TA-18 Brief Description

4.12.1 Site Description
TA-18 [Table 4-10 and Figure 4-12 (index map of 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 normally open to the public but may be closed while hazardous materials
are being moved or for other security or safety reasons. TA-18 is referred to as the Los Alamos
Critical Experiments Facility (LACEF). It is also known as Pajarito Laboratory or Pajarito Site. The
TA is a restricted area surrounded by a security fence with several additional layers of security and
LACEF, which has operated since 1946, is the last general-purpose nuclear experiments facility in
the US. It supports a variety of programs that range 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. Currently, the primary purposes of LACEF are the design, construction,
research, development, and application of critical experiments. In addition to criticality
work, activities at LACEF include teaching and training related to criticality safety and applications
of radiation detection and instrumentation.

4.12.2 Facilities Description
At present, the LACEF complex consists of 10 operating machines that fall into roughly five types
of assemblies:
• benchmark critical assemblies,
• assembly machines used to remotely assemble critical experiments,
• solution assemblies in which the fuel is a fissile solution,
• prototype reactor assemblies that operate 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.


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