Rocky Flats Plant, Final Assembly and Shipping Facility
HAER No. CO-83-U (Rocky Flats Plant, Building 991)
Rocky Flats Environmental Technology Site, Highway 93, Golden, Jefferson
County, Colorado. Building 991 is located in the eastern portion of the Rocky Flats Plant. The building is located south of Spruce Avenue, east of Tenth Street, and north
of Central Avenue.
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 991, the first building constructed at the plant, was designed for shipping and receiving and for final assembly of weapon components.
Plutonium, enriched uranium, and depleted uranium components fabricated on-site, along
with components manufactured from the Hanford Site and Oak Ridge Reservation were
assembled into final products, inspected, tested, and placed back in storage prior to
off-site shipment in Building 991. Administrative services for the plant were also carried
out in Building 991 until Building 111 was completed in 1953.
Building 991 is a rectangular, concrete, one-story structure
encompassing approximately 40,600 square feet (35,400 square feet on the first floor, and
5,200 square feet in the basement). Three major additions have been built since the
original construction in 1952: a loading dock on the west side in 1957, a radiography
vault in the northwest corner in 1959, and a covered loading dock and storage area on the
southeast side in 1964.
The building is set on a concrete foundation with a partial basement. The foundations
are comprised of footings (individual spread footings, combined footings, and wall
footings) and foundation walls.
The exterior walls and intermediate concrete columns constitute the structural framing
for the building. The exterior walls contain reinforced concrete, varying in thickness
from 12 to 18 inches. The building walls vary in height from 14 feet on the south, to 27 feet in
the center, to 18 feet on the north side. Interior bearing walls are reinforced concrete. The
walls of the covered dock and shop located at the eastern end of the structure are
constructed of reinforced concrete. Four feet of the walls are above-grade.
Depending on the location and function, four different roof types are present. These
roof types include a reinforced concrete slab supported by concrete beams, a structural steel
roof frame covered with corrugated asbestos, an open-web steel with metal decking, and
reinforced cement. Ceilings consist mostly of the undersides of the various roofs.
Doors in the building are either hollow metal or wood. The south wing of the structure
contains the only windows (multi-paned within metal sashings).
Building 991 is the main structure of the 991 Complex. Additional structures in the
complex include three underground tunnels (Tunnels 996, 997, and 998), four underground
vaults (Vaults 996, 997, 998, and 999), a guard post (Building 992), an emergency
generator building (Building 989), and a filter plenum building (Building 985). Vaults
996, 997, 998, and 999 are connected to the building via Tunnels 996, 997, and 998.
Tunnels and vaults in the complex are maintained at a slight negative air pressure by the
building heating, ventilating, and air conditioning system.
Support operations located in Building 991 included laboratories, utilities, and
maintenance operations. The Metallurgical Laboratory, located in Rooms 109, 110, and 111,
was used to perform metallographic analysis. A modular laboratory was located in Room 143.
This area supported the inspection of glove box gloves and supplied air-breathing
garments. Maintenance alarms are located in Rooms 140 and 141. The Utility Group,
located in Rooms 130 and 137, operated the building ventilation system.
In terms of operation, the building was divided into the following areas: north of the
main floor, center section, and south side.
North of the Main Floor: The north side of the main floor contained a storage area for
packed plutonium, enriched uranium, and depleted uranium components fabricated at the
plant and received from other U.S. Department of Energy (DOE) facilities; packaged final
assemblies of nuclear weapon triggers; and incoming raw nuclear materials certified for
distribution. Room 150 was used as a storage vault for radioactive materials; Room 158 was
used for document storage.
Center Section: The center section of the main floor, between the north and south
corridors, contains a covered loading dock at either end. The east loading dock has a
small room for maintenance storage. Specialized rooms within the building include: Room
130, which houses most of the building utility equipment; Room 134, which contains
facilities for metal machining and ultrasonic nondestructive testing; Room 137, the
boiler room; and Room 166, which houses a nondestructive test area for barrels, liners,
and waste boxes used for shipping.
South Side: The southern end of the building contains administrative offices,
plant protection and safe secure transport personnel offices, and nondestructive testing
The plant was originally divided into four separate areas: Plant A
(Building 444, depleted uranium), Plant B (Building 881, enriched uranium), Plant C
(Building 771, plutonium), and Plant D (Building 991, assembly and shipping). Building
991, constructed between 1951 and 1952, was the first to be completed.
Building 991 was designed for shipping and receiving and for final assembly of weapon
components. Plutonium, enriched uranium, and depleted uranium components fabricated
on site, along with components manufactured from the Hanford Site and Oak Ridge
Reservation were assembled into final products, inspected, tested, and placed back in
storage prior to off-site shipment in Building 991. Administrative services for the plant
were also carried out in Building 991 until Building 111 was completed in 1953.
Initially, radioactive components were coated in nickel or encased in plastic allowing
assembly of the early concept design products in open rooms, not in enclosed glove boxes
or B-boxes (similar to a lab hood). In 1957, production began on a new weapon design,
requiring changes in the amount of materials used in the trigger, the amount of machining
and handling required, and the need for tighter controls. Because of the new design, final
trigger assembly took place in the newly constructed Building 777. Assembly of older
uranium-based weapons continued in Building 991 until the 1960s. A limited number of
plutonium-based triggers may have been assembled in Building 991 during the early 1960s.
After 1957, the mission of Building 991 focused on shipping, receiving, and storage.
Materials handled included special nuclear, nonradioactive raw, and classified materials,
other metal components, partially finished products, purchase order items, special order
items, samples, instruments, and documents. All radioactive materials received and stored
in Building 991 were in U.S. Department of Transportation, DOE, or intraplant-approved
shipping containers. For a brief period of time, between 1975 and 1976, shipping was moved
to Buildings 439 and 440. Due to security concerns, shipping was moved back to Building
991 after 1976.
In addition to material shipping, receiving, and storage, a number of research and
development projects were conducted in Building 991 from the 1960s to the mid-1970s. These
projects included radiation studies, beryllium coating processes, and an
explosives-forming project. Most special projects and research and development operations
were moved out of the building by 1976.
Building 991 was used to test the quality of nonnuclear raw material and nonnuclear
nonclassified parts fabricated by offsite vendors. A metallography laboratory was used
for the testing. In the mid-1970s, Building 991 took over storage and inventory functions
from Building 881 for these nonnuclear raw materials and nonnuclear, non-classified
parts. In the late 1980s, handling of nonclassified materials and parts was moved to
Buildings 130 and 460. Materials and parts ready for assembly were moved directly to
Until the mid-1980s, materials were shipped and received from the eastern dock areas
(Room 166). The west dock was added in the mid-1980s to provide a covered shipping area
specifically designed for the safe secure transports used to ship production materials.
Until 1994, when a special loading dock was added to Building 371, Building 991 had the
only shipping/receiving dock at the plant capable of handling off-site shipments of
special nuclear and classified materials. The building also housed nondestructive testing
operations and other support operations. Radioactive and nonradioactive raw materials,
special order items, packaging items, components, and samples were stored in the Building
991 vaults. All nonnuclear and nuclear materials sent to Building 991 were handled in
Rooms 170 (shipping dock) and 134. Primary materials handled included 55-gallon and
30-gallon drums of uranium and plutonium parts from off- and on-site parts.
The final activity in Building 991 was waste storage.
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.
United States Department of Energy. Public Affairs, n.d. Tour Information, Rocky
Flats Facilities, Golden, Colorado: DOE, Office of Communications and Economic
United States Department of Energy. Historical Release Report (HRR) (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,
Weaver, Jack, employed at the plant since 1961 by the site contractor. Personal
communication, January 1998.
D. Jayne Aaron, Environmental Designer, engineering-environmental
Management, Inc. (e2M), 1997. Judith Berryman, Ph.D., Archaeologist, e2M,
Index to Photographs
Located on the eastern portion of the plant site, south of Spruce Avenue,
east of Tenth Street, and north of Central Avenue, Golden Vicinity, Jefferson County, Colorado.
Photographs CO-83-U-1 through CO-83-U-5 were taken by various site photography
contractors, dates are indicated in parentheses.
CO-83-U-1 – Aerial view of Building 991, looking west. Building 991 was designed for shipping and receiving and for final assembly of weapons components. (6/26/91)
CO-83-U-2 – View of interior of Building 991 loading dock area. The dock provided a covered shipping area specifically designed for the safe secure trailers that were used to ship production materials. (6/11/87)
CO-83-U-3 – View of integrity-testing equipment using cryogenic baths in Building 991. (6/7/68)
CO-83-U-4 – View of ultrasonic testing equipment in Building 991. This equipment nondestructively tested weapons components for flaws and cracks. (9/11/85)
CO-83-U-5 – View of the heating elements and the vacuum gauge of a pump-down station in Building 991. The pump-down station removed out-gases from inside the triggers. (9/26/61)