Answer to Question #1794 Submitted to "Ask the Experts"

The following information was compiled and edited from information provided by William Ward and Douglas Broaddus of the United States Nuclear Regulatory Commission (NRC). ISO 2919 is the international standard for sealed sources. The manufacturer of a device makes a determination as to the maximum heat a device is likely to see during accident and normal conditions, and selects sources to meet that condition. The highest classification, temperature-wise, is a 6, and that is 800^o C for 1 hour. In other words, if a manufacturer chose a source rated at 6 for temperature, it should last for 1 hour at 800^o C without its boundary failing. Anything beyond that requires special testing and classification. There won't be many sources designed for a more extreme temperature condition. There is no testing for chemical conditions such as an acid/caustic environment. Generally, the system is designed to avoid placing a source in such conditions. But such a condition may arise in an accident scenario. Generally, it is assumed that any lead will melt away in a fire (structural containment of lead is assumed to have failed), so it is not included in shielding calculations in fire situations. Other testing of sources, required by ISO 2919, can give an idea as to the method and likelihood of failure of the source containment (over-pressurization, impact, etc.) for various postulated situations. It is up to the applicant to propose likely extreme situations and how they would be handled. For a 1,000^o C chemical fire for 1 hour, an applicant would likely assume lead is gone and containment has failed and discuss a measured approach to fighting the fire and source recovery. This would likely be based on health physics principles since engineering designs have failed. However, in a fresh reactor fuel fire in Springfield, Massachusetts, they let it burn rather than put water on it. The fear was thermally shocking the metal, causing it to fail. The responders decided it would likely survive the fire, since it had up to the point when the decision was made. In general, the NRC does not specify requirements concerning accident analysis. We expect the applicant to propose scenarios and explain why they don't present a problem that would prevent the NRC from issuing the certificate of registration [see Title 10 of the United States Code of Federal Regulations Part 32.210(c) & (d)]. The only example of a health physics-based analysis similar to this situation that could be readily found is in the NRC regulatory guidance document NUREG-1556, Volume 8, Appendix O, Attachment 1. NUREