ORAU TEAM

Dose Reconstruction

Project for NIOSH

Oak Ridge Associated Universities I Dade Moeller I MJW Technical Services

Page 1 of 11

DOE Review Release 02/10/2012

Document Title:

External Exposure to Technetium-99 at the 

Gaseous Diffusion Plants

Document Number: ORAUT-RPRT-0059

Revision: 00

Effective Date: 02/07/2012

Type of Document: Report

Supersedes: None

Subject Expert(s): Matthew H. Smith

Approval: Signature on File Approval Date: 02/02/2012

Matthew H. Smith, Document Owner

Concurrence: Signature on File Concurrence Date: 02/02/2012

John M. Byrne, Objective 1 Manager

Concurrence: Signature on File Concurrence Date: 02/02/2012

Edward F. Maher, Objective 3 Manager

Concurrence: Vickie S. Short Signature on File for Concurrence Date: 02/02/2012

Kate Kimpan, Project Director

Approval: Signature on File Approval Date: 02/07/2012

James W. Neton, Associate Director for Science

New Total Rewrite Revision Page Change

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

REVISION AND DISCARD / DESTROY ALL COPIES OF THE PRIOR REVISION.
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 2 of 11

PUBLICATION RECORD

EFFECTIVE 

DATE

REVISION 

NUMBER DESCRIPTION

02/07/2012 00 New document initiated for evaluation of external dose from 99Tc at 

the Oak Ridge Gaseous Diffusion Plant (K-25), Paducah Gaseous 

Diffusion Plant, and Portsmouth Gaseous Diffusion Plant. 

Incorporates formal internal formal review comments. There were no 

comments as a result of formal NIOSH review. Training required: As 

determined by the Objective Manager. Initiated by Matthew H.

Smith.
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 3 of 11

TABLE OF CONTENTS

SECTION TITLE PAGE

Acronyms and Abbreviations ............................................................................................................... 4

1.0 Introduction .............................................................................................................................. 5

2.0 Background.............................................................................................................................. 5

2.1 Potential for Exposure .................................................................................................. 5

2.2 Magnitude of Exposure................................................................................................. 7

3.0 Proposed Approach for Dose Assignment................................................................................ 8

3.1 Assignment of External Dose........................................................................................ 8

3.2 Assignment of Skin Contamination Dose Due to Radiological Contamination 

Incident......................................................................................................................... 9

4.0 Summary and Conclusions ...................................................................................................... 9

References ........................................................................................................................................ 10

LIST OF TABLES

TABLE TITLE PAGE

2-1 Portsmouth GDP facilities with 99Tc exposure potential............................................................ 6

2-2 Paducah GDP facilities with 99Tc exposure potential................................................................ 6

2-3 K-25 GDP facilities with 99Tc exposure potential ...................................................................... 6

2-4 Job titles for GDP workers with 99Tc exposure potential ........................................................... 7
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 4 of 11

ACRONYMS AND ABBREVIATIONS

cm centimeter

cpm counts per minute

DOE U.S. Department of Energy

dpm disintegrations per minute

g gram

GDP gaseous diffusion plant

hr hour

in. inch

keV kiloelectron-volt, 1,000 electron-volts

mg milligram

mm millimeter

mrem millirem

ORAU Oak Ridge Associated Universities

PPE personal protective equipment

SRDB Ref ID Site Research Database reference identification (number)

TBD technical basis document

yr year
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 5 of 11

1.0 INTRODUCTION

External exposure to 99Tc at the Paducah, Portsmouth, and Oak Ridge (K-25) gaseous diffusion 

plants (GDPs) has been discussed in varying detail in the external dose technical basis documents

(TBDs) for those sites. The information for 99Tc in those TBDs has been inconsistent, and the 

conclusions have been inadequate for the purpose of dose assignment. 

This report provides guidance for the assignment of 99Tc external dose to energy employees at the 

Paducah, Portsmouth, and K-25 GDPs. Due to its nonpenetrating characteristics – and the routine 

use of effective personal protective equipment (PPE) – the dose from 99Tc is low. The assignment of 

99Tc dose in this report is based on information about work location, job title, and shallow dose data 

that can be used by dose reconstructors to identify energy employees that could have had exposure 

to 99Tc. 

2.0 BACKGROUND

Technetium-99 has been present at all three GDPs as a contaminant from the introduction of recycled 

uranium into the cascades. It is a long-lived fission product with a half-life of 213,000 years. It is a 

pure low-energy electron emitter with a maximum energy emission of 293.6 keV and an average 

energy of 84.6 keV (Shleien, Slaback, and Birky 1998). Although difficult to detect due to its lowenergy electron emission, this same characteristic results in minimal external dose potential. Site 

exposure evaluation data indicate that the maximum range of 99Tc electrons in air is approximately 24 

in. At electron energies this low, even the effective depth of the dead layer of the skin (5 to 10 

mg/cm2

) is a significant shield for the germinal layers of the skin. In addition, PPE such as coveralls 

and gloves afforded attenuation factors of 95% and 98%, respectively (Jenkins, Mitchell, and Baker

1961). These observations are corroborated by other studies that show the fraction of 99Tc dose 

transmitted through two pairs of coveralls to be approximately 0.7% (Martz, Rich, and Johnson 1986). 

Further, an analysis of attenuation using the computer program VARSKIN 3 showed a transmission 

factor of less than 1% for a standard outer glove, which has a thickness of 0.45 mm and a density of

1.1 g/cm3 as recommended in NUREG/CR-6918 (Durham 2006).

2.1 POTENTIAL FOR EXPOSURE

It is apparent from operational documents that the potential for dose from 99Tc was known and 

addressed (Saraceno 1981):

However, when cascade equipment containing significantly high amounts of 

technetium is removed for replacement or maintenance, special precautions must be 

taken to protect workers from exposure to technetium as is the case for any toxic 

material.

and

For most of the cascade, the same safety precautions implemented to avoid 

contamination of personnel by uranium are adequate to prevent the technetium 

exposure. In the upper cascade, where technetium tends to accumulate, more 

stringent measures are taken.

In summary, the control measures in place to prevent contamination due to uranium and its progeny 

provided an even greater protection factor for 99Tc exposure. Routine control measures included 

gloves and coveralls (Baker et al. 1978). 
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 6 of 11

The work activities that could have resulted in 99Tc contamination included:

• Technetium recovery operations,

• Removal of equipment from the cascade for routine maintenance, and

• Removal and replacement of cascade equipment during the Cascade Improvement Program 

and Cascade Upgrade Program.

Tables 2-1 to 2-3 list the facilities with 99Tc exposure potential.

Table 2-1. Portsmouth GDP facilities with 99Tc

exposure potential (ORAUT 2006).

Building Facility

X-326 Gaseous Diffusion Process Building

X-330 Gaseous Diffusion Process Building

X-333 Gaseous Diffusion Process Building

X-344 UF6 Feed Manufacturing Plant

X-345 Special Nuclear Materials Storage

X-700 Maintenance Building

X-701B Holding Pond

X-705 Decontamination and Cleaning Building

X-705E Oxide Conversion Plant

X-720 Compressor Shop

X-744G Smelter and Aluminum Recovery

Table 2-2. Paducah GDP facilities with 99Tc

exposure potential (ORAUT 2007a).

Building Facility

C-409 Stabilization Building

C-410 Feed Plant

C-420 Oxide Conversion Plant

C-331 Gaseous Diffusion Process Building

C-333 Gaseous Diffusion Process Building

C-335 Gaseous Diffusion Process Building

C-337 Gaseous Diffusion Process Building

C-310 Purge and Product Withdrawal Building

C-710 Analytical Lab

C-400 Decontamination and Cleaning Building

C-720 Maintenance Building

Table 2-3. K-25 GDP facilities with 99Tc exposure potential (BJC and 

Haselwood Enterprises 2000, DOE 2000).

