Radiological Safety Traning for Uranium Facilities
Module 105 - Criticality Safety
enrichment of 235U (i.e., the concentration of 235U in relation to other uranium isotopes),
the greater t he opportuni ty for critic ality.
The volume of material in which fissile material is in solution can also play an important
role in preventing criticality. For a given concentration or density of fissile material, the
amount of fissile material will increase as the volume increases.
Neutron interaction in an array of containers of fissile material is dependent upon
geometric factors, including: size, shape, and separation of the containers, as well as the
size and shape of the array. Materials that may surround or be intermingled with the
containers are also important. A close-packed array may be come critical if flooded with
water wh ich will thermali ze neutro ns. Also, a less cl osely-pac ked array may become
critical if the water is removed, allowing less neutron absorption to take place.
Safety Policies and Controls
Achieving criticality involves bringing together many factors that promote a sustained nuclear
chain reaction. To avoid criticality, one should be aware of the conditions that would promote a
criticality for the particular materials they encounter, and avoid those conditions that promote
General Criticality Safety Principles
Some things done to promote criticality safety include: