Module 105 -Criticality Safety

DOE-HDBK-1113-98

Module 105 Criticality Safety

Lesson Plan

Instructor's Notes

Show OT-37

V. MODULE 105 - Criticality Safety

Objectives

NOTE: The training

EO8

Describe the criticality safety control measures for

material in this module is

uranium, including inventory control measures.

not a substitute for

EO9

Identify criticality monitoring techniques used

criticality safety training.

with uranium.

Show OT-38

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.