Performance Capabilities for Internal Exposure Monitoring

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

through air and surface contamination monitoring programs. Individual monitoring for intakes is

commonly performed using bioassay procedures. Bioassay monitoring includes both direct (in vivo)

measurements of radioactivity in the body and indirect (in vitro) measurements of material excreted or

removed from the body.

10 CFR 835.402 requires participation in a bioassay program if a general employee is likely to

exceed 0.1 rem committed effective dose equivalent (CEDE) from all intakes for all radionuclides in a

year. Participation in a bioassay program is generally based on the possibility that a single intake

causing a dose in excess of 0.1 rem CEDE might occur.

Indications of intake include (but are not limited to) detection of facial or nasal contamination, positive

air monitoring or sampling results that may indicate internal exposure, or any wound in which

contamination is detected or suspected. The most common internal exposure monitoring program for

workers is the bioassay program, which must be designed for the specific nuclides and forms of material at

a particular facility. Likely candidates for internal exposure monitoring include personnel who may be

routinely exposed to surface or airborne contamination, or those identified by workplace indicators.

Workplace monitoring for potential internal exposures is performed to verify the adequacy of

containment and work practices. This monitoring includes air sampling, continuous air monitoring,

personal contamination surveys, and workplace contamination surveys. Facilities are to be designed and

operated to minimize internal exposure. Details regarding workplace monitoring and control practices are

discussed in Chapter 4, Contamination Control.

5.1.1 Performance Capabilities for Internal Exposure Monitoring

Bioassay programs must be capable of showing compliance with the 5-rem/year stochastic and 50-

rem/year nonstochastic dose limits of 10 CFR 835.202. 10 CFR 835.402(c)(1) identifies 0.1 rem CEDE for

all likely intakes as a level above which workers must participate in a bioassay program. Therefore, ideally,

such bioassay monitoring programs should be capable of detecting individual doses at that level. To meet

this requirement, reliance must be placed on workplace monitoring to identify potential intakes at the time

they occur so that special bioassay monitoring can be initiated.

Performance capabilities for bioassay and internal dosimetry programs can be expressed as the

minimum detectable dose, based on some combination of minimum detectable activity and frequency of

measurement or time post-intake at which the measurement is made. The term "minimum detectable dose"

is preferred over any variants of the occasionally encountered terms "dose-missed" or "potentially

undetected dose," which were usually defined as the same thing. The connotation of the latter terms is that

of an actual intake which was not detected, whereas the intent was to define a measure of program

sensitivity to doses that might have gone undetected had an intake occurred. The preferred term "minimum

detectable dose" (MDD) ties the concept to the recognized terminology of minimum detectable activity

(MDA).

The MDD for a bioassay program must meet the aforementioned dose limit requirements of 10 CFR

835.202. A design goal of 0.1 rem CEDE from all intakes of similar nuclides in a year is desirable but

unrealistic for a routine program. To meet these requirements, bioassay programs should have measurement

sensitivities (i.e., MDAs for bioassay measurements) established based on the material to which workers

might be exposed. Examples of such sensitivities are given in Tables 5-1 through 5- 3 for pure 238U

monitored by urinalysis, fecal analysis, and lung counting, respectively. The bioassay goals

5- 2