Page 1 of 51

DOE Review Release 01/10/2017

Site Profile for Clarksville Modification 

Center with Supplementary Guidance for the 

Medina Modification Center

ORAUT-TKBS-0039 Rev. 03

Effective Date: 01/04/2017

Supersedes: Revision 02

Subject Expert(s): Dale D. Thomas

Document Owner 

Approval: Signature on File

Dale D. Thomas, Document Owner

Approval Date: 12/20/2016

Concurrence: Signature on File

John M. Byrne, Objective 1 Manager

Concurrence Date: 12/15/2016

Concurrence: Signature on File

Edward F. Maher, Objective 3 Manager

Concurrence Date: 12/15/2016

Concurrence: Vickie S. Short Signature on File for

Kate Kimpan, Project Director

Concurrence Date: 12/15/2016

Approval: Signature on File

James W. Neton, Associate Director for Science

Approval Date: 01/04/2017

FOR DOCUMENTS MARKED AS A TOTAL REWRITE, REVISION, OR PAGE CHANGE, REPLACE THE PRIOR 

REVISION AND DISCARD / DESTROY ALL COPIES OF THE PRIOR REVISION. 

New Total Rewrite Revision Page Change
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 2 of 51

 

PUBLICATION RECORD

EFFECTIVE REVISION 

DATE NUMBER DESCRIPTION

11/14/2006 00 New Site Profile for Clarksville Base Weapons Storage Area and 

Modification Center with Supplementary Guidance for Medina. First 

approved issue. Incorporated responses to internal formal review 

comments. Added sections 5.2.2 and 6.5 covering guidance for 

1966-67 after operations had ceased. Changes made in response to 

NIOSH formal review comments including: use of “favorable to 

claimants” throughout; removal of HT-to-HTO conversion factor for all 

sections dealing with tritium; Sections 4.0 and 5.1.1 – use of Pantex 

1989 accident doses as surrogate for Clarksville tritium release 

accident; Section 5 – clarification of operation years and 

postoperative years, also added to Glossary; Section 5.2.1 – revised 

DU intakes during weapons disassembly to include room ventilation 

and 8-hr shift; Section 5.2.3 – added DU intake from burning 

contaminated HE; Section 5.3 – added intake from alpha 

contamination on capsules or pits; Section 6.1 – added description of 

roles of SNL, AEC, and military personnel; Section 6.4 – clarified that 

the dose rate from Pu metal is sum of photons and neutrons; Section 

A1.1 – added to description of Medina site and operation; Section 

A2.0 – extended period of medical X-rays to October 1958; Section 

A3.2.2 – clarified dates soil samples were taken; Section A5.0 – 

enhanced the description of the radiography source incident. There 

is an increase in assigned dose and a PER is required. Training 

required: As determined by the Task Manager. Initiated by Donald 

E. Bihl.

10/05/2012 01 Revision initiated to incorporate Special Exposure Cohort (SEC) 

Petitions SEC-00202 and SEC-00203. Added Section 1.3 to 

incorporate the SEC class definition. Revised Section 5.0 and 

deleted subsections in accordance with dose reconstruction 

limitations per SEC-00202. Added Section A.1 to incorporate the 

SEC class definition. Revised Section A.4 in accordance with dose 

reconstruction limitations per SEC-00203. Incorporates formal 

internal and NIOSH review comments. Constitutes a total rewrite of 

the document. Training required: As determined by the Objective 

Manager. Initiated by Dale D. Thomas.

04/08/2013 02 Revision initiated to clarify guidance for assigning external dose in 

Section A.6 and Table A-1. Updated Section 1.0 text. Incorporates 

formal internal and NIOSH review comments. Training required: As 

determined by the Objective Manager. Initiated by Dale D. Thomas.

01/04/2017 03 Revision initiated to update external dose reconstruction guidance 

due to revisions in ORAUT-TKBS-0013-6, Pantex Plant – 

Occupational External Dose. Revised Sections 6.2, 6.2.1, 6.2.2.2, 

6.2.5.1, 6.3, 6.3.1, 6.3.2 and added Attachment B. Updated Table B1 to incorporate values from Tables A-1 through A-3, Pantex Plant – 

Occupational External Dose Technical Basis Document (ORAUTTKBS-0013-6, Rev. 03), and updated references. Incorporates 

formal internal and NIOSH review comments. Constitutes a total 

rewrite of the document. Training required: As determined by the 

Objective Manager. Initiated by Dale D. Thomas.
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TABLE OF CONTENTS

SECTION TITLE PAGE

Acronyms and Abbreviations ............................................................................................................... 5

1.0 Introduction .............................................................................................................................. 7

1.1 Purpose........................................................................................................................ 8

1.2 Scope........................................................................................................................... 8

1.3 Special Exposure Cohort.............................................................................................. 8

2.0 Site Description and Operational History.................................................................................. 9

2.1 Site Description ............................................................................................................ 9

2.2 Source Terms............................................................................................................. 12

2.3 Job Descriptions......................................................................................................... 14

3.0 Occupational Medical Dose.................................................................................................... 15

4.0 Occupational Environmental Dose ......................................................................................... 16

5.0 Occupational Internal Dose.................................................................................................... 18

6.0 Occupational External Dose................................................................................................... 19

6.1 Introduction................................................................................................................. 19

6.2 External Radiation Dosimeters and Records .............................................................. 19

6.2.1 Historical Administrative Practices ............................................................... 20

6.2.2 Dosimetry Technology ................................................................................. 20

6.2.2.1 Beta/Photon Dosimeters............................................................ 20

6.2.2.2 Neutron Dosimeters .................................................................. 21

6.2.3 Dosimeter Calibration Procedures................................................................ 22

6.2.3.1 Beta/Photon Dosimeters............................................................ 22

6.2.3.2 Neutron Dosimeters .................................................................. 22

6.2.4 Workplace Radiation Fields.......................................................................... 22

6.2.4.1 Depleted Uranium ..................................................................... 23

6.2.4.2 Photon Radiation....................................................................... 24

6.2.4.3 Neutron Radiation ..................................................................... 24

6.2.5 Dosimeter Response to Radiation Fields ..................................................... 24

6.2.5.1 Beta/Photon/Neutron Film Dosimeter Response ....................... 24

6.2.5.2 Neutron Dose Weighting Factor ................................................ 24

6.3 Recommendations for External Dose Reconstruction, Operative Years ..................... 25

6.3.1 Unmonitored External Dose ......................................................................... 25

6.3.2 Recorded and Missed External Dose for Monitored Workers ....................... 26

6.3.3 Radiation Dose Fraction ............................................................................... 26

6.4 Organ Dose, Operative Years..................................................................................... 26

6.5 Organ Dose, Postoperative Years .............................................................................. 27

7.0 Attributions and Annotations .................................................................................................. 29

References ........................................................................................................................................ 30

Glossary ............................................................................................................................................ 34
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ATTACHMENT A GUIDANCE FOR THE MEDINA MODIFICATION CENTER............................ 40

ATTACHMENT B ASSIGNMENT OF UNMONITORED EXTERNAL DOSE FOR 

CLARKSVILLE AND MEDINA......................................................................... 51

LIST OF TABLES

TABLE TITLE PAGE

2-1 Job categories........................................................................................................................14

4-1 Summary of environmental external dose .............................................................................. 17

6-1 Dosimeter LOD/2 values for dose reconstruction by period.................................................... 20

6-2 Beta, photon, and neutron radiation energies and percentages for Clarksville facilities.......... 23

6-3 Neutron dose energies, percentages, and associated ICRP (1991) correction factors ........... 25

6-4 Exposure categories and applicable job titles......................................................................... 26

6-5 Annual external dose to organs from natural uranium surface contamination at or below 

release criterion, 1966 to 1967............................................................................................... 28

LIST OF FIGURES

FIGURE TITLE PAGE

2-1 General plan view of ABC Structure....................................................................................... 10

2-2 Plan view of the A Structure................................................................................................... 11

2-3 Cross-sectional view of the A Structure.................................................................................. 11

2-4 Plan view of the B and C Structures in the tunnel complex..................................................... 12

2-5 Typical bird cage....................................................................................................................13

6-1 Comparison of Hp(10) for photons with energy responses for DuPont 502 emulsion in 

two-element film badge and DuPont 555 emulsion in multielement film badge....................... 21

A-1 San Antonio, Texas, area showing location of Lackland Training Annex (previously 

called Medina Base)...............................................................................................................42

A-2 Medina Base..........................................................................................................................43

B-1 Unmonitored external doses by year, Clarksville and Medina Modification Centers ............... 51
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ACRONYMS AND ABBREVIATIONS 

AEC U.S. Atomic Energy Commission

AFB Air Force Base

AP anterior-posterior

AWE atomic weapons employer

CD compact disk

CFR Code of Federal Regulations

Ci curie

cm centimeter

CONEX container express

DOE U.S. Department of Energy

DOL U.S. Department of Labor

dpm disintegrations per minute

DU depleted uranium

EEOICPA Energy Employees Occupational Illness Compensation Program Act of 2000

FGR Federal Guidance Report

ft foot

gal gallon

GSD geometric standard deviation

HE high explosive

HEPA high-efficiency particulate air

HEU highly enriched uranium

hr hour

HT elemental tritium (tritiated gas)

HTO tritiated water vapor

ICRP International Commission on Radiological Protection

in. inch

IREP Interactive RadioEpidemiological Program

keV kiloelectron-volt

kg kilogram

LAT lateral

lb pound

LLRW low-level radioactive waste

LOD limit of detection

MeV megaelectron-volt, 1 million electron volts

MHSMC Mason & Hanger-Silas Mason Company

MRD minimum recordable dose

mrad millirad

mrem millirem

NCRP National Council on Radiological Protection and Measurements

NIOSH National Institute for Occupational Safety and Health
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NTA nuclear track emulsion, type A

ORAU Oak Ridge Associated Universities

PA posterior-anterior

PER program evaluation report

PM10 particulate matter in the air with an aerodynamic diameter less than or equal to 

10 micrometers

SEC Special Exposure Cohort

SNL Sandia National Laboratories

SRDB Ref ID Site Research Database Reference Identification (number)

TLD thermoluminescent dosimeter

TNT trinitrotoluene

U.S.C. United States Code

UST underground storage tank

WSA weapons storage area

yr year

Z atomic number

§ section or sections
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1.0 INTRODUCTION

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 historical background information and guidance to assist in the preparation of 

dose reconstructions at particular Department of Energy (DOE) or Atomic Weapons Employer (AWE) 

facilities or categories of DOE or AWE facilities. They will be revised in the event additional relevant 

information is obtained about the affected DOE or AWE facility(ies). These documents may be used 

to assist NIOSH staff in the evaluation of Special Exposure Cohort (SEC) petitions and the completion 

of the individual work required for each dose reconstruction.

In this document the word “facility” is used to refer to an area, building, or group of buildings that 

served a specific purpose at a DOE or AWE facility. It does not mean nor should it be equated to an 

“AWE facility” or a “DOE facility.” The terms AWE and DOE facility are defined in sections 7384l(5) 

and (12) of the Energy Employees Occupational Illness Compensation Program Act of 2000 

(EEOICPA), respectively. An AWE facility means “a facility, owned by an atomic weapons employer, 

that is or was used to process or produce, for use by the United States, material that emitted radiation 

and was used in the production of an atomic weapon, excluding uranium mining or milling.” 42 U.S.C. 

§ 7384l(5). On the other hand, a DOE facility is defined as “any building, structure, or premise, 

including the grounds upon which such building, structure, or premise is located ... in which 

operations are, or have been, conducted by, or on behalf of, the [DOE] (except for buildings, 

structures, premises, grounds, or operations ... pertaining to the Naval Nuclear Propulsion Program);” 

and with regard to which DOE has or had a proprietary interest, or “entered into a contract with an 

entity to provide management and operation, management and integration, environmental 

remediation services, construction, or maintenance services.” 42 U.S.C. § 7384l(12). The Department 

of Energy (DOE) determines whether a site meets the statutory definition of an AWE facility and the 

Department of Labor (DOL) determines if a site is a DOE facility and, if it is, designates it as such.

Accordingly, a Part B claim for benefits must be based on an energy employee’s eligible employment 

and occupational radiation exposure at a DOE or AWE facility during the facility’s designated time 

period and location (i.e., covered employee). After DOL determines that a claim meets the eligibility 

requirements under EEOICPA, DOL transmits the claim to NIOSH for a dose reconstruction. 

EEOICPA provides, among other things, guidance on eligible employment and the types of radiation 

exposure to be included in an individual dose reconstruction. Under EEOICPA, eligible employment 

at a DOE facility includes individuals who are or were employed by DOE and its predecessor 

agencies, as well as their contractors and subcontractors at the facility. Unlike the abovementioned 

statutory provisions on DOE facility definitions that contain specific descriptions or exclusions on 

facility designation, the statutory provision governing types of exposure to be included in dose 

reconstructions for DOE covered employees only requires that such exposures be incurred in the 

performance of duty. As such, NIOSH broadly construes radiation exposures incurred in the 

performance of duty to include all radiation exposures received as a condition of employment at 

covered DOE facilities in its dose reconstructions for covered employees. For covered employees at 

DOE facilities, individual dose reconstructions may also include radiation exposures related to the 

Naval Nuclear Propulsion Program at DOE facilities, if applicable. No efforts are made to determine 

the eligibility of any fraction of total measured exposure for inclusion in dose reconstruction.

NIOSH does not consider the following types of exposure as those incurred in the performance of 

duty as a condition of employment at a DOE facility. Therefore these exposures are not included in 

dose reconstructions for covered employees (NIOSH 2010a):

• 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
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1.1 PURPOSE

This site profile provides information about U.S. Atomic Energy Commission (AEC) operations at 

Clarksville Modification Center at Fort Campbell in Tennessee pertaining to radiation exposures for 

monitored or unmonitored workers. Because the Medina Modification Center in Texas was similar in 

purpose and operation to Clarksville Modification Center, Attachment A of this document contains 

information about Medina.

1.2 SCOPE

Section 2.0 describes the Clarksville site, operations with potential for possible radiation exposures, 

and source terms. Section 3.0 provides guidance for determining occupational medical dose. 

Section 4.0 provides guidance for determining dose to workers outside radiological facilities due to 

releases of radioactive materials to the environment. Section 5.0 provides guidance for determining 

intakes of radionuclides inside facilities. Section 6.0 provides guidance for determining external doses 

from measured doses or for periods when records of measured doses are missing. Attributions and 

annotations, indicated by bracketed callouts and used to identify the source, justification, or 

clarification of the associated information, are presented in Section 7.0.

1.3 SPECIAL EXPOSURE COHORT

On August 23, 2012, as provided for under 42 U.S.C. 7384q(b), the Secretary of Health and Human 

Services designated the following class of employees as an addition to the SEC (Sebelius 2012a):

All employees of the Department of Energy, its predecessor agencies, and their 

contractors and subcontractors, who worked at the Clarksville Modification Center, Ft. 

Campbell, in Clarksville, Tennessee, from August 1, 1949 through December 31, 1967, 

for a number of work days aggregating at least 250 work days, occurring either solely 

under this employment, or in combination with work days within the parameters 

established for one or more other classes of employees included in the Special Exposure 

Cohort.

In its evaluation (NIOSH 2012a), NIOSH found it lacks sufficient information to reconstruct internal 

radiation doses adequately for all Clarksville Modification Center employees for all potential radiation 

exposures. Specifically, this includes internal personnel monitoring data, air monitoring data, process 

data, and radiological source term information that would allow NIOSH to estimate with sufficient 

accuracy potential internal exposures to uranium, plutonium, and tritium. However, NIOSH has 

determined that the occupational medical dose and external doses can be reconstructed based on 

available data. Based on the occupational medical and external data available and the available dose 

reconstruction methods, NIOSH believes that it is possible to either (1) estimate the maximum 

external dose for every type of cancer for which radiation doses are reconstructed that could have 

been incurred under plausible circumstances by any member of the class, or (2) estimate the external 

doses to members of the class more precisely than a maximum dose estimate. Although NIOSH 

found that it is not possible to reconstruct internal radiation doses completely for the proposed class, it 

intends to use any internal monitoring data that might become available for an individual claim (and 

that can be interpreted using existing NIOSH dose reconstruction processes or procedures). 

Therefore, dose reconstructions for employees at Clarksville Modification Center during the period 

from August 1, 1949, through December 31, 1967, but who do not qualify for inclusion in the SEC, can 

be performed using these data as appropriate to support a partial dose reconstruction.
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2.0 SITE DESCRIPTION AND OPERATIONAL HISTORY

2.1 SITE DESCRIPTION

The Clarksville Modification Center was one of 13 weapons storage areas (WSAs) created under the 

Armed Forces Special Weapons Project. The Clarksville Base was constructed on the Fort Campbell 

Military Reservation in the mid- to late 1940s (the first weapon components arrived in July 1949) and 

was supported by Sandia Corporation for the AEC and the U.S. Navy. [The Sandia site became 

Sandia National Laboratories (SNL); for convenience, this site profile uses SNL throughout.] SNL, 

AEC, and the Navy were all active at Clarksville Modification Center from 1949 until 1958 performing 

maintenance and quality assurance on nuclear components of weapons. From 1958 until 1965, 

Mason & Hanger-Silas Mason Company (MHSMC) operated Clarksville Modification Center for the 

AEC as a weapons modification and disassembly facility (Lamb and Halliburton 1996; ORAUT 2006a; 

Mitchell 2003).

Clarksville Base was originally separate from Fort Campbell, which was operated by the U.S. Army. 

In 1965, AEC activities transferred elsewhere, although AEC was responsible for the Base through 

1967. The Base was returned to the Army and incorporated into Fort Campbell in 1969 (Last, 

Gilmore, and Bronson 1998). It is unclear what activities occurred between 1967 and 1969, but 

storage of nuclear materials had ceased.

During AEC tenure, nuclear weapons and weapon components were stored by AEC and maintained 

by SNL and military personnel at the WSAs. WSAs consisted of storage buildings that housed 

nuclear capsules, maintenance structures, waste burial sites, and bunkers for storage of weapons 

casings. SNL personnel worked at Clarksville Modification Center under contract to the AEC until 

early 1962 (Lamb and Halliburton 1996; Last, Gilmore, and Bronson 1998; ORAUT 2006a).

Storage of nuclear capsules at Clarksville Modification Center was in an underground complex known 

as the ABC Structure. The ABC Structure consisted of the A Structure, which was the nuclear 

capsule storage area that was secured behind a bank-type locking vault door at the end of a 600-ftlong tunnel; the C Structure, which was used for nuclear materials inspection and maintenance; and 

the B Structure, which was a backup facility for the C Structure but was used only as a medical wing. 

C Structure activities involved dismantling the nuclear assembly system, checking the activity of the 

fissile material, and replacing the Po-Be initiators (Lamb and Halliburton 1996; Last, Gilmore, and 

Bronson 1998; ORAUT 2006a). Figure 2-1 is an overall plan view of the ABC Structure. Figure 2-2 

shows a close-up plan view of the A Structure, and Figure 2-3 shows a cross-sectional view. 

Figure 2-4 shows a plan view of the B and C Structures. The figures refer to “Fort Campbell” because 

the ABC Structure was inactive in 1998; however, at the time of use they were the Clarksville WSA.

A second C Structure, constructed in 1957, was an aboveground brick building AEC used only to 

service nonnuclear components. Once this structure opened, operations at the original C Structure 

ceased due to moisture intrusion. In addition, the Clarksville WSA included a gravel gertie for 

weapons maintenance and modification. The newer C Structure and gravel gertie had large overhead 

rails to support weapon subassemblies during maintenance. Standard aboveground igloos were used 

for storage, including the storage of sealed weapons. No nuclear maintenance activities occurred in 

these igloos (Lamb and Halliburton 1996; Last, Gilmore, and Bronson 1998; ORAUT 2006a).

Some of the claimant interviews refer to the “bird cage.” This term was used officially to describe the 

criticality-safe framework around a nuclear package (see Figure 2-5); however, the term appears to 

have been used unofficially to refer to the entire Clarksville Modification Center, meaning the fenced, 

heavily guarded area where an AEC Q-level clearance was required (more than just the tunnel 

complex).
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Figure 2-1. General plan view of ABC Structure (Last, Gilmore, and Bronson 1998). 
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Figure 2-2. Plan view of the A Structure (Last, Gilmore, and Bronson 1998). 

Figure 2-3. Cross-sectional view of the A Structure (Last, 

Gilmore, and Bronson 1998). 
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Figure 2-4. Plan view of the B and C Structures in the tunnel complex (Last, 

Gilmore, and Bronson 1998). 

2.2 SOURCE TERMS

Early weapon designs were in-flight insertables. Weapons of this type had removable nuclear 

capsules (also known as the physics package or pit) and were stored in a bird cage. The bird cage 

ensured storage in a criticality-safe manner. The capsules were pressure-sealed. Figure 2-5 shows a 

typical bird cage. The bird cage held the nuclear capsule, which contained plutonium, highly enriched 

uranium (HEU), and a Po-Be initiator. Periodic maintenance was required on these early weapon pits 

to exchange the Po-Be initiators due to the short half-life of 210Po. This required disassembly of the 

weapon pit to remove the initiator, which was at the pit center.
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Figure 2-5. Typical bird cage. 

Later weapon designs were not in-flight insertables and did not have Po-Be initiators, which 

eliminated the need to disassemble the weapon pit for modification. The Po-Be initiators were phased 

out over time, until 1956, and replaced by external neutron generators. The weapon pits are referred 

to as sealed pit designs. These designs included the potential for exposure to tritium. The 

introduction of tritium could have occurred as early as 1954 (ORAUT 2006a; Mitchell 2003).

Another source of radioactive material in early nuclear weapons was the spark gap tube. These 

tubes, which were part of the firing circuits, were used to switch large amounts of electrical current. A 

small amount of 137Cs was used in spark gap tubes to stabilize the electrical properties. These tubes, 

which were manufactured of thick glass to prevent breakage, were a minor exposure pathway 

(ORAUT 2006a).

As part of the maintenance activities, Clarksville personnel performed radiographs of the weapon 

components using a large 60Co source. The exact location of this source was not discovered, but the 

newer C Structure is a likely candidate (ORAUT 2006a).

In summary, the radioactive materials of interest at Clarksville Modification Center are tritium as a 

gas, weapons-grade plutonium, HEU, depleted uranium (DU; also used in weapons construction), 

210Po in a Po-Be neutron initiator, a 60Co radiograph source, and small activities of 137Cs.
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2.3 JOB DESCRIPTIONS

Table 2-1 lists job descriptions from the claims files or interviews of former employees (ORAUT 

2006b, 2006c).

Table 2-1. Job categories. 

Title Description

Material handler Moved nuclear devices to and from storage and disassembly areas or 

among magazines; unloaded devices from trucks, railcars, and aircraft and 

drove them to storage areas.

Production operator, operator, 

operator trainee

Assembled and disassembled nuclear devices.

Inspector, quality control 

specialist, quality control 

inspector

Nuclear components inspectors observed assembly and disassembly, 

recorded condition of components, and ensured correct assembly of 

components; it is possible these workers performed gamma/X-ray 

inspections of devices. Not all inspectors were responsible for nuclear 

components; some would have had only incidental exposure to complete 

weapons. The latter should be considered in same category as material 

handlers. 

Warehouseman Received, stored, shipped nuclear devices; conducted inventory of nuclear 

devices. One claimant interview indicated a warehouseman worked in 

storage igloos for 1 week conducting inventory about every 6 months. 

Safety/security inspector Performed security inspection and control of all buildings including 

magazines; probably spent some time in all secure locations but did not 

handle nuclear devices.

Mechanic Repaired equipment, moved nuclear devices; mechanics might have been 

responsible for replacing filters in ventilation systems including contaminated 

filters; spent time in igloos when necessary.

Truck driver, heavy equipment 

operator

Probably involved with transporting nuclear devices to and from railcars and

airport.

Firemen Firemen were present with a fire extinguisher during disassemblies.

Sheet metal worker, electrician, 

refrigerator/cooling mechanic, 

janitor

Probably worked anywhere and might have had some exposure in igloos.

Clerk-typist Worked in offices in Bird Cage; might have entered disassembly areas to 

deliver messages.

Accountant Had office in Bird Cage; occasionally entered igloos.

Bus driver, grounds laborer, 

power plant operator, sewage 

disposal operator

Probably did not have any exposure except environmental.
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3.0 OCCUPATIONAL MEDICAL DOSE

It is not known if medical X-rays were required for all workers or selected workers as a condition of 

employment. No documentation on X-ray policies, procedures, or equipment has been found. An 

SNL safety engineer familiar with work at WSAs did not recall X-rays being part of medical 

examinations at any of the WSAs during the period when SNL was the principal AEC contractor 

(ORAUT 2006a). Records on Clarksville workers from Pantex do not list any X-rays before 1960, 

even for workers who continued employment into the years when MHSMC was the principal AEC 

contractor. A review of the claims information revealed that, for employment between 1960 and 1965, 

53% of the workers had at least one chest X-ray and 35% had at least one lumbar spine X-ray. Most 

of the X-rays are either labeled as preemployment or occurred in the first year of employment. The 

pattern does not support additional routine X-rays; only four workers had more than one chest X-ray 

and only one had a second lumbar spine X-ray. In terms of job categories, no pattern was evident in 

relation to who had preemployment X-rays and who did not. For instance, the records for the two

claims showed one chest X-ray each, whereas some craft workers had no record of X-rays.

Based on the limited information available for workers during 1960 through 1967 with no X-ray 

records, the dose reconstructor should assume one chest X-ray and one lumbar spine examination for 

the entire employment period (not each year). As described below, a lumbar spine examination is 

assumed to consist of four exposures. The dose from X-rays should be assigned in 1960 or the first 

year of employment after 1960, but not for employment before 1960.

No information about X-ray equipment manufacturers, models, examination techniques, or exposure 

rates for the X-rays has been found. Therefore, assumptions that are favorable to claimants and 

guidance in ORAUT-OTIB-0006, Dose Reconstruction from Occupational Medical X-Ray Procedures

(ORAUT 2011), were used. The actual film was not sent to the Pantex Plant for archiving, only the 

information that an X-ray occurred, the type, and the date. The film size and therefore type of 

radiography are not known. For small DOE sites, conventional chest X-rays are assumed.

Lumbar spine X-rays at the Pantex Plant were given only to men. None of the lumbar spine X-rays in 

the Clarksville claim files were given to women, but the number of female workers among the 

Clarksville claims is small. Nevertheless, because lumbar spine X-rays were given to screen for back 

injuries that might preclude heavy lifting, and considering that heavy lifting was culturally a man’s job 

in the workplace in the 1960s, it is reasonable to assign the default lumbar spine X-ray only to men.

