Differing internal dose calculations for the revised 10 CFR 20

The revised 10 CFR 20 allows licensees several ways to calculate internal dose equivalent-related quantities. These include using the Federal Guidance Report No. 11, using the annual limit on intake (ALI), using the derived air concentration (DAC), and using the International Commission on Radiological Protection (ICRP) 26/30 methodology and metabolic models (or a commercially available software package which implements this methodology). The difference in calculated dosimetry results can be important for demonstrating regulatory compliance, especially for significant intakes. A scenario can occur that would cause a licensees to report a significant intake as an overexposure of the applicable limit if only a rudimentary internal dose calculation is performed. An example demonstrating this problem is presented. The simplified dose calculation methods allowed by section 20.1003, section 20.1202(b)(2), section 20.1204(c), and section 20.1204(h) are also summarized. The internal dose calculation methodology used by the NRC Radiation Exposure Monitoring and Information Transmittal (REMIT) computer program, which many small- to mid-size licensees use for manipulating and reporting occupational radiation exposure data, is also discussed. Additionally, this paper introduces the principal references used in internal dose assessments and briefly summarizes the major changes resulting from the new Part 20