External Exposure Surveys - doe-std-1128-98

DOE-STD-1128-98

This document concerns release to controlled areas only. The detailed

requirements for unrestricted release of materials and equipment are found in

DOE Order 5400.5 (DOE, 1993b). Refer to that document for guidance

regarding unrestricted releases.

4.2.4.3 External Exposure Surveys

To delineate the levels involved, measurements of external exposure should

be made at the time a program is established at all locations where personnel

exposure occurs. Additional photon and neutron measurements should be

made at the same frequency as the contamination surveys. The buildup of

plutonium contamination in glove boxes and on gloves and equipment may

contribute substantially to the external dose rates.

4.2.4.4 Measurement and Survey Techniques

This section discusses four types of contamination surveys that are typically

used in DOE facilities. Surveys for removable contamination include a large-

area wipe survey and a technical swipe or smear survey. Surveys for

total/fixed contamination include a scan survey and a statistically based

survey. These surveys, or a combination of them, are used to survey material

for release from radiological control. The appropriate use of each type of

survey is discussed.

Surveys for Removable Contamination

Two types of surveys are used for removable contamination: a large-area

wipe survey and a technical swipe or smear survey.

A large-area wipe survey is used to detect gross removable contamination. A

large-area wipe survey is typically performed using a large floor cloth and a

dust mop type handle to wipe large areas. This technique tends to concentrate

any low levels of removable contamination that may be present. The surface

to be wiped and the wiping material should be industrially clean (i.e., free of

debris, grease, etc.) to reduce self-absorption of alpha contamination. The

survey is performed by wiping the surface of the area being surveyed and

conducting frequent checks of the cloth using a portable instrument. For

detection of alpha-emitting isotopes, a nonabsorbent material should be used.

Removable contamination will be accumulated and concentrated on the wipe,

increasing the probability of its detection. Checking for contamination is

conducted by placing an alpha measurement instrument approximately 0.25

in. (0.6 cm) from the surface of the wipe for 5 seconds, and the count rate

observed. If there is no increase above background, then the wipe may be

placed in contact with the detector. If no radioactivity above background is

measured, then the material is not contaminated with removable

contamination. If radioactivity above background is measured, the material is

contaminated. Depending upon the specific circumstances, a series of

technical smears may be required to locate and quantify the contamination

within the area covered by the large-area wipe. In most instances, if

contamination is detected on the large-area wipe, decontamination should be

considered.

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