ORAU TEAM

Dose Reconstruction

Project for NIOSH

Oak Ridge Associated Universities I Dade Moeller & Associates I MJW Corporation

Page 1 of 35

Document Title:

Y-12 National Security Complex – Site Description

Document Number: ORAUT-TKBS-0014-2

Revision: 02

Effective Date: 11/08/2007

Type of Document: TBD

Supersedes: Revision 01 

Subject Expert(s): William E. Murray

Site Expert(s): Karin Jessen

Approval: Signature on File Approval Date: 11/06/2007

William E. Murray, Document Owner

Concurrence: Signature on File Concurrence Date: 11/06/2007

John M. Byrne, Task 3 Manager

Concurrence: Signature on File Concurrence Date: 11/05/2007

Edward F. Maher, Task 5 Manager

Concurrence: Signature on File Concurrence Date: 11/07/2007

Kate Kimpan, Project Director

Approval: Brant A. Ulsh Signature on File for Approval Date: 11/08/2007

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-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 2 of 35

PUBLICATION RECORD

EFFECTIVE 

DATE

REVISION 

NUMBER DESCRIPTION

11/19/2003 00 Technical Basis Document for the Y-12 National Security Complex –

Site Description. First approved issue. Initiated by William E. Murray.

09/09/2004 00 PC-1 Deletes unused reference on page 22. First approved page change 

revision. Initiated by William E. Murray.

01/19/2005 01 Revises document to incorporate changes from NIOSH Office of 

General Counsel (OGC), to include a glossary and additional acronyms, 

to delete two unused references and add one new reference, to update 

the contents, and to make editorial changes. Approved issue of 

Revision 01. Initiated by William E. Murray.

10/11/2005 01 PC-1 Page change initiated to incorporate the definition of U.S.C. on page 5 

and details for the definition of a DOE facility on pages 6 and 7. No 

sections were deleted. First approved page change revision of Revision 

01. Retraining is not required. Initiated by William E. Murray. Approval:

William E. Murray, Document Owner

Signature on File 10/06/2005

Judson L. Kenoyer, Task 3 Manager

Signature on File 10/04/2005

Richard E. Toohey, Project Director

Signature on File 10/04/2005

James W. Neton, Associate Director for Science

Signature on File 10/11/2005

10/25/2006 01 PC-2 Approved page change revision initiated to add Purpose and Scope 

Sections on page 8; text and tables were modified to clarify the use of 

the term recycled uranium and when it was present on the site; and text 

was added or modified on pages 7 and 8 in Section 2.1. Section 2.4.4 

was incorporated into Section 2.4.3. Changes occurred on pages 11-19 

and 32-34. This revision results in no change to the assigned dose and 

no PER is required. Initiated by William E. Murray. The document was 

revised in response to comments from NIOSH during formal review. 

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

William E. Murray. Approval:

William E. Murray, Document Owner

Signature on File 10/12/2006

John M. Byrne, Task 3 Manager

Signature on File 10/18/2006

Edward F. Maher, Task 5 Manager

Signature on File 10/12/2006

Kate Kimpan, Project Director

Signature on File 10/23/2006

James W. Neton, Associate Director for Science

Brant A. Ulsh Signature on File for 10/25/2006
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 3 of 35

11/08/2007 02 Approved revision initiated to add Attributions and Annotations section 

and additional references in response to review. The previous Section 

A-3, Y-12 Facilities, was eliminated. No further changes occurred as a 

result of formal internal review. Incorporates formal NIOSH review 

comments. Constitutes a total rewrite of the document. Training 

required: As determined by the Task Manager. Initiated by William E. 

Murray.
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 4 of 35

TABLE OF CONTENTS

SECTION TITLE

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

PAGE

6

2.1 Introduction ..............................................................................................................................8

2.1.1 Purpose........................................................................................................................9

2.1.2 Scope...........................................................................................................................9

2.1.3 The Missions of the Y-12 Plant.....................................................................................9

2.2 Operating Contractors............................................................................................................ 10

2.3 Site Activities..........................................................................................................................10

2.4 Site Processes .......................................................................................................................12

2.4.1 Electromagnetic Enrichment, 1943 to 1947 ................................................................12

2.4.2 Feed Preparation for Enrichment, 1943 to 1947 .........................................................12

2.4.3 Uranium Reclamation and Salvage, 1944 to 1951......................................................12

2.4.4 Uranium Preparation and Recycling for Weapons Components, 

1949 to 1995 ..............................................................................................................15

2.4.5 Uranium Forming and Machining for Weapons Components, 

1949 to 1995 ..............................................................................................................15

2.4.6 Weapons Components Assembly, 1952 to 1995 ........................................................16

2.4.7 Stockpile Stewardship and Management, 1996 to 2007 ............................................. 16

2.5 Facilities.................................................................................................................................16

2.6 Waste Treatment and Disposal Operations............................................................................ 18

2.7 Criticality Accident..................................................................................................................19

2.8 Radionuclides and Radiation Sources.................................................................................... 19

2.8.1 Uranium......................................................................................................................20

2.8.2 Recycled Uranium ......................................................................................................20

2.8.3 X-Ray and Electron-Generating Equipment................................................................20

2.8.4 Radionuclide and Neutron Sources ............................................................................20

2.8.5 Special Nuclear Material.............................................................................................21

2.8.6 Transuranic Elements.................................................................................................21

2.8.7 Thorium ......................................................................................................................21

2.8.8 Lithium........................................................................................................................22

2.9 Solubility and Insolubility ........................................................................................................ 22

2.10 Attributions and Annotations .................................................................................................. 25

References ........................................................................................................................................26

Glossary ............................................................................................................................................28
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 5 of 35

ATTACHMENT A, SITE DESCRIPTION............................................................................................30

A.1 Sources of Exposure..............................................................................................................31

A.2 Chronology of Uranium Operations ........................................................................................ 32

A.3 Solubility of Radionuclides ..................................................................................................... 34

LIST OF TABLES

TABLE TITLE

2-1 Radionuclides of concern.......................................................................................................

PAGE

11

2-2 Chronology by building of operations ..................................................................................... 13

2-3 Key uranium operations ......................................................................................................... 14

2-4 Known sealed radiation sources............................................................................................. 21

2-5 RWP bioassay indicators for routine uranium handling jobs ................................................... 23

2-6 Solubility of material for various buildings and work areas as calculated by DOSE 66 

program .................................................................................................................................24

A-1 Radionuclides of concern....................................................................................................... 31

A-2 Known sealed radiation sources............................................................................................. 31

A-3 Primary uranium operations ................................................................................................... 32

A-4 Process chronology by building of operations ........................................................................ 32

A-5 Radionuclides and solubility types.......................................................................................... 34

A-6 Radioelements and default solubility types............................................................................. 34

A-7 RWP bioassay indicators for routine uranium handling jobs ................................................... 35

A-8 Solubility of material for various buildings and work areas as calculated by DOSE 66 

program .................................................................................................................................35
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 6 of 35

ACRONYMS AND ABBREVIATIONS

ACE U.S. Army Corps of Engineers

AEC U.S. Atomic Energy Commission

CEDE committed effective dose equivalent

Ci curie

COLEX column exchange

D&D decontamination and decommissioning

DOE U.S. Department of Energy

DU depleted uranium

EEOICPA Energy Employees Occupational Illness Compensation Program Act of 2000

ELEX electrical exchange

EU enriched uranium

ft foot or feet

gal gallon

HEU highly enriched uranium

ICRP International Commission on Radiological Protection

in inch

keV kiloelectronvolt, 1 keV = 1,000 electronvolts

kg kilogram

LEU low enriched uranium

LLW low-level waste

mCi millicurie

MED Manhattan Engineer District

MeV megaelectronvolt, 1 MeV = 1 million electronvolts

mg milligram

mi mile

mrem millirem

NIOSH National Institute for Occupational Safety and Health

NU natural or normal uranium

ORGDP Oak Ridge Gaseous Diffusion Plant

ORNL Oak Ridge National Laboratory

ORR Oak Ridge Reservation

POC probability of causation

RCRA Resource Conservation and Recovery Act

RU recycled uranium

RWP radiological work permit
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 7 of 35

SNM special nuclear material

SRDB Ref ID Site Research Database Reference Identification (number)

SRS Savannah River Site

TBD Technical Basis Document

TEC Tennessee Eastman Corporation

TRU transuranic

UNH uranyl nitrate hexahydrate

U.S.C. United States Code

WETF West End Treatment Facility

wt % weight percent

y year

§ section or sections
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 8 of 35

2.1 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 historic background information and guidance to assist in the preparation of 

dose reconstructions for particular sites or categories of sites. They will be revised in the event 

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

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

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

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

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

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

EEOICPA defines a DOE facility 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 Department of Energy (except for buildings, structures, premises, 

grounds, or operations ... pertaining to the Naval Nuclear Propulsion Program)” [42 U.S.C. 

§ 7384l(12)]. Accordingly, except for the exclusion for the Naval Nuclear Propulsion Program noted 

above, any facility that performs or performed DOE operations of any nature whatsoever is a DOE 

facility encompassed by EEOICPA.

For employees of DOE or its contractors with cancer, the DOE facility definition only determines 

eligibility for a dose reconstruction, which is a prerequisite to a compensation decision (except for 

members of the Special Exposure Cohort). The compensation decision for cancer claimants is based 

on a section of the statute entitled “Exposure in the Performance of Duty.” That provision [42 U.S.C. 

§ 7384n(b)] says that an individual with cancer “shall be determined to have sustained that cancer in 

the performance of duty for purposes of the compensation program if, and only if, the cancer ... was 

at least as likely as not related to employment at the facility [where the employee worked], as 

determined in accordance with the POC [probability of causation1

As noted above, the statute includes a definition of a DOE facility that excludes “buildings, structures, 

premises, grounds, or operations covered by Executive Order No. 12344, dated February 1, 1982 

(42 U.S.C. 7158 note), pertaining to the Naval Nuclear Propulsion Program” [42 U.S.C. § 7384l(12)]. 

While this definition contains an exclusion with respect to the Naval Nuclear Propulsion Program, the 

section of EEOICPA that deals with the compensation decision for covered employees with cancer 

[i.e., 42 U.S.C. § 7384n(b), entitled “Exposure in the Performance of Duty”] does not contain such an 

exclusion. Therefore, the statute requires NIOSH to include all occupationally derived radiation 

exposures at covered facilities in its dose reconstructions for employees at DOE facilities, including 

radiation exposures related to the Naval Nuclear Propulsion Program. As a result, all internal and 

external dosimetry monitoring results are considered valid for use in dose reconstruction. No efforts 

are made to determine the eligibility of any fraction of total measured exposure for inclusion in dose 

reconstruction. NIOSH, however, does not consider the following exposures to be occupationally 

derived:

] guidelines established under 

subsection (c) ...” [42 U.S.C. § 7384n(b)]. Neither the statute nor the probability of causation 

guidelines (nor the dose reconstruction regulation) define “performance of duty” for DOE employees 

with a covered cancer or restrict the “duty” to nuclear weapons work.

• Radiation from naturally occurring radon present in conventional structures

• Radiation from diagnostic X-rays received in the treatment of work-related injuries

 1 The U.S. Department of Labor is ultimately responsible under the EEOICPA for determining the POC.
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 9 of 35

2.1.1

The purpose of this Technical Basis Document (TBD) is to describe the activities, facilities, and 

radiation sources at the Y-12 National Security Complex (formerly the Y-12 Plant) over its operating 

history. The TBD provides the historical technical information on plant operations and facilities that is 

needed to reconstruct doses for both monitored and unmonitored workers. Y-12 was a code name for 

the plant during the Manhattan Project and has been in use since that time. This TBD is part of the 

overall Y-12 Site Profile, which describes Complex facilities and processes, historical information, and 

environmental data in relation to dose reconstruction for Y-12 workers. It contains technical 

information to assist in the reconstruction radiation doses from these activities for both monitored and 

unmonitored workers.

Purpose

2.1.2

This document provides an historical overview of the activities and processes that have occurred in 

the buildings and facilities on the Y-12 site, the treatment and storage of radioactive wastes, the 

onsite radionuclides and their solubility and radiation sources, and the accidents that have affected 

large groups of workers or large areas of the site.

Scope

Y-12 is in the eastern section of the Oak Ridge Reservation (ORR) near Oak Ridge, Tennessee. The 

Complex occupies approximately 811 acres (0.67 mi wide and 3.2 mi long) and consists of 

approximately 531 buildings that cover more than 7.5 million ft2

. Construction of Y-12 as part of the 

Manhattan Project began in late 1942 and was completed in 1943. 

The information in this TBD is based on reports and other sources of information that are not 

classified. In some cases, classified documents have been redacted to allow their release and use as 

unclassified information. We are fully aware that more information is available that may be of use in 

reconstructing worker doses. Due to classification restrictions, such information can not be included 

in this document. Even though the classified information is not included in the TBD, it will be taken 

into account by the dose reconstructor in estimating dose incurred at the facility.

2.1.3

Y-12 has played an important role in the development of the U.S. nuclear weapons program. The first 

mission of Y-12 was to separate the fissionable isotope of uranium, 235U, for use in nuclear weapons. 

The second was manufacturing of nuclear weapons parts during the Cold War, and today the mission 

focuses on support of U.S. nuclear defense policies. At its peak, Y-12 employed approximately 

22,000 workers. 

The Missions of the Y-12 Plant

First Era, Uranium Isotope Separation, 1942 to 1947

The Y-12 Plant, which was conceived in 1942 by the Manhattan Engineer District (MED) of the U.S. 

Army Corps of Engineers (ACE), was constructed by Stone and Webster Construction Company at a 

cost of about $427 million. Before completion, the operating contractor, the Tennessee Eastman 

Company (TEC) of Kingsport, Tennessee, moved its people in to start operations. The Calutron Pilot 

Plant and training facility (Building 9731) was the first building to begin operations, in the fall of 1943. 

(calutron is from California University Cyclotron

Despite technical problems, this first-of-a-kind electromagnetic isotope separation (calutron) plant

succeeded in its mission. In a little over 2 years, the uranium fuel was separated for the Hiroshima 

nuclear weapon. The gaseous diffusion process at the Oak Ridge Gaseous Diffusion Plant (ORGDP) 

).
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 10 of 35

was the MED’s backup for enriching uranium. Because this process was workable and much less 

costly, Y-12 was shutdown in December 1946 and employment was cut drastically.

Second Era, Cold War Nuclear Weapons Components Manufacturing, 1947 to 1992

Y-12 eventually became one of twelve production facilities with a unique role. Its new mission was to

produce the key components of nuclear weapons and test the devices necessary for expansion of the 

nuclear weapons stockpile, and for the safekeeping of the nation’s highly enriched uranium (HEU) 

stockpile. Many support tasks were given to Y-12, notably the production of the enriched lithium that 

was urgently needed for the thermonuclear program in the 1950s and 1960s. Y-12 succeeded in 

carrying out these challenging missions to develop state-of-the-art technologies necessary to new 

weapons designs over a period of almost 50 years.

Third Era, Multiple New Missions, 1992 to present

The nation’s stockpile of nuclear weapons was reduced by 90% during this time. The number of 

operational buildings was reduced, and Y-12 manufacturing technology was transferred to industry, 

where that was allowed. Ongoing missions include: 

• Storing HEU for DOE 

• Disassembling weapons or components to study aging and other effects

• Producing a small number of nuclear weapons parts and assemblies

• Decontamination and decommissioning (D&D) of unused buildings

• Conducting major efforts in environmental and waste management 

By the end of 1992, 50 research and development agreements were negotiated between Y-12 and 

governmental and commercial entities. Informally termed “Work for Others,” challenging problems 

were successfully solved for other Federal agencies. 

2.2 OPERATING CONTRACTORS

The TEC was the original Y-12 contractor under agreement with the U.S. ACE. On January 1, 1947, 

in accordance with the Atomic Energy Act of 1946, all activities were turned over to the U.S. Atomic 

Energy Commission (AEC). During the same year, the MED was disbanded and TEC was replaced 

by Carbide and Carbon Chemicals Corporation as the Y-12 site contractor. The following is a list of 

the site’s prime contractors throughout Y-12 history.

Operating Contractora Perioda

Tennessee Eastman Corporation 1943 to 1947

Carbide and Carbon Chemicals Corporation 1947 to 1950

Carbide and Carbon Chemicals, Division of 

Union Carbide and Carbon Corporation

1951 to 1956

Union Carbide Nuclear Company, Division of 

Union Carbide and Chemicals Corporation

1957 to 1963

Union Carbide Corporation, Nuclear Division 1963 to 1984

Martin Marietta Energy Systems, Incorporated 1984 to 1994

Lockheed Martin Energy Systems 1994 to 1998

BWXT Y-12 1998 to present

a. ChemRisk 1993, p. 174.

2.3 SITE ACTIVITIES

From inception, Y-12 was specifically designed to enrich uranium via an electromagnetic separation 

process. The actual device used for enrichment, the calutron, used a massive magnetic field to 
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 11 of 35

separate isotopes of uranium based on slight differences in mass. Two stages of separation and 

enrichment were required. The first and larger stage, designated alpha, produced slightly enriched 

feed material for the second stage, known as the beta stage. The alpha and beta chemical operations 

were required to produce feed material for the calutrons, to recover valuable waste and byproducts, 

and to produce the final material for use in a nuclear weapon.

Early operations at Y-12 were narrowly focused. The primary hazards at the facility were uraniumbearing chemicals including, but not limited to the following: (ChemRisk 1993, p. 222; ChemRisk 

1999, pp. 172-185; BWXT 2003a, p.11): 

• Uranium dioxide (UO2),

• Uranium trioxide (UO3),

• Uranium tetroxide (UO4), 

• Triuranium octoxide [also uranium oxide] (U3O8)

• Uranium tetrafluoride (UF4) 

• Uranium hexafluoride (UF6),

• Uranium tetrachloride (UCl4),

• Ammonium diuranate [(NH4)2U2O7],

• Uranyl nitrate [UO2(NO3)2], 

• Uranyl nitrate hexahydrate (UNH) [UO2(NO3)2 × 6H2O], 

• Uranyl fluoride [UO2F2],

• Uranium metal

• Uranium aluminum (U-Al)

In addition, bulk quantities of industrial chemicals [e.g., carbon tetrachloride (CCl4), hydrogen peroxide 

(H2O2), dibutyl carbitol (C12H26O3), nitric acid (HNO3), and hydrochloric acid (HCl)] were used or 

produced at the plant. Because Y-12 was basically a heavy industry site, many other common 

industrial materials such as asbestos, solvents, acids, alkalis, and oils were used and available for 

potential worker exposure. 

Electromagnetic operations at Y-12 continued for a number of years after 1947. However, these 

activities were chiefly directed toward research on new radionuclides for medical or other uses.

Over the following years, Y-12 became a highly sophisticated nuclear weapons component 

manufacturing facility and development engineering organization. The Complex receives, stores, and 

protects uranium and lithium materials and parts; dismantles nuclear weapons components; and 

serves as a government repository for enriched uranium (EU). In addition, Y-12 has many treatment, 

storage, and disposal facilities for hazardous and radioactive materials. Table 2-1 (BWXT 2003a, pp. 

30-31) shows the radionuclides of concern at Y-12. Some building numbers and their corresponding 

radionuclides are not available at this time.

 Table 2-1. Radionuclides of concern.

a

Radionuclide Type of emission Radioactive 

half life (y) Radionuclide Type of emission Radioactive half life (y)

99Tc Beta 2.13 × 105 236U Alpha 2.34 × 107

228Th Alpha 1.91 × 100 238U Alpha 4.47 × 109

230Th Alpha 7.54 × 104 237Np Alpha 2.14 × 106

232Th Alpha 1.45 × 1010 238Pu Alpha 8.64 × 101

234U Alpha 2.47 × 105 239Pu Alpha 2.4 × 104

235U Alpha, some gamma 7.4 × 108 241Am Alpha 4.32 × 102

a. Adapted from BWXT 2003b, pp. 30–31.
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 12 of 35

2.4 SITE PROCESSES 

Over the years, the mission of Y-12 has evolved from separating uranium isotopes to encompass a 

multitude of new missions. Manufacturers conduct their own research using unique machinery 

available at Y-12 as well as expertise throughout the ORR. In addition, Y-12 provides landlord 

services for DOE as well as other types of management, such as the Transportation and Safeguards 

Division and the Oak Ridge National Laboratory (ORNL). Other responsibilities include environmental 

restoration and waste management; putting facilities into a safe, legally compliant condition for 

shutdown; and providing protection of government property. Tables 2-2 and 2-3 provide a chronology 

by building of Y-12 operations and key uranium operations, respectively, from the beginning to the 

present.

2.4.1

Uranium was enriched for use in atomic weapons by processing large amounts of UCl4 in calutrons 

(ChemRisk 1999, p. 172). These operations were housed in the alpha buildings (Buildings 9201-1, 

9201-2, 9201-3, 9201-4, and 9201-5) and beta buildings (Buildings 9204-1, 9204-2, 9204-3, and 

9204-4) that contained the first and second stages, respectively, of the enrichment processes. 

Electromagnetic Enrichment, 1943 to 1947 

2.4.2

Feed preparation involved conversion of large quantities of uranium oxides (including UO2, UO3, and 

U3O8) into UCl4 – the feed material for the calutrons (ChemRisk 1999, p. 174). Most operations 

occurred in Buildings 9202, 9203, 9206, and 9212.

Feed Preparation for Enrichment, 1943 to 1947 

2.4.3

An elaborate system of mechanical and chemical processes was used to recover and reclaim residual 

uranium feed and product material found on equipment and scrap material associated with the 

calutron operations or on material shipped from the AEC’s Weldon Spring (Missouri) Plant that had 

235U content worth recovering. (It is important to point out that, in many early reports, this is referred 

to as recycling uranium and the product is referred to as recycled uranium (RU). The uranium 

reclaimed in these operations contains only the original feed material introduced into the calutrons 

and does not contain the added radioactive contaminants associated with the RU from reactor 

plutonium production targets and fuel elements.) These operations included mechanical scraping and 

brushing, nitric acid washing, and distillation and reclamation of solid uranium compounds adhering to 

surfaces. Uranium-contaminated materials included condensates, scrubber solutions, raffinates, 

destructive distillates, oils, and miscellaneous residues. These facilities handled mostly natural 

uranium (NU) and depleted uranium (DU). These operations occurred primarily in Buildings 9202, 

9203, and 9206.

Uranium Reclamation and Salvage, 1944 to 1951 

Salvage operations involved EU recovery from all non-product components or byproducts of the 

operations. Uranium was reclaimed from materials that are not considered to be production 

equipment, such as liquid and solid waste materials from maintenance and cleanup activities (e.g., 

mop water, laundry washes, and floor drain residues). Other salvage operations included mechanical 

scraping and brushing, nitric acid washing, and distillations and reclamation of solid uranium 

compounds. Some uranium was recovered for future use, while that in wash fluids was discharged to 

East Fork Poplar Creek (ChemRisk 1999, p. 178). Combustible materials such as wood, rags, 

sponges, filter paper, and carbon solids were burned in muffle furnaces and incinerators to recover 

the uranium. Scraps and materials that could not be decontaminated were buried within the ORR 
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/0

8/2007 Page 13 of 35

Table 2-2. Chronology by building of operations (ChemRisk 1999, p. 171; Oliver 2003, 2007). Building 1943–1948 1949–1951 1952–1963 1964–1995 1996–2007

9201-1 Tracks 1 and 2, α – I calutrons 

(uranium enrichment).

Uranium enrichment 

operations.

Uranium reclamation and 

salvage operations.

Fusion energy research 

operations.

General manufacturing for tooling, 

including work for others. Almost all 

clean work.

9201-2 Tracks 3 and 4, α - I calutrons 

(uranium enrichment).

Uranium enrichment 

operations.

COLEX lithium/ mercury 

enrichment.

Research and development 

operations.

ORNL facility.

9201-3 Track 5, α - I calutrons (uranium 

enrichment).

Uranium enrichment 

operations.

Uranium reclamation and 

salvage.

Fusion energy research 

operations.

Currently used for office space.

9201-4 Tracks 6 and 7, α - II calutrons 

(uranium enrichment).

Uranium enrichment 

operations.

COLEX lithium/ mercury 

enrichment.

Engineering and administrative 

facilities.

Awaiting D&D.

9201-5 Tracks 8 and 9, α - II calutrons 

(uranium enrichment).

Uranium enrichment 

operations.

COLEX lithium/ mercury 

enrichment.

NU/DU press, rolling, and 

machining operations.

NU/DU press, rolling, and machining 

operations; building evacuated 

(2007); surveillances occur; storage; 

awaiting D&D.

9202 α and chemical preparation and 

reclamation operations.

Uranium product 

reclamation operations.

Uranium process 

development and 

improvement.

Uranium process development 

and improvement operations.

Technology development.

9203 235U analysis and initial uranium 

product processing

Uranium product 

reclamation operations.

Reclamation and salvage 

operations.

Y-12 production development and 

research operations.

Technology development.

9204-1 Tracks 1 and 2, ß calutrons 

(uranium enrichment).

Uranium enrichment 

operations.

Stable isotope separation 

operations.

Fusion energy research 

operations.

ORNL facility; however, BWXT Y-12 

occupies office space.

9204-2 Tracks 3 and 4, ß calutrons 

(uranium enrichment).

Uranium enrichment 

operations.

Special material operations. Special material operations. Special material operations.

9204-2E -- -- -- Uranium assembly operations. Uranium assembly operations.

9204-3 Tracks 5 and 6, ß calutrons 

(uranium enrichment).

Uranium enrichment 

operations.

Stable isotope (e.g., copper) 

separation.

Stable isotope (e.g., copper) 

separation.

ORNL facility.

9204-4 Tracks 7 and 8, ß calutrons 

(uranium enrichment).

Uranium enrichment 

operations.

ELEX lithium/mercury pilotscale.NU/DU press and rolling. Material storage operations.

9206 ß chemical reclamation and 

product processing.

Uranium product 

reclamation and 

salvage operations.

Uranium chemical 

processing and metal 

production.

Uranium chemical processing and 

metal production.

No longer a Material Access Area. 

Currently undergoing deactivation. 

D&D initiated.

9207 Uranium reclamation and salvage. Uranium reclamation, 

salvage operations.

Maintenance and 

reclamation and salvage.

ORNL biological research. ORNL facility (vacated in 2005); 

awaiting D&D.

9211 Uranium reclamation and salvage. Uranium salvage and 

product reclamation 

operations.

Uranium salvage and 

product reclamation.

ORNL biological research. ORNL biological research 

operations; (vacated in 2005); 

awaiting D&D.

9212 ß product processing. Uranium conversion 

and reclamation 

operations.

UF6 conversion, chemical 

and weapons production 

operations.

Chemical and weapons 

production.

Chemical operations and weapons 

production.

9215 -- -- EU machining and metal 

finishing operations.

EU machining and metal finishing 

operations.

EU machining, metal finishing; DU 

H-1 foundry.

9998 -- NU H-1 foundry. DU H-1 foundry. DU H-1 foundry. DU processing operations.
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/0

8/2007 Page 14 of 35

Table 2-3. Key uranium operations (ChemRisk 1999, pp. 172-185).

Key uranium operations Buildings involved

Dates of 

operation

Electromagnetic Enrichment: Y-12 processed about 50,000 kg of UCl4 in calutrons in both 

alpha and beta enrichment buildings. To obtain a desired enrichment, UCl4 was processed 

through many calutrons and reclaimed and reprocessed frequently. Alpha operations enriched 

from 10 to 20% 235U. Beta operations further enriched partially-enriched, reclaimed alpha material 

up to 98% 235U. EU compounds were recovered and converted to uranium oxide for shipment or 

reclaimed for further alpha or beta enrichment. DU was removed from process equipment and 

disposed of through building vents and storm sewer drains.

Alpha Buildings 9201-1,2,3,4,5 

Beta Buildings 9204-1,2,3,4

1943–1947

Feed Preparation and Product Processing: Volatile UCl4 was the chemical form of uranium fed 

into the alpha and beta calutrons. UCl4 was produced using two chemical conversions involving 

UO3 and CCl4. The first method was liquid phase chlorination in which uranium and CCl4 were 

heated under pressure and formed UCl4 crystals. The second method was vapor phase 

chlorination in which CCl4 was gradually added to UO3 and heated inside a chemical reactor bowl 

for about eight hours and then purged with nitrogen to exhaust phosgene vapors from the system. 

From both methods, UCl4 crystals were collected and placed in charge bottles which were loaded 

into calutrons for enrichment. 

9202, 9203, 9206, 9212

9202 and 9203 housed alpha uranium feed preparations and 

product recovery operations. They also handled EU, DU, and 

NU.

9206 was used to recover beta product with higher enrichment 

levels (>50%). Highly enriched material was converted to UCl4

for further enrichment.

9212 received ~ 4,700 kg of UF6 with an average 235U content 

of 30% between 1945 and 1947.

1943–1947

Uranium Recovery and Reclamation: Y-12 stopped enriching uranium after WWII. Operations 

now centered on reclaiming residual uranium found on equipment and scrap material. These 

operations included mechanical scraping and brushing, nitric acid washing, and distillation and 

reclamation of solid uranium compounds adhering to surfaces. Uranium-contaminated materials 

included condensates, scrubber solutions, raffinates, destructive distillates, oils, and 

miscellaneous residues. These facilities handled mostly NU and DU.

9202, 9203, 9206, 9212

9202, 9203 received DU, slightly EU, and NU.

9206 was the main uranium reclamation facility and housed 

sanding, grinding, chemistry, and incinerator operations.

1944–1951

1950s–1990s

Uranium Salvage: Salvage operations reclaimed uranium from materials that are not considered 

to be production equipment, such as liquid and solid waste materials from maintenance/ cleanup 

activities such as mop water, laundry washes, and floor drain residues. Combustible materials 

such as wood, rags, sponges, filter paper, and carbon solids were burned in muffle furnaces and 

incinerators to recover uranium. Other salvage operations included mechanical scraping and 

brushing, nitric acid washing, and distillations and reclamation of solid uranium compounds.

9206, 9207, 9211

9206 housed salvage operations and process operations were 

similar to 9207 and 9211.

9207 and 9211 processed incinerated solid waste and 

reclaimed NU and slightly EU.

1947–1951

Uranium Preparation and Reclamation: Y-12 began a continuous growth of uranium weapons 

component manufacturing operations handling a variety of uranium compounds and enrichment. 

EU prepared for reduction to metal involved conversion of UF6 to UF4 purification of uranyl nitrate 

solutions, precipitation for uranium reclamation, and then reduction to uranium metal.

9202, 9206, 9211, 9212

9212 housed the largest chemical operations for EU 

purification, reclamation and chemical conversion, as well as 

NU and DU machining operations.

1952–1995

Uranium Forming/Machining: Y-12 had operations capable of casting, rolling, and machining 

uranium metal. These operations handled EU, DU, and NU. Uranium was pressed, rolled, 

shaped, and machined into finished weapons components.

9201-5, 9204-4, 9215, 9998

9201-5, 9204-4 housed DU.

