Module 105 Criticality Safety
V. MODULE 105 - Criticality Safety
NOTE: The training
Describe the criticality safety control measures for
material in this module is
uranium, including inventory control measures.
not a substitute for
Identify criticality monitoring techniques used
criticality safety training.
Explanation of Criticality
Uranium is a fissionable material, which means that it can Energy given off during
fission is approximately
undergo nuclear fission. Nuclear fission is a process in
which a very heavy unstable atom primarily splits in two, 200 MeV.
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.