Radioactive Properties cont'd

DOE-HDBK-1113-98

Module 101 Properties of Uranium

Lesson Plan

Instructor's Notes

which can be helpful or harmful depending on how they are

controlled.

All isotopes of uranium are fissionable, which means they

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

235

U, 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 Sa fety.

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

234

Th, 234mPa, 231Th, and 99Tc. The degree of

emitters:

enrichment also affects the controls that are required for

external radiation exposure because of the increase in the

amount of gamma-emittin g 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-

emmission 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.