Table 2-12. Determination of "Dividing Line" Enrichments Above Which Radiological Monitoring Requirements Become Limiting

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

Table 2-12 shows the values used for fb and fk, ALI, and the resulting "dividing line" enrichments for

acute and chronic exposures. Several aspects of these derivations must be kept in mind when using this

information. First, the derivation is based on standard metabolic models and therefore does not necessarily

reflect the effects of a uranium uptake on a real person. Because individual metabolism's will not necessarily

agree with the model, the enrichment at which chemical and radiological effects are equally limiting cannot

be precisely determined. Uncertainty in the relationship between enrichment and specific activity introduces

additional imprecision. Consequently, exposures for both chemical and radiological impact for uranium

uptakes at enrichments near the calculated "dividing line" enrichment should be evaluated.

Table 2 -12.

Determination of "Dividing Line" Enrichments Above Which Radiological

Monitoring Requirements Become Limiting

Specific Activity

Annual

"Dividing Line"

of "Dividing

Limit on

Enrichment for

Line"

Intake

Class

Enrichment

Radiological Dose

2% Monitoring

Limit

Threshold

for Radiological

Dose Limit

0.476

0.12

169.5 Ci/g

(b)

7.38%

0.12

0.7(a)

29.9 Ci/g

52.8%

0.52%

0.05

0.12

0.04

0.71 Ci/g

0.82%

(c)

234

235

238

U and 0.8 Ci for U and U. This difference is the

ICRP Publication 30 lists Class W ALIs of 0.7 Ci for

(a)

result of rounding to one significant figure. Non-rounded values for the three isotopes are all approximately 0.75

microCi.

(b) The resulting enrichment is greater than 100 %. Consequently, chemical toxicity is limiting for acute exposures to

Class D uranium approaching the radiological dose limit.

(c) The resulting enrichment is lower than that of depleted uranium. Consequently, radiological concerns are limiting for

acute exposures to Class Y uranium at the monitoring threshold.

The impact of the requirement to perform individual radiological monitoring at 2% of the regulatory

dose limits can be assessed by reducing ALIs by a factor of 50, then repeating the calculations described in

Examples 3a and 3b. Table 2-13 summarizes the results of these calculations.

The effects that enrichment, chemical form, and physical form have on the hazards associated with

uranium are summarized in Table 2-13. The comparison of relative chemical and radiological hazards is

based on a derived kidney burden resulting from an acute exposure at the "no effect" threshold. The effect

of using the OSHA exposure limits of 0.05 mg/ m3 for soluble forms of uranium (Class D) and 0.25 mg/m3

for insoluble forms (Classes W and Y) is shown for chronic exposures. The derivations used here can be

applied to any limit on radiological or chemical toxicity, be it a regulatory or an internal dose control

limit. It should be emphasized, however, that the radiological impact should be considered for all intakes,

even for exposure situations where chemical toxicity is limiting.

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