Organ Dose Calculations

ORAUT (2011) organ doses should be used because no site-specific information is available for 

Clarksville. Dose reconstructors should use the most recent update of that document. Dose 

reconstructors should assume that a posterior-anterior (PA) chest projection was performed on 

Clarksville workers. Organ dose equivalents for chest projections for all periods are in Table A-7 of 

ORAUT (2011), and skin doses from chest projections are in Tables A-8 and A-9 of that document.

According to ORAUT (2011), two anterior-posterior (AP) and two lateral exposures should be 

assumed for lumbar spine examinations when the site-specific protocol is not known. However, the 

doses in ORAUT (2011) include only one exposure per projection. The organ doses for lumbar spine 

X-rays in ORAUT (2011) for one exposure per projection are listed in Table A-10 of that document. 

Dose reconstructors should double these doses when assuming two exposures per projection for 

Clarksville claims (see footnote b to Table A-10). Skin doses from lumbar spine projections are in 

Table A-11 of ORAUT (2011). These values should also be doubled when assuming two exposures 

per projection. Enter the doubled values from ORAUT (2011) into the Interactive 

RadioEpidemiological Program (IREP) as an acute dose due to photons with energies between 30 

and 250 keV. Assume a normal distribution with a standard deviation of ±30%.
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4.0 OCCUPATIONAL ENVIRONMENTAL DOSE

Occupational environmental dose refers to the dose received by workers outside normal production 

facilities. These doses can be internal or external (e.g., from effluents or scattered radiation through 

building walls or ceilings). No records on environmental releases from Clarksville Modification Center 

have been discovered. Before 1959, complete disassemblies were not performed at Clarksville 

Modification Center, only storage, maintenance, and inspection. Maintenance included replacement 

of major components.

Plutonium and enriched uranium sources in the weapons were always sealed, as were polonium in 

the initiators and other radionuclides in the radiography sources. There was risk of DU oxide 

contamination in the cells. The underground C Structure had exhaust vents at the top of the hillside 

under which the tunnel was located (Last, Gilmore, and Bronson 1998). Whether the exhaust passed 

through high-efficiency particulate air (HEPA) filters is not known. According to a former employee, 

portable gloveboxes with HEPA-filtered exhausts were used to contain oxidized DU when weapons 

underwent inspections, maintenance, and refurbishment during the SNL years (ORAUT 2006a). The 

DU was cleaned from the nuclear components and deposited as solid waste on cleaning rags.

The same employee mentioned that the DU contamination came from spalling, which produced large 

nonrespirable particles. Environmental intake of DU was insignificant because (1) the likelihood of a 

significant release outside the tunnel was small and (2) the location of the exhaust vent made it 

unlikely that DU that might have exhausted from the C Structure would have returned to occupied 

areas (ORAUT 2006a). 

After tritium reservoirs became part of the weapons, leaks of tritium into the disassembly cell and out 

the cell exhaust duct were possible. The employee was not aware of any releases of tritium from the 

disassembly cells, but most handling of the tritium reservoirs occurred during the years MHSMC 

operated the facility (ORAUT 2006a). No documentation about tritium releases into the cells or 

through exhaust stacks has been found. Tritium in the reservoirs was in the form of tritiated gas, 

which has essentially no significance for intakes. Tritium gas converts slowly to tritiated water vapor 

as it mingles with humid air. Not all the gas would convert to water vapor during the time workers 

would be exposed (Peterson and Davis 2002), but it is favorable to claimants to assume 100% water 

vapor.

Based on similar work at the Pantex Plant, the release of tritium from the reservoirs during normal 

operations does not produce airborne concentrations that could result in intakes that result in annual 

organ doses of greater than 0.001 rem (ORAUT 2015). Therefore, with the exception of 1962 as 

described below, environmental intakes of tritium and the resultant internal dose for the Clarksville 

Modification Center should not be assigned.

A Clarksville worker described an accident involving a damaged weapon that was sent to Clarksville 

Modification Center from the military (ORAUT 2006b). The accident was corroborated in a claimant 

interview. At the time of the accident, both individuals were told the damaged weapon was leaking 

tritium. No documentation of the accident or information about the amount of tritium that might have 

leaked has been found. The interview indicated that the accident occurred in 1962.

Because the worker was told that they had been exposed to tritium while moving the weapon from the 

airport to the storage igloo, it is assumed that the tritium leak had been occurring for some time before 

its discovery. The reservoirs were under considerable pressure, so most of the contents would have 

leaked before arrival at Clarksville. However, there was sufficient leakage still occurring to set off the 

tritium monitors the next day when the weapon was taken into the cell, according to the claimant 

interview.
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 17 of 51

An accidental release of tritium during a disassembly occurred at the Pantex Plant in 1989 (ORAUT 

2015). This was a major release that caused severe contamination of a cell. Workers were present 

at the initiation of the release and therefore subject to the highest release rate. All of the release 

occurred at Pantex, whereas most of the 1962 leak probably did not occur at Clarksville. It is unlikely 

that the accidental release at Clarksville was worse than the Pantex release. Clarksville workers 

stopped the leak within a few hours of its discovery, whereas the release at Pantex was so significant 

no attempt was made to stop the leak until it had run its course. Therefore, it is reasonable to 

conclude that the amount of tritium release at Clarksville was much less than the amount during the 

1989 Pantex accident. Therefore, because NIOSH has concluded that it lacks sufficient information, 

which includes monitoring data, sufficient air monitoring information, or sufficient process and 

radiological source information, that would allow it to estimate the intakes of tritium to which the 

proposed class may have been exposed, no internal dose for intakes of environmental airborne 

concentrations should be assigned for the Clarksville Modification Center.

External radiation dose greater than the ambient rate outside a building where frequent radiography 

was performed might have occurred via direct radiation penetration through walls or from scattered 

radiation. Dose rates are usually quite small in noncontrolled areas near radiography sources. For 

instance, at the Hanford Radiological Calibration Facility, the total annual dose as measured by 

thermoluminescent dosimeters (TLDs) on the outside of an interior wall at about 25 ft from a 20-Ci 

137Cs source (662-keV gamma ray), which was used almost daily, was 7 mrem. A 60Co radiography 

source would be expected to have less activity, but the gamma radiation strength of 60Co (1,173- and 

1,332-keV gamma rays) is about 4 times that of 137Cs. Assuming a smaller activity 60Co source 

produces about the same annual dose rate outside the radiography building as the 20-Ci 137Cs source 

and, assuming an environmental occupancy factor outside the building of 0.5, dose reconstructors 

should assign a 4-mrem whole-body dose per year from external radiation (see Table 4-1). Assume a 

100% 30- to 250-keV photon energy category. Calculate organ doses of interest using OCAS-IG-001, 

External Dose Reconstruction Implementation Guideline (NIOSH 2007). Because this dose rate was 

made by inference from a similar situation, rather than by direct measurement, an uncertainty factor of 

2 is reasonable.

Table 4-1. Summary of environmental external dose. 

Period of application Annual whole-body dose Photon energy category Distribution

July 1949–1965 4 mrem 30–250 keV GSD = 2

1966–1967 0 mrem Not applicable Not applicable
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 18 of 51

 

5.0 OCCUPATIONAL INTERNAL DOSE

NIOSH has concluded that it is not possible to reconstruct internal doses completely for any period at 

the Clarksville Modification Center. Therefore, in the absence of monitoring data for an individual 

claim, no occupational internal doses should be assigned. For claims in which individual internal 

monitoring data are available, the internal dose should be reconstructed based on interpretation of the 

monitoring data using existing NIOSH dose reconstruction processes and procedures.
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 19 of 51

6.0 OCCUPATIONAL EXTERNAL DOSE

6.1 INTRODUCTION

Workers at Clarksville Modification Center were employed by either SNL or MHSMC, but not both. A 

few SNL workers (fewer than 20) performed the maintenance operations involving nuclear

components between July 1949 and September 1958 (ORAUT 2006a). A similar number of MHSMC 

workers performed inspections and modifications on nuclear weapons from 1959 to September 1965 

(Mitchell 2003).

Work activities at Clarksville Modification Center undoubtedly varied over time. Analysis of historical 

information showed that maintenance activities at Clarksville began in 1949, which corresponds to the 

first record of personnel monitoring (ORAUT 2006a). The nature of the radiation fields a Clarksville 

worker could have encountered depends on the type of weapon on which work occurred. Nuclear 

weapons components emit alpha and beta particles, X- and gamma rays, and neutrons, but doses to 

workers depend strongly on the configuration (i.e., material and shielding) of the source of radiation 

and the work performed (Oxley 2001).

There were three major groups of workers at Clarksville. AEC employees served primarily in 

oversight positions and generally did not perform hands-on work. SNL and (later) MHSMC 

employees were responsible for maintenance of the weapons and would likely have the highest 

doses. Military personnel would likely receive doses that were less than the SNL or MHSMC 

employees; the military primarily loaded the weapons on airplanes and performed in-flight operations 

that were necessary.

6.2 EXTERNAL RADIATION DOSIMETERS AND RECORDS 

External dosimetry records for Clarksville Modification Center are sparse, and the connection between 

the dose record and the worker might be missing. Statistical analysis of doses known to have been 

received at Clarksville cannot be performed with the few records found to date.

Dosimetry data for several Clarksville workers were found and incorporated into the site research 

database and subsequently linked to individual claimant records. SNL dosimetry records spanned 

1949 through 1959. Until 1953, specific nuclear components present in the WSAs contained 210Po. 

The presence of these components accounts for approximately 10 annual doses (from all WSAs) of 

nominally 1 rem. After 1953, the maximum annual dose from the aggregate of all WSAs was 

nominally 0.100 rem (ORAUT 2006a). The Pantex Plant maintains a limited database for MHSMC 

workers at Clarksville Modification Center that contains weekly dose information for a few workers 

from October 1960 to 1965. Although MHSMC began its management of Clarksville Modification 

Center in early 1959, no dosimetry records were found for 1959 through September 1960. Annual 

dose reports to AEC for 1960 to 1965 included individual whole-body dose equivalent from photons 

and neutrons. At Clarksville, dosimeters were issued to only a few workers who had direct contact 

with nuclear weapon components.

The first dosimetry records found for MHSMC workers are from October 1960. Commercial film 

badge service was supplied by Tracerlab from 1960 to 1965. During this period, a small number of 

workers (from 3 to 27) were monitored with the results mostly less than the minimum recordable dose

(MRD). Of approximately 5,900 individual weekly film badges, only about 40 results were at or above 

the MRD. The highest annual dose to a worker from film data was less than 200 mrem in a year. 

Eastman Kodak nuclear track emulsion, type A (NTA) film was probably added for neutron dosimetry 

in January 1960; the exact date has not been determined. A former employee thought the first use of 

neutron dosimetry might have been 1959. Pantex Plant dosimetry data show that NTA film was in 

use by January 1960 (ORAUT 2006a). Because Clarksville and Pantex were operated by the same 
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 20 of 51

 

contractor, it is reasonable to assume that identical dosimetry service was provided for both sites. 

Only one positive (12-mrem) result was reported from nearly 3,900 individual weekly film badges 

(Tracerlab 1965).

6.2.1 Historical Administrative Practices

Clarksville Modification Center started monitoring workers for radiation exposure in July 1949. SNL 

provided the dosimeters at that time. Table 6-1 summarizes the monitoring technique, exchange 

frequency, and values for one-half the limit of detection (LOD/2). The SNL MRD for nonpenetrating 

skin and penetrating whole-body dose was probably similar to the minimum detection levels (MDLs) 

determined by others (Wilson 1960, 1987; NIOSH 1993; NRC 1989; Wilson et al. 1990). Dosimeters 

were supplied by Tracerlab from October 1960 to 1965 for MHSMC workers. No dosimetry records 

were found for 1959 through September 1960. The Tracerlab MRDs were 30 and 10 mrem, 

respectively (Tracerlab 1965). Actual MDLs are typically higher because of additional uncertainty in 

field use and the use of dose recording thresholds.

Table 6-1. Dosimeter LOD values (mrem) for dose reconstruction by period (ORAUT 2016a).a

Dosimeter type–provider Period

Exchange 

frequency

Skin 

LOD Deep LOD

Neutron 

LOD

Beta-gamma film–SNL 07/1949–1959 Monthly 30 10 Not 

applicable

Beta-gamma film–Tracerlab 10/1960–1963 Weekly 30 10 15

Beta-gamma, NTA film–Tracerlab 1964–1966 Weekly 40 10 20

a. Adapted from Table 6-3 of ORAUT (2016a). 

The routine practice at Clarksville Modification Center appears to have required assigning dosimeters 

to designated radiation workers who could receive an external radiation dose greater than 10% of the 

radiation protection guidelines in effect. Dosimeters were exchanged on a routine schedule. 

However, from 1960 to 1965 when Tracerlab provided film badges, individual worker names were not 

recorded with specific film badge numbers. In addition, dose components appear to be missing for 

some workers based on such designations as blanks or “damaged film” in records. These missing 

components can be reconstructed from other recorded dosimeter data by using recommended 

methods described below in this site profile.

