Resolution of Generic Safety Issues: NMSS-0013. Use of Different Dose Equivalent Models to Show Compliance (Rev. 1) ( NUREG-0933, Main Report with Supplements 1–34 )
This issue was identified1723 by NMSS to allow licensees to establish ALIs and DACs for use at their facilities based on new models to show compliance. NMSS believed that 10 CFR 20 needed to be revised so that Appendix B and all references to variables associated with converting dose to dose equivalent, such as weighting factors and quality factors, are removed thus allowing dose equivalent limits to remain. The revision to 10 CFR 20 was expected to eliminate all aspects of regulations that cause elusive use of particular mathematical models, i.e., ICRP 26 and 30. Simultaneously, a Regulatory Guide would be developed to contain NRC-acceptable models and parameters, including the ALIs and DACs and concentrations removed from Appendix B of 10 CFR 20, that could be used by the majority of licensees to show compliance.
This issue was given a medium priority ranking and resolution was pursued. The staff considered initiating a major rulemaking to remove all dose modeling parameters from 10 CFR 20 and issue them as guidance. However, only a few licensees requested permission to use newer models for dose calculations, and initiating such a significant rulemaking would have been a resource-intensive effort. In addition, there were great uncertainties in the doses calculated by the different models. The level of uncertainty in newer models was no better than older models for many isotopes. The primary benefit of the rulemaking would have been to minimize requests for exemptions from 10 CFR 20. It was believed that rulemaking would have established a means of authorizing the use of new dose models for those relatively few licensees that requested the use of new models. Instead of pursuing rulemaking, the staff decided to address licensee requests on a case-by-case basis.1772