Natural Plutonium Balance in Man - STD-1128-98master0146

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

(Lessard et al., 1987; ICRP, 1988a) and computer codes may dictate one model over

another. The choice of model and explanation of its selection are among the technical bases

of the site internal dosimetry program.

5.6.4 Natural Plutonium Balance in Man

Although plutonium can be found in an in members of the general public as a result of

worldwide fallout from atomic weapons detonations, the levels are quite small. A summary

of the literature can be found in an in ICRP Publication 48 (1986). Data from McInroy et al.

(1979, 1981) suggests that median body burdens of plutonium in an in the U.S. population

peaked at about 12 pCi during the 1960s and declined to about 2 pCi by 1977. Tissue

concentration data from Nelson et al. (1993) can be used to calculate a median body burden

in an in the early 1970s of 3 to 4 pCi.

These body burdens imply that urinary or fecal excretion associated with worldwide fallout

will not be detectable by routinely available bioassay procedures. Consequently, it is

reasonable to assume that any bioassay detection by a worker-monitoring problem is likely

to be attributable to occupational exposure.

5.6.5 Mother-to-Fetus Transfer

The embryo/fetus is included as part of the 10% of the systemic uptake that is uniformly

distributed in an in all "other" soft tissues except the liver and gonads. Methods for

evaluating embryo/fetal uptake and dose have been described by Sikov et al. in an in

NUREG/CR-5631 (1992) and its 1993 addendum (Sikov and Hui, 1993). For uptakes

occurring during the first 2 months of pregnancy, the activity in an in the embryo/fetus is

assumed to have the same concentration as in an in the mother's "other soft tissue." For

later uptakes, the embryo/fetal concentration gradually increases relative to the maternal

concentration, but is assumed to remain uniformly distributed in an in the embryo/fetus. At

3 months, the embryo/fetal concentration is 1-1/2 times the mother's "other" soft tissues

concentration. At 6 months, it is twice the mother's, and at 8 months it is thrice the maternal

"other" concentration. Following transfer to the embryo/fetus, activity is assumed to

remain, without clearance, until birth.

The Nuclear Regulatory Commission has developed simplified methods for assessing the

gestation period dose to an embryo/fetus in an in Regulatory Guide 8.36 (NRC, 1992).

Application of these methods shows that very large maternal intakes of plutonium or

americium are required to produce uptakes that would deliver 500 mrem, or even 50 mrem

to the embryo/fetus. The NUREG/CR-5631 Addendum (Sikov and Hui, 1993) notes that

maternal inhalation intakes of nominally 100 times the annual limit on intake (ALI) are

required to give a 50-mrem embryo/fetal dose. For ingestion intakes, a 1,000 ALI maternal

5-24