Alternate Methods of Intake Assessment

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

Intake can also be estimated from air sample data, as described in Section 5.7.4. This method is

appropriate if bioassay data are not available or insufficiently sensitive. Intake estimates based on air

samples and bioassay data are also appropriate as a check on each other. Valid bioassay data showing

detectable results should be given preference over intake estimates based on air sample results.

5.8.2 Alternate Methods of Intake Assessment

Historically, intake as described in the foregoing section was not always calculated when assessing

uranium exposures. Estimates of uptake using recognized methods (Langham 1956, Healy 1957,

Lawrence 1987) focused on assessing the magnitude of radioactivity retained in the body, rather than

intake (which includes material not retained and of no dosimetric significance). These methods were (and

are) dosimetrically sound in so far as estimates of deposition and uptake are concerned.

5.8.3 Estimating Effective Dose Equivalent from Intakes of Uranium

The committed dose equivalent resulting from an intake of uranium may be calculated by

multiplying the estimated intake (I) by an appropriate dose conversion factor (DCF):

H50 =I DCF

(5.11)

Dose conversion factors can be obtained from tabulated data in Federal Guidance Report No. 11 ,

ICRP Publication 30, Part 4, in the Supplement to Part 1 of ICRP Publication 30, or calculated directly

using computer programs. Substituting the ICRP Publication 48 (ICRP 1986) model parameters of 50%

skeleton and 30% liver translocation for the assumptions in ICRP Publication 30, Parts 1 or 4, has little

impact on the HE,50 per unit intake, but does alter the committed organ dose equivalent per unit intake. Such

substitution of models is acceptable, provided that the model is documented and consistently applied.

Values for simplified dose conversion factors can be obtained by dividing a dose limit by the

corresponding value for the ALI. A caution must be observed with this approach: not all tabulated values

of ALIs are the same. The ALIs are commonly rounded in most tabulations to one significant figure (e.g.,

as in ICRP Publication 30 and Federal Guidance Report No. 11). Substantial variation can occur as a result

of units conversion. For example, Federal Guidance Report No. 11 lists the ALI for 239Pu class Y

inhalation as both 6 x 10-4 MBq (600 Bq) and 0.006 Ci (740 Bq). Such rounding errors can introduce

significant discrepancies in dosimetry calculations. This method also raises a question about which ALI

should be used if compliance monitoring is being based on comparison with secondary limits, such as the

ALI rather than the primary dose limits.

Where individual-specific data are available, the models should be adjusted. However, the general

lack of capability to monitor organ-specific retention for uranium (i.e., content and clearance half-times)

makes the use of default models most practical.

Ideally, one should obtain as much bioassay information as possible to determine the intake and track

the retention of uranium in the body to reduce the uncertainty associated with the daily variation in the

measurements. A regression analysis should be used to fit the measurement values for estimating the initial

intake and clearance half-times.

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