12

become long-term Plant employees, transcending

changes in Federal oversight organizations and transitions

in contractors.

Demands on the Plant and the workers were high,

given the requirements of the Cold War. Work was

difficult, production schedules were challenging, and

the work environment was often hot, loud, dirty, and

laden with noxious fumes. The security demands of

the Cold War also affected worker awareness of hazards

in that, prior to 1989, documents discussing many

aspects of operations were classified and, at the direction

of line management and AEC security, detailed

knowledge of work activities was based on a ìstrict

need to know.î The workersí sense of loyalty and

service would also translate into acceptance of these

security policies and the expectation that they would be

told everything that they needed to know.

From the 1950s to the 1990s, government oversight

of ES&H elements of PGDP contractor activities

evolved. The primary offices of the Federal regulatory

organizations for the diffusion plants ó the AEC,

ERDA, and DOE ó have always been located in Oak

Ridge, although there was a Federal presence at PGDP

for most of the period 1952 to 1990. Records indicate

AEC involvement in collaborative research activities

related to radiation and health physics in the 1950s

through the 1970s, but there is little evidence of direct

observation of, or direction to, the PGDP contractor

regarding ES&H, which was not an uncommon practice

for a regulatory agency during that period. Carbide

provided quarterly progress reports to the AEC

summarizing operational, maintenance, construction,

industrial hygiene, health physics, and accident data and

analysis and responded to information requests on health

physics issues. However, the interactions between the

contractor and AEC clearly emphasized maintaining or

increasing production. In the 1970s, as new

environmental regulations were enacted, there is

evidence of growing involvement by the Commonwealth

of Kentucky and OR in site activities and in the effects

of site activities on the environment and the public. In

the 1980s, increased DOE oversight was evidenced by

additional ES&H inspections by the local site office

and OR. On September 18, 1985, then-Secretary of

Energy John Herrington announced that DOE-wide

environmental surveys would be conducted; the PGDP

survey occurred in November and December 1987.

These surveys led to changes in DOE and contractor

ES&H programs. However, the 1990 DOE Tiger Team

identified ineffective DOE oversight and unclear

oversight roles and responsibilities as key management

findings.

2.2 Operations

Although major construction activities would

continue through 1956, Union Carbide began hiring

approximately 1,700 permanent Plant workers in 1951.

The first process buildings, C-331, C-333, C-310, and

C-315, were completed and started operation in

September 1952, and the first product was withdrawn

in November. The purpose of the gaseous diffusion

plant has been and continues to be the enrichment of

uranium, initially for military applications and

subsequently for commercial reactor fuel. PGDP

enriches feed material in the form of UF6 gas with

approximately 0.7 percent uranium-235 to UF6 with

one to three percent uranium-235. The enriched product

from PGDP was sent to other DOE sites at Portsmouth

or Oak Ridge for further enrichment. Most UF6 feed

material came from the depleted tails produced during

normal diffusion operations at PGDP and from Oak

Ridge and Portsmouth. From 1952 through 1977, UF6

feed material was also produced from uranium trioxide

or UO3

 (called ìyellowcakeî) at PGDP in Buildings C410 and C-420; this feed material was supplied by

sources such as El Dorado Mining and Refining,

Mallinkrodt Chemical Works, and General Chemicals

(now Allied Chemical) and comprised less than 10

percent of the UF6 fed to the cascade. From 1953

through 1964 and intermittently from 1968 through

1977, the feed plant also produced UF6

 from UO3 from

spent reactor fuel processed at the Hanford and

Savannah River sites. After 1977, all feed came in the

form of UF6

 from outside sources such as Oak Ridge,

Portsmouth, and Allied Chemical.

Although natural uranium is not a highly radioactive

material, it is toxic, both chemically and radiologically,

when inside the body. The uranium exposure pathway

of greatest hazard at PGDP was inhalation of uranium

dust. Feed material was made from production reactor

tails from 1953 until 1964, and intermittently from 1968

to 1977. The percentage of PGDP cascade feed

material from reactor tails averaged 19 percent during

the 19 years this material was used, ranging from 3

percent in 1975 to 65 percent in 1973. Processing of

UO3

 into UF6 was accomplished in three steps:

reduction, hydro-fluorination, and fluorination (see

Figure 3).

Reduction involved transforming UO3

 into UO2

(commonly referred to as ìblack oxideî) using hydrogen

gas. Hydro-fluorination of UO2

 into UF4 (commonly

referred to as ìgreen saltî) was accomplished by adding

anhydrous hydrofluoric acid (HF). Fluorination was
13

Source Material

ï UO , Some with Trace

Transuranic Elements

and Fission Product

Impurities (from Reactor

Tails)

3

Conversion to UF Conversion to UF

ï Building C-410

ï Addition of

Fluorine Gas

ï Steam

ï Receiver Ash

ï Non-volatile Products

Containing Np, Pu &

Tc Compounds

ï Building C-420

ï Addition of

Hydrogen Gas

ï Addition of Hydrogen

Fluoride

Byproduct Byproducts

4 6

4

6 6

ï Building C-340

U

(Green Salt)

Potentially Contaminated

with Pu and Np

F4

Further Enrichment

at Portsmouth and

Oak Ridge

Gaseous Diffusion

Plants

Reduction to UF

ï 37,000 Cylinders ï Addition of

Hydrogen Gas

Enrichment of UF Enriched

UF with

Tc-99

Onsite Storage

in Cylinder Yards

ï

ï

ï Buildings C-331,

C-333, C-335,

and C-337

Hydro

Fluor

Figure 3. Historical Uranium Enrichment Process
14

conducted in C-410 using heated elemental fluorine gas

in tower reactors. The first two steps were performed

in C-410 on vibration tray reactors (shaker trays) from

1953 to 1956. In 1956, due to frequent equipment

failures, spills, leaks, and the increased demand for feed,

Building C-420 (commonly called the ìgreen saltî plant)

was completed and green salt production at C-410 was

phased out. In C-420, the reduction was performed in

two-stage fluidized bed reductors; the hydro-fluorination

was performed in three sets of horizontal screw reactors

or in a two-stage fluidized bed hydro-fluorinator.

Working conditions in C-410 and C-420 were hot and

loud; surface areas were coated with yellowcake, green

salt, black oxide, and airborne uranium dust. High

radiation areas existed near the fluorination towers and

ash receivers. Respirators were specified for most work

activities, but compliance was inconsistent. The feed

plant was shut down in 1977.

The main process buildings at PGDP (C-331, C333, C-335, and C-337) contain the ìcascades,î which

are a series of compressor and converter stages and

supporting equipment arranged in cells and units that

progressively enrich the UF6 feed. Enrichment occurs

as the UF6 passes through barriers in the converters

allowing isotopes of lower molecular weight to pass

through. The series of converters results in two streams,

or cascades, of UF6: one of progressively higherpercentage uranium-235 that moves to the product

withdrawal station in C-310, and one of progressively

lower-percentage uranium-238 that moves toward the

tails withdrawal station in C-315. Both the enriched

product and the depleted tails are fed into cylinders and

allowed to cool until solid, with the product shipped to

Portsmouth and the depleted material either re-fed to

the cascade or stored on site. The process building

work areas were hot, but clean, except during

maintenance or modification activities that required

system entry. The process buildings were also the source

of several major explosions, fires, and UF6 releases and

frequent smaller releases during connection and

disconnection of sample bottles and feed and product

cylinders. Generally, personal protective equipment

(PPE) was only specified for maintenance or nonroutine work activities.

In 1957, the presence of neptunium-237 and

technetium-99 at PGDP was documented, and between

1959 and 1966 numerous studies related to the behavior,

health effects, and controls for these elements were

conducted by the Paducah Health Physics and Hygiene

Department and the AEC. The percentage of

transuranics, such as neptunium and plutonium, and

fission products, such as technetium, in the reactor tails

material was very small, estimated at approximately 0.2

parts per million (ppm) neptunium, 4 parts per billion

plutonium, and 7 ppm technetium. However, these

elements are much more hazardous than natural

uranium and were concentrated by the cascade at certain

specific locations, presenting increased hazards to certain

workers. Neptunium has a specific activity up to 2,000

times greater than an equivalent amount of uranium,

depending on the level of enrichment. Plutonium is

significantly more radioactive than neptunium, but

constituted a lesser hazard because it was present in

much lower concentrations. Both plutonium and

neptunium are significant radiation hazards if inhaled

or ingested. Technetium is primarily a beta emitter

with a higher specific activity than uranium, and is highly

mobile in groundwater.

Approximately 25 percent of the neptunium in the

feed material remained in the feed plant as dust or ash.

