Volume - doe-hdbk-1113-98_reaffirm_2005

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 criticality.

8. 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.

9. 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.