Module 105 Criticality Safety
MODULE 105 - Criticality Safety
NOTE: The training material in
Describe the criticality safety control measures for
this module is not a substitute
uranium, including inventory control measures.
for criticality safety training.
Identify criticality monitoring techniques used with
Explanation of Criticality
Energy given off during fission
Uranium is a fissionable material, which means that it can
is approximately 200 MeV.
undergo nuclear fission. Nuclear fission is a process in
which a very heavy unstable atom primarily splits in two, or
"fissions". When an atom fissions, one large atom
primarily becomes two smaller atoms, between one and
seven neutrons are given off, and a great deal of energy in
radiation and other forms, such as the kinetic energy of the
fission fragments, is released.
Some unstable atoms, such as 235U, undergo a small amount
of fission without any outside influences. This small
amount of spontaneous fission does not present a
significant hazard on its own, but the neutrons from this
fission may be absorbed by other fissionable atoms. When
an atom of fissionable material absorbs a neutron, the
already unstable atom gains additional energy and becomes
even more unstable. One way the unstable atom can get rid
of its excess energy is through fission.