Uranium Contamination Detection

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

Measurements performed to release material should be made in a low-background area unless the

MDA of the instrument in a high-background area is known and appropriate considerations are made. If

material is being surveyed for release from a radiological area, performing measurements in a low-

background area may not be possible. If background count rates are high enough that the release guideline

values cannot be measured in the radiological area by using portable survey instruments, a survey for

removable contamination should be performed to avoid spreading removable contamination from the

radiological area. If the survey for removable contamination does not indicate the presence of

contamination in excess of background levels, the material may be moved to an area with a lower

background for an immediate fixed contamination survey.

4.2.3.1 Uranium Contamination Detection

The detection and measurement of uranium contamination is necessary to ensure control of

contamination and compliance with DOE requirements. Typically, detection of uranium contamination

has been performed using the alpha activity. However, for some conditions and situations, detection of the

beta/gamma radiations from uranium decay products may be a more sensitive and more appropriate

monitoring technique. For natural uranium, depleted uranium, and the lower levels of enriched uranium

that are in equilibrium with their decay products, the detection sensitivity for the beta/gamma radiations is

about five times more sensitive than by the detection of the alpha alone. If the uranium is highly enriched

or has been very recently processed, detection using the alpha radiation is necessary because there may be

little or no decay product radiations present.

Detection of uranium contamination may require use of beta/gamma-sensitive instruments when

surveying upholstery material, rugs, cloth and wet surfaces. Because of the range and ease of shielding

alpha particles, burial or surface liquid may preclude the detection of the alpha radiation. The use of GM

detectors, such as the thin-window detector probe, are particularly useful in these situations. In some

instances, a thin Nal detector may be better than a GM detector for detecting low-energy photons from

uranium contamination.

Many of the processes used in uranium facilities may separate and/or concentrate impurities or decay

products of uranium. Examples of these processes are uranium recovery from ore, reduction of green salt to

metal, UF6 conversion, casting of metal, and uranium oxidation. Radionuclides of particular importance are

234m

Pa and other decay products and trace impurities such as 99Tc, 239Pu, and 231Np. In addition to the

separation processes, some of the decay products of uranium may be selectively accumulated in tank and

pipe liner material. Dose rates of up to 150 mR/h, attributed to radium accumulation, have been measured

from neoprene liner material. Dose rates from furnace lids and crucibles have been measured as high as 30

rad/h.

Detection and measurement of uranium contamination, both surface and airborne, require a

knowledge of the process and of the separation and concentration mechanisms. Depending upon the

process, the time since separation, and the isotopic ratios of the uranium, contamination resulting from

uranium operations may be almost totally alpha or totally beta/gamma-emitters. Consequently, detection

techniques may require the capability to detect all types of radiations. Appropriate monitoring in most

facilities requires both types of surveys, but on differing frequencies.

4.2.4 ALARA Guidelines

Contamination levels should be maintained ALARA to minimize the potential for the spread of

contamination and to reduce the protective measures and equipment required. Control of radioactive

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