9215 housed EU.

9998 contained H-1 foundry operations that included DU 

reclamation and parts manufacturing.

1952–1995

Uranium Component Assembly: Machined components were sent through finishing operations 

that included drilling, welding, brazing, polishing and final specification checks. Bldg. 9202 was 

primarily used for early pilot scale operations that involved design and implementation of 

fabrications and assembly processes and final inspection procedures. Assembly operations 

generally were not associated with significant releases of uranium compounds. Any measurable 

amounts of uranium were recovered and reclaimed and were reintroduced into the production 

stream. Uranium was routinely recovered and reclaimed from articles such as rags, paper towels, 

oils and liquid waste products. Process exhaust stacks were equipped with HEPA filtrations and 

periodically inspected for buildup of uranium.

9202, 9204-2, 9204-2E

9204-2, 9204-2E housed uranium assembly operations.

1952–1995
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(ChemRisk 1993, p. 243-245). These operations occurred primarily in Buildings 9206, 9207, and 

9211.

In these operations, no radioactive contaminants were added that were different from the original 

uranium feed materials.

2.4.4

Uranium for weapons production was first processed in recovery, purification, and conversion 

operations. From about 1949 to 1964, Y-12 received cylinders of highly-enriched (93.5%) UF6 as feed 

material for nuclear weapons parts manufacturing. Once purified and converted to metallic form, the 

uranium was transferred to processing operations for forming and shaping the metal into weapons 

part configurations. After 1964, the majority of EU processed at Y-12 was reclaimed from nuclear 

weapons stockpiles (Owings 1995, pp. 22-23). 

Uranium Preparation and Recycling for Weapons Components, 1949 to 1995 

Uranium recycle and purification processes began in 1953 and continue through today. These 

operations occurred primarily in Buildings 9202, 9206, and 9212. RU contains transuranic (TRU) 

material (e.g. plutonium and neptunium-237), fission products, (e.g. technetium-99), and reactorgenerated uranium products (e.g. 236U) (BWXT Y-12 2000, p. 21). Thus, the processing and reenrichment of RU might present an increased potential hazard for occupational and environmental 

exposure that is greater than is normally associated with the processing of unirradiated uranium. The 

RU streams encompassed a variety of material forms including UNH, molten UNH, UO2, UO3, UF4, 

uranium metal, uranium alloys, and a variety of associated wastes (BWXT Y-12 2000, p. 34). Y-12 

was involved with highly-enriched RU processing operations at five different locations. Chemical 

processing of highly enriched RU occurred in the 9212 complex until the early 1970s and later in 

Building 9206 (BWXT Y-12 2000, p. 34). The EU product was stored in Building 9720-5. The S-3 

ponds served as impoundments for process wastewater until the mid-1980s (BWXT Y-12 2000, p. 

36). After the ponds were closed, the RU process wastewater was treated by a variety of methods at 

the West End Treatment Facility (WETF). 

2.4.5

Formed uranium metal parts were machined into finished weapons parts and then transferred to Y-12 

assembly operations. Numerous buildings were needed to support these diverse operations, and the 

buildings were frequently modified to meet changes in production needs. These operations occurred 

primarily in Buildings 9201-5, 9204-4, 9215, and 9998. 

Uranium Forming and Machining for Weapons Components, 1949 to 1995 

DU operations for the production of weapons components have existed at Y-12 since the early 1950s. 

DU is a form of uranium that consists of over 99.28% 238U and less than 0.72% 235U by mass. The DU 

and DU alloy operations typically included melting and casting, forging and rolling into plates, forming 

or extruding into shapes, and final heat treating to obtain the desired properties. The depleted forms 

were then machined into the final design specifications for weapons components. Buildings 9998, 

9215, 9201-5, and 9204-4 housed the majority of the Y-12 DU processing operations. Particle or dust 

collectors, such as cyclones and bag houses, were used in most of the processes to capture the 

larger particles. Airborne losses from the foundry and other operations were relatively large from 

1948 to 1956. When production levels increased, additional filters were installed sometime in 1955. 

Potentially large uranium losses might have occurred in 1954 and July 1956 because a minimal 

amount of dust was collected or filtered in comparison to the amount of uranium collected after the 

new filtering equipment was operating efficiently. The losses during 1956 from stack monitoring were 

estimated to be about 0.1 kg of DU per day. Continuous monitors were installed on the exhaust 

stacks in the mid-1950s (ChemRisk 1993, p.225).
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 16 of 35

2.4.6

Weapons parts were assembled into finished products, inspected and tested against design criteria, 

and then shipped off the site. The majority of these operations were housed in Buildings 9204-2 and 

9204-2E. Table 2-3 shows the key uranium operations over time at Y-12.

Weapons Components Assembly, 1952 to 1995 

2.4.7

DOE is responsible for maintaining the safety and reliability of the nation’s nuclear weapons. Y-12 

supports DOE in that mission by providing resources to address safety, programmatic, and 

operational considerations. This includes maintaining skills and physical assets critical to weapons 

production and technology.

Stockpile Stewardship and Management, 1996 to 2007 

2.5 FACILITIES

Building 9731: The first building to become operational was the Calutron Pilot Plant in Building 9731 

in the fall of 1943. This building, also known as XAX/XBX, contained two each of the alpha and beta 

calutrons. This facility was also used as a training facility. During the first 4 months of operation, only 

4% of the uranium in the source (called charge bottles) actually ended up in the receivers, while the 

remaining 96% either remained in the source, coated the electrodes, missed the receiver slits, or was 

splattered all over the liner. All side streams were collected to recover EU. A major concern was the 

growing amount of uranium of partial enrichment in product streams that needed to be reclaimed, 

purified, and further enriched (Wilcox 2001, p.15).

9212 Complex: The 9212 Complex includes Buildings 9212, 9809, 9812, 9818, 9815, and 9980. 

More than 100 operations or processes have been performed in this Complex. The largest, Building 

9212, originally had four wings, A, B, C, and D, and its primary activity was uranium recovery and 

reclamation. This complex originally recovered and reclaimed HEU from the calutrons (BWXT Y-12 

2000, p. 30). After WW II, Building 9212 was expanded to accommodate the increased production of 

uranium from the ORGDP and to provide the capability to recover and reclaim uranium from waste 

materials. In 1948, new structures were built between the four wings. In 1951, the E Wing was added 

to facilitate the casting and machining of uranium components. The UF6 conversion facility in the D 

Wing was shutdown in 1964, essentially stopping the introduction of new HEU metal in the weapons 

stockpile (BWXT Y-12 2000, p. 30).

The 9212 Complex currently performs four primary functions (BWXT Y-12 2000, p. 31):

• Casting of HEU metal 

• Accountability of HEU from plant activities

• Recovery and reclamation of HEU in a form suitable for storage

• Serving as the U.S. source of all HEU used in test, research, or propulsion reactors and for 

isotope production

The 9212 Complex also supports the International Atomic Energy Agency in sampling surplus EU, 

packaging HEU for offsite shipment, and producing specialized uranium compounds and metal for 

research reactor fuel.
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Building 9202: Building 9202 became operational late in 1943. This is a bulk treatment facility that 

was designed to process UO3 to UO2 to UCl5 to UCl4 – the feed material for the alpha calutron 

sources.

Building 9203: Building 9203 became operational in November 1943. In this building, UCl4 was 

made from UO2 for the alpha calutron feed (charge bottles). Other activities included washing alpha 

collector pockets to reclaim the product, developing two different beta chemical reclamation 

processes (i.e., precipitation and electrochemical processes, later extraction processes), analytical 

chemistry laboratories, and mass spectrometry and fission counting labs to determine enrichment 

levels (assays).

Alpha Buildings and Beta Buildings: Over the course of one (1) year starting in 1943, Y-12 put into 

operation eight of nine electromagnetic enrichment process buildings, including five first-stage 

enrichment operations called alpha buildings (9201-1, 9201-2, 9201-3, 9201-4, 9201-5) and three 

second-stage enrichment operations called beta buildings (9204-1, 9204-2, 9204-3). A fourth beta 

building, 9204-4, was operating by November 1945. As part of the war effort, Y-12 processed roughly 

50,000 kg of UCl4 in the alpha and beta calutron buildings (ChemRisk 1999, p. 172). The calutrons

were arranged in large groups called racetracks, typically with 96 calutrons per alpha track and 36 

calutrons per beta track (1,248 calutrons total). Each building typically housed two tracks. To obtain 

a desired enrichment, UCl4 was processed through many calutrons and reclaimed and reprocessed 

frequently. Alpha operations enriched uranium from 10% to 20% 235U. Beta operations further 

enriched the reclaimed alpha material up to 98% 235U (Owings 1995, p. 18). EU compounds were 

reclaimed and converted to an oxide form for shipment to Los Alamos, or reclaimed for further alpha 

or beta enrichment. The DU was removed from process equipment and disposed of through building 

vents and storm sewer drains (ChemRisk 1999, p. 172).

9206 Complex: Building 9206, centrally located at Y-12, has been used extensively for the chemical 

processing of uranium. Related structures that house supporting or process services and/or 

equipment, are Buildings 9768, 9720-17, 9409-17, 9510-2, and 9767-2 and the east and west tank

farm pits.

Building 9206 has carried out several EU processes and activities (BWXT Y-12 2000, p. 32):

• Chemical reclamation, charge preparation, HEU recovery, and product processing for the 

electromagnetic process (1945 to 1946)

• Recovery of EU from programs at Y-12 and many other sites (1947 to 1994)

• Production of uranium compounds for other sites (1949 to 1972)

• Conversion of UF6 to UF4 to uranium metal for weapons (1954 to 1964)

• Casting and machining of HEU metal for weapons (1955 to 1965)

• Recovery of HEU from the Savannah River Site (SRS) solutions and other scrap for return to 

SRS as uranium metal (1972 to 1989)

• Conversion of excess HEU metal to oxide feed for the Portsmouth Gaseous Diffusion Plant 

(1980 to 1985)

• Storage of in-process materials (1950 to present)
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The following non-EU processes and activities at Building 9206 include (BWXT Y-12 2000, p. 32):

• Reclaiming DU chips (1951 to late 1950s)

• Production of uranium compounds for other sites (1949 to 1972)

• Canning of normal assay uranium slugs for nuclear reactor use (1950 to 1952)

• Storage of in-process materials (1950 to present)

Building 9720-5: Building 9720-5 is used as a warehouse for short- and long-term storage of 

strategic materials. Built in 1944, it has been renovated several times. This building serves as a 

shipping and receiving facility for Special Nuclear Material (SNM) and the primary storage facility for 

interim and prolonged low-maintenance storage of HEU (BWXT Y-12 2000, p. 33).

Building 9215: Building 9215 was used to manufacture parts from DU and EU. The uranium was 

pressed, rolled, shaped, and machined into finished weapons components. 

Building 9995: Building 9995 is used as an analytical laboratory to assay nuclear components. The 

activities allowed Y-12 to move into the forefront of the nuclear weapons complex in the analytical 

chemistry field during the years after 1952. 

2.6 WASTE TREATMENT AND DISPOSAL OPERATIONS

The S-3 Ponds: Between 1951 and 1984, four seepage pits known as the S-3 ponds were used to 

dispose of over 2.7 million gal of a variety of liquid wastes including concentrated acids, caustic 

solutions, mop waters, and byproducts from the uranium recovery processes including uranium and 

other heavy metals. These unlined pits were designed to allow liquid either to evaporate or percolate 

into the ground (BWXT Y-12 2000, p. 110). Various metal impurities and radionuclides that were 

stripped from HEU during the solvent extraction steps in Buildings 9212 and 9206 (approximately 10% 

to 30% of RU, plutonium, neptunium, and technetium) were discharged with the dilute nitric acid and 

other process-derived acid wastewater to the S-3 ponds before the mid-1980s (BWXT Y-12 2000, p. 

33).

The S-3 Ponds served as impoundments for process wastewater until the mid-1980s. The four 

earthen basins had no direct discharge to any local creek or river tributary. After the ponds were 

closed, RU process wastewater was treated by a variety of methods at the WETF, and New Hope 

Pond served as a surface-water impoundment that captured entrained solids from rainwater and 

secondary wastewaters.

Clean-up and closure of the ponds began in 1984. The site has been covered with gravel and clay, 

paved, lined, and it is now a parking lot. Sludge removed from the pond sediments is stored in 

aboveground tanks. The S-3 ponds were finally closed in 1989 in accordance with the Resource 

Conservation and Recovery Act (RCRA). Before capping the ponds, sludge samples were taken from 

each pond to ascertain the airborne (internal) exposure potential for workers who would place the cap 

materials. Based on the first evaluation, no special precautions were needed for this work, other than 

the normal requirements for handling DU. However, the second evaluation included the effects from 

thorium and strontium and concluded the material should be treated as a mixture of 45 wt% 238U. The 

primary reason for the increased exposure potential was the inclusion of 230Th and 228Th. These two 

radionuclides contributed about 90% of the exposure potential (BWXT Y-12 2000, p. 110-111).

WETF, Building 9616-7: Beginning in the mid-1980s, after closure of the S-3 ponds, the WETF was 

constructed to treat mixed low-level waste (LLW) and LLW-contaminated wastewater from Y-12 

production and other ORR processes. Nitrate wastewater that was contaminated with EU was mixed 
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 19 of 35

with much larger quantities of wastewater that was contaminated with DU. The EU component was 

diluted to less than normal assay uranium (BWXT Y-12 2000, pp. 33-34). Wastewaters are 

discharged into East Fork Poplar Creek, under a National Pollutant Discharge Elimination System 

permit. In 1997, sludge from the WETF was analyzed for radionuclides. Elevated levels of 228Th, 

230Th, and 237Np were found (BWXT Y-12 2000, p. 113). Sampling is now conducted on an ongoing 

basis. Both the tanks as well as incoming tankers are sampled periodically. 

New Hope Pond: New Hope Pond was constructed and placed in operation in the 1950s to provide 

a retention basin on East Fork Poplar Creek at the east end of Y-12. The pond facilitated mixing of 

water and offered a sampling point for rainwater runoff, once-through cooling water, steam plant boiler 

blow-down, and secondary production process wastewaters. The pond also functioned to remove any 

suspended contamination from rainwater, miscellaneous releases from various tank farms and 

storage yards, and inadvertent releases from process buildings.

In 1973, New Hope Pond was dredged, and the resultant sludge was transferred to a basin on 

Chestnut Ridge. In 1983, samples were taken to determine if the sediment that had accumulated in 

the pond was hazardous. It was concluded that the data from the leach test showed no hazardous 

material by the RCRA definition (BWXT Y-12 2000, p. 113).

2.7 CRITICALITY ACCIDENT

On June 16, 1958, there was an accidental, prompt–critical neutron chain reaction in a solution 

system at Y-12. The accident occurred in the C-1 Wing of Building 9212, in a 55-gal stainless-steel 

drum. The cause of the accident was a super-critical quantity of highly enriched uranyl nitrate solution 

that accumulated in the drum due to a leaky valve (Wilcox 2001, p. 34).

The accident occurred in a process phase that was a temporary arrangement that used portions of a 

new and an old installation. Both installations were necessary to maintain production during an 

interim phase of remodeling a process. This temporary arrangement split the responsibility for the 

operation among three different supervisors in three separate areas. This contributed to the cause of 

the accident by complicating communications and control. The incident occurred during the draining 

of material, thought to be water, from a safe geometry (5-in. storage pipes) into an unsafe geometrical 

drum. During this incident, approximately 1.0 x 1018 fissions occurred (ORAUT 2006, p. 10).

Eight employees were in the vicinity of the drum. Based on their reported proximity and on the 

activation of the indium foil strip in their badges, these eight employees received the highest radiation 

doses of any who might have been exposed. One of the eight was within 3 to 6 ft of the drum. The 

other seven were from 15 to 50 ft away. Special, post-hoc methods were used to determine the 

neutron and gamma exposures of the involved employees.

As employees left the plant for the day, their badges were collected and taken to the secondary 

control center to obtain activity readings on the indium foil. A list was compiled of the 31 employees 

with potentially significant neutron doses. (The doses received by these employees have been 

calculated for use in dose reconstruction [ORAUT 2006, p. 17]). These employees were routed 

through the medical test routine (UCNC 1958, pp. 10, 44). 

2.8 RADIONUCLIDES AND RADIATION SOURCES

The three main exposure fields at Y-12 are from process and other radioactive materials, radiationgenerating equipment (X-rays and accelerators), and criticality or nuclear accidents. The most 
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 20 of 35

common process materials are EU (235U) and DU (238U). Both radionuclides are primarily alpha 

emitters but 235U does emit 0.185 MeV gamma rays (BWXT Y-12 2001b, p. 11). 

2.8.1

Uranium is a naturally-occurring radioactive element that is used for nuclear reactor fuel and in 

nuclear weapons components. The two principal natural isotopes are 235U (0.72%) and 238U 

(99.28%). NU also includes a trace amount of 234U progeny by mass (0.0055%) (DOE 2000, p. 21). 

Uranium

DU is a by-product of the enrichment process and it is depleted in both the 235U and 234U isotopes. 

Typical DU isotopic abundances are 99.80 % 238U, 0.20% 235U, and 0007% 234U (DOE 2000, p. 21). 

However, DU is commonly referred to as D38 at Y-12. The D38 refers to the nominal assay of the DU 

which was usually 0.0038% 235U (Owings 1995, p. 44).

EU is uranium that has been processed to raise the concentration of 235U above the natural 

abundance of 0.72%. The first known records for EU are from the calutron era when the product had 

been produced by the electromagnetic process at Y-12. NU was enriched in the 235U isotope in a two 

stage process. The alpha calutrons produced EU that contained from 10% to 20% 235U. This material 

was the feed material for the second stage enrichment by the beta calutrons that increased the 235U

isotopic abundance up to 98% of the final product. After 1947, the low enriched (<20% 235U) uranium 

(LEU) was produced by the diffusion plants (Owings 1995, pp. 16, 18).

The degree of internal hazard from uranium exposure depends on its chemical and physical form and 

its enrichment. In past enrichment processes, 234U and 235U could not be separated because of the 

small difference in their mass. Thus, 234U was enriched along with 235U. Because 234U is a small 

fraction of the weight of NU, it contributes as much as one-half of its total radioactivity (ChemRisk 

1999, p. 23). Thus, 234U becomes the major internal radiation source (ORAUT 2005, p. 4). Most of 

the external dose from DU results from 234Th and 234Pa progeny (BWXT 2001b, p. 11).

2.8.2

RU is defined as any uranium that has been irradiated in a reactor. As a result, RU contains TRU 

material, fission products, and reactor-generated uranium products. The primary buildings and 

facilities that handled RU were Buildings 9212 and 9206, the WETF, and the S-3 ponds. In addition, 

RU is stored in Building 9720-5. 

Recycled Uranium

2.8.3

The X-ray and electron-generating equipment that has been used at Y-12 includes linear electron 

beams, electron beam welders, scanning electron microscopes, X-ray photoelectron spectrometers, 

secondary ion mass spectrometers, enclosed beam diffraction equipment, and medical diagnostic 

X-ray equipment. The emitted energy range is from 15 keV to 9 MeV (BWXT Y-12 2001b, p. 11).

X-Ray and Electron-Generating Equipment

2.8.4

The most common radionuclide source facilities are segmented gamma scanners with 169Yb (emits a 

63.1-keV gamma ray), a 60Co well source (1.33- and 1.17-MeV gamma rays) for calibration of 

radiation monitoring equipment, and 252Cf spontaneous fission neutron sources (average neutron 

energy is 2 MeV) for nondestructive testing and material inventories (BWXT Y-12 2001b, p. 11). 

Radionuclide and Neutron Sources
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Three gamma-ray sources, 4.55 mg 226Ra, 23.0 mg 226Ra, and 250 mCi 60Co, are used in the 

calibration of personnel meters and low-range radiation instruments. A 9-Ci 60Co source is used in 

the calibration of high-range survey meters. A large 15-Ci 60Co gamma source is used in the 

Radiographic Laboratory (CCCC 1951, p. 10). The types of sources and locations are in Table 2-4. 

Table 2-4. Known sealed radiation sources.

(CCCC 1951, p. 10)

Sources Buildings

Ra-Be, Po-Be 9203

Ra, Co, Ta, Po-Be 9983

Po-Be, Ra-226 9737, 9201-2, 9204-3

Ra-226 9212

Ra-226, Co 9212

Ra-226 9206,9706-2

2.8.5

There has been a wide variety of SNM, source material, and other nuclear materials at Y-12. The 

various materials include HEU (>20% 235U), LEU (< 20% 235U), DU, NU, thorium, enriched lithium 

(40%, 60%, and 95% 6

Li), 2H, plutonium, and 233U (Owings 1995, p.7).

