Example 4.1. DIL for Class D Natural Uranium

DOE-STD-1121-98

AMDD in a year for a given radionuclide or group of radionuclides j, it is necessary to consider the

number of independent sources n to which an individual worker may be exposed, as shown in Figure 1.

For each independent source j, a judgement must be made concerning whether intakes of that group are

characterized as "rare, single" intakes or whether there is a possibility of multiple or chronic intakes. In

the latter case, if the nuclide is rapidly clearing, then a dummy variable, pj, is set to 1. For "rare, single"

Example 4.1. DIL for Class D Natural Uranium

Assume we have chosen a sampling frequency f = 12 samples per year. For class D uranium,

IRFu(30 days) = 0.0017 Bq per day per Bq of intake as calculated by the computer code CINDY

using the ICRP 30 models. From p. 150 of Federal Guidance Report 11, hE,50 for inhalation of class

D 234U = 7.37E-7 Sv/Bq, 235U = 6.85E-7 Sv/Bq, and 238U = 6.62E-7 Sv/Bq. Natural uranium is a

mixture of these three isotopes. Since 234U gives the highest dose per unit intake by a small margin,

one may conservatively use the value for 234U. Then, the DIL becomes

Since the intake retention fraction decreases as the interval between samples increases (i.e.,

as f decreases), and the sample frequency f appears explicitly in the denominator of the DIL equation

above, there is some optimum choice of f that requires the least detection capability. However, since

annual cost is directly proportional to f, there are trade-offs between cost and detection capability.

intakes or for possible multiple or chronic intakes of slowly-clearing nuclides, pj = 0. The AMDD (mrem

per year) for each independent source then becomes

(4)

In other words, AMDDs for rare intake radionuclides and slowly clearing multiple or chronic intake

radionuclides are equal to the IL, and those for possible multiple intake or chronic intake groups that clear

quickly are reduced by a factor of l/k, where k is the number of radionuclides or radionuclide groups j for

which multiple or chronic intakes are possible.

A lower limit on the DIL for radionuclide group j as a function of sampling frequency can be

determined. This limit is the detection sensitivity needed for a bioassay measurement, that is, the

minimum change one would need to detect in each bioassay measurement to detect a series of small