Rocky Flats Plant,
Plutonium Manufacturing Facility
HAER No. CO-83-M (Rocky Flats Plant, Building 707)
Rocky Flats Environmental Technology Site, Highway 93, Golden, Jefferson
County, Colorado. Building 707 is located in the central section of the protected area of
the Rocky Flats Plant.
Date of Construction: 1970.
Fabricator: C.F. Braun and Company, Alhambra, California.
Present Owner: U.S. Department of Energy (DOE).
Present Use: Plutonium Weapons Components Manufacturing.
This building is a primary contributor to the Rocky Flats Plant
historic district associated with the U.S. strategy of nuclear military
deterrence during the Cold War, a strategy considered of major importance in preventing
Soviet nuclear attack. Building 707 was the primary plutonium manufacturing and assembly
facility at the plant from 1970 until curtailment of operations in 1989. The design of
Building 707 incorporated extensive control and safety features, including the first-time
use of inert atmosphere in the glove boxes, primarily in response to two earlier fires (in
Buildings 771 and 776/777). The building was originally intended to house new fabrication
processes associated with new plutonium weapons designs, but many of the existing foundry
and fabrication operations from Building 776/777 were transferred to Building 707 as the
result of a 1969 fire in Building 776/777.
In 1995, an inventory and an evaluation was conducted of facilities at the Rocky Flats
Plant for their potential eligibility for listing in the National Register of Historic
Places. The primary goal of this investigation was to determine the significance of the
Cold War era facilities at the plant in order to assess potential effects of the long-term
goals and objectives of DOE. These goals and objectives have not been finalized, but include waste cleanup and demolition.
Recommendations regarding National Register of Historic Places eligibility were developed
to allow DOE to submit a formal determination of significance to the Colorado State
Historic Preservation Officer for review and concurrence, and to provide for management of
historic properties at the plant.
From this determination and negotiations with the Colorado State Historic Preservation
Officer, the Advisory Council, and the National Park Service, a Historic American
Engineering Record project began in 1997 to document the plants resources prior to
their demolition. The plant was officially listed in the National Register of Historic
Places in 1997. The archives for the Historic American Engineering Record project are
located in the Library of Congress in Washington, D.C.
The plant is one of 13 DOE facilities that constitute the Nuclear Weapons
Complex, which designed, manufactured, tested, and maintained weapons for the U.S.
arsenal. The plant was established in 1951 to manufacture triggers for use in nuclear
weapons and to purify plutonium recovered from retired weapons. The trigger consisted of a
first-stage fission bomb that set off a second-stage fusion reaction in a hydrogen bomb.
Parts were formed from plutonium, uranium, beryllium, stainless steel, and other
A tense political atmosphere both at home and abroad during the Cold War years drove
U.S. weapons research and development. By the 1970s, both the U.S. and the Soviet Union
maintained thousands of nuclear weapons aimed at each other. These weapons were based on
submarines, aircraft, and intercontinental ballistic missiles. Both the North Atlantic
Treaty Organization and Warsaw Pact countries in Europe had small nuclear warheads called
theater weapons used as part of the Mutually Assured Destruction program. (The Mutually
Assured Destruction program acted as a deterrent in that if one side attacked with nuclear
weapons, the other would retaliate and both sides would perish.) The final nuclear weapons
program at the plant was the W-88 nuclear warhead for the Trident II missile. This mission
ended in 1992 when President Bush canceled production of the Trident II missile.
The plant was a top-secret weapons production plant, and employees worked with a
recently man-made substance, plutonium, about which little was known concerning its
chemistry, interactions with other materials, and shelf life. The Historic American
Engineering Record documentation effort focuses on four aspects of the plant and its role
in the Nuclear Weapons Complex: manufacturing operations; research and development; health
and safety of workers; and security.
|Chronology of Building 707:
||Construction of Building 707 began.
||The first plutonium operations in Building 707 began on May 25. Operations
focused on casting and fabrication of plutonium components and final assembly of the
||The Building 707 Annex (Building 707A) was constructed.
||The X-Y retriever used for handling and storing plutonium began operations in the
||Operations including metallurgy, fabrication, assembly, inspection, and
testing of plutonium and plutonium parts ceased in November following a Federal Bureau of
Investigation raid on the plant.
||Operations included removal of oxides from plutonium metal and repackaging
the cleaned metal; storage of removed oxides began under the new plant mission of
Building 707 became the primary plutonium fabrication building at the plant when
operations commenced on May 25, 1970. The design of Building 707 incorporated extensive
control and safety features, including the first-time use of inert atmosphere in the glove
boxes, primarily in response to two earlier fires (in Buildings 771 and 776/777). The
building was originally intended to house new fabrication processes associated with new
plutonium weapons designs, but many of the existing foundry and fabrication operations
from Building 776/777 were transferred to Building 707 as the result of a 1969 fire in
Building 776/777. The transferred operations were not changed significantly. Building 707A
was built in 1971 to accommodate plutonium casting and fabrication processes moved from
Building 776/777 as a result of the 1969 fire.
The Building 707 Complex was a manufacturing facility for fabrication of plutonium
parts, and assembly of parts made of plutonium and other materials into nuclear weapons
components. The major structures of the complex include Building 707, Building 707 Annex
(707A), and Building 708. Building 708 houses emergency generators and three brine chiller
systems for Building 707 temperature control and dehumidification in plutonium handling
areas. Other structures in the complex are a cooling tower, an electrical distribution
station, a process waste station, and outside storage tanks for inert gases, such as argon
Building 707 is located in the north-central section of the plant, within the protected
area and just south of Building 776/777. Building 707 is a two-story building with a
single-story section on the east side. The two-story portion is 160 by 464 feet. The
single-story section is 40 by 464 feet. The two-story portion of the building is 74,240 square
feet per floor and the single-story section is 18,560 square feet. A small basement in
Building 707 contains an additional 1,000 square feet.
Building 707 has precast, prestressed concrete exterior walls, supported on precast
concrete columns. The first floor is a concrete slab on grade. All floors in the
production areas are reinforced concrete finished with an epoxy coating designed to
facilitate decontamination. The roof is constructed of prestressed, precast concrete
twin-tee panels. There are no windows in the exterior walls.
The single-story portion of Building 707 contains office and support areas, and is
divided into three main sections. The northern section consists of offices, a conference
room, a data processing equipment room, restrooms, janitor closets, and an entrance lobby,
all opening into a corridor. An airlock separates non-plutonium handling areas from
plutonium production areas. The middle portion of the single-story section was used for
radiographic inspection. The radiography area consists of two vaults housing radiographic
inspection equipment and an adjoining support area. The southern section of the
single-story section houses a shipping and receiving area. This area contains production
storage, offices, shipping and receiving space, a waste drum counting and storage area, a
maintenance area, and two docks with airlocks opening to a recessed loading area under the
Building 707A, a freestanding two-story structure, is 104 by 125 feet and abuts the
northwest side of Building 707. It contains 13,000 square feet per floor. Although
Building 707A is a separate structure, with its own east wall, it is considered to be part
of Building 707. Operations within the two buildings were integrated.
Building 707/707A is divided into ten modules, which are separate rooms, sets of rooms,
or workstations, segregated from other non-plutonium production areas. Letters A-K are
used to designate the modules. There is no Module I.
The main floor of Building 707 is compartmentalized into eight side-by-side modules (A
through H) which contained one or more of the primary production operations. Each module
is 140 by 49 feet with an area of approximately 6,860 square feet. Modules A though E were
identical in size and shape, but contained various glove box configurations designed to
support the specific operation performed in each module. The main floor of Building 707A
is divided into two modules, Modules J and K, that contained plutonium foundry operations
and two plutonium storage vaults. One storage vault, on the north end of Module K, was
equipped with a remotely controlled, computerized, three-axis retriever (the X-Y
retriever). The basement room (under Module C) was used for filtering and storing
machining coolants and other process liquids.
Inert atmospheres were provided for the glove boxes and conveyors of Modules A, B, C,
D, E, F, J, and K to prevent the propagation of fire. An enclosed chain conveyor connected
glove box workstations in and between the modules. Leaded gloves were affixed to ports in
the equipment to allow operator access. Temperature and humidity controlled air was
provided to other plutonium handling areas.
Module F is divided into two areas, one for special assembly operations which required
specialized atmospheric controls, the other for final processing. The temperature,
humidity, and airflow in Module F were precisely controlled. The module has airlocks for
equipment and personnel, alarms, an escape door, and a tall equipment door. Downdraft
tables are equipped with a mesh screen work surface and high-efficiency particulate air
filters to draw air in the room toward the table, through the filter, and out through the
exhaust ventilation plenum. A conveyor line connects one of the downdraft tables to Module
Module G is divided into separate areas for offices, sub-assembly processes for
non-radioactive areas, inspection, and two laboratories (standards and nondestructive
Module H contains six high-pressure process chambers, an open process area, and a
storage vault. The storage vault is freestanding and does not form a part of the main
building structure. The vault is constructed of concrete to provide additional radiation
The second floor of Building 707 contains heating, ventilating and air conditioning
equipment, and air filtration systems. Some equipment, tanks, and pumps are also located
on the second floor. Utility equipment located on the second floor provides air
filtration, ventilation, and dehumidification to the modules and glove boxes. Two inert
atmosphere systems maintain a dry, inert atmosphere of nitrogen, with less than five
percent oxygen. Each system includes a separate exhaust plenum equipped with a four-stage,
high-efficiency particulate air filter. A standby filter is connected to the two plenums
to allow high-efficiency particulate air filters in either system to be changed without
interruption of service. The arrangement of the northern end of the two-story portion of
Building 707 is duplicated in Building 707A. Two production modules, J and K, divide the
first floor, and heating, ventilating, and air conditioning equipment is located on the
Operations in Building 707 included metallurgy, parts fabrication, inspection and
testing, assembly, and storage. Plutonium, particularly in finely divided forms, was
subject to oxidation and spontaneous combustion, and required a controlled environment for
processing and storage. Control was achieved by enclosing plutonium metal and associated
equipment within glove boxes and conveyors and by providing certain work areas with an
inert atmosphere to control the pyrophoric nature of plutonium. The general flow of work
and materials was from north to south within the building, starting with Modules A, J, and
K, then sequentially from Module B to Module H.
Modules A, J, and K: Modules A, J, and K were used for metallurgy, primarily casting and sampling of
plutonium metal. These modules contained casting furnaces, glove boxes, and casting molds
made of graphite and other metals. Operations were conducted in an inert atmosphere. The
primary difference between casting operations in Modules K and J were the types of molds
used: graphite molds were used in Module J, and molds made of other metals were used in
Module K. Ingots were sampled by breaking a small nodule off the side of the casting.
Limited casting operations were conducted in Module A. Other activities in this module
included sampling of cast ingots for analysis of chemical purity, and removal of plutonium
oxides and other impurities from the casting molds.
The casting process created feed ingots and War Reserve ingots of plutonium metal.
Materials used for the creation of feed ingots included plutonium buttons from recovery
processes, briquettes, and scrap plutonium metal. The first casting process created the
feed ingot, which was then sampled. The sample was transferred to Building 559 and
analyzed for chemical composition and purity. Production control personnel maintained all
records of ingot composition, and used this data to calculate the precise feed ingot
mixture that would produce a War Reserve ingot of specific purity. The second casting
process used this feed ingot recipe to create the War Reserve ingot. The War Reserve ingot
was used to fabricate weapons components, the purity of which was identified by design
specifications. Samples were taken to verify the chemical makeup of the War Reserve ingot
The casting process, conducted in a vacuum, consisted of weighing the metal, placing it
in tantalum crucibles, and melting it in one of four electric induction furnaces. Molten
metal was poured into graphite, tantalum, or erbium oxide-coated stainless steel molds to
form ingots. Although four furnaces were present in Module K, only two were used during
routine casting operations. Rejected ingots from casting in Modules A, J, and K were cut
with a shear press within a glove box and returned to the X-Y retriever for storage.
Module B: Plutonium War Reserve ingots cast in Modules A, J, and K were
rolled, formed, and heat-treated in Module B under an inert atmosphere. War Reserve ingots were rolled to a specified thickness, and then moved to another glove
box where shapes were cut in a blanking press. Cut blanks were sent to adjacent glove
boxes for thermal treatment (annealing and homogenizing). Following thermal treatment,
blanks were formed into hemi-shells (1/2 shells) in a hydroform press. After forming, the
parts were annealed and measured on a density balance. A percentage of the parts were
selected for further quality assurance evaluation. Scraps left from cutting were cut into
smaller pieces in the same glove box, placed in a container, and sent to the briquetting
process in Module C.