Special Nuclear Material

Since the weapons material flow was initiated, pure metal has been shipped and received as 100% 

uranium. The SNM metal that was generated in the early days of weapons production at Y-12 was 

not as pure as later products. The primary impurity was carbon.

2.8.6

The primary sources of TRU materials (238, 239, 240Pu and 237Np] were RU from SRS and the Idaho 

Chemical Processing Plant (BWXT Y-12 2000, p. 179). The Rocky Flats Plant returned HEU parts 

that had potential TRU contamination, and special development projects (BWXT Y-12 2000, p. 71-

72). Y-12 proactively evaluated RU receipts from its inception against a specification that would 

maintain uranium as the dominant dose hazard. Dose estimates did not indicate a significant TRU 

problem (BWXT Y-12 2000, p. 147). In comparison to the current regulatory monitoring criteria, it 

would not warrant the initiation of special bioassay sampling beyond that necessary for uranium. 

Recent workplace sampling confirmed that the historical specification ensured that uranium was the 

dominant radiological hazard, even against current regulatory requirements (BWXT Y-12 2000, p. 

147). The exception was waste streams, as evidenced by sludge samples from the WETF. The other 

radionuclides present were 99Tc, 237Np, 238, 239, 240Pu, and 241Am (BWXT Y-12 2000, p. 113).

Transuranic Elements

2.8.7

The first record of thorium at Y-12 is from January 1947 (Owings 1995, p. 63). At that time, the 

inventory was used in research and development studies, primarily by ORNL personnel at Y-12. It 

was not until fiscal year 1952 that thorium activity increased significantly. Shipments and receipts 

were primarily between Y-12 and ORNL (Owings 1995, p. 63). 

Thorium 

Processing of thorium at Y-12 began in the early 1960s (BWXT Y-12 2001a, p. 11). The thorium 

metal in pellet form was pressed into electrodes and two arc meltings were made. The metal from 

these melts was pressed and/or rolled, formed, and machined. Metal scraps and chips were salvaged 

and also pressed into electrodes for the arc-melting process.
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The following activities by facility occurred as part of the process (BWXT Y-12 2001a, pp. 11-12):

• Pellet/scrap preparation, arc melting, crop and trim machining, and sawing (Building 9205-1)

• Mold press sintering, ingot forging, canning and annealing after first cold roll, and final 

inspection/assembly (Building 9204-4)

• Ingots canned before first cold roll (Building 9201-1)

• Cold and hot rolling (Building 9215)

• Cleaning and final plating (Building 9206)

• Machining activities (Building 9766)

• Development activities (Building 9202)

Sludge samples were taken from the S-3 ponds before capping to determine whether there was any 

airborne (internal) exposure potential for workers who would place the cap materials. Initially, no 

special precautions were deemed necessary for this work, other than the normal requirements for 

handling DU. However, a second analysis to include the effects of strontium and thorium indicated 

that there was a dramatic increase in the exposure potential of 228Th and 230Th that contributed to 90% 

of the internal exposure potential (BWXT Y-12 2000, p. 111). More information is provided in the 

discussion of the S-3 ponds in Section 2.6.

2.8.8

In 1951, Y-12 was brought into the lithium isotope separation project. A method for enriching natural 

lithium (7.6% 6

Li and 92.4% 7Li) in the 6Li isotope was needed for use in the thermonuclear weapons 

program. Two methods, column exchange (COLEX) and electrical exchange (ELEX), were 

developed and tested simultaneously. Pilot plants were built to evaluate both methods. The COLEX 

process was selected as the method of choice and production continued into the early 1960s (Wilcox 

2001, pp. 28, 35).

Lithium

Significant quantities of lithium materials were machined and crushed to fine dust. Some unmeasured 

quantity ended up in the ventilation system, in mop water, in cleanup solutions, and in nonhomogeneous salvage that was awaiting recovery (Owings 1995, p. 77).

Impurities in lithium metal react with deuterium. In many cases, the reaction productions distill out the 

lithium deuteride at the reaction temperatures and condense wherever the vessel is cooler (lid and 

upper 2 or 3 in of the reactor). This represents a loss of deuterium that is not accounted for (Owings 

1995, p. 77).

2.9 SOLUBILITY AND INSOLUBILITY

Y-12 has processed uranium mainly in the forms of UO2 and uranium metal. Chemical conversions 

from UNH to both UO2 and uranium metal have been performed as well. Although the solubility type 

for uranium metal is not addressed by the guidance documents, experience at uranium process 

facilities has shown that uranium metal generally behaves as a type M compound. However, the 

possibility of slow oxidation of a significant portion of the surface of the metal to UO2 and/or U3O8 over 

time must be considered (Rucker et al., 2001, p. 5).
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 23 of 35

Y-12 defined a class Q material as a mixture of 90% class W and 10% class Y. Class Q represents 

the circumstance when there is only a thin layer of UO2 on the surface of uranium metal. It can also 

provide a reasonable representation of the solubility half-time that has been observed for UO2 that has 

not been high-fired (approximately 120 to 140 days) than would the assumed half-time for class W (50 

days) (Rucker et al., p. 6). However, the use of the International Commission on Radiological 

Protection (ICRP) Publication 66 lung model (ICRP 1994) overcomes the need for the contrived 

class Q compound because type M assumes 90% of the material has a half-time of 140 days. Under 

the Publication 66 lung model, only uranium that is high-fired UO2 or the product of slow oxidation of 

uranium metal should be classified as type S (Rucker et al., p. 6). 

Y-12 uses three default solubility assumptions for workers who have participated exclusively in the 

urine bioassay program (BWXT Y-12 2003b, p. 18): 

• 100% type S

• 75% type S and 25% type M

• 50% type S and 50% type M 

These defaults are designed to be conservative and to provide adequate protection for workers while, 

at the same time, being representative of the actual exposure material. The defaults are determined 

by the radiological work permit (RWP) bioassay indicator code, the last character of the RWP 

identifier. When working with soluble materials such as uranyl nitrate, the solubility can be defaulted 

to 100% type M or 100% type F, depending on the material. However, to be conservative, persons 

working exclusively with soluble uranium are defaulted to 50% type M and 50% type S. If an 

individual uses RWPs that indicate the work is with insoluble uranium materials, such as uranium 

oxide, then the solubility should be determined by dose calculation software. If the RWP indicates the 

work with uranium had both a soluble and insoluble component, then the solubility should be 

defaulted to 25% type M and 75% type S. If the RWP is for low exposure potential to insoluble 

uranium that requires only urinalysis, then the solubility should be defaulted to 100% type S. The 

RWP bioassay indicators used for routine uranium handling jobs (F, Y, W, and M) are summarized in 

Table 2-5 (BWXT Y-12 2003b, p. 18).

Table 2-5. RWP bioassay indicators for routine uranium handling jobs (BWXT Y-12 2003b, p. 15).

Bioassay 

indicator Solubility Bioassay method

F Primarily (>75%) insoluble. Derived solubility will be determined by 

DOSE 66

Bi-monthly urine and fecal 

sampling

Y Primarily (>75%) insoluble but low exposure potential. Assumed 

solubility for dose calculations is 100% type S.

Quarterly urine sampling

M Insoluble component between 25% and 75%. Assumed solubility 

for dose calculations is 75% type S and 25% type M.

Quarterly urine sampling

W No insoluble component expected. Assumed solubility for dose 

calculation is 50% type S and 50% type M.

Quarterly urine sampling

Historically from 1990 to 1998, the default solubility type for internal dose assessments was 90% W 

and 10% class Y for both EU and DU (BWXT 2003a, p. 120). Almost all internal exposures at Y-12 

involve uranium that has either been enriched or depleted in 235U through the process of gaseous 

diffusion.

In 1999, DOE gave the Y-12 Radiological Control Dosimetry Department permission to use the ICRP 

Publication 66 (1994) lung model for estimating intakes and doses received by personnel. Before 

this, the ICRP 30 (1979) lung model was used from 1989-1999. The ICRP 66 (1994) report includes 

a considerably more detailed respiratory tract model than ICRP 30 (1979). The default material 
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 24 of 35

assumptions recommended in ICRP 66 (1994) more closely reflect those observed at Y-12 (BWXT Y12 2003b, pp. 9-11).

Y-12 developed the DOSE 66 program, and it was validated and verified in 2000 (BWXT Y-12 2003b, 

p.12). This program uses the ICRP Publication 66 methodology for inhalation intakes (ICRP 1994). A 

major advantage of the DOSE 66 program is the calculation of a derived mixture for intake material 

type when both urine and fecal bioassay data are available. The program calculates an intake that is 

based only on fecal bioassay results. It then estimates an intake that is based on the urine results. If 

the fecal and urine intake estimates differ by a significant amount (set by the user), it adjusts the 

solubility of the material until the urine estimate of intake matches that for the fecal data (BWXT Y-12 

2003b, p. 12).

Several Y-12 studies have been conducted in an attempt to better characterize the work area in 

relation to material solubility at Y-12 using the DOSE 66 program. These studies include a 3-month 

investigation with participants from various areas from October to December 1999, recalculation of 

solubility of 1999 incident investigations, and a review of the 2000 incident investigation (BWXT Y-12 

2003b, p. 12). The results of these studies have been combined and are given in Table 2-6.

Table 2-6. Solubility of material for various 

buildings and work areas as calculated by 

DOSE 66 program (BWXT Y-12 2003b, p. 15).

Building Na % type S % type M

9202 1 51 49

9206 2 31 69

9212 48 68 32

9215 54 82 18

9995 4 78 22

9998 2 64 36

9201-5 2 36 64

9201-5N 12 77 23

9204-2E 5 89 11

9204-4 8 74 26

9704-2 1 0 100

a. N represents the number of data points.

Uranium is considered to be primarily an internal dosimetric hazard because it emits alpha particles, 

beta particles, and only weak gamma and X-ray photons. Y-12 is unique in that workers are assumed 

to be routinely exposed to low levels of uranium (BWXT Y-12 2003b, p.9). This chronic intake 

assumption places a premium on the accurate assessment of the committed effective dose 

equivalents (CEDE) received by workers. 

A review of the DOSE 66 data reveals a high correlation between the assumed solubility type and the 

estimated CEDE values when only urine bioassay data is used. As the solubility of the material is 

increased, the CEDE values drop dramatically. This phenomenon, coupled with the potential for 

exposure of workers to varying solubility mixtures, illustrates the importance of solubility in internal 

dose assessments. Fecal sampling is the preferred bioassay method for areas and work that could 

lead to significant insoluble uranium intakes. For areas and work functions that could lead to intakes 

that are both soluble and insoluble, urine sampling alone is sufficient if the insoluble intake results in a 

CEDE of less than 100 mrem (BWXT Y-12 2003b, p.20).
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 25 of 35

2.10 ATTRIBUTIONS AND ANNOTATIONS

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

section of this document.

