Figure 2-4. Estimated Uranium Specific Activity for Laser Enrichment (of natural uranium)

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities

Figure 2-4. Estimated Uranium Specific Activity for Laser Enrichment (of natural uranium)

The Derived Air Concentration (DAC) values for several radionuclides are shown in Table 2-6.

Because the ALIs for the three primary uranium isotopes are expressed in activity units, enrichment

has little impact on inhalation and ingestion ALIs. However, as illustrated in Table 2-5, as enrichment

increases from 2% to 20%, the specific activity increases nine-fold. Consequently, the mass of

material that corresponds to one ALI decreases by a factor of nine. The degree of enrichment also

affects the controls that are required for external penetrating radiation exposure because of the increase

in the amount of gamma-emitting 235U that is present.

As a historical note, some of the earlier documentation refers to the "special curie" of natural uranium,

which was defined as 3.7 x 1010 d/s of 234U, 3.7 x 1010 d/s of 235U, and 1.7 x 109 d/s of 235U. Thus, 1

"curie" of natural uranium was actually slightly more than 2 curies of uranium alpha activity. This

essentially obsolete term has caused considerable confusion. Readers are cautioned to be aware of the

use of this special curie in the older literature. Use of this unit in any current application is strongly

discouraged.

2.1.4 Contaminants from Recycled Uranium and Associated Hazards

Some of the uranium feed material that was handled at DOE facilities had been reclaimed or

recycled from reprocessed, spent reactor fuel. The chemical processes by which recycled uranium was

purified left trace amounts of transuranic elements (neptunium, americium, and plutonium) and fission

products (mainly 99Tc). The recycled uranium also contained trace amounts of uranium isotopes not

found in nature, such as 236U. At the minute concentration levels in uranium from fuel reprocessing

facilities, the radiological impact of these impurities was negligible in most cases. However, there

were many routine chemical processes that tended to concentrate these impurities, either in the

uranium product or in reaction by-products, such that radiological controls and environmental

monitoring programs must consider these impurities.

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