Table 2 -1. Typical Isotopic Abundances

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

Table 2 -1. Typical Isotopic Abundances

Typical

Neutron

Specific

Commercial

Capture

Isotope

Natural

Depleted

Activity

Feed

Cross Section

Ci/g

Enrichment

(barns)

238

99.28

97.01

99.80

3.3 E-7

2.7

235

0.72*

2.96

0.20

2.1 E-6

101

234

0.0055

0.03

0.0007

6.2 E-3

The amount of uranium present determines the grade of the ore. Most of the ores found in the

U.S. contain from 0.1 to 1% uranium and are considered medium grade. Lower-grade ores are

mined commercially if they are a byproduct of mining for another material, such as gold or

phosphate.

Uranium that has been processed to raise the concentration of 235U is referred to as enriched

uranium. The extent of enrichment depends on the intended end use of the uranium. Commercial light

water reactors are designed for use with the 235U enriched to around 3%. Higher enrichment is

required for; high-temperature gas-cooled reactors, naval nuclear propulsion reactors, most research

reactors and weapons. The 235U enrichment process also increases the concentration of 234U. The

higher activity of enriched uranium is due more to increased 234U than to increased 235U.

Depleted uranium is a by-product of the enrichment process and is depleted in both the 235U and

234

U isotopes. Depleted uranium, with its reduced activity and very high density, has many uses;

among them are radiation shielding, counterweights, projectiles, and target elements in DOE

plutonium production reactors.

In addition to the uranium isotopes discussed above, the daughter products of uranium decay and

byproducts of uranium processing can have significant radiological impacts in uranium-handling

facilities. Table 2-2 presents the properties of these radionuclides.

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