United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

Question 427: The word "external" in 10 CFR 20.1302 (b)

(2) (ii) refers to any radiation source which could

irradiate an individual from outside the body. Since

sources include both airborne radioactive materials and

contained sources, the dose from airborne radioactive

materials could be double-counted -- as a concentration

pursuant to 10 CFR 20.1302 (b) (2) (i) and as direct

radiation pursuant to 10 CFR 20.1302 (b) (2) (ii). In a

situation where the licensee was approaching the 50 mrem/yr

limit from direct radiation from contained sources, the

additional direct radiation component from airborne

releases may cause this limit to be exceeded. Clearly,

this situation could be addressed through use of 10 CFR

20.1302 (b) (1); however, the intent of the revised Part 20

appears to provide viable alternatives to complying with

the regulations whenever feasible. Must a licensee who

elects to use the method of 10 CFR 20.1302 (b) (2) for

demonstrating compliance with the public dose limits

"double-count" the dose from airborne radioactive materials?

Answer: No. External sources ordinarily include all

radiation sources outside of the body, such as direct

radiation from contained sources and direct radiation from

airborne radioactive materials. To the extent that doses

from airborne radioactive materials (e.g., noble gases) are

accounted for as concentration values pursuant to 10 CFR

20.1302 (b) (2) (i), they need not be accounted for as

external sources under 10 CFR 20.1302 (b) (2) (ii) in

determining compliance with the 50 mrem/yr limit.

(However, airborne radioactive material does need to be

accounted for in determining compliance with the limit of 2

mrem in any one hour). (References: 10 CFR 20.1302, 10

CFR 20.1301).

Page Last Reviewed/Updated Thursday, March 29, 2012