Volume - hdbk1113cn10101

DOE-HDBK-1113-98

Module 105 Criticality Safety

Lesson Plan

Instructor's Notes

Obviously, the enrichment of uranium plays an

important role in criticality because the amount of

fissile material available for criticality is greater.

For example, the higher the enrichment of 235U (i.e.,

the concentration of 235U in relation to other

uranium isotopes), the greater the opportunity for

criticali ty.

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 depends on geometric factors,

including size, shape, and separation of the

containers, as well as the size and shape of the

array itself. 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, which will thermalize neutrons.

Also, a less closely-packed array may become

critical if the water is removed, allowing less

neutron absorption to take place.