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
16

and C-340, C-400, C-410, and C-420 could have

exposed maintenance mechanics to concentrated

inhalation and contamination hazards.

Several formal cascade improvement programs (CIPs)

and cascade uprating programs (CUPs) involving

replacement of major components to increase diffusion

process reliability, capacity, and efficiency started as early

as 1954. The second major CIP/CUP started in March

1973 and continued for eight years. This CIP/CUP process

involved cell by cell removal of compressors and

converters, process piping, and support system components

while the remainder of the cascades remained in operation.

After removal, compressors and converters were taken to

C-400 for disassembly, cleaning, and decontamination and

then to C-720, where they were modified and reassembled

prior to reinstallation. In addition to releases of UF6, these

disassembly activities exposed maintenance workers to

transuranics and fission products adhering to surfaces inside

the system and to trichloroethene (TCE) during degreasing

and decontamination. Workers could have received

significant radiation exposures by inhaling neptunium-237

dust. At the completion of the CIP/CUP activities,

converter and compressor disassembly remained a routine

operation.

Between March and May of 1977, C-340

underwent a slow and deliberate shutdown for an

indefinite period. During the shutdown period, which

lasted until the mid-1980s, Building C-340 was used as

a valve rebuilding shop and routine maintenance facility.

2.4 Unusual Occurrences and

Accidents

During its first 40 years of operation, PGDP

experienced numerous operational upsets, releases,

exposures, and other accidents. Documentation,

investigation, and reporting of these unusual events were

very inconsistent and infrequent until the initiation of

DOEís formal occurrence reporting systems in the late

1980s. One of the most frequent and notable unusual

events was the release of UF6

 gas into work areas or

the environment. The releases ranged from very small

amounts, commonly referred to as ìpuffs,î to significant

amounts that resulted in HF burns, and uranium intakes

requiring bioassay or medical attention for dozens of

workers. The sources of these releases included the

process system during system upgrade work, equipment

failures, and maintenance activities; cylinder connection

and disconnection activities at feed and withdrawal

stations; and process equipment disassembly during

shop maintenance activities in C-400 and C-720.

Several evaluation reports on UF6

 releases and their

effects, as well as other site documents, identified

approximately 50 UF6 releases, each in excess of 10

pounds of uranium. However, reviews of health physics

reports and the site quarterly progress reports from the

early 1960s revealed references to many hundreds of

releases of varying sizes (described often only as minor,

large, or major). These reports identified many

employees who were exposed from these releases and

required medical examinations and bioassay. Burns and

respiratory tract bleeding from exposures to or inhalation

of HF were frequent occurrences. Many health physics

reports indicated that these releases were not

documented in operations shift logs and were often not

addressed in the Plantís quarterly progress reports to

the AEC, which was the regulatory agency at that time.

At least 15 events were identified in the first ten

years of Plant operation that each released a minimum

of 100 pounds of uranium, with a 1960 event releasing

approximately 6,800 pounds and a 1962 event releasing

approximately 3,400 pounds. As better equipment was

installed and major system upgrade work ended,

operational practices improved and the number and

quantity of UF6

 releases decreased significantly. In the

1980s, reported releases were on the order of one to

five per month and were measured in grams instead of

pounds. The number of persons placed on recall for

bioassay decreased from 30 or more per month in the

1950s to one to six per year in the 1980s.

Other significant Plant events included a major fire

in Building C-310 in 1956, overexposure of two

maintenance mechanics to beta radiation, and an

explosion and fire in C-315 in 1978. Major releases

affecting groundwater included a spill of 17,000 gallons

of diesel oil migrating as far as 2 miles from the site

boundary via surface water and the identification of

C-337 Fire and Explosion - December 1962