U.S. Nuclear Regulatory Commission
Question 1: If a licensee decides to implement Part 20 in mid-year, how does the licensee treat the annual dose limits? Prorated? Add contributions from beginning of year before the revised Part 20 was adopted?
Answer: The licensee must define the "year" consistent with the definition in 10 CFR 20.1003. If a licensee intends to implement the revised Part 20 at any time other than the beginning of the year, the licensee must subtract the dose received for the current year prior to the revised Part 20 dose being adopted from the revised Part 20 dose limit. The difference need not be prorated. For example, assume a licensee adopts the revised Part 20 on July 1, 1992, and defines its dose year as January 1 - December 31.
If the worker had received 1.5 rems between January 1 and June 30, 1992, he or she would have (5 - 1.5) = 3.5 rems available for the remainder of the year. If the worker already has more than 5 rem (e.g., two 3-rem quarters), the licensee must shift the worker to tasks in which the worker will receive no occupational radiation exposure.
(Reference: 10 CFR 20.1003)