Karin Jessen served as one of the initial Subject Experts for this document. Ms. Jessen was 

previously employed at Y-12 and her work involved management, direction, or implementation of 

radiation protection and/or health physics program policies, procedures, or practices related to atomic 

weapons activities at the site. This revision has been overseen by a Document Owner who is fully 

responsible for the content, including all findings and conclusions. Ms. Jessen continues to serve as 

a Site Expert for this document because she possesses or is aware of information relevant for 

reconstructing radiation doses experienced by claimants who worked at the site. In all cases where 

such information or prior studies or writings are included or relied upon by Ms. Jessen, those 

materials are fully attributed to the source. Ms. Jessen’s Disclosure Statement is available at 

www.oraucoc.org.
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 26 of 35

REFERENCES

BWXT Y-12, 2000, Recycled Uranium Mass Balance Project Y-12 National Security Complex Site 

Report, Y/LB-16,036, Rev. 1, Y-12 Plant, Oak Ridge, Tennessee, December. [SRDB Ref ID: 

16500]

BWXT Y-12, 2001a, Atypical Radionuclide Assessment at the Y-12 National Security Complex, 

RCO/TR-013, Y-12 Plant, Oak Ridge, Tennessee, May 17. [SRDB Ref ID: 12492]

BWXT Y-12, 2001b, Technical Basis Document 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]

BWXT Y-12, 2003a, Technical Basis for the Internal Dosimetry Program, RCO/TBD-024, Rev. 4, 

BWXT Y-12, Y-12 National Security Complex, Oak Ridge, Tennessee, March 5. [SRDB Ref 

ID: 12324]

BWXT Y-12, 2003b, Technical Basis for Uranium Solubility Determination and Bioassay Sampling 

Protocols at Y-12 National Security Complex, RCO/TBD-040, Rev. 1, BWXT Y-12, Y-12 

National Security Complex, Oak Ridge, Tennessee, March 12. [SRDB Ref ID: 8514]

CCCC, 1951, Progress Report Health Physics, November 1, 1950 – December 31, 1950, Y-780, Y-12 

Plant, Oak Ridge, Tennessee, July 9. [SRDB Ref ID: 8520]

ChemRisk, 1993, Tasks 1 & 2, A Summary of Historical Activities on the Oak Ridge Reservation with 

Emphasis on Information Concerning Off-Site Emission of Hazardous Materials, Oak Ridge 

Health Studies, Phase 1 Report, Volume ll – Part A, Dose Reconstruction Feasibility Study, 

Nashville, Tennessee, September. [SRDB Ref ID: 13188]

ChemRisk, 1999, Uranium Releases from the Oak Ridge Reservation – a Review of the Quality of 

Historical Effluent Monitoring Data and a Screening Evaluation of Potential Off-Site Exposures, 

Reports of the Oak Ridge Dose Reconstruction, Vol. 5, Task 6, Alameda, California, July. 

[SRDB Ref ID: 12175]

DOE (Department of Energy), 2000, Guide of Good Practices for Occupational Radiological 

Protection in Uranium Facilities, DOE-STD-1136-2000, Washington, D.C., August. [SRDB Ref 

ID: 4617]

ICRP (International Commission on Radiological Protection), 1979, Limits for the Intake of 

Radionuclides by Workers, Part 1, Publication 30, Part 1, Pergamon Press, Oxford, England.

ICRP (International Commission on Radiological Protection), 1994, Human Respiratory Tract Model 

for Radiological Protection, Publication 66, Pergamon Press, Oxford, England.

Oliver, R.W., 2003, “Truhistory,” Personal Correspondence (email), August 28. [SRDB Ref ID: 8519]

Oliver, R.W., 2007, “Y-12 Questions,” Personal Correspondence (email), September 4.

ORAUT (Oak Ridge Associated Universities Team), 2005, Internal Dosimetry Coworker Data for Y-12, 

ORAUT-OTIB-0029, Rev. 00, Oak Ridge, Tennessee, April 5. 
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 27 of 35

ORAUT (Oak Ridge Associated Universities Team), 2006, External Radiation Dose Estimates for 

Individuals Near the 1958 Criticality Accident at the Oak Ridge Y-12 Plant, ORAUT-OTIB0057, Rev. 00, Oak Ridge, Tennessee, May 15. 

Owings, E., 1995, Historical Review of Accountable Nuclear Materials at the Y-12 Plant, Y/EXT00153/DEL REV, Y-12 Plant, Oak Ridge, Tennessee, July 28. [SRDB Ref ID: 691]

Rucker, T. L., J. D. Slack, K. N. Fleming, S. W. Stevens, R. M. Moody, M. Johnson Jr., and S. W. 

Green, 2001, Uranium Lung Solubility Class Selection at Bechtel Jacobs Company LLCOperated Facilities, presented at Bioassay Analytical & Environmental Radiochemistry 

Conference, Honolulu, Hawaii, November 6. [SRDB Ref ID: 8160]

UCNC (United Carbide Nuclear Company), 1958, Accidental Radiation Excursion at the Y-12 Plant, 

June 16, 1958, Final Report, Y-1234, Y-12, Oak Ridge, Tennessee, July 28. [SRDB Ref ID 

8387]

Wilcox, W.J., Jr., 2001, An Overview of the History of Y-12 1942-1992, American Museum of Science 

and Energy, Oak Ridge, Tennessee, August. [SRDB Ref ID: 9609]

Y-12 , 2007, Y-12 Fact Sheet, available at http://www.y12.doe.gov/about/factsheet.php .
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 28 of 35

GLOSSARY

alpha stage

The first stage of the calutron that enriched uranium up to 20% 235U. 

beta stage

The second stage of the calutron process that further enriched the uranium from the alpha 

stage up to 98% 235U.

calutron

An electromagnetic apparatus for separating isotopes according to their masses. Strong 

magnetic fields were used to separate the lighter 235U isotope from the heavier, more naturally 

abundant 238U isotope.

class Q

A mixture of 90% class W and 10% class Y uranium. The class Q represents the 

circumstance when there is only a thin layer of UO2 on the surface of uranium metal. 

column exchange (COLEX)

A column-based chemical exchange process to enrich natural lithium in its 6

Li isotope.

committed effective dose equivalent (CEDE)

The sum of the committed dose equivalents to various tissues in the body, each multiplied by 

its weighting factor, for 50 years post intake. It does not include contributions from external 

doses. Committed effective dose equivalent is expressed in units of rem or sievert.

depleted uranium (DU)

A form of uranium that contains less than 0.72% 235U.

electrical exchange (ELEX)

An electrical process to enrich natural lithium in its 6

Li isotope.

enriched uranium (EU)

Contains more than the natural abundance of 235U than found in natural uranium (0.72%). 

feed material

Uranium tetrachloride (UCl4) produced by the conversion of uranium oxides (including UO2, 

UO3, and U3O8) for use in the calutrons.

fusion

The process in which nuclei of lighter elements (e.g., deuterium and tritium) combine to form 

the nucleus of a heavier element, with the release of energy.

highly enriched uranium (HEU)

Uranium having enrichment above 20 percent of the fissionable isotope 235U.

low enriched uranium

Uranium having enrichment below 20 percent of the fissionable isotope 235U.
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 29 of 35

natural uranium (NU)

Uranium as it is found in nature. It consists of two principal isotopes, 235U (0.72%) and 238U 

(99.28%), and includes a trace amount of 234U by mass (0.0055%). 

normal uranium (NU)

Uranium that has been isotopically blended to approximate the natural isotopic range of 

uranium.

recycled uranium (RU)

Any uranium that has been irradiated in a reactor. As a result, RU contains transuranic 

material, fission products, and reactor-generated uranium products. 

solubility type

Type F, M, and S are inhalation solubility types established by the ICRP. Type F material is 

very soluble, type M material is moderately soluble, and type S material is relatively insoluble. 

These types are equivalent to the older class D, W, and Y, respectively. 

source material

(1) Material containing any combination of uranium or thorium in any physical or chemical 

form, or (2) ores containing 0.05 wt % or more uranium, thorium, or both. Source material 

excludes Special Nuclear Material.

special nuclear material (SNM)

Plutonium or uranium enriched to a higher-than-natural assay, and includes plutonium-239, 

uranium-233, uranium containing more than the natural abundance of uranium-235, or any 

material artificially enriched in one of these isotopes.

thermal neutrons

Low speed neutrons that are in thermal equilibrium with their surroundings and have energies 

less than approximately 0.5 electronvolt.

transuranic (TRU)

Elements with an atomic number greater than uranium (atomic number 92), e.g., 238, 239, 240Pu 

and 237Np.
Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 30 of 35

TABLE OF CONTENTS 

SECTION TITLE

A.1 Sources of Exposure..............................................................................................................

PAGE

31

A.2 Chronology of Uranium Operations ........................................................................................ 32

A.3 Solubility of Radionuclides ..................................................................................................... 34

LIST OF TABLES

TABLE TITLE

A-1 Radionuclides of concern.......................................................................................................

PAGE

31

A-2 Known sealed radiation sources............................................................................................. 31

A-3 Primary uranium operations ................................................................................................... 32

A-4 Process chronology by building of operations ........................................................................ 32

A-5 Radionuclides and solubility types.......................................................................................... 34

A-6 Radioelements and default solubility types............................................................................. 34

A-7 RWP bioassay indicators for routine uranium handling jobs ................................................... 35

A-8 Solubility of material for various buildings and work areas as calculated by DOSE 66 

program .................................................................................................................................35

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Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 31 of 35

A.1 SOURCES OF EXPOSURE

Y-12 became a highly sophisticated nuclear weapons component manufacturing facility and 

development engineering organization. The plant receives, stores, and protects uranium and lithium 

materials and parts, dismantles nuclear weapons components, and serves as a government 

repository for EU. In addition, Y-12 has many treatment, storage, and disposal facilities for hazardous 

and radioactive materials. 

Today, the current mission at Y-12 includes the:

• production, rework, and dismantlement of nuclear weapon components; 

• receipt, storage, and protection of special nuclear materials; 

• quality evaluation/enhanced surveillance of the nation’s nuclear weapon stockpile; 

• prevention of the spread of weapons of mass destruction; and 

• support to DOE, other federal agencies, and other national priorities through a complementary 

work program. 