Building Facility

K-25 (K-310-3a and K-311-1)a Gaseous Diffusion Process Building

K-27 (K-402-8a and K-402-9)a Gaseous Diffusion Process Building

K-29 Gaseous Diffusion Process Building

K-31 Gaseous Diffusion Process Building

K-33 Gaseous Diffusion Process Building

K-631 Gaseous Diffusion Process Building

K-131 Feed Facility and Decontamination and Recovery

K-413 Product Withdrawal Facility

K-770 Scrap Metal Yard

K-1004-A, -B, -C, -E Analytical Laboratory Facilities

K-1031 Power and Utilities Storage Facility

K-1131 Feed Manufacturing Plant

K-1231 Ash Pulverization and Uranium Recovery Facility
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 7 of 11

Building Facility

K-1401 Maintenance Facility

K-1410 Decontamination and Plating Facility

K-1420 Decontamination Facility

K-1421 Incinerator Building

a. These were purge cascade units with high concentrations of Tc-99.

Energy employees with the job titles in Table 2-4 could have had exposure to 99Tc while performing 

the above-listed activities while in facilities in Tables 2-1, 2-2, or 2-3. The highest exposure potential 

would have been to maintenance workers on the top purge cells or doing change outs of trapping 

media near the top purge cells.

Table 2-4. Job titles for GDP workers with 99Tc 

exposure potential.

Cascade operators/workers

Feed plant operators

Maintenance mechanics

Chemical operators

Radiological workers

Construction trade workers

Decontamination and decommissioning workers

2.2 MAGNITUDE OF EXPOSURE

Site evaluations at Paducah assessed the potential for an external 99Tc exposure problem from 99Tc

recovery operations and found that the likelihood of high exposure was low due to the following 

reasons (Baker et al. 1978):

• Gloves were worn routinely for all operations involving the handling of containers.

• All material was transferred remotely from point to point with one exception. When moved 

from one container to another, the transfer was done by pumping – the container was never 

dumped by hand.

• The solutions were dilute. 

• Less than 20% of employee work time was spent at jobs with the potential to generate 99Tc

contamination.

Information about the magnitude of 99Tc exposure is available in Tc-99 Contamination (Swinth 2004). 

A range of measured contamination exposure levels at Paducah (from 10,000 to 335,849 

cpm/100 cm2

) were considered, which resulted in average dose rates to the skin (using VARSKIN to 

calculate dose rates) that ranged from 0.212 mrem/hr (on contact) to 0.013 mrem/hr (10 cm of 

distance in air. These rates include the use of coveralls with a density thickness of 28 mg/cm2

). To 

estimate the skin dose from a contamination event, a contamination level of 25,000 dpm/100 cm2 was

assumed (based on the action limit for 99Tc contamination on work surface and hand tools) (PORTS 

1963). The dose would be given by (Swinth 2004):

250 dpm/cm2 × 0.081 mrem per dpm/cm2 = 20 mrem (2-1)

Note that the assumed contamination value is greater than the average contamination level 

(13,540 cpm/100 cm2

) identified by Swinth (2004). The value of 0.081 mrem per dpm/cm2 derives 

from data in Swinth (2004), namely 1.6 × 10-3 mrem per dpm/cm2 multiplied by a residence half-time 
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 8 of 11

of 1.5 days. A residence half-time of 1.5 days is assumed because 99Tc can be difficult to remove 

from the skin (Swinth 2004).

Because the low-energy 99Tc electrons would not have been detected by dosimetry, the potential 

unmeasured external electron dose can be estimated by assuming an ambient dose rate level of 

0.2 mrem/hr, a technetium-to-uranium progeny ratio of 0.4, and a 2,000-hour work year (Bassett 

1986):

0.2 mrem/hr (maximum ambient level) × 0.4 (Tc:U progeny ratio) × 2000 hr/yr = 160 mrem/yr (2-2)

Since the facilities, processes, and contaminants were similar at all three GDP sites, the magnitude of 

exposure discussed here is likely valid for each site.

3.0 PROPOSED APPROACH FOR DOSE ASSIGNMENT

The three GDP external dose technical basis documents (TBDs) are not specific about how to assign 

dose due to 99Tc exposure. 

It is clear from review of the properties of 99Tc and the site evaluations of control practices (which 

included the routine use of PPE as discussed in Sections 2.1 and 2.2), that automatic assignment of 

99Tc dose due to skin contamination is not warranted. Guidance for assignment of 99Tc skin 

contamination dose on a case-by-case basis is given below. It is apparent, however, that external 

exposure to 99Tc was unlikely to be measured by dosimetry due to its low-energy electron 

characteristics. In certain cases – as described below – an annual assignment of 99Tc external dose 

should be included in the dose estimate under the Energy Employees Occupational Illness 

Compensation Program Act of 2000.

3.1 ASSIGNMENT OF EXTERNAL DOSE

External dose due to the presence of 99Tc should be applied under certain circumstances for cancer 

sites involving the extremities (hands). Dose assignment is limited to the hands because the 99Tc

dose rate at distances beyond 30 cm is less than 0.08 mrem/hr and drops off rapidly at greater 

distances (ORAUT 2007b). The following conditions determine if a dose should be assigned:

1. Claimant has skin cancer on the hand(s); and

2. Claimant worked in a facility where 99Tc was present (Tables 2-1 to 2-3); and

3. Claimant performed a job function that could have involved 99Tc exposure (Table 2-4); and

4. Claimant dosimetry indicates a relatively high ratio (more than 2) of shallow to deep dose 

(NIOSH 2007).

If and only if all four of the above conditions are met, then the dose reconstructor should:

• Assign an external electron dose of 8 mrem/yr.

This value derives from an annual external dose of 160 mrem reduced by a protection factor of 95% 

to account for PPE.
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 9 of 11

3.2 ASSIGNMENT OF SKIN CONTAMINATION DOSE DUE TO RADIOLOGICAL 

CONTAMINATION INCIDENT

Skin contamination dose due to 99Tc should be applied under certain circumstances for cancer sites 

where a documented skin contamination event occurred. The following conditions determine if a dose 

should be assigned:

1. Claimant has skin cancer on a potentially uncovered area of the skin; and

2. Claimant worked in a facility where 99Tc was present (Tables 2-1 to 2-3); and

3. Claimant performed a job function that could have involved 99Tc exposure (Table 2-4); and

4. Claimant records indicate a contamination incident involving the area of the skin cancer site.

If and only if all four of the above conditions are met, then the dose reconstructor should:

• Assign a skin dose of 20 mrem per documented incident. 

4.0 SUMMARY AND CONCLUSIONS

The presence of 99Tc as a contaminant at the GDPs was known to health physics personnel, and the 

protection measures in place to protect workers from exposure to uranium progeny also protected 

against 99Tc exposure. Due to its low-energy electron characteristics, the potential for 99Tc dose was 

very low, especially considering the high (95% or greater) attenuation factor afforded by the routine 

use of PPE such as coveralls and gloves.