6.2.2 Dosimetry Technology

SNL radiation workers were monitored by film badges provided by SNL. The film badge initially 

consisted of a piece of dental X-ray film in a plastic pouch with a pin for fastening to clothing. A lead 

filter was later added to the plastic pouch. The Oak Ridge metal film badge holder with three filters 

was used from 1957 through 1958. NTA film for neutron dosimetry was added in 1959 or 1960. 

Results from film badges were reported on “cardex” dosimetry records. However, records from these

dosimeters have not been found in the SNL archives (ORAUT 2006a). The maximum reported 

radiation dose was as high as 1 rem/yr from 1949 to 1952 (ORAUT 2006a). After 1952, maximum 

radiation doses were about 100 mrem/yr (ORAUT 2006a).

The first commercial dosimeter MHSMC used at Clarksville was a two-element film badge from 

Tracerlab for measuring beta, X-ray, and gamma exposures (Tracerlab 1965). Beginning in July 

1962, Clarksville used a multielement film badge that incorporated NTA film to measure beta, X-rays, 

gamma rays, and fast neutrons (Tracerlab 1965).

6.2.2.1 Beta/Photon Dosimeters

Figure 6-1 shows the response of two film badges to photon radiation of different energies along with 

the Hp(10) response: one for a sensitive DuPont 502 emulsion in a two-element badge (Pardue, 
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 21 of 51

Goldstein, and Wollan 1944), and one for a sensitive DuPont 555 emulsion in the multielement badge 

(Thornton, Davis, and Gupton 1961). The response of the sensitive Eastman Type 2 film in a 

multielement film badge is similar to that of the sensitive DuPont 555 emulsion. The film badges show 

an over-response at photon energies around 100 keV, due primarily to relatively high atomic numbers 

(Z) [silver (47) and bromine (35)] in the film emulsions (in comparison with tissue). The film badges 

under-respond to lower energy photons, but the relative response of the two-element film badge to 

60-keV photons from 241Am is nearly unity. The multielement film badge typically over-responds to 

60-keV photons.

Hp(10)

Two-Element Film Badge

Multi-Element Film Badge

0.01 0.1 1

Photon Energy (MeV)

0.1

1

10

Relative Response

Figure 6-1. Comparison of Hp(10) for photons with energy responses 

for DuPont 502 emulsion in two-element film badge (Pardue, 

Goldstein, and Wollan 1944) and DuPont 555 emulsion in 

multielement film badge (Thornton, Davis, and Gupton 1961).

6.2.2.2 Neutron Dosimeters

The response of film dosimeters to neutron radiation was not good. NTA film was added to the holder 

for the Clarksville beta/gamma dosimeter in 1958 and from July 1962 through 1965 (ORAUT 2005). 

In general, the response of the NTA film decreases with decreasing neutron energies greater than a 

minimum threshold energy for laboratory studies, estimated to be about 500 keV (IAEA 1990). The 

minimum threshold energy for routine use in Clarksville mixed photon and neutron radiation fields is 

probably about 1 MeV. Results reported at the first AEC neutron dosimetry workshop indicated that 

laboratory dose measurements with NTA film were about one-half to one-fourth of those measured 

with other methods, including the neutron TLD (Vallario, Hankins, and Unruh 1969). Based on current 

knowledge of the general characteristics and response of NTA film, and the expected under-response 

in workplace conditions with significant scattering of neutrons, use of the film for personnel neutron 

dose monitoring can have biases. Testing of NTA film clearly showed that neutrons with energies 

below 500 keV were not measurable, and overall neutron doses were probably underestimated. 

Based on this, correction factors should be applied to the recorded NTA film results to account for 

threshold response (1.4), angular dependence (1.33), and uncorrected fading (1.56) (ORAUT 2016a). 

Combining these factors, the total correction factor of 2.9 should be applied to the NTA film results in 

addition to the International Commission on Radiological Protection (ICRP) correction factor (1.91) 

(ORAUT 2016a).
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 22 of 51

6.2.3 Dosimeter Calibration Procedures

6.2.3.1 Beta/Photon Dosimeters

Clarksville film badges were originally calibrated with 226Ra sources, with exposure measured by 

Victoreen R chambers. Deliberately irradiated film badges were sent periodically to SNL and 

Tracerlab, and reported doses were compared with measured doses for calibration (ORAUT 2006a).

6.2.3.2 Neutron Dosimeters

An account of the historical aspects of the calibration of Clarksville neutron dosimeters is not 

available.

6.2.4 Workplace Radiation Fields

The main workplace radiation fields at Clarksville Modification Center arose from the handling of 

nuclear weapon components containing plutonium, HEU, Po-Be initiators, and DU. The highest dose 

rates were encountered from the handling of bare pits and Po-Be initiators. The nuclides in the 

sealed nuclear weapon component pits emitted alpha, beta, X-, gamma, and neutron radiation. From 

an external dosimetry perspective, the radiations of concern are beta particles, photons (X- and 

gamma rays), and neutrons. Radiation exposure to workers depends significantly on the processes 

used in the preparation, design, and construction of the weapons.

With few exceptions, the following sections show that, for external dose reconstruction purposes, all 

beta radiation fields are greater than 15 keV, all photon radiation fields are between 30 and 250 keV, 

and all neutron fields are between 0.1 and 2 MeV. Presuming that 100% of the radiation fields are 

within these ranges is a simplifying, conservative assumption that is generally favorable to claimants. 

Table 6-2 summarizes the radiation energy categories.
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 23 of 51

Table 6-2. Beta, photon, and neutron radiation energies and percentages for Clarksville facilities. 

Process/

buildings Description

Operations

period

Radioactive

material

Radiation

type

Energy

selection

Percent

(notes)

Bays

Cells

Tunnel complex

Assembly/disass

embly of nuclear 

weapons

1949–1965 DU Beta >15 keV 100a

Photons 30–250 keV 100b

Bays

Cells

Tunnel complex

Assembly/disass

embly of nuclear 

weapons

1958–1965 Tritium Beta <15 keV 100c

Bays

Cells

Tunnel complex

Assembly/disass

embly of nuclear 

weapons

1949–1965 Plutonium, HEU Photons 30–250 keV 100

Neutrons 0.1–2 MeV 100d

Bays

Cells

Tunnel complex

Casual 

surveillance, 

minor 

maintenance

1966–1967 DU Beta >15 keV 100

Photons 30–250 keV 100

Igloos Staging of 

weapons and 

plutonium pits

1949–1965 Plutonium, HEU Photons 30–250 keV 100

Neutrons 0.1–2 MeV 100d

Igloos Casual 

surveillance,

minor 

maintenance

1966–1967 DU Beta >15 keV 100

Photons 30–250 keV 100

Transportation Movement of 

weapons

1949–1965 DU, HEU, 

plutonium

Photons 30–250 keV 100b

Neutrons 0.1–2 MeV 100d

Warehouse Packaging 

components

1949–1965 Weapon 

components

Beta >15 keV 100a

Photons 30–250 keV 100b

Neutrons 0.1–2 MeV 100d

Warehouse Packaging 

components

1954–1965 Tritium Beta <15 keV 100c

a. Workplace beta radiation has energy greater than 15 keV.

b. Most photons from DU have energies greater than 30 keV; some have energies greater than 250 keV. If shielding

materials are present, fewer photons are in the categories less than 30 keV or greater than 250 keV. The simplifying

conservative assumption that 100% of the photons from DU are between 30 and 250 keV is recommended as generally

favorable to claimants.

c. Beta particles from tritium are classified in the less-than-15-keV category.

d. The energy of neutrons in the workplace is predominately in one of two ranges: Between 0.1 and 2 MeV or between 2

and 20 MeV. In some cases, with significant moderating materials, some neutrons are less than 0.1 MeV. However,

the simplifying conservative assumption that 100% of the neutrons are between 0.1 and 2 MeV is recommended as

generally favorable to claimants.

6.2.4.1 Depleted Uranium

Clarksville workers handled DU (primarily 238U) during assembly and disassembly of weapon 

components and during maintenance operations. An important progeny nuclide for potential worker 

exposure in 238U decay is 234mPa with a half-life of 24 days. In a few months after purification, DU 

components have 234mPa activities nearly equal to that of 238U. Protactinium-234m emits beta 

radiation 98.6% of the time when it changes to its ground state with a maximum energy of 2.28 MeV 

and an average energy of 0.825 MeV (Shleien, Slaback, and Birky 1998; ICRP 1973). An additional 

source of exposure in the Clarksville workplace was from bremsstrahlung produced in high-Z

materials from interactions with higher energy beta particles. Beta particles emitted by 234mPa excite 

both bremsstrahlung and characteristic X-rays in DU or 238U.

Beta radiation from DU could have contributed to extremity and skin dose to workers unless 

precautions were taken to protect workers from the radiation. Protective clothing and gloves provide a 

protection factor of 2 or more, depending on the thickness. A bare slab source of natural uranium 

contributes an Hp(0.07) dose of approximately 230 mrad/hr at the surface in comparison with an 
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 24 of 51

Hp(10) dose at 1 ft of approximately 2 mrad/hr (Kathren 1975). However, significant beta exposures 

to Clarksville workers were rarely detected by film badges, based on a review of shallow and deep 

dosimetry data.

6.2.4.2 Photon Radiation

Photon radiation in the workplace could have been readily measured at Clarksville Modification 

Center with available dosimeter technology during all years of operation. It is assumed that all 

photons at Clarksville were within the 30- to 250-keV range, similar to data from the Pantex Plant.

6.2.4.3 Neutron Radiation

The in-flight-insertable design of nuclear weapons required a neutron initiator source. The first 

initiator sources were 210Po mixed which could be combined with beryllium to produce neutrons

(ORAUT 2006a). The average energy of the neutrons was 4.2 MeV (Shleien, Slaback, and Birky 

1998). The energies of the photons and neutrons were 0.8 and 4.45 MeV, respectively (Shleien and 

Terpilak 1984). Unfortunately, the half-life of 210Po is only 138.4 days (Shleien, Slaback, and Birky 

1998), so the initiator sources had to be exchanged frequently (ORAUT 2006a).

Until 1957, the primary radiological task was periodically changing the Po-Be initiators. Between 1954 

and 1956, Po-Be initiators were gradually replaced with a newer type of sealed neutron generator that 

did not require routine replacement. Maintenance activities were reduced to annual disassembly of 

capsules to verify the integrity of fissile materials, and radiation exposures to workers were reduced 

(Lamb and Halliburton 1996).

6.2.5 Dosimeter Response to Radiation Fields

6.2.5.1 Beta/Photon/Neutron Film Dosimeter Response

The dosimeters Clarksville used after 1957 contained an open window with little filtration, a lower 

energy window for allowing beta particles and lower energy photons to enter a film area with a plastic 

filter, and a film area with a metal (usually aluminum) filter. The open window enabled measurement 

of beta particles and lower energy photons. The plastic filter enabled measurement of intermediate 

energy photons and the metal filter enabled measurement of higher energy photons (1-cm depth).

Tracerlab provided commercial dosimetry services from October 1960 through 1965. The AEC tested 

film badges from Tracerlab with exposures to 40-, 70-, and 210-keV X-rays and 60Co gamma rays, 

and mixed-energy exposures of all four radiations (AEC 1955). The film badges generally responded 

well “with a tendency to interpret most exposures too high.” The over-response (in the 100- to

200-keV region) tended to yield conservatively high results.

The film badge dosimetry reports from Tracerlab are less than adequate because few names are 

recorded in relation to specific film badge numbers. Radiation doses to workers were probably low 

during this period, and many positive doses less than the MRD would have been recorded as zero. 

The weekly film badge exchange frequency increased the probability that low doses were truncated to 

zero. An uncertainty correction factor of 1.3 is a reasonable estimate of the uncertainty for recorded 

photon doses for organs other than the skin. The factor of 2.9 applied to recorded neutron doses 

accounts for uncertainties in dosimeter response.

6.2.5.2 Neutron Dose Weighting Factor

The coworker neutron doses for Clarksville were based on Pantex dosimeter readings. At Pantex, 

thermoluminescent neutron dosimeters were calibrated with measurements based on fluence-to-dose 
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 25 of 51

conversion factors and quality factors similar to those from ICRP Publication 21 (ICRP 1973) and 

National Council on Radiation Protection and Measurement (NCRP) Report 38 (NCRP 1971). It is 

necessary to adjust the neutron dose to account for the change in neutron quality factors between 

historic and current scientific guidance, as discussed in NIOSH (2007). Table 6-3, excerpted from 

ORAUT (2015b), lists the correction factor to use.

Table 6-3. Neutron dose energies, percentages, and associated ICRP (1991) correction factors. 

Process Description

Neutron 

energy

(MeV)

Default dose

fractiona (%)

ICRP (1991)/ 

NCRP (1971)

correction 

factor

Nuclear weapons 

component assembly

Neutron exposure associated with weapons 

assembly and disassembly activities

0.1–2 100 1.91

a. From Table 6-2; assuming all neutron energies are between 0.1 and 2 MeV is favorable to claimants.

6.3 RECOMMENDATIONS FOR EXTERNAL DOSE RECONSTRUCTION, OPERATIVE YEARS

Dose reconstruction for Clarksville Modification Center workers is based on the foregoing information, 

which requires assessment of external dose considering these primary factors:

• Adjustments to recorded photon dose to account for dosimeter response uncertainty;

• Adjustment of neutron doses to account for energy dependence, angular response, and fading

using a factor of 2.9;

• Multiplication of the calculated neutron dose by an ICRP (1991) neutron weighting factor

adjustment of 1.91 for neutron energies between 0.1 and 2 MeV; and

• Adjustments to account for non-uniform fields for doses to the extremities and lower torso

organs associated with workers performing pit maintenance operations with bare pits on the

lap in a sitting position. This is discussed later in Section 6.4.

6.3.1 Unmonitored External Dose

For Clarksville, the concept of “unmonitored worker” must be expanded to include “monitored but 

records not found.” Few dosimetry records have been found for Clarksville; those that have been 

found do not always identify the person who received the radiation dose. Therefore, it was necessary 

to estimate the radiation doses Clarksville workers might have received. To perform these estimates, 

four job categories with relative exposure potentials were identified (Table 6-4). Category 1 consists 

of individuals who worked with nuclear devices on a daily basis; these were considered full-time 

radiation workers who received the highest doses. Category 2 consists of individuals who routinely 

entered radiation work areas but were not in close contact with nuclear devices or were not exposed 

full time; they were assumed to be occupationally exposed, but to a lesser extent than those working 

with nuclear components. Category 3 consists of individuals who were only occasionally exposed and 

were not in close contact with nuclear components. Category 4 consists of individuals who did not 

enter radiation areas; they were assumed to have received only environmental dose.

Operations at Clarksville Modification Center between 1958 and 1965 were similar to those at the 

Pantex Plant; MHSMC operated both facilities. Therefore, the coworker doses in ORAUT-TKBS0013-6, Pantex Plant – Occupational External Dose (ORAUT 2016a) are assumed to be 

representative for unmonitored workers at Clarksville for the MHSMC years. See Attachment B for 

unmonitored dose tables.
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 26 of 51

Table 6-4. Exposure categories and applicable job titles. 

Exposure 

category Conditions Job titles

1 Extensive work with pits; full-time exposure 

(typically apply the 95th-percentile coworker

dose).

Production operator, operator, operator 

trainee, nuclear inspector, nuclear quality 

control inspector

2 Worked predominantly in radiation areas but did 

not handle nuclear components routinely

(typically apply the 50th-percentile coworker 

dose)

Material handler, warehouseman, safety/ 

security inspector, fireman, nuclear quality 

control specialists, inspectors not associated 

with nuclear components

3 Infrequent entry into radiation areas (apply 

either the 50th-percentile coworker dose or 

onsite ambient dose depending on job 

description or statements in the interview).

All job categories not explicitly listed in this 

table

4 Did not enter radiation areas; exposure from 

environmental sources only (apply on-site 

ambient dose).

Bus driver, grounds laborer, power plant 

operator, sewage disposal operator

For the SNL years, 1949 to 1958, workers handled sealed components rather than performing 

intimate handling of pits, so doses would be expected to be smaller than those for MHSMC 

operations. Therefore, the assignment of unmonitored worker doses from Attachment B should be 

considered representative of the doses that the Clarksville workers likely received.

6.3.2 Recorded and Missed External Dose for Monitored Workers

The vast majority of records reflect only annual summary information. If external dose data are found 

in a worker’s file, the dose reconstructor should assign the recorded annual dose along with missed 

dose based on the LOD/2s and the number of exchange periods from Table 6-1 for the respective 

dosimetry systems, using the guidance in Attachment A of ORAUT-PROC-0006, External Dose 

Reconstruction (ORAUT 2006d).

6.3.3 Radiation Dose Fraction

Table 6-2 summarizes the recommended energy fractions for Clarksville dose according to facilities, 

processes or activities, and energy categories required by IREP.

6.4 ORGAN DOSE, OPERATIVE YEARS

Once the Hp(10) adjusted doses have been calculated for each year, the values are used to calculate 

organ doses of interest using the external dose reconstruction implementation guidelines (NIOSH 

2007). Dose reconstructors should assume the use of the AP (front-to-back) geometry for the 

irradiation geometry and for conversion to organ dose. Multiply the calculated neutron doses by the 

neutron deep dose equivalent organ dose conversion factors for AP irradiation from Appendix B of 

NIOSH (2007). For photons applicable to Clarksville Modification Center (i.e., film badge era), use the 

conversion factor from exposure to organ dose.

Some workers at Clarksville Modification Center, generally production operators, operators, or 

operator trainees, might have handled unshielded pits with gloved hands or by holding the unshielded 

pits in their laps. If the individual has skin cancer on the hands and handled unshielded pits, dose 

reconstructors should apply the guidance in DCAS-TIB-0013, Selected Geometric Exposure Scenario 

Considerations for External Dose Reconstruction at Uranium Facilities (NIOSH 2010b). For cancers 

of the lower torso organs, the 95th-percentile glovebox correction factor in DCAS-TIB-0010, Best 

Estimate External Dose Reconstruction for Glovebox Workers, (NIOSH 2011) is recommended to 

ensure a result favorable to the claimant. This type of activity was generally limited to a relatively 
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 27 of 51

 

small fraction of time during the average workday. Because of this, a scaling factor should be applied 

to the 95th-percentile glovebox correction. For example, the actual pit handling activity likely took no 

more than 1 to 2 hr/d. Assuming that the claimant actually performed pit handling maintenance 

operations for 1 hr/d 5 d/wk, the appropriate correction to apply would equate to the 95th-percentile 

correction multiplied by 0.125 (5 hr/d divided by the 40-hour work week).

In likely compensable cases that include cancers on the extremities, a more realistic dose estimate 

should be performed using actual surface dose rates, attenuation factors, or both. Further, it is 

unlikely that individuals would have contact with the bare metal for extended periods.

6.5 ORGAN DOSE, POSTOPERATIVE YEARS

External dose might have been received by persons doing minor maintenance or surveillance of the 

site after the facility was shut down in 1966 and 1967, due to possible residual DU contamination on 

floors or surfaces. A radiological survey in 1997 found no contamination above release criteria (Last, 

Gilmore, and Bronson 1998). The release criterion for combined fixed and removable contamination 

was 5,000 dpm/100 cm2

. Organ dose rates were calculated assuming the following:

• A geometry of standing on a contaminated floor, 

• 5,000 dpm/100 cm2 of natural uranium, which would be favorable to claimants in relation to 

DU, and

• Progeny radionuclides after 5-year ingrowth

Calculations were based on dose factors provided in the compact disk (CD) supplement to Federal 

Guidance Report (FGR) No. 13 (Eckerman et al. 1999). The dose rates to the skin are averages over 

the entire phantom used for the calculations, and no credit for protective clothing or shoes was 

applied in the calculations. It was assumed that time spent in proximity to contaminated surfaces was 

limited to a few hours a month, so an occupancy factor of 0.02 was applied. The annual organ doses 

are listed in Table 6-5.

Because all measurements were reported as simply less than the release criterion, the above 

calculations are analogous with missed dose calculations. Therefore, a triangular distribution should 

be applied with a minimum of zero, a mode based on the surface contamination at one-half the 

release criterion, and a maximum based on the surface contamination at the release criterion. 

However, the doses are all less than 1 mrem/yr and can be ignored. They are provided in case a 

dose reconstructor believes it appropriate to use a larger occupancy factor. No neutron doses should 

be applied.
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Table 6-5. Annual external dose (rem) to organs from 

natural uranium surface contamination at or below 

release criterion, 1966 to 1967. 

Organ Mode Maximum

Adrenals 7.28E-07 1.46E-06

Bladder wall 7.98E-07 1.60E-06

Bone surface 2.08E-06 4.16E-06

Brain 7.58E-07 1.52E-06

Breasts 1.06E-06 2.12E-06

Esophagus 6.73E-07 1.35E-06

Stomach wall 7.95E-07 1.59E-06

Small intestine wall 7.46E-07 1.49E-06

Upper large intestine wall 7.68E-07 1.54E-06

Lower large intestine wall 7.74E-07 1.55E-06

Kidneys 8.07E-07 1.61E-06

Liver 7.96E-07 1.59E-06

Lungs 8.44E-07 1.69E-06

Muscle 1.00E-06 2.00E-06

Ovaries 7.41E-07 1.48E-06

Pancreas 7.10E-07 1.42E-06

Red marrow 8.27E-07 1.65E-06

Skin 2.80E-04 5.60E-04

Spleen 8.01E-07 1.60E-06

Testes 1.05E-06 2.10E-06

Thymus 7.86E-07 1.57E-06

Thyroid 8.78E-07 1.76E-06

Uterus 7.42E-07 1.48E-06
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 29 of 51

7.0 ATTRIBUTIONS AND ANNOTATIONS

All information requiring identification was addressed via references integrated into the reference 

section of this document.
Document No. ORAUT-TKBS-0039 Revision No. 03 Effective Date: 01/04/2017 Page 30 of 51

REFERENCES

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Isotopics, volume 2, number 5, pp. 8–23. [SRDB Ref ID: 3640]

Carr, B. H., ca. 1992, Pantex History, 1942 to 1992, Mason & Hanger-Silas Mason Company, Pantex 

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Eckerman, K. F., and J. C. Ryman, 1993, External Exposure to Radionuclides in Air, Water, and Soil, 

Federal Guidance Report No. 12, EPA-402-R-93-081, U.S. Environmental Protection Agency, 

Office of Radiation and Indoor Air, Washington, D.C., September. [SRDB Ref ID: 11997]

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Radiogenic Cancer Risk Coefficients for the U.S. Population, Based on Age-Dependent 

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NIOSH (National Institute for Occupational Safety and Health), 1993, NIOSH Research Issues 

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Implementation Guideline, OCAS-IG-001, Rev. 3, Office of Compensation Analysis and 

Support, Cincinnati, Ohio, August.

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for Dose Reconstructions Under Part B of the Energy Employees Occupational Illness 

Compensation Program Act, DCAS-IG-003, Rev. 1, Division of Compensation Analysis and 

Support, Cincinnati, Ohio, October 5.

NIOSH (National Institute for Occupational Safety and Health), 2010b, Selected Geometric Exposure 

Scenario Considerations for External Dose Reconstruction at Uranium Facilities, DCAS-TIB0013, Rev. 1, Division of Compensation Analysis and Support, Cincinnati, Ohio, November 23. 

NIOSH (National Institute for Occupational Safety and Health), 2011, Best Estimate External Dose 

Reconstruction for Glovebox Workers, DCAS-TIB-0010, Rev. 04, Division of Compensation 

Analysis and Support, Cincinnati, Ohio, November 28. 

NIOSH (National Institute for Occupational Safety and Health), 2012a, Special Exposure Cohort, 

Petition Evaluation Report Petition SEC-00202, Division of Compensation Analysis and 

Support, Cincinnati, Ohio, May 31.

NIOSH (National Institute for Occupational Safety and Health), 2012b, Special Exposure Cohort, 

Petition Evaluation Report Petition SEC-00203, Division of Compensation Analysis and 

Support, Cincinnati, Ohio, May 31.

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ORAUT (Oak Ridge Associated Universities Team), 2005, “Dosimetry Records for Clarksville,” 

memorandum to file, Oak Ridge, Tennessee, September 30. [SRDB Ref ID: 23591]

ORAUT (Oak Ridge Associated Universities Team), 2006a, “Interview with [Name redacted] 

Concerning Operation and Worker Exposures at Clarksville on December 29, 2005, and 

Subsequent Electronic Mail Messages,” letter to [Name redacted] (Albuquerque, New Mexico), 

Oak Ridge, Tennessee, March 7. [SRDB Ref ID: 22750]

ORAUT (Oak Ridge Associated Universities Team), 2006b, “Interview with [Name redacted] 

Concerning Activities at the Clarksville Facility, February 26, 2006,” letter to [Name redacted] 

(Edieville, Kentucky), Oak Ridge, Tennessee, February 7. [SRDB Ref ID: 22290]

ORAUT (Oak Ridge Associated Universities Team), 2006c, “Interview with [Name redacted] 

Concerning Activities at the Clarksville Facility, February 8, 2006,” letter to [Name redacted] 

(Hopkinsville, Kentucky), Oak Ridge, Tennessee, February 10. [SRDB Ref ID: 22291]

ORAUT (Oak Ridge Associated Universities Team), 2006d, External Dose Reconstruction, ORAUTPROC-0006, Rev. 01, Oak Ridge, Tennessee, June 5.
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ORAUT (Oak Ridge Associated Universities Team), 2006e, “Personal communication with [Name 

redacted],” Oak Ridge, Tennessee, May 6. [SRDB Ref ID: 46684]

ORAUT (Oak Ridge Associated Universities Team), 2006f, “Notes from Phone Conversation with 

[Name redacted], Pantex, re: Pu Contamination on Early Pits,” letter to file, Oak Ridge, 

Tennessee, August 10. [SRDB Ref ID: 27014]

ORAUT (Oak Ridge Associated Universities Team), 2006g, “Medina Dose Records, 1959-1966,” 

memorandum to file, Oak Ridge, Tennessee. [SRDB Ref ID: 24735]

ORAUT (Oak Ridge Associated Universities Team), 2011, Dose Reconstruction from Occupational 

Medical X-Ray Procedures, ORAUT-OTIB-0006, Rev. 04, Oak Ridge, Tennessee, June 20.

ORAUT (Oak Ridge Associated Universities Team), 2015, Pantex Plant – Occupational Internal Dose, 

ORAUT-TKBS-0013-5, Rev. 04, Oak Ridge, Tennessee, June 1.

