Surveys for Removable Contamination - STD-1128-98master0111

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

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.

For transuranic radionuclides, the guideline values for removable contamination are

lower than the MDA of portable instruments. During a wipe survey, the surface

area of the material must be large enough that the quantity of radioactivity

collected on the swipe will be greater than the MDA of the instrument. Wipe

surveys of areas smaller than this minimum surface area require more sophisticated

measuring instruments, such as a scaler measurement, and the entire surface of the

material should be wiped. The minimum area for using a large-area wipe survey is

given by

MDA

X 100 cm2

A minimum =

(4.1)

where L is the removable surface radioactivity value in dpm/100 cm2 of the

potential contaminant, given in Table 4.1. and MDA is in dpm.

The purpose of a technical smear survey is to locate and quantify removable

contamination that is known or suspected to exist. For small items, a technical

smear may be used at any time to verify the item's contamination status. A

technical smear or swipe survey is performed by wiping a cloth, paper, plastic

foam, or fiberglass disk over a 100-cm2 area of the surface. The wipe should be

taken with a dry medium using moderate pressure. A common field practice is to

use two fingers to press the wipe medium against the surface to be wiped. The

wipe is then moved along an "S" shaped path that has a nominal length of 8 in.

(20 cm) to 10 in. (25 cm).

When the potential contaminant emits alpha radiation, paper or fiberglass filter

papers should be used to assure that alpha activity is not attenuated by becoming

imbedded in the wipe. To improve the detection limit, smears may be taken over

areas larger than 100 cm2. However, the size of the area smeared should be limited

to prevent buildup of material (radioactive or otherwise) that would attenuate alpha

radiation. The current practice at DOE facilities is to use the 100-cm2 area as the

minimum size of objects being smeared. Appropriate corrections should be made

for objects smaller than 100 cm2.

4-15