Only the existing external technical basis document (TBD) for Portsmouth contains well-referenced 

dose calculations for skin contamination and external exposure scenarios for 99Tc. However, it does 

not provide specific guidance about the assignment of dose values. This document provides 

guidance for the assignment of 99Tc dose based on information about work location, job title, shallow 

dose data, and cancer type and location. The three GDP external TBDs should be revised to include 

the dose calculation information from this report. In addition, the methods for assignment of 99Tc dose 

in Section 3.0 should also be included in each GDP external TBD document.
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 10 of 11

REFERENCES

Baker, R. C., C. R. Conner, K. A. Davis, and B. E. McDougal, 1978, PDGP Technetium-99, Section V,

Health Protection, Paducah Gaseous Diffusion Plant, Paducah, Kentucky, June 6. [SRDB Ref 

ID: 36544]

Bassett, A. C., 1986, Thermoluminescent Dosimeter Response and Calibration, GAT-S-56, Goodyear 

Atomic Corporation, Piketon, Ohio, April 20. [SRDB Ref ID: 8136]

BJC (Bechtel Jacobs Company) and Haselwood Enterprises, 2000, Recycled Uranium Mass Balance 

Project, Oak Ridge Gaseous Diffusion Plant (Currently Known as East Tennessee Technology 

Park) Site Report, BJC/OR-584, East Tennessee Technology Park, Oak Ridge, Tennessee, 

June. [SRDB Ref ID: 16497]

DOE (U.S. Department of Energy), 2000, Independent Investigation of the East Tennessee 

Technology Park, Office of Oversight, Washington, D.C., October. [SRDB Ref ID: 13787]

Durham, J. S., 2006, VARSKIN 3: A Computer Code for Assessing Skin Dose from Skin 

Contamination, NUREG/CR-6918, U.S. Nuclear Regulatory Commission, Office of Nuclear 

Regulatory Research, Washington, D.C., October. [SRDB Ref ID: 42490]

Jenkins, G. R. Jr., K. K. Mitchell, and R. C. Baker, 1961, Radiation Hazard Evaluation of Technetium99 at the Paducah Plant, Paducah Gaseous Diffusion Plant, Paducah, Kentucky. [SRDB Ref 

ID: 30621]

Martz, O. E., B. L. Rich, and L. O. Johnson, 1986, “Measuring the Skin Dose Protection Afforded by 

Protective Apparel with a Beta Spectrometer,” Radiation Protection Management, volume 3, 

number 5, pp. 61–70, October.

NIOSH (National Institute for Occupational Safety and Health, 2007, Neutron Exposures at the 

Savannah River Site, OCAS-TIB-007, Rev. 1, Office of Compensation Analysis and Support, 

Cincinnati, Ohio, October 15.

ORAUT (Oak Ridge Associated Universities Team), 2006, Portsmouth Gaseous Diffusion Plant – Site 

Description, ORAUT-TBKS-0015-2, Rev. 01, Oak Ridge, Tennessee, October 4.

ORAUT (Oak Ridge Associated Universities Team), 2007a, Paducah Gaseous Diffusion Plant – Site 

Description, ORAUT-TBKS-0019-2, Rev. 02, Oak Ridge, Tennessee, May 8.

ORAUT (Oak Ridge Associated Universities Team), 2007b, Portsmouth Gaseous Diffusion Plant –

Occupational External Dose, ORAUT-TKBS-0015-6, Rev. 01 PC-1, Oak Ridge, Tennessee, 

August 20.

PORTS (Portsmouth Gaseous Diffusion Plant), 1963, Acceptable Plant Limits for Radiation and 

Radioactive Contamination, Piketon, Ohio, April 1. [SRDB Ref ID: 14575, p. 100]

Saraceno, A. J., 1981, The Control of Technetium at the Portsmouth Gaseous Diffusion Plant, 

Goodyear Atomic Corporation, GAT-2010, Goodyear Atomic Corporation, Portsmouth 

Gaseous Diffusion Plant, Piketon, Ohio, November 13. [SRDB Ref ID: 62115]

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. [SRDB 

Ref ID: 22737]
Document No. ORAUT-RPRT-0059 Revision No. 00 Effective Date: 02/07/2012 Page 11 of 11

Swinth, K. L., 2004, Tc-99 Contamination, March 5. [SRDB Ref ID: 13683, p. 3]