Module C: Activities in Module C were conducted in an inert atmosphere. The module was used for
final machining of plutonium parts and also contained equipment for the briquetting
process. Glove boxes within Module C contained lathes, mills, a drill box, a
high-precision drill press, cleaning solvents, and a hydraulic press. Machining operations
included jig boring, slot cutting, and threading. All tools, gauges, and fixtures remained
within the glove boxes for the useful life of the device and were removed only for
disposal. When machining operations were completed, the parts were cleaned, degreased, and
stored to await assembly.
The briquetting process was used to generate hockey-puck-sized briquettes of plutonium
metal scrap. Machine turnings and scrap from the blanking press were cleaned in a solvent
bath to remove cutting oils and then pressed into small briquettes. These briquettes were
returned to the foundries for casting of feed ingots.
Module D: In Module D, each machined part was marked with a serial number, cleaned, weighed, and
inspected. As part of the cleaning process, parts were also repeatedly wire brushed to
remove oxides. Completed parts were transferred to Module E by a chain conveyor.
Module E: In Module E, plutonium parts were welded with electron beam welders in glove boxes,
then inspected for leaks using nondestructive testing methods. These methods included
radiography x-ray examination of plutonium parts to identify structural flaws; eddy
current testing on plutonium parts to check the depth of weld penetration; and weld
scanners and fluorescent dye penetrant processes to qualify welds and detect minute cracks
and voids in parts. The washing, welding, and leak detection processes in Modules D and E
were repeated several times.
Module F: Module F contained an assembly area referred to as the super-dry room, where plutonium
parts were assembled and tested. The super-dry room provided space for special assembly
operations that required precisely controlled conditions of humidity, temperature, and
airflow. As part of the assembly process, an outer metal casing was welded onto the
plutonium components. One area of the super-dry room was divided into two compartments,
each was provided with a downdraft table. One of the downdraft tables opened into the end
of a conveyor line that crossed over Module E. At this downdraft table, uncoated plutonium
parts and other parts from previous glove box operations were assembled into units that
could be safely transported, processed, and stored outside the protection of a glove box.
Leak testing was conducted on stainless steel and beryllium parts. Each part was placed
on one of ten pump-down tables and vacuum was exerted on the part to check for leaks and
to remove moisture. The encased parts were then transferred to Module G for further
Module G: Activities in Module G included brazing, machining, nondestructive testing, and
non-plutonium parts assembly and disassembly. Plutonium parts encased in other metals were
brazed under vacuum. The machining process used two lathes inside B-boxes (similar to lab hoods) and
a milling machine. Subassembly of non-radioactive parts occurred in a portion of the
Rejected aluminum, stainless steel, and beryllium parts were also disassembled in
Module G and either recycled or processed for disposal. Glove boxes were not used in this
Module H: Assembly processes in Module H included brazing and high-pressure assembly whereby
parts comprised of various metals including beryllium, plutonium, and uranium were bonded
together under pressure. Final assemblies were transferred to Building 991 for eventual
Testing and Inspection: Individual parts, subassemblies, and assemblies were inspected and tested throughout
the metallurgical machining and assembling operations to ensure that specifications were
met. Inspection involved dimensional inspection (measuring). Testing processes were both
nondestructive and destructive. Precision hand and electronic gauges, scales, rings,
optical- and computer-assisted instruments, and laser beam instruments were used during
dimensional inspections to verify that directly measurable dimensions were within
specified tolerances. Parts were matched for physical and dimensional characteristics. Nondestructive testing was used to inspect interior characteristics or properties of a
part or assembly. The techniques most commonly used were radiographic x-ray examination,
ultrasonic acoustic emission, and eddy current scanning. Other nondestructive
measurement methods included weight and density determinations and leak tests. Radiography
detected cracks, voids, and gaps in parts and assemblies. These testing techniques
identified structural flaws, weld depth, minute cracks, voids, and gaps. Vacuum tests were
conducted on plutonium, stainless steel, and beryllium parts to check for leaks and to
remove moisture and other impurities.
Destructive testing was used to verify the chemical content and the physical integrity
of a part or assembly. Parts and assemblies were subjected to gravity force analyses, tensile strength, stress, and vibration testing. Parts were also cored and sawed for
spectroscopy and chemical analyses.
Assembly: Assembly included such operations as machining, cleaning, matching parts, brazing,
welding, heating under vacuum for trace contaminant removal, marking, weighing,
monitoring for surface contamination, and packaging for shipment. Inspection and testing
processes occurred throughout the assembly process. Parts were matched for physical and
dimensional characteristics, assembled, then welded or brazed into subassemblies. The
subassemblies and additional parts were cleaned, physically assembled, welded, machined to
the required contour, and marked. The assembled parts were subjected to final processing
steps, final testing and inspection and then stored to await shipment.
Storage: Several locations in Building 707 were used to store nuclear and nonnuclear materials.
Materials stored included raw materials needed for casting, feed ingots, War Reserve
ingots, parts cast within the building, and finished components.
The X-Y retriever, which began operations in 1971, was housed in Module K, and was used
to sort and retrieve plutonium metal for distribution to other processes in Building 707.
Using the X-Y retriever, operators retrieved plutonium metal from storage and conveyed it
to the X-Y shuttle area where it was cut and weighed. The cut pieces were then conveyed to
Modules A, J, or K for casting, or Module B for rolling and forming. Rooms 141 and 142 in
Module J (the J Vault) were used for storage of oxides, plutonium buttons received from
other DOE facilities, and to some extent, Building 771 molten salt extracts.
Support Operations: Support groups assigned permanently to Building 707 included departments common to all
process buildings, such as radiation monitoring, utilities, maintenance, custodial, tool
crib, and industrial engineering. Support groups unique to Building 707 included several
manufacturing technical support groups, production control, process material control,
final product certification, and DOE inspection. The production engineering support
group was responsible for troubleshooting equipment problems, coordinating appropriate
repairs, utilizing maintenance and assistance from the research and development group,
ensuring compliance with specifications and adherence to production schedules, tracking
production programs, and providing input for new production systems. The production
foreman was responsible for tracking worker training and new worker indoctrination, and
provided input to production engineering regarding production schedules and new production
The metallurgical support group was responsible for administration of plutonium metal
used for casting, scrap plutonium metal, and operation of a control system for laboratory
analysis data on plutonium metal.
Plutonium Recovery: Plutonium was a rare substance and supply seldom kept up with demand. Only a fraction
of the feed plutonium that entered Modules A, J, or K came from Module D as machined
production parts. Every effort was made to salvage the excess material. Plutonium fines,
chips, and scraps generated from the parts fabrication processes were collected in cans at
each workstation or individual machine. These fines, never leaving the inert atmosphere
system, were transferred via the chain conveyor to a workstation in Module C where the
material was compressed into briquettes for later use. Residues produced by the casting
operations were burned to oxide, packaged, and transferred to residue processing
operations in Building 771 for plutonium recovery. This thermal stabilization process was
used to convert pyrophoric plutonium to a non-pyrophoric plutonium oxide that could be
more safely handled.
Operations Since 1989:
Following a raid by the Federal Bureau of Investigation in 1989, production at the
plant was curtailed. In 1992, the mission of the plant was officially changed from weapons
component production to environmental restoration and waste management. At that time, the
mission of Building 707 was changed to plutonium stabilization operations.
Colorado Department of Health. Project Tasks 3 & 4 Final Draft
Report. Reconstruction of Historical Rocky Flats Operations and Identification of Release
Points (1992), by ChemRisk. Rocky Flats Repository. Golden, Colorado.
Sasa, Paul, employed at the plant since September of 1978 by the site contractor.
Personal communication, November 1997 and January 1998.
United States Department of Energy. Site Safety Analysis Report, Building 707 (1987),
by EG&G Rocky Flats, Inc.
Rocky Flats Repository. Golden, Colorado, 1987.
United States Department of Energy. Historical Release Report (HRR)- Building
Histories (1994), by EG&G. Rocky Flats Plant Repository. Golden, Colorado, 1994.
United States Department of Energy. Final Cultural Resources Survey Report (1995), by Science Applications International Corporation. Rocky Flats Repository. Golden,
D. Jayne Aaron, Environmental Designer,
engineering-environmental Management, Inc. (e2M), 1997. Judith Berryman, Ph.D.,
Archaeologist, e2M, 1997.
Index to Photographs
Located in the north-central section of the plant, within the protected area, just
south of Building 776/777, Golden, Vicinity, Jefferson County, Colorado.
Photographs CO-83-M-1 through CO-83-M-20 were taken by various site
photography contractors, dates are indicated in parentheses.
CO-83-M-1 – View of the control room for the X-Y retriever. Using the X-Y retriever, operators retrieved plutonium metal from the plutonium storage vaults (in Module K) and conveyed it to the X-Y shuttle area where it was cut and weighed. From the shuttle area the plutonium was conveyed to Modules A, J, or K for casting, or Module B for rolling and forming. (5/17/71)
CO-83-M-2 – View of interior of X-Y retriever. The X-Y retriever was housed in Module K and was used to sort and retrieve plutonium metal from a storage vault for distribution to other processes in Building 707. (11/29/88)
CO-83-M-3 – View of chainveyor. An enclosed chain conveyor connected glove boxes within and between modular work areas. Leaded gloves were affixed to ports along the chainveyor pathway to allow operator access. (1/25/93)
CO-83-M-4 – View of plutonium canister on chainveyor. Scrap plutonium was collected into cans at individual workstations. The cans were transferred via the chain conveyor to a workstation in Module C where the material was compressed into briquettes for later use. (6/20/93)
CO-83-M-5 – View of a glove box firewall detail. The firewall was a safety feature to prevent the spread of fire between interconnected glove boxes. Plutonium is pyrophoric and may ignite in the presence of oxygen. (5/8/70)
CO-83-M-6 – View of Building 707 interior. Glove box workstations are being constructed for foundry processes in Module A. (10/6/69)
CO-83-M-7 – View of the interior of Module A, one of the three plutonium foundry modules. Although casting furnaces were present in the module, it was used primarily for sampling cast plutonium. (11/6/73)
CO-83-M-8 – View of foundry induction furnaces, Module J. The foundry casting process was conducted in a vacuum. Plutonium metal was melted in one of four electric induction furnaces to form ingots.
CO-83-M-9 – View of bag-in-bag-out port in Module J, associated with plutonium casting processes. (2/98)
CO-83-M-10 – View of Module B, installation of a hydraulic press. The press will eventually be connected to a glove box line. (9/29/69)
CO-83-M-11 – Detail view of a lathe in Module C. The lathe was used for final machining of trigger components. Lathe turnings were collected from the back of the lathe for disposal. (2/22/84)
CO-83-M-12 – View of the inspection Module D. The glove box in the forefront of the photograph contains a drill press; other glove boxes are used for parts inspection. (5/70)
CO-83-M-13 – View of a vacuum chamber and welding equipment in Module E. Parts were welded under a vacuum to prevent corrosion. (11/6/73)
CO-83-M-14 – View of downdraft tables in the super dry room of Module F. Air is drawn toward the downdraft table, through the mesh-screen work surface, and out of the building through a bank of filters. At the downdraft table, uncoated plutonium parts and other parts from previous glove box operations were assembled into units that could be safely transported, processed, and stored outside the protection of a glove box. (11/6/73)
CO-83-M-15 – View of Module H, the high-pressure assembly area. Processes in this module occurred under high pressures and temperatures. (5/70)
CO-83-M-16 – View of the stationary operating engineer control panel installation. The panel controls air-handling equipment and air pressure within the building. (10/6/69)
CO-83-M-17 – View of air lock entry door. Banks of air filters are visible to the sides of the doors. The building was divided into zones by airlock doors and air filters. Air pressure differentials were maintained in the zones, such that airflow was progressively toward areas with the highest potential for contamination. (9/24/91)
CO-83-M-18 – View of the second floor of Building 707. Air exhaust fans are used to maintain pressure differentials within the building. (5/70)
CO-83-M-19 – View of second floor, southern portion of Building 707. The storage tanks contain machine coolants and solvents used in fabrication processes. (5/70)
CO-83-M-20 – View of low-pressure pumping equipment on the second floor of Building 707. The equipment maintains proper coolant pressure in machines. (5/70)