Performance Capabilities for Internal Exposure Monitoring

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

designed and operated to minimize internal exposure. Details regarding workplace monitoring and

control practices are discussed in Section 4.0.

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.

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