Radioactive Properties cont'd - doe-hdbk-1113-98_reaffirm_2005

DOE-HDBK-1113-98

Module 101 Properties of Uranium

Lesson Plan

Instructor's Notes

All isotopes of uranium are fissionable, which means they

can be fissioned by fast neutrons. Two isotopes, 233U and

235U, are fissile, which means they can also be fissioned

by slow (thermal) neutrons. A fissile material can be

involved in a criticality accident, resulting in the release

of a lethal amount of radiation. Criticality is discussed in

more detail in Module 105- Criticality Safety.

The primary isotopes of uranium are all long-lived alpha

emitters. However, several other radionuclides can be

radiologically significant at uranium facilities, depending

on the history of the uranium materials and the

processing. These other radionuclides include the

following beta emitters: 234Th, 234mPa, 231Th, and

99Tc. The degree of enrichment also affects the controls

that are required for external radiation exposure because

of the increase in the amount of gamma-emitting 235U

that is present. The uranium daughter products may also

include some low energy gamma and x-ray radiation. For

example, the daughter products of 232U represent a

potential gamma emission hazard.

Although there are several isotopes of uranium, only three

exist naturally, and all three are radioactive. See the table

below for half-lives and natural percent abundance for

important uranium isotopes in the nuclear fuel cycle.