ORAUT (Oak Ridge Associated Universities Team), 2016a, Pantex Plant – Occupational External 

Dose, ORAUT-TKBS-0013-6, Rev. 03, Oak Ridge, Tennessee, November 29.

ORAUT (Oak Ridge Associated Universities Team), 2016b, Technical Information Bulletin: Guidance 

on Assigning Occupational X-Ray Dose under EEOICPA for X-Rays Administered Off Site, 

ORAUT-OTIB-0079, Rev 01, Oak Ridge, Tennessee, March 18.

Oxley, L. S., 2001, Technical Basis for the External Dosimetry Program at the Y-12 National Security 

Complex, RCO/TBD-007, Rev. 3, BWXT Y-12, Y-12 National Security Complex, Oak Ridge 

Tennessee, August 2. [SRDB Ref ID: 8467]

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pp. 213–225.

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Tennessee, U.S. Department of Health and Human Services, Office of the Secretary, 

Washington, D.C., August 23.

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the Energy Employees Occupational Illness Compensation Program Act of 2000, Designating 

a Class of Employees from the Medina Modification Center, San Antonio, Texas, U.S. 

Department of Health and Human Services, Office of the Secretary, Washington, D.C., 

August 23.
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Shleien, B., L. A. Slaback, Jr., and B. K. Birky, editors, 1998, Handbook of Health Physics and 

Radiological Health, Third Edition, Williams & Wilkins, Baltimore, Maryland, January.

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Nucleon Lectern Associates, Olney, Maryland.

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Monitoring Applications, ORNL-3126, Union Carbide Corporation, Oak Ridge National 

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GLOSSARY

absorption

In external dosimetry, process in which radiation energy is imparted to material. In internal 

dosimetry, movement of material to blood regardless of mechanism.

absorption type

Categories for materials according to their rate of absorption from the respiratory tract to the 

blood, which replaced the earlier inhalation clearance classes. Defined by the International 

Commission on Radiological Protection, the absorption types are F: deposited materials that 

are readily absorbed into blood from the respiratory tract (fast solubilization), M: deposited 

materials that have intermediate rates of absorption into blood from the respiratory tract 

(moderate rate of solubilization), and S: deposited materials that are relatively insoluble in the 

respiratory tract (slow solubilization).

activity

Amount of radioactivity. The International System unit of activity is the becquerel 

(1 disintegration per second); the traditional unit is the curie [37 billion (3.7 × 1010) becquerels].

acute exposure

Radiation exposure to the body delivered in a short period. See chronic exposure.

alpha radiation

Positively charged particle emitted from the nuclei of some radioactive elements. An alpha 

particle consists of two neutrons and two protons (a helium nucleus) and has an electrostatic 

charge of +2.

anterior-posterior (AP)

Physical orientation of the body relative to a penetrating directional radiation such that the 

radiation passes through the body from the front to the back. See exposure geometry.

background radiation

Radiation from cosmic sources, naturally occurring radioactive materials including naturally 

occurring radon, and global fallout from the testing of nuclear explosives. Background 

radiation does not include radiation from source, byproduct, or Special Nuclear Materials 

regulated by the U.S. Nuclear Regulatory Commission. The average individual exposure from 

background radiation is about 360 millirem per year.

beta radiation

Charged particle emitted from some radioactive elements with a mass equal to 1/1,837 that of 

a proton. A negatively charged beta particle is identical to an electron. A positively charged 

beta particle is a positron.

bird cage

(1) Criticality-safe framework around a nuclear capsule in the in-flight insertable design; 

(2) common expression for Clarksville secured area.

bremsstrahlung

Electromagnetic radiation released as a result of inelastic scattering of a moving charged 

particle within the nucleus of an atom. X-rays produced in a typical medical X-ray tube 

frequently originate from inelastic scattering of accelerated electrons in the anode material.
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chronic exposure

Radiation dose to the body delivered in small amounts over a long period (e.g., days or years). 

See acute exposure.

contamination

Radioactive material in an undesired location including air, soil, buildings, animals, and 

persons.

decay

(1) Disintegration of atomic nuclei from spontaneous radioactivity including alpha, beta, and 

neutron radiation, often accompanied by gamma radiation. (2) Decrease in the amount of 

radioactive material over time due to nuclear transformation. See half-life.

deep dose equivalent [Hp(10)]

Dose equivalent in units of rem or sievert for a 1-centimeter depth in tissue (1,000 milligrams 

per square centimeter). See dose.

depleted uranium (DU)

Uranium with a percentage of 235U lower than the 0.7% found in natural uranium.

dose

In general, the specific amount of energy from ionizing radiation that is absorbed per unit of 

mass. Effective and equivalent doses are in units of rem or sievert; other types of dose are in 

units of, rad, rep, or gray.

dose equivalent

In units of rem or sievert, product of absorbed dose in tissue multiplied by a weighting factor 

and sometimes by other modifying factors to account for the potential for a biological effect 

from the absorbed dose. See dose.

dosimeter

Device that measures the quantity of received radiation, usually a holder with radiationabsorbing filters and radiation-sensitive inserts packaged to provide a record of absorbed dose 

received by an individual. See film dosimeter and thermoluminescent dosimeter.

dosimeter holder

Plastic holder for a dosimeter card, which typically includes one or more metallic filters that 

modify the response of the phosphor to radiation.

dosimetry

Measurement and calculation of internal and external radiation doses.

enriched uranium (EU)

Uranium in which processing has increased the proportion of 235U to 238U to above the natural 

level of 0.7% by mass. Reactor-grade uranium is usually about 3.5% 235U; weapons-grade 

uranium contains greater than 90% 235U.

exchange period (frequency)

Period (weekly, biweekly, monthly, quarterly, etc.) for routine exchange of dosimeters.
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exposure geometry

Orientation (physical positioning) of a person or object in relation to a radiation source. This 

geometry is a factor in the radiation dose to various parts of the body. See anterior-posterior, 

posterior-anterior, and lateral.

film

(1) In the context of external dosimetry, radiation-sensitive photographic film in a light-tight 

wrapping. See film dosimeter. (2) X-ray film.

film badge

See film dosimeter.

film dosimeter

Package of film for measurement of ionizing radiation exposure for personnel monitoring 

purposes. A film dosimeter can contain two or three films of different sensitivities, and it can 

contain one or more filters that shield parts of the film from certain types of radiation. When 

developed, the film has an image caused by radiation measurable with an optical 

densitometer. Also called film badge.

filter

Material used (1) in a dosimeter to adjust radiation response to provide an improved tissue 

equivalent or dose response and (2) in an X-ray machine to selectively absorb photons from 

the beam to reduce unnecessary exposure of individuals or to improve radiographic quality.

gamma radiation

Electromagnetic radiation (photons) of short wavelength and high energy (10 kiloelectron-volts 

to 9 megaelectron-volts) that originates in atomic nuclei and accompanies many nuclear 

reactions (e.g., fission, radioactive decay, and neutron capture). Gamma photons are identical 

to X-ray photons of high energy; the difference is that X-rays do not originate in the nucleus.

geometric standard deviation (GSD)

In probability theory and statistics, the geometric standard deviation describes the spread of a 

set of numbers whose preferred average is the geometric mean.

gravel gertie

Facility with the distinguishing characteristic of having blow-out roof panels overlain with gravel 

to dissipate the pressure surge and energy of a conventional high-explosive detonation. This 

design was developed to allow the energy of the blast to be dissipated while minimizing the 

spread of contamination of any radioactive material present. Also called gertie.

half-life

Time in which half of a given quantity of a particular radionuclide disintegrates (decays) into 

another nuclear form. During one half-life, the number of atoms of a particular radionuclide 

decreases by one half. Each radionuclide has a unique half-life ranging from millionths of a 

second to billions of years.

high-efficiency particulate air (HEPA) filter

Dense filter that removes contaminants from air flows before return to the working environment 

or discharge to the outside air (exhaust).

highly enriched uranium (HEU)

Uranium enriched to at least 20% 235U for use as fissile material in nuclear weapons 

components and some reactor fuels. Also called high-enriched uranium.
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igloo

Earth-covered storage area for items that might explode, such as ammunition, high explosives, 

bombs, or bomb parts.

in-flight insertable

Historical weapons design in which final assembly of the nuclear and nonnuclear components 

of an air-drop weapon did not occur until just before use. Military technicians completed the 

assembly en route to the target by inserting the nuclear materials capsule into the mechanical 

assembly.

lateral (LAT)

Orientation of the body during an X-ray procedure in which the X-rays pass from one side of 

the body to the other. See exposure geometry.

minimum detectable activity or amount (MDA)

Smallest amount (activity or mass) of an analyte in a sample that can be detected with a 

probability β of nondetection (Type II error) while accepting a probability α of erroneously 

deciding that a positive (nonzero) quantity of analyte is present in an appropriate blank sample 

(Type I error).

neutron (n)

Basic nucleic particle that is electrically neutral with mass slightly greater than that of a proton. 

There are neutrons in the nuclei of every atom heavier than normal hydrogen.

neutron film dosimeter

Film dosimeter with a nuclear track emulsion, type A, film packet.

neutron radiation

Radiation that consists of free neutrons unattached to other subatomic particles emitted from a 

decaying radionuclide. Neutron radiation can cause further fission in fissionable material such 

as the chain reactions in nuclear reactors, and nonradioactive nuclides can become 

radioactive by absorbing free neutrons. See neutron.

neutron-to-photon dose ratio

Ratio applied to the photon fraction to estimate the unmeasured neutron dose based on 

knowledge and measurements in a specified location.

nuclear emulsion

Thick photographic coating in which the tracks of various fundamental particles show as black 

traces after development. The number of tracks in a given area is a measure of the dose from 

that radiation. See nuclear track emulsion, type A.

nuclear track emulsion, type A (NTA)

Film sensitive to fast neutrons. Made by the Eastman Kodak Company, the developed image 

has tracks caused by neutrons that become visible under oil immersion with about 1,000-

power magnification.

open window

Area of a film dosimeter that has little to no radiation shielding (e.g., only a holder and visible 

light protection). The open window measures nonpenetrating as well as penetrating dose, 

which minimizes the potential for beta radiation to contribute to the interpreted penetrating 

dose. See film dosimeter.
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operational years

Period of U.S. Atomic Energy Commission responsibility during which the site had an active 

mission that involved handling or storing radioactive materials.

personal dose equivalent [Hp(d)]

Dose equivalent in units of rem or sievert in soft tissue below a specified point on the body at 

an appropriate depth d. The depths selected for personal dosimetry are 0.07 millimeter 

(7 milligrams per square centimeter) and 10 millimeters (1,000 milligrams per square 

centimeter), respectively, for the skin (shallow) and whole-body (deep) doses. These are 

noted as Hp(0.07) and Hp(10), respectively. The International Commission on Radiological 

Measurement and Units recommended Hp(d) in 1993 as dose quantity for radiological 

protection.

photon

Quantum of electromagnetic energy generally regarded as a discrete particle having zero rest 

mass, no electric charge, and an indefinitely long lifetime. The entire range of electromagnetic 

radiation that extends in frequency from 1023 cycles per second (hertz) to 0 hertz.

photon radiation

Electromagnetic radiation that consists of quanta of energy (photons) from radiofrequency 

waves to gamma rays.

PM10

Particles less than 10 micrometers in aerodynamic median diameter that include both fine and 

coarse dust particles; essentially particles of respirable size.

posterior-anterior (PA)

Physical orientation of the body relative to a penetrating directional radiation field such that the 

radiation passes through the body from the back to the front. See exposure geometry.

postoperative years

Period of U.S. Atomic Energy Commission responsibility during which no active functions were 

performed that involved handling or storing radioactive materials. The period after the site was 

shut down and major radioactive materials were removed, but the site was still under 

Commission jurisdiction.

progeny

Nuclides that result from decay of other nuclides. Also called decay products and formerly 

called daughter products.

radiograph

Static images produced on radiographic film by gamma rays or X-rays after passing through 

matter. In the context of the Energy Employees Occupational Illness Compensation Program 

Act of 2000, radiographs are X-ray images of the various parts of the body used to screen for 

disease.

radiography

The process of producing images on film (or other media) with radiation.

radon (Rn)

Radioactive gaseous element with atomic number 86. Radon is a decay product (progeny) of 

other radioactive elements such as thorium and radium.
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shallow dose equivalent [Hp(0.07)]

Dose equivalent in units of rem or sievert at a depth of 0.07 millimeter (7 milligrams per square 

centimeter) in tissue equal to the sum of the penetrating and nonpenetrating doses.

thermoluminescent dosimeter (TLD)

Device for measuring radiation dose that consists of a holder containing solid chips of material 

that, when heated, release the stored energy as light. The measurement of this light provides 

a measurement of absorbed dose.

U.S. Atomic Energy Commission (AEC)

Federal agency created in 1946 to assume the responsibilities of the Manhattan Engineer 

District (nuclear weapons) and to manage the development, use, and control of nuclear energy 

for military and civilian applications. The U.S. Energy Research and Development 

Administration and the U.S. Nuclear Regulatory Commission assumed separate duties from 

the AEC in 1974. The U.S. Department of Energy succeeded the U.S. Energy Research and 

Development Administration in 1979.

whole-body (WB) dose

Dose to the entire body excluding the contents of the gastrointestinal tract, urinary bladder, 

and gall bladder and commonly defined as the absorbed dose at a tissue depth of 

10 millimeters (1,000 milligrams per square centimeter). Also called penetrating dose. 

See dose.

X-ray

(1) See X-ray radiation. (2) See radiograph.

X-ray radiation

Electromagnetic radiation (photons) produced by bombardment of atoms by accelerated 

particles. X-rays are produced by various mechanisms including bremsstrahlung and electron 

shell transitions within atoms (characteristic X-rays). Once formed, there is no difference 

between X-rays and gamma rays, but gamma photons originate inside the nucleus of an atom.
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ATTACHMENT A 

GUIDANCE FOR THE MEDINA MODIFICATION CENTER

TABLE OF CONTENTS

SECTION TITLE PAGE

A.1 Special Exposure Cohort........................................................................................................ 41

A.2 Site Description and Functions............................................................................................... 41

A.2.1 Site Description .......................................................................................................... 42

A.2.2 Operational History as a Weapons Storage Area, 1954 to 1960................................. 45

A.2.3 Operation as a Modification and Disassembly Center................................................. 46

A.3 Occupational Medical Dose.................................................................................................... 47

A.4 Environmental Dose............................................................................................................... 47

A.4.1 Routine Doses............................................................................................................ 47

A.4.2 November 13, 1963, Explosion................................................................................... 47

A.4.2.1 Background.................................................................................................. 47

A.4.2.2 Direct Radiation ........................................................................................... 48

A.5 Internal Dose.......................................................................................................................... 49

A.6 External Dosimetry................................................................................................................. 49

LIST OF FIGURES

FIGURES TITLE PAGE

A-1 San Antonio, Texas, area showing location of Lackland Training Annex (previously 

called Medina Base)...............................................................................................................42

A-2 Medina Base..........................................................................................................................43
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A.1 SPECIAL EXPOSURE COHORT

On August 23, 2012, as provided for under 42 U.S.C. 7384q(b), the Secretary of Health and Human 

Services designated the following class of employees as an addition to the SEC (Sebelius 2012b):

All employees of the Department of Energy, its predecessor agencies, and their 

contractors and subcontractors who worked at the Medina Modification Center in San 

Antonio, Texas, from January 1, 1958 through December 31, 1966, for a number of work 

days aggregating at least 250 work days, occurring either solely under this employment 

or in combination with work days within the parameters established for one or more other 

classes of employees included in the Special Exposure Cohort.

In its evaluation (NIOSH 2012b), NIOSH found that it lacks sufficient information to reconstruct 

internal radiation doses adequately for all Medina Modification Center employees for all potential 

radiation exposures. Specifically, this includes internal personnel monitoring data, air monitoring data, 

process data, and radiological source term information that would allow NIOSH to estimate with 

sufficient accuracy potential internal exposures to uranium, plutonium, and tritium. However, NIOSH 

has determined that occupational medical and external doses can be reconstructed based on 

available data. Based on the occupational medical and external data available, and the available 

dose reconstruction methods, NIOSH believes it is possible to either: (1) estimate the maximum 

external dose for every type of cancer for which radiation doses are reconstructed that could have 

been incurred under plausible circumstances by any member of the class; or (2) estimate the external 

doses to members of the class more precisely than a maximum dose estimate. Although NIOSH 

found that it is not possible to reconstruct internal radiation doses completely for the proposed class, 

NIOSH intends to use any internal monitoring data that might become available for an individual claim 

(and that can be interpreted using existing NIOSH dose reconstruction processes or procedures). 

Therefore, dose reconstructions for employees at Medina Modification Center, San Antonio, Texas, 

during the period from January 1, 1958, through December 31, 1966, but who do not qualify for 

inclusion in the SEC, can be performed using these data as appropriate to support a partial dose 

reconstruction.

A.2 SITE DESCRIPTION AND FUNCTIONS

Medina Base, located on about 3,700 acres of Lackland Air Force Base (AFB) southwest of San 

Antonio, Texas, was one of 13 WSAs created under the Armed Forces Special Weapons Project. 

Medina Base was constructed by the U.S. Air Force and the AEC between 1953 and 1955, with the 

first weapons components arriving in 1955. It was supported by SNL for the AEC and the Air Force. 

SNL, AEC, and the Air Force were all active at Medina from 1955 until early 1959, performing 

maintenance and quality assurance on nuclear components of weapons (Mitchell 2003).

NOTE: The approved dates for applicability under EEOICPA for this site are limited to 1958 

through 1966 only.

AEC stored nuclear weapons and components that were maintained by SNL and Air Force personnel 

at the Medina WSA, which consisted of storage buildings that housed nuclear capsules, maintenance 

structures, waste burial sites, and bunkers for storage of weapons casings. SNL personnel worked at 

Medina under contract to the AEC until early 1959 (ORAUT 2006e).

In 1958, MHSMC was chosen by the AEC to manage Medina Base, and construction of new facilities 

was undertaken. Three gravel gertie cells were constructed along with other specialized facilities that 
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made up the Medina Modification Center (Mitchell 2003). From April 1959 until 1966, MHSMC 

operated Medina for the AEC as a weapons modification and disassembly facility. The mission was 

to perform stockpile surveillance, modifications, retrofits, and weapon retirements (Carr ca. 1992). 

This work included inspections for corrosion and replacement of tritium reservoirs. Medina was 

operated by MHSMC until January 1966, when its mission was transferred to the Pantex Plant and 

Medina Base was transferred back to the Air Force.

A.2.1 Site Description

Lackland AFB is in the San Antonio metropolitan area in Bexar County, Texas (Figure A-1). 

Commercial and residential developments border Lackland AFB on the north, west, and south sides, 

and Kelly AFB borders it on the east. The western portion of Lackland AFB was the Medina Base, 

which is now the Lackland Training Annex. The Medina Base consisted of four main areas: the 

200 Area (general shops and stores), 300 Area (operations and storage), 400 Area (Plants 1 and 2, 

main production operations), and 500 Area (igloos and storage facilities). Two additional areas were 

the Burning Ground and the Railhead (Figure A-2) (Lamb and Halliburton 1995).

Figure A-1. San Antonio, Texas, area showing location of Lackland Training Annex (previously called 

Medina Base; Rand McNally 2005).
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Figure A-2. Medina Base (Lamb and Halliburton 1995).

There were seven main types of structures at the Medina Base, including A Structures, C Structure, 

Base Spares Warehouse, assembly/maintenance buildings, S Structure, storage igloos, and the 

plants for modification disassembly (Lamb and Halliburton 1995). The site also included low-level 
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radioactive waste (LLRW) disposal areas and emergency underground storage tanks (USTs; also 

underground holding tanks). Each of these structures is described in the following paragraphs.

A Structures included Buildings 301, 402, 403, 404, 552, 556, 562, 571, and 585 in the 300, 400, and 

500 Areas. A Structures were used to store nuclear capsules for weapon systems (Lamb and 

Halliburton 1995). The buildings, although massive concrete structures, had only four small storage 

rooms, each approximately 10 ft wide, 13 ft deep, and 9 ft high. Each room had a capacity for 

approximately 30 nuclear capsules that were stored in criticality-safe bird cage containers 

(Figure 2-5). Each room had a bank vault type door equipped with dual combination locks. The 10-ftthick walls and massive berms around the rooms were designed to protect the nuclear capsules from 

external attacks, rather than as containment of possible accidental detonations in the buildings. 

Maintenance activities always took place in the C Structure, never in the vault where the capsules 

were stored. Therefore, no nuclear material was ever exposed in an A Structure and there was little 

or no potential for a release of radioactive material with these buildings. Activities in the A Structures 

ended in 1960 (Lamb and Halliburton 1995).

Building 307, a C Structure, was used as a nuclear materials inspection laboratory and maintenance 

building for the nuclear weapons at Medina Base. The C Structure provided bench space to perform 

required maintenance operations, storage space for neutron calibration and assay sources, and 

support facilities that included a change room and storage areas. Nuclear capsules destined for 

maintenance were transported in their bird cages to the C Structure; when maintenance was 

completed, the capsules were placed back in their bird cages, sealed, and returned to one of the A 

Structure buildings (Lamb and Halliburton 1995).

Workrooms in the C Structure were constructed with floor drains that were connected to an 

emergency UST in the building. If there had been an accident, the UST would have collected the 

decontamination wash water and any released plutonium. No accidental releases of plutonium are 

known to have occurred at Medina Base during 1955 through 1966 (Lamb and Halliburton 1995).

The C Structure had an extensive ventilation system that prevented the release of uranium oxides to 

the atmosphere. Based on review of environmental reports, there are no indications that spills or 

releases of radioactive material occurred in the C Structure during its operational lifetime (Lamb and 

Halliburton 1995).

The Base Spares Warehouse was used to store spare weapon components for maintenance 

purposes (Lamb and Halliburton 1995).

The Assembly/Maintenance Buildings were also called Plants 1 and 2; each plant consisted of two 

buildings used for maintaining nonnuclear components of weapons at Medina. The buildings 

contained several bays, and activities included inspection, testing, and assembly of nonnuclear 

mechanical and electrical systems. The buildings featured heavy blast doors and earthworks that 

would have deflected the effects of an accidental explosion upward. The design is typical for facilities 

in which large amounts of high explosive (HE) are handled (Lamb and Halliburton 1995).

An S, or Surveillance, Structure (Building 444) was used for inspections and testing of weapons in the 

stockpile. The S Structure separated quality assurance activities from the routine maintenance and 

assembly functions at Plants 1 and 2. Building 444 contained electrical and mechanical bays and a 

calibration room, but did not have a floor drain connected to a UST. The building was modified in 

1959 for the modification and disassembly mission managed by MHSMC (Lamb and 

Halliburton 1995).
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One hundred igloos were constructed in the 500 Area for the storage of weapon components, 

assembled weapons, and weapon casings. All nuclear materials in the igloos were sealed in the 

weapons. No maintenance activities took place in the igloos and, therefore, there was little or no 

potential for a release of radioactive or hazardous materials (Lamb and Halliburton 1995).

In 1959, three gravel gertie cells were built for modifying and disassembling weapons. HE shells were 

removed from nuclear assemblies in these structures. Several tons of gravel were above the ceiling 

of each structure for containment of fissile material in the event of an accidental detonation of the HE

system. The gravel gerties were used between 1959 and 1965 (Lamb and Halliburton 1995).

Three sites at Medina (RW-15, RW-17, and RW-19) were designed for the collection of dry and liquid 

LLRW. RW-15 was a landfill for the disposal of LLRW, and might have received classified limited-life 

components disposed of during weapons modification and disassembly operations between 1959 and 

1965. The LLRW was excavated in 1965 and transferred in container express (CONEX) containers to 

the Pantex Plant. The RW-15 site was cleared by the AEC as decontaminated when the site was 

closed in 1965 (Lamb and Halliburton 1995). Dry LLRW from operations in the C Structure was 

packed in cardboard boxes and disposed of in the RW-17 site. RW-17 was an unlined pit that was 

fenced and considered a classified waste landfill. RW-19 was a small gravel leaching area behind 

Building 444. The site reportedly received intermittent LLRW wastewater discharges from 

Building 444. Gravel and soil from the area were excavated in 1965 and transferred in CONEX 

containers to the Pantex Plant (Lamb and Halliburton 1995).

Three emergency USTs were designated RW-16, RW-18, and RW-20. The USTs were intended for 

the collection of liquid LLRW in the event of an accidental release; however, no evidence has been 

found that any of the USTs were ever used (Lamb and Halliburton 1995). RW-16 and RW-18 are 

1,000-gal steel tanks; RW-20 is a 5,000-gal steel tank.

A.2.2 Operational History as a Weapons Storage Area, 1954 to 1960

The early nuclear weapons used Po-Be initiators to generate neutrons during the explosion sequence. 

Because 210Po has a half-life of only 138 days, the initiators had to be replaced periodically. 

According to former SNL personnel (ORAUT 2006e), these devices were maintained following precise 

quality control methods that required maintenance personnel to:

1. Release pressure from the bird cage container through a filter and check the filter for alpha 

activity. If no activity was found, remove the capsule from the container using a handling tool.

2. Place the capsule on a table top with an alpha probe at one end. (The table was covered with 

a large piece of butcher paper to contain any spalling of uranium oxides.)

3. Place a plexiglass glovebox over the capsule.

4. Disassemble the capsule parts and check the integrity of the coatings.

5. Remove the glovebox.

6. Remove uranium oxide deposits from the threads using a small cloth or paper swipe and 

trichloroethylene. Wipe the threads with ethyl alcohol to dry the components.
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7. Use acetone to remove previous markings made with blue machinist’s dye and make new 

markings. (Later components had serial numbers etched on their surfaces.)

8. Check the activity of the fissile material using beta and gamma radiation measurements.

9. Assay the nuclear material by accurately weighing it and perform subcritical multiplication 

measurements using external neutron sources.

10. Replace the Po-Be initiators. (These were later replaced with nonradioactive initiators.)

11. Reassemble the capsule.

12. Place the capsule and a sack of desiccant in the bird cage container.

13. Screw on the bird cage container top. Repressurize and wire seal the bird cage container 

(positive pressure was maintained to ensure dryness and keep O-rings in place) (Lamb and 

Halliburton 1995). [Later designs used a vacuum rather than overpressure (ORAUT 2006f).]

Contaminants from the maintenance process were the chemicals mentioned above and uranium

oxides. Polonium-210 waste was not generated (Lamb and Halliburton 1995). Used (decayed) 

initiators were sent to Los Alamos National Laboratory for storage, regeneration, or disposal. The 

spalled uranium oxides, swipes contaminated with solvents, lead-wire seals, and gloves were 

wrapped in butcher paper and placed in 18- by 18- by 24-in. cardboard boxes for disposal in the dry 

LLRW disposal area (currently designated RW-17) (Lamb and Halliburton 1995).

A source safe (a cylindrical apparatus below the floor surface with a polyethylene neutron absorber at 

the top) was in a corner of the laboratory room in the C Structure. Below the neutron absorber, the 

source safe had a tray for storing check sources for verifying the activity of the fissile material in the 

weapons (Lamb and Halliburton 1995).

Between 1954 and 1957, the Po-Be initiators and plated pits in the in-flight-insertable design were 

phased out and replaced with sealed pits and a newer type of sealed neutron generator that did not 

require routine replacement (Lamb and Halliburton 1995; Mitchell 2003). Therefore, while some SNL 

workers handled Po-Be initiators and plated pits before 1957, no MHSMC workers were exposed to 

the initiators or plated pits. After 1957, maintenance activities were reduced to annual disassembly of 

capsules to determine their condition and to verify the integrity of the fissile materials. Maintenance of 

the newer capsules generated the same types of waste, but in smaller quantities because of the less 

frequent maintenance schedule. By 1960, nuclear capsules had been phased out of the stockpile and 

maintenance activities no longer involved exposed nuclear material (Lamb and Halliburton 1995).

A.2.3 Operation as a Modification and Disassembly Center

Between 1959 and 1966, the mission of MHSMC workers was to perform stockpile surveillance, 

modifications, retrofits, and weapon retirements (Carr ca. 1992). Typical modifications involved 

disassembly and reassembly with some modified components and replacement of tritium reservoirs. 

Weapon retirements involved complete disassembly and return of nuclear components to other DOE 

sites. Some damaged weapons were returned to Medina during these years. Their ultimate 

disposition has not been determined, but they were no longer at Medina after shutdown. During this 

period, the MHSMC workers at Medina were exposed to the same types of radiation and levels of 
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contamination as Pantex workers because their work activities were nearly identical (except there 

were no hydroshot operations at Medina) (Mitchell 2003).

A.3 OCCUPATIONAL MEDICAL DOSE

Similar to the Clarksville Modification Center, the Pantex Plant has the X-ray histories of Medina 

workers during the MHSMC years. Only written histories, not film, are available. Because essentially 

the same work was done by the same contractor, it is assumed that the X-ray guidance for Clarksville 

Modification Center should be applied to Medina workers for the MHSMC years, 1958 to 1966. There 

is evidence in the claims files that MHSMC gave some pre-employment X-rays to Medina workers in 

October 1958 (see Section 3.0). However, several of the X-ray records in the claim files for workers 

at Medina suggest that the X-rays may have been performed at the Minter X-ray Clinic. If the dose 

reconstructor is certain that the X-rays were performed off the site at a non-covered facility, then the 

dose from the X-rays cannot be included in dose reconstruction per ORAUT-OTIB-0079.

A.4 ENVIRONMENTAL DOSE

A.4.1 Routine Doses

Insufficient information has been obtained about Medina Base to develop site-specific considerations 

for environmental releases. The only environmental doses to be assigned for the Pantex Plant are 

from radon and a large accidental release of tritium. Similarly, environmental doses at Clarksville 

Modification Center resulted from a tritium accident modeled after the Pantex accident and from direct 

radiation from use of radiography sources. Throughputs, in terms of number of disassemblies, for 

instance, of the four assembly and disassembly sites (Pantex, Iowa Army Ammunition Plant, 

Clarksville, and Medina) are classified, so comparison of effluents by relationships to throughput is not 

permissible in an unclassified document. Medina had three gravel gerties in comparison with one at 

Clarksville.

The average tritium release from the Pantex Plant from 1981 through 1988, when a large number of 

disassemblies was performed, was 70,000 μCi/yr. Assuming that Medina Base operations were 

similar to those of the Clarksville Modification Center and Pantex, the annual doses from tritium 

intakes are also less than 0.001 rem. Therefore, the annual dose to any organ from tritium intakes at 

the Medina Base are less than 0.001 rem and can be ignored.

There is no reason not to believe that Medina Base had the same radiography sources as Clarksville 

Modification Center. Dose reconstructors should assign Medina workers the same 4-mrem external 

dose from radiography as for Clarksville workers (Section 4.0 and Table 4-1.). The 4-mrem annual 

dose is applied as a lognormal distribution with a GSD of 2.0 with a photon energy range of 100% 

30 to 250 keV.

A.4.2 November 13, 1963, Explosion

A.4.2.1 Background

On November 13, 1963, an explosion involving 50,500 kg (123,000 lb) of chemical HE components of 

nuclear weapons occurred at the Medina site. Workers were placing subassemblies from dismantled 

atomic bombs into storage Igloo 572. The subassemblies, which were being stored for further 

processing and disposal, contained chemical HE, natural uranium, and DU. They were handled by a 
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three-man crew – two forklift operators who moved them from a straddle carrier into the igloo and one 

man on the carrier.

Most of the load was in the igloo when, at about 10:24 a.m., the explosive in one of the 

subassemblies ignited. Seeing the flash, the drivers sprinted for cover, alerting the workers outside. 

For about 45 seconds the explosive burned, then it detonated with a force of more than 60 tons of 

trinitrotoluene (TNT). The first explosion set off other subassemblies in the igloo and those still on the 

carrier. The igloo disappeared in a cloud of smoke and dust, leaving a crater some 20 ft deep. A 

large cloud of dust was seen near the ground moving downwind of the event.

In the 45 seconds between ignition and detonation, the three workers got away. Their injuries were 

minor. Adjacent igloos were not disturbed. The only known radioactive material involved was a 

mixture of DU and natural uranium. Fissile materials (enriched uranium or plutonium) were not 

involved in the accident.

A.4.2.2 Direct Radiation

Assuming an infinite plane source and the distribution of natural uranium (which has a higher 

compounded dose rate than DU) in equilibrium with its short-lived progeny, external doses can be 

calculated. Dose rates can be calculated for each organ using organ-specific, dose rate conversion 

factors such as those in FGR 12 (Eckerman and Ryman 1993) or the CD supporting FGR 13 

(Eckerman et al. 1999).

Using the factors from FGR 13 CD (Eckerman et al. 1999), the rate of effective dose per μCi/m2 would 

be:

(A-1)

( ) ( )

( ) ( )

( ) ( )

238 234 234m 6 2

235 231 6 2

231 6 2

U Th Pa 0 489 49 5 876 12 600 10 rem/yr per μCi/m

 U Th 0 0225 16 4

 

00 1 720 10 rem/yr pe

 

r μCi/m

 Th 0 489 68 4 10 rem/yr per μCi/m

00 52

.. ,

. ,,

. .

.

−

−

−

+ + = ++ ×

+ + = ×

=

+

+= ×

2

 rem/yr

= 25 mrem/yr per μCi/m for full-time occupancy

However, this value is somewhat misleading because FGR 13 (Eckerman et al. 1999) factors include 

a tissue-weighting factor for skin dose. Using FGR 13 factors but omitting the contribution from the 

weighted skin dose, the gamma dose rate, which more closely approximates the average organ dose, 

is:

(A-2)

( ) ( )

( ) ( )

( ) ( )

238 234 234m 6 2

235 231 6 2

231 6 2

U Th Pa 0 489 40 7 856 1 600 10 rem/yr per μCi/m

 U Th 0 0225 16 40

 

0 1820 10 rem/yr per μCi/m

 Th 0 489 57 8 10 rem/yr per μCi/m

0 0017

.. ,

. ,,

.

.

.

−

−

−

++ = ×

+

+ +

+

=

= +×

+= ×

2

 rem/yr

= 1 7 mrem/yr per . μCi/m for full-time occupancy

For an occupational exposure of 2,000 hr/yr, this would be 0.39 mrem/yr per μCi/m2

. The highest 

onsite location, 60 μCi/m2

, might have resulted in 23 mrem/yr. For regularly occupied areas 
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downwind, a value of one-tenth of that, or 2.3 mrem/yr, would be appropriate. Most of the site is 

upwind of the footprint left by the plume, so the external dose from uranium in the soil would be 

negligible. However, at present there is no way to discriminate between workers in offices upwind 

versus downwind of the plume footprint. Therefore, dose reconstructors should apply a 2.3-mrem/yr 

external dose from photons with energy from 30 to 250 keV.

A.5 INTERNAL DOSE

NIOSH has concluded that is not possible to reconstruct internal doses completely during the 

operational period of the Medina Modification Center. Therefore, in the absence of monitoring data 

for an individual claim, no occupational internal doses should be assigned. For claims in which 

individual internal monitoring data are available, the internal dose should be reconstructed based on 

interpretation of the monitoring data using existing NIOSH dose reconstruction processes and 

procedures.

A.6 EXTERNAL DOSIMETRY

The MHSMC dosimetry records for Medina began on April 27, 1959, and extended through 

January 24, 1966 (Pantex Plant 1959–1966). It is possible that some earlier dosimetry records exist 

for SNL personnel, but none have been found to date. Exposures to the few (less than 10) SNL 

personnel between 1955 and 1959 did not involve exchange of Po-Be initiators, and a former 

employee estimated maximum exposures at 100 mrem/yr (ORAUT 2006e). However, the approved 

EEOICPA dates for this site are 1958 through 1966 only. MHSMC used weekly dosimetry services 

from Tracerlab from April 1959 until July 1964 (Tracerlab 1965) and from Nuclear Service 

Laboratories of Knoxville, Tennessee, from July 1964 until January 1966 (Pantex 1959–1966). Work 

at Medina was completed in January 1966, and dosimetry services were terminated on January 24, 

1966. Most of the MHSMC workers left the site in January and February 1966. Many of the workers 

transferred to the Pantex Plant in Amarillo, Texas.

The clerical maintenance of the dosimetry records was not rigorous. For example, individual names 

were consistently assigned to only 11 film badge numbers, and some numbers were reused when an 

individual left the program. More than 100 other film badges were assigned to different people each 

week and the individual names, for nonzero results only, were recorded on the film badge dose report 

after it was received. In some weeks, the task of recording names associated with nonzero dose 

results was not completed, so it is impossible to reconstruct who received nonzero doses. Because 

more than one individual was assigned to a given film badge number, the quarterly and annual totals 

maintained by the film badge processor were not useful.

Therefore, the dose records from Pantex were carefully examined, corrected, and summarized in a 

letter to the Project file, “Medina Dose Records, 1959–1966” (ORAUT 2006g). Dose reconstructors 

should disregard any incomplete dose records provided with the claims and use ORAUT (2006g).

Because the doses received by Medina and Clarksville workers appear similar in magnitude within the 

uncertainties in how annual doses were calculated, the recommendations for Medina are the same as 

those for Clarksville. However, the exception is that the exchange frequency at Medina was weekly 

for all years of operation (Pantex Plant 1959–1966). Because the work at Medina was similar to that 

at Clarksville, it is reasonable to apply the same dose assignment recommendations as for Clarksville.
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Radiation Incident at Medina on September 7, 1959

On September 7, 1959, there was a radiation exposure incident at Medina that involved a radiography 

source (Pantex Plant 1959–1966). The details were provided in claimant interviews. A vendor came 

to the site to demonstrate a new type of portable radiography source with shield that was air operated 

(apparently referred to as a “Puff” camera). The device could pneumatically transfer a source from 

the safe shielded position, through a 30-ft tube, to a radiography exposure location. The end of the 

tube was located such that it could take an X-ray of an electronic part. The vendor representative first 

performed the transfer of the capsule out to the end of the tube and back into the lead shield using a 

dummy (nonradioactive) capsule. The transfer was successfully demonstrated several times and the 

Medina radiography staff successfully used the equipment with the dummy capsule in a training 

exercise. While the vendor representative was leaving the site, he realized he did not have the 

dummy capsule with him and there could be a problem. An investigation revealed that the dummy 

capsule was still in the lead shield and when the air flow was reversed, the 30-Ci 192Ir source could not 

enter the shield because the dummy capsule was in it. When the air flow stopped, the 192Ir source fell 

back down the tube to an area where personnel were present. As a result of this incident, three 

individuals received unusually high radiation exposures, as follows: Individual A – 6,600 mrem 

gamma, Individual B – 3,000 mrem gamma, and Individual C – 2,370 mrem gamma. These 

exposures are included in the summarized records (ORAUT 2006g).
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ATTACHMENT B 

ASSIGNMENT OF UNMONITORED EXTERNAL DOSE FOR CLARKSVILLE AND MEDINA

The following table was adapted from Tables A-1 through A-3 of ORAUT-TKBS-0013-6, Pantex Plant 

– Occupational External Dose (ORAUT 2016a).

Table B-1. Unmonitored external doses by year (rem), Clarksville and Medina

Modification Centers.

Year

Photon

50th%

Photon

95th%

Neutron

50th%

Neutron

95th%

Electron

50th%

Electron

95th%

1946 - 1963 0.010 0.302 0.007 0.482 0.012 0.112

1964 0.101 1.007 0.043 0.645 0.056 0.148

1965 0.029 0.440 0.015 0.168 0.036 0.180

1966 a 0.042 0.442 0.022 1.147 0.051 0.160

a. All nuclear materials were removed for the Clarksville site in 1965. Therefore, unmonitored 

external doses should not be applied for 1966 at the Clarksville Modification Center.