Approximately 50 percent remained in cylinder heels

after feeding, and approximately 25 percent was

vaporized in the cascade, plating out toward the upper

end of the cascade. Technetium tended to migrate to

the top of the cascade, and much was drained off into

the product or vented to the atmosphere. In 1958, a

neptunium recovery process was initiated in C-400 to

recover neptunium from the fluorination ash and cylinder

heels for classified uses. In response to a demand for

technetium for use at Oak Ridge, a program to recover

technetium from the cylinder wash water and raffinate

(e.g., solvents) from neptunium recovery operations

began in April 1960. Due to the concentrated quantities

of these materials, the recovery operations presented

additional radiation protection problems requiring special

protective measures. Air samples collected from areas

contaminated with neptunium indicate the potential for

Major Facilities at PGDP

ï C-331, C-333, C-335, and C-337 ñ Gaseous

Diffusion Process Buildings

ï C-410/420 ñ UF6 Feed Plant

ï C-300 ñ Central Control Building

ï C-310 ñ Purge and Product Withdrawal

ï C-315 ñ Surge and Waste Building

ï C-340 ñ Metals Plant

ï C-400 ñ Cleaning Building
15

high radiation doses to workers in these areas (e.g.,

reports of continuous sampling for February and March

1959 indicated an average of 10 and 27 dpm per m3

respectively in the neptunium recovery area in C-710).

In September 1961, magnesium fluoride pellet traps

were installed in the feed plant to capture neptunium

and technetium; in January 1963, similar traps were

installed at the C-310 product withdrawal stations. By

March 1962, neptunium recovery operations had ended,

and in June 1963, technetium recovery operations also

ceased. A different technetium recovery process was

initiated in the mid-1970s to remove technetium from

aqueous waste streams for the purpose of

environmental protection.

Before the mid-1970s, a complex uranium recovery

process was operated in C-400 for separating uranium

from waste and scrap materials, concentrating it, and

converting it to an oxide. The uranium recovery system

was not leak-tight, and leaks were common. However,

steps were taken to control operatorsí exposure to

process materials. Routine surveys were conducted to

monitor the concentration of radioactivity on surfaces

and in the air in C-400, and the health physics staff

recommended changes in work practices based on the

results of these surveys. In the mid-1970s, the solvent

extraction process for uranium recovery was replaced

with a simpler precipitation and filtration process. The

filtrate, containing low concentrations of radionuclides,

was discharged to the environment via the C-400 drains.

Sludges and filter cake were processed at PGDP for

uranium recovery or sent to Fernald for recovery.

From December 1956 through December 1962 and

from January 1968 through October 1973, PGDP

produced UF4

 and uranium metal in C-340 for weapons

uses. The uranium metal production process involved

reducing UF6 (normally from the tails cylinder) to UF4

by combining it with hydrogen in a heated tower. The

UF4 was mixed with magnesium and fed into lined firing

reduction vessels (commonly referred to as ìbombsî),

placed in furnaces, and heated until it fired into a metal

ingot, called a ìderby.î The derbies were removed

from the bomb, cleaned, cut, and shipped to Oak Ridge.

This process created a dusty environment in the metals

plant with airborne UF4 and magnesium powders,

uranium metal oxides, radionuclide uranium daughter

products, and magnesium fluoride dusts. The

production of UF4 continued until 1977, primarily to

provide HF for feed operations. Working conditions

were dirty, with airborne uranium and HF leaks. The

use of army assault masks or respirators was specified

for many metals plant activities, although workers did

not always use them. The metals plant was responsible

for much of the fluoride released to the environment at

PGDP.

During the 1950s and 1960s, in order to retain certain

skills and to maintain local employment levels after initial

construction, a variety of non-enrichment work for other

Federal agencies was performed. These activities

included manufacturing missile components,

superconducting electromagnets, and fuel shipping

casks. In addition, until 1985, disassembly of weapons

components and recovery of metals were performed at

PGDP. While the work involved limited amounts of

hazardous materials (e.g., lead), the primary exposure

risk to workers on these projects was presented by

normal Plant work activities in adjacent areas of the

buildings. Nickel and aluminum recovery was performed

in three smelters in C-746A; gold recovery occurred

principally in the C-746A disassembly room and in C400. Primary hazards in smelting operations were heat,

working with molten metals, noxious fumes, and some

potential for airborne radioactive contaminants.

2.3 Maintenance and Modifications

Much of the exposure to radioactive and hazardous

materials at the PGDP resulted from system

maintenance and improvement activities. The amount

and complexity of equipment in continuous operation

at high speeds, temperatures, and pressures resulted in

frequent intrusions into piping systems to repair valves,

compressors, motors, feed pulverizers and conveyors,

and supporting piping and components. Opening of

systems and components exposed residual UF6

 to

moisture in the air, forming caustic HF gas and depositing

uranium fluoride (UO2F2) around the immediate area.

Changing of dust bag collection filters in process buildings

Aerial View of PGDP Circa 1952