Table A-1 shows the radionuclides of concern. Table A-2 shows the locations of known sealed 

radiation sources. Some building numbers and their corresponding radionuclides are not available at 

this time.

Table A-1. Radionuclides of concern.

a

Radionuclide Type of emission

Radioactive 

half life (y)

99Tc Beta 2.13 × 105

228Th Alpha 1.91 × 100

230Th Alpha 7.54 × 104

232Th Alpha 1.45 × 1010

234U Alpha 2.47 × 105

235U Alpha, some gamma 7.4 × 108

236U Alpha 2.34 × 107

238U Alpha 4.47 × 109

237Np Alpha 2.14 × 106

238Pu Alpha 8.64 × 101

239Pu Alpha 2.4 × 104

241Am Alpha 4.32 × 102

a. Adapted from BWXT Y-12, 2003a, pp. 30–31).

Table A-2. Known sealed radiation sources 

(CCCC 1951, p. 10).

Sources Building

Ra-Be, Po-Be 9203

Ra, Co, Ta, Po-Be 9983

Po-Be, Ra-226 9737, 9201-2, 9204-3

Ra-226 9212

Ra-226, Co 9212

Ra-226 9206,9706-2

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A.2 CHRONOLOGY OF URANIUM OPERATIONS

Tables A-3 and A-4 contain descriptions of historical Y-12 uranium process operations. Specific key 

buildings and their functions are highlighted to better understand the Y-12 uranium operations. Y-12 

experienced significant changes from the original mission of electromagnetic enrichment to the 

current multiple missions of storing HEU, weapons disassembly, and major efforts in environmental 

and waste management. 

Table A-3. Primary uranium operations (ChemRisk 1999, pp. 172-184; Y-12 2007).

Key uranium operations Buildings involved

Dates of 

operation

Electromagnetic enrichment Alpha buildings 9201-1,2,3,4,5 

Beta buildings 9204-1,2,3,4

1943–1947

Feed preparation and product processing 9202, 9203, 9206, 9212 1943–1947

Uranium reclamation 9202, 9203, 9206, 9212 1945–1951

Uranium recycle 9202, 9203, 9206, 9212 1953–1990s

Uranium salvage 9206, 9207, 9211 1945–1951

Uranium preparation/recycle 9202, 9206, 9211, 9212 1953–1995

Uranium forming/machining 9201-5, 9204-4, 9215, 9998 1952–1995

Uranium component assembly 9202, 9204-2, 9204-2E 1952–1995

Stockpile stewardship and management 9201-5, 9204-4, 9215 1952–2007

Table A-4. Process chronology by building of operations (ChemRisk 1999, p. 171; Oliver 2003, 

2007).

Building 1943–1948 1949–1951 1952–1963 1964–1995 1996–2007

9201-1 Tracks 1 and 2, 

α - I calutrons 

(uranium 

enrichment).

Uranium 

enrichment 

operations. 

Uranium 

reclamation and 

salvage 

operations. 

Fusion energy 

research 

operations. 

General 

manufacturing for 

tooling, including 

work for others. 

Almost all clean 

work.

9201-2 Tracks 3 and 4, 

α - I calutrons 

(uranium 

enrichment).

Uranium 

enrichment 

operations.

COLEX lithium/ 

mercury 

enrichment 

operations.

Research and 

development 

operations.

ORNL facility.

9201-3 Track 5, 

α - I calutrons.

Uranium 

enrichment 

operations.

Uranium 

reclamation and 

salvage 

operations.

Fusion energy 

research 

operations. 

Currently used for 

office space.

201-4 Tracks 6 and 7, 

α - II calutrons 

(uranium 

enrichment).

Uranium 

enrichment 

operations.

COLEX lithium/ 

mercury 

enrichment 

operations.

Engineering and 

administrative 

facilities.

Awaiting D&D.

9201-5 Tracks 8 and 9, 

α – II calutrons 

(uranium 

enrichment).

Uranium 

enrichment 

operations.

COLEX lithium/ 

mercury 

enrichment 

operations.

NU/DU press, 

rolling, and 

machining 

operations.

NU/DU press, 

rolling, and 

machining 

operations; 

building 

evacuated (2007); 

surveillances 

occur; storage; 

awaiting D&D.

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Document No. ORAUT-TKBS-0014-2 Revision No. 02 Effective Date: 11/08/2007 Page 33 of 35

Building 1943–1948 1949–1951 1952–1963 1964–1995 1996–2003

9202 Alpha and 

chemical 

preparation and 

reclamation 

operations.

Uranium product 

reclamation 

operations.

Uranium process 

development & 

improvement 

operations.

Uranium process 

development & 

improvement 

operations.

Technology 

development.

9203 235U analysis and 

initial uranium 

product 

processing.

Uranium product 

reclamation 

operations.

Reclamation and 

salvage 

operations.

Y-12 production 

development and 

research 

operations.

Technology 

development.

9204-1 Tracks 1 and 2, 

ß calutrons 

(uranium 

enrichment)

Uranium 

enrichment 

operations.

Stable isotope 

separation 

operations.

Fusion energy 

research

operations.

ORNL facility; 

however BWXT 

Y-12 occupies 

office space.

9204-2 Tracks 3 and 4, 

β calutrons 

(uranium 

enrichment).

Uranium 

enrichment 

operations.

Special material 

operations.

Special material 

operations.

Special material 

operations.

9204-2E -- -- -- Uranium 

assembly 

operations.

Uranium 

assembly 

operations.

9204-3 Tracks 5 and 6, 

β calutrons 

(uranium 

enrichment).

Uranium 

enrichment 

operations.

Stable isotope 

(e.g., copper) 

separation 

operations.

Stable isotope 

(e.g., copper) 

separation 

operations.

ORNL facility.

9204-4 Tracks 7 and 8, 

β calutrons(uraniu

m enrichment).

Uranium 

enrichment 

operations.

ELEX 

lithium/mercury 

pilot-scale 

operations.

NU/DU press and 

rolling operations.

Material storage 

operations.

9206 β chemical 

reclamation and 

product 

processing.

Uranium product 

reclamation and 

salvage 

operations.

Uranium chemical 

processing and 

metal production 

operations.

Uranium chemical 

processing and 

metal production 

operations.

Currently 

undergoing 

deactivation. No 

longer a Material 

Access Area; 

D&D has been 

initiated.

9207 Uranium 

reclamation and 

salvage 

operations.

Uranium 

reclamation and 

salvage 

operations.

Maintenance, 

reclamation and 

salvage 

operations.

ORNL biological 

research 

operations.

ORNL facility 

(vacated in 2005); 

awaiting D&D.

9211 Uranium 

reclamation and 

salvage 

operations.

Uranium salvage 

and product 

recovery 

operations.

Uranium salvage 

and product 

reclamation 

operations.

ORNL biological 

research 

operations.

ORNL biological 

research 

operations 

(vacated in 2005); 

awaiting D&D.

9212 β product 

processing.

Uranium 

conversion and 

reclamation 

operations.

UF6 conversion, 

chemical 

operations, and 

weapons 

production 

operations.

Chemical 

operations and 

weapons 

production 

operations.

Chemical 

operations and 

weapons 

production 

operations.

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Building 1943–1948 1949–1951 1952–1963 1964–1995 1996–2003

9215 -- -- EU machining and 

metal finishing 

operations.

EU machining and 

metal finishing 

operations.

EU machining 

and metal 

finishing 

operations; 

DU H-1 foundry 

operations.

9998 -- NU H-1 foundry 

operations.

DU H-1 foundry 

operations.

DU H-1 foundry 

operations.

DU processing.

A.3 SOLUBILITY OF RADIONUCLIDES

Workers at Y-12 have routinely performed work with various compounds of uranium. These 

compounds have different retention times and clearance pathways. Because the clearance of soluble 

materials is primarily through the blood, urine bioassay is the preferred method for detecting these 

forms of compounds. For insoluble compounds, the material is cleared from the lungs. The majority 

of the insoluble material is excreted via the feces, with only a small fraction clearing through the urine. 

(BWXT Y-12 2003b p. 11) Tables A-5 and A-6 show the solubility types for specific radionuclides and 

default solubility for radioelements present at Y-12.

Table A-5. Radionuclides and solubility types

(BWXT 2003a, p. 31)

Radionuclides Solubility types

Tc-99 F and M

Np-237 M

Pu-238 M

Pu-239 S

Am-241 M

Table A-6. Radioelements and default 

solubility types (BWXT 2003a, p. 38)

Radioelement Solubility types

Americium M

Neptunium M

Plutonium S

Strontium S

Technetium M

Thorium Y

3

H Vapor

Uranium As determined by RWP

Y-12 uses three default solubility assumptions for workers who participate exclusively in the urine 

bioassay program: 100% type S, 75% type S and 25% type M, and 50% type S and 50% type M. 

These defaults are designed to be conservative and provide adequate protection for workers while at 

the same time being representative of the actual exposure material (BWXT Y-12 2003b, p. 18). Table 

A-7 summarizes the bioassay indicators.

Studies have been conducted in an attempt to better characterize the work areas at Y-12 in relation to 

material solubility. These studies have included a 3-month investigation with participants from various 

areas from October to December 1999. The results are shown in Table A-8 (BWXT Y-12 2003b, 

p 15).

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ATTACHMENT A

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Table A-7. RWP bioassay indicators for routine uranium handling jobs (BWXT Y-12 2003b, p. 18).

Bioassay 

indicator Solubility Bioassay method

F Primarily (>75%) insoluble. Derived solubility will be determined by 

DOSE 66

Bi-monthly urine and fecal 

sampling

Y Primarily (>75%) insoluble but low exposure potential. Assumed 

solubility for dose calculations is 100% type S.

Quarterly urine sampling

M Insoluble component between 25% and 75%. Assumed solubility 

for dose calculations is 75% type S and 25% type M.

Quarterly urine sampling

W No insoluble component expected. Assumed solubility for dose 

calculation is 50% type S and 50% type M.

Quarterly urine sampling

Table A-8. Solubility of material for various 

buildings and work areas as calculated by 

DOSE 66 program (BWXT Y-12 2003b, p. 15)

Building Na % type S % type M

9202 1 51 49

9206 2 31 69

9212 48 68 32

9215 54 82 18

9995 4 78 22

9998 2 64 36

9201-5 2 36 64

9201-5N 12 77 23

9204-2E 5 89 11

9204-4 8 74 26

9704-2 1 0 100

a. N represents the number of data points.

ATTACHMENT A

SITE DESCRIPTION

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