External Exposure Surveys - doe-std-1136-20040090

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

considered contaminated are listed in Appendix D of 10 CFR 835. That document also specifies the

criteria for the release of materials and equipment from radiological areas to controlled areas.

Detailed requirements for unrestricted release of materials and equipment from controlled areas are

found in DOE Order 5400.5 Ch. 2, Radiation Protection of the Public and Environment (DOE 1993b).

Figure IV-1 of DOE Order 5400.5 indicates that the allowable total residual surface contamination for

transuranics is reserved, i.e., no value is given. In essence, this requires release values for transuranic

contamination to be developed through the project offices in the field and approved by the DOE

Headquarters Program Office.

4.2.2.3 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

contamination in glove boxes and on gloves and equipment may contribute substantially to the external

dose rates.

4.2.2.4 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 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 swipe or

smear survey.

A large-area wipe survey is used to qualitatively 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 us ing 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 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. Technical smears (i.e. 100 cm2)

need to be taken to quantify removable contamination levels. Depending upon the specific circumstances,

a series of smears ma y 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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