Los Alamos National Laboratory Technical Area 18 - Pajarito Site

TA-18 is located in an arid canyon (Pajarito Canyon) about 4 mi (6.4 km) southeast of TA-3 on a DOE-owned and -controlled roadway (Pajarito Road). This roadway is closed to the public. TA-18 was referred to as the Los Alamos Critical Experiments Facility (LACEF). It was also known as Pajarito Laboratory or Pajarito Site. The TA was a restricted area surrounded by a security fence with several additional layers of security and safeguards. LACEF, which has operated since 1946, is the last general-purpose nuclear experiments facility in the US. It was closed in 2007. It supported a variety of programs that ranged from national security programs, such as the Nuclear Emergency Search Team, Strategic Defense Initiative research, and Strategic Arms Reduction Treaty verification research, to development of instrumentation for nuclear waste assay and high-explosives detection. The primary purposes of LACEF were the design, construction, research, development, and application of critical experiments. In addition to criticality work, activities at LACEF included teaching and training related to criticality safety and applications of radiation detection and instrumentation.
The LACEF complex consisted of 10 operating machines that fell into roughly five types of assemblies:
• benchmark critical assemblies,
• assembly machines used to remotely assemble critical experiments,
• solution assemblies in which the fuel was a fissile solution,
• prototype reactor assemblies that operated at low power without the need for heat rejection systems, and
• fast-burst assemblies for producing fast neutron pulses.
A significant feature of critical assemblies is that they are designed to operate at low power and at temperatures well below phase temperatures. This key feature sets critical assemblies apart from normal reactors. Critical assemblies therefore require no forced-convection cooling; thus, a potential source of stored energy is eliminated, as is the potential for the spread of fission products.
Four buildings in TA-18 were categorized as Hazard Category 2 nuclear facilities. These buildings are the Kiva 1 (Building 23), Kiva 2 (Building 32), and Kiva 3 (Building 116)—all of which were critical assembly buildings—and the Hillside Vault (Building 26). Each kiva was surrounded by a security fence, and entrance to the kivas was controlled by several layers of security and safeguards. Each kiva contained its own storage vault equipped with metal lockers for storing SNM containers. Permissible load limits were posted at the vaults. Because the vaults had no outside entrances, personnel had to enter through the kiva building.
The kivas were constructed of reinforced concrete and masonry block and were designed to minimize fire risks. Each kiva was equipped with a traveling crane in the main assembly area. Gas-fired furnaces were used for heating, and the building was equipped with forced-draft ventilation. Each kiva has rooms for storing SNM, which are locked and show posted load limits. Fire-fighting equipment, consisting of an automatic sprinkler system and a fire alarm system, was provided in the control rooms.
Electrical power, water, and sewer were the only systems shared by the kivas. Loss of power to LACEF deenergized all control circuits, aborted the operation and thereby prevented startup of the reactor or experiment. Sharing common systems could not result in a critical assembly incident. Because critical assemblies do not need to be cooled, no emergency power was needed to prevent exceeding fuel temperatures at which damage occurs.
Each kiva was surrounded by a physical security boundary. The area inside the security boundaries was evacuated before remote operation began, and automatic signal alarms forewarned anyone who was overlooked.