Detection and Confirmation of Intakes

DOE-STD-1121-98

6.0 DETECTION AND CONFIRMATION OF INTAKES

Two fundamentally different kinds of signals may indicate the possibility that intakes of

radionuclides have occurred. Most often, possible intakes may be indicated by workplace monitoring

results (CAM alarms, survey and frisking results, air sample results) or observations (an accident,

explosion, spill, leak, equipment failure). Possible intakes are more rarely signaled first by unexpected,

elevated bioassay results. In some events, there is no question that intakes were possible, so special

bioassay procedures and investigations are initiated to confirm or rule out intakes. In situations where the

possibility is less clear, the suspicion of an intake should be investigated, that is, efforts should be made to

confirm or rule out intakes, if preliminary results indicate the possibility for a significant dose. If

preliminary results do not indicate the possibility of a dose above the IL of 100 mrem, then a dose may

simply be assigned without investigation.

A suspected intake based solely on workplace monitoring data cannot be confirmed in the same

sense that repeated bioassay measurements can confirm an intake of radionuclides that can be detected by

bioassay. There are, however, some checks that can be used to help validate the result. This is

particularly important for larger predicted intakes. For example, one can look at coworker BZ data,

evidence of concomitant external contamination, job-specific air monitoring information, and results of

nasal smears. None of these sources provides confirmation, but collectively they can sometimes help

flesh out the details of the exposure.

6.1 USE OF WORKPLACE MONITORING DATA FOR DETECTING AND

CONFIRMING INTAKES

The identity of radionuclides inadvertently taken into the body and the amount of intake may be

inferred using workplace monitoring data (e.g., airborne contamination concentration measurements,

nasal-smear activity measurements, application of resuspension factors to measured surface

contamination levels, etc.). Airborne radioactive material concentration data may be used as a direct

indication of intake, especially if information on particle size distribution can be obtained. Evaluation of

other workplace indicators proved to be useful in identifying possible intakes. However, there is no

generally accepted quantitative method for correlating such indicators with intake. Heid and Jech (1972)

concluded from review of several plutonium inhalation cases that the amount of activity on a nasal smear

collected shortly after intake was about the same as the amount deposited in the deep lung for nose

breathers and about half the deposited activity for mouth breathers. Brodsky (1980) suggested that a

resuspension factor could be applied to surface contamination levels to assess the corresponding airborne

contamination levels. Due to the provisional acceptance of dose assessments based on workplace

monitoring data, detailed methods are not described here. Where use of such data appear to be

appropriate for dose assessment, the facility should establish a protocol for their use as part of the internal

dosimetry program, and document it in the technical basis documentation.

6.2 USE OF BIOASSAY DATA FOR DETECTING AND CONFIRMING INTAKES

According to the Internal Dosimetry Program Guide (DOE 1999b), intakes of radioactive materials

that are suspected on the basis of a single bioassay measurement must be confirmed by one of several

means. "False alarms" based on erroneous bioassay results carry a heavy penalty in terms of cost,

paperwork, and public relations for both DOE and its contractors. The decision to confirm an intake

based on bioassay measurements currently uses a statistical comparison of one or more results with an