Rocky Flats Plant, Critical Mass Laboratory
HAER No. CO-83-A
(Rocky Flats Plant, Building 886)
Rocky Flats Environmental Technology Site, Highway 93,
Golden, Jefferson County, Colorado. Building 886 is in the southeast section of the
industrial area of the Rocky Flats site, located at the intersection of Central Avenue and
Date of Construction: 1964.
Fabricator: Stearns-Rogers Corporation, Denver, Colorado.
Present Owner: U.S. Department of Energy (DOE).
Present Use: Inactive (experiments ceased in 1987).
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 on the U.S. This building was one of five critical mass laboratories in the nation
that performed criticality measurements on a variety of fissile materials. The purpose of
these experiments was to set safety standards for fissile material safety. These safety
data have been used worldwide.
The Rocky Flats Plant had unique site operations support organizations due to
the handling of large amounts of radioactive materials. One such organization was the
Nuclear Safety Group. The plant's Critical Mass Laboratory conducted experiments directly
tied to plant operations.
In 1995, an inventory and an evaluation of facilities at
the plant for their potential eligibility for listing in the National Register of Historic
Places was conducted. 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 yet been formalized, 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, an Historic American
Engineering Record project began in 1997 to document the plants resources prior to
their demolition. 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 nuclear
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 materials.
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, its interactions with other materials, and its shelf-life. The Historic
American Engineering Record documentation effort focused 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 886:
|| Construction completed.
||January 28 technical readiness meeting held, permission to conduct
criticality experiments granted.
||Office space added to northeast corner of building. Fissile metal storage room
extended to southeast side of building to double storage space. Several programs for the
Nuclear Regulatory Commission performed on a contract basis, in addition to supporting the
||Office trailer was added to the northeast corner.
||October last criticality experiment conducted.
||Plant curtailed production.
||Plant mission was changed to environmental restoration and waste management.
||Nuclear fuel removed from Building 886.
The continued presence of large quantities of fissile material in numerous forms at the
Rocky Flats Plant made it necessary to maintain an active criticality safety program. A
Nuclear Safety Group was formed in 1953 to perform the criticality experiments. At that
time, the group did not have its own facility. In those early years, the group performed
subcritical experiments in the areas in which the materials were handled, using the actual
materials which went into the production of the product. The experimenter would set up the
production materials in various arrays to perform multiplication-type experiments
(in situ experiments, which were always subcritical) and to measure critical
nuclear conditions with respect to safe geometries for various kinds of production
vessels, spacing parameters, shipping containers, and other items. Once Building 886 was
commissioned, the Nuclear Safety Group conducted its work there. Since that time, the
Nuclear Safety Group conducted about 1,700 critical mass experiments using uranium and
plutonium in solutions (900 tests), compacted powder (300), and metallic forms (500).
Nuclear criticality safety can be defined as anything associated with avoiding an
accidental nuclear criticality event. A criticality is an instantaneous nuclear fission
chain reaction caused when too much fissile material is placed within too small an area. A
criticality event would not result in a nuclear explosion, but could liberate a
large amount of energy and high levels of radiation. While criticality events can vary
widely in power level, the amount of radiation that could be generated in a criticality
could be fatal to nearby personnel. Since the beginning of the nuclear industry to 1967,
there have been a few dozen nuclear criticality accidents nation-wide. These extensively
studied incidents, none of which occurred at the Rocky Flats Plant, caused eight deaths and,
in some cases, resulted in property damage (Rothe).
The Building 886 (originally called Building 86) complex consists of: Building 886
(Critical Mass Laboratory); Building 880 (storage facility); Building 875 (filter plenum
facility); and an underground tunnel containing ventilation ducts that connects Building
886 to Building 875. Building 886 is rectangular with a shallow-pitched gabled roof. Two
shed-roof wings extend from its northeast and southeast corners. A 37-foot tall concrete
windowless building (room 101) is attached to the south. A temporary pre-fabricated
trailer housing offices is attached to the northeast wing by a breezeway. Building 886 is
10,360 square feet on a single level.
Building 886 consists of three areas: the Radiological Controlled Area; office space;
and a small electronics and machine shop. The Radiological Controlled Area is comprised of
three rooms and a hallway. Almost all criticality experiments were conducted in room 101,
the assembly room. The ceiling is 2 feet thick. Room 102, a storage vault, was constructed
in the mid-1970s to meet the U.S. Department of Energy requirements for a special nuclear
material vault. Both rooms, 101 and 102, have double reinforced concrete walls integrally
case to the ceiling. Room 103, the mixing room, is a fissile solution storage area; three
walls are reinforced concrete, and the west wall is cinder blocks. The remainder of the
load bearing walls in Building 886 are constructed of cinder blocks.
The primary mission of Building 886 was to perform criticality
measurements on a variety of fissile material configurations in support of plant
activities. The criticality experiments and measurements were performed in order to
establish criticality limits and ensure the safe handling and processing of fissile
materials. A simplified sequence of events in performing a typical critical mass
measurement involved removing the fissile material from storage, placing it in one of the
reactivity addition devices, operating the device remotely until criticality was achieved,
measuring the slightly super critical parameters, reversing the operation of the device to
slightly subcritical and measuring these parameters, completing the reversal to well below
subcritical, and returning the fissile material to storage (Rothe). This effort supported
the plant's activities and assisted the Nuclear Regulatory Commission in setting of
industry safety standards. The measurements were essential to validate computer models
that were, in turn, used to establish nuclear criticality safety limits now called
Criticality Safety Operating Limits.
The experiments were conducted in a manner to control the approach to criticality, for
example, by varying the distance between pieces of metal and depth of solutions. Only
rarely were the radiation levels such that it was not possible to directly touch the
fissile material and testing apparatus immediately after the experiments. The experiments
conducted in Building 886 generally involved power levels generated of no
more than 10 milliwatts for no more than one hour. Approximately half of the experiments
conducted in Building 886 actually achieved criticality.
Highly enriched uranium was introduced into the building in the summer of 1965 and the
first experiments were performed in September 1965. Since then, the building was used
to perform experiments on enriched uranium metal and solution, plutonium metal, low
enriched uranium oxide, and several special applications. After 1983, experiments were
conducted primarily with uranyl nitrate solutions, and did not involve solid materials.
Experiments to validate the safety parameters for the storage of fissionable solutions
in Raschig Ring tanks resulted in the design of two substitute storage tank
configurations: the Annular tank and the Poison Tube tank (Rothe). These designs allowed
for more economical solution testing with no decrease in safety. The Poison Tube tanks
were not used at the Plant due to the change in the overall site mission; however, they
have been used at other DOE facilities. Experiments were also conducted to validate the
cross-sections and usefulness of materials (i.e., concrete, polyvinyl chloride) used at
the Plant. Data generated from decades of experiments at the plant is still being used to
set new safety standards and validate computer models.
Rothe, Dr. Robert E., nuclear criticality experimenter in nuclear
safety employed at the plant since August 1964.
Personal communication, 1997.
United States Department of Energy, Public Affairs. n.d. Tour Information. Rocky
Flats Facilities. U.S. Department of Energy, Office of Communications and Economic
Development. Rocky Flats Repository. Golden, Colorado.
United States Department of Energy. Mission Transition Program Management Plan, Site
Support Facilities Element. Appendix A-1, A-2, A-3, A-5 Revision 7, A-4 Revision 4 (1992),
by EG&G. Rocky Flats Plant Repository,
Golden, Colorado, 1992.
United States Department of Energy. Reconstruction of Historical Rocky Flats
Operations and Identification of Release Points: Final Draft Report (1992), by
ChemRisk. Rocky Flats Repository. Golden, Colorado, 1992.
United States Department of Energy. Basis for Interim Operations, Building 886,
Revision A (Daft) (1995), by EG&G.
Rocky Flats Repository. Golden, Colorado, 1995.
United States Department of Energy. Final Cultural Resources Survey Report, Rocky
Flats Environmental Technology Site, The Industrial Area, Rocky Flats Repository.
Golden, Colorado, 1995.
D. Jayne Aaron, Environmental Designer,
engineering-environmental Management, Inc. (e²M), 1997. Alexandra Cole, Architectural
Historian, Science Applications International Corporation, 1997.
Index to Photographs
Located at the intersection of Central Avenue and 86 Drive, Golden Vicinity, Jefferson County, Colorado.
Photographs from the Rocky Flats Environmental Technology Site Archives. Photographs
were taken by various site photography contractors.
CO-83-A-1 – View of the west elevation, looking east, of Building 886 while under construction in 1964. On the right of the photograph is the criticality assembly room, Room 101, constructed of double reinforced concrete walls integrally cast to the 2-feet-thick ceiling. In the foreground is the 19-foot-deep pit area intended to house waste solution storage tanks. Only one tank was used to store wastewater.
CO-83-A-2 – View of the experiment control panel in 1970. The nuclear safety group conducted about 1,700 critical mass experiments using uranium and plutonium in solutions (900 tests), compacted powder (300), and metallic forms (500). All 1,700 criticality assemblies were controlled from this panel.
CO-83-A-3 – View of the depression pit in Room 103, in 1965, wherein fissile solution was stored. This photograph shows the uranium solution tanks on the left and the plutonium system on the right. No plutonium solution was ever stored in Building 886.
CO-83-A-4 – View of Room 103 in 1980. Six of the nine uranium nitrate storage tanks are shown. Highly enriched uranium was introduced into the building in the summer of 1965, and the first experiments were performed in September 1965. Experiments were performed on enriched uranium metal and solution, plutonium metal, low-enriched uranium oxide, and several special applications. After 1983, experiments were conducted primarily with uranyl nitrate solutions and did not involve solid materials.
CO-83-A-5 – View of the inspection port on the side of a typical uranium solution storage tank in 1996. Inside the tank are Raschig rings, which act as neutron absorbers to control fission and keep the solution at subcritical.