Performance Capabilities for Internal Exposure Monitoring

DOE-STD-1128-98

5.1.1

Performance Capabilities for Internal Exposure Monitoring

Bioassay monitoring 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

(DOE, 1998a). 10 CFR 835.402(c) (1) (DOE, 1998a) identifies 100-mrem CEDE

and/or 5 rem CDE to any organ or tissue 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 those levels. In fact,

this is not technically achievable for most routine plutonium bioassay programs. In

order 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. Routine, periodic bioassay measurements have little chance of

detecting a CEDE of 0.1 rem and can even have difficulty showing compliance

with dose limits.

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 monitoring program must meet the aforementioned dose

limit requirements of 10 CFR 835.202. A design goal of 100-mrem 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 and 5.2 for pure 239Pu monitored by urinalysis

and fecal analysis, respectively. Table 5.3 provides an example of the 241Am

sensitivity required for monitoring a mixture of weapons-grade plutonium, aged 5

years for ingrowth at time of intake. These tables illustrate the difficulty in relying

on routine bioassay to demonstrate compliance with the limits and design goal.

5-3