.6 Ingestion

In the case where inhalation intakes are calculated from air concentrations, ingestion intakes are also to be 

considered. Neton (NIOSH 2004) indicates that the ingestion rate, in terms of pCi for an 8-hour workday, 

can be estimated by multiplying the air concentration by a factor of 0.0985. 

The ingestion rate must be adjusted for the fact that IMBA assumes chronic intakes, even during 

weekends, and that the number of hours worked in a year changed over time (Battelle Team 2006). These 

adjustments result in an IMBA chronic intake rate 

I Ah 5

IMBA 3.373 10

 

, where IIMBA is the daily 

intake (pCi/d), A is the median air concentration (pCi/m3), and h is the number of hours in a working 

year.

Making similar adjustments to Neton’s (NIOSH 2004) equations for incidental hand-to-mouth ingestion 

the chronic IMBA daily intake rate is 

I Ah 5

IMBA 3.425 10

 

, where IIMBA is the daily chronic intake 

rate (pCi/d), h is the number of hours in a work year, and A is the median dust concentration (pCi/m3).

The total ingestion rate is the sum of the food contamination and incidental hand-to-mouth ingestion rates. 

Incorporating a conversion factor of (1 pCi per 2.22 dpm) gives a 

I

I Ah 5MBA 3.062 10

 

where the air 

concentration is given in units of dpm/m3and the daily intake is in units of pCi/d. Intakes for the metal 

processes are given in Table 7.9. Intake values are assumed to be the geometric mean of a lognormal 

distribution with a GSD of 5.
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Table 7.9. Daily uranium intakes from uranium ingestion by process and job category

Process Job Title Years

Ingestion 

Intake, 

pCi/d

Extrusion

Operator Up To 

12/31 

1950

73

General Laborer 10.8

Supervisor 5.4

Clerical 0.5

Extrusion

Operator 1951 

to 

12/31 

1955

67

General Laborer 9.9

Supervisor 4.9

Clerical 0.5

Extrusion

Operator 1/1 

1956 

onward

61

General Laborer 9.0

Supervisor 4.5

Clerical 0.4

Rolling

Operator Up To 

12/31 

1950

260

General Laborer 48

Supervisor 24

Clerical 2.4

Rolling

Operator 1951 

to 

12/31 

1955

238

General Laborer 44

Supervisor 22

Clerical 2.2

Rolling

Operator 1/1 

1956 

onward

216

General Laborer 40

Supervisor 20

Clerical 2.0

Forging

Operator Up To 

12/31 

1950

86

General Laborer 27

Supervisor 13

Clerical 1.3

Forging

Operator 1951 

to 

12/31 

1955

79

General Laborer 24

Supervisor 12

Clerical 1.2

Forging

Operator 1/1 

1956 

onward

72

General Laborer 22

Supervisor 11

Clerical 1.1

Machining

Operator Up To 

12/31 

1950

403

General Laborer 201

Supervisor 101

Clerical 10.1

Machining

Operator 1951 

to

12/31 

1955

369

General Laborer 185

Supervisor 92

Clerical 9.2
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Process Job Title Years

Ingestion 

Intake, 

pCi/d

Machining

Operator 1/1 

1956 

onward

336

General Laborer 168

Supervisor 84

Clerical 8.4

Slug Production

Operator Up To 

12/31 

1950

15

General Laborer 7.3

Supervisor 3.7

Clerical 0.4

Slug Production

Operator 1951 

to 

12/31 

1955

13

General Laborer 6.7

Supervisor 3.4

Clerical 0.3

Slug Production

Operator 1/1 

1956 

onward

12

General Laborer 6.1

Supervisor 3.1

Clerical 0.3

Scrap Recovery

Operator Up To 

12/31 

1950

124

General Laborer 62

Supervisor 31

Clerical 3.1

Scrap Recovery

Operator 1951 

to 

12/31 

1955

114

General Laborer 57

Supervisor 28

Clerical 2.8

Scrap Recovery

Operator 1/1 

1956 

onward

103

General Laborer 52

Supervisor 26

Clerical 2.6
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8.0 References

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