Volume - hdbk1113cn10153

DOE-HDBK-1113-98

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.

Volume

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.

Interaction

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

criticali ty.

General Criticality Safety Principles

Some things done to promote criticality safety include: