United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

Question 38: Can the results of bioassays alone be used to

determine if the licensee must sum internal and external

doses under Part 20?

Answer: No. Summation is required if the licensee is

required to monitor for both external and internal doses.

The results of bioassays alone cannot be used to determine

if the licensee must monitor internal exposures or sum

internal and external dose under 10 CFR Part 20.

Monitoring for internal is required for adults "likely to

receive" in a year an intake greater than 10% of the limit.

Determination of what an individual is likely to receive is

a prospective assessment of intake. Bioassay is a

retrospective assessment of intake. Future intakes are not

necessarily the same as past intakes. However, bioassay

data may be used together with other information as a basis

for the prospective intake assessment. For example, if the

uses of radioactive materials in a facility are not going

to change significantly and bioassays of individuals

employed in the facility have shown that no one has ever

received an intake greater than 10%, then one might

reasonably conclude that no one is "likely to receive" an

intake in excess of 10% of the limit. (Reference: 10 CFR


Page Last Reviewed/Updated Thursday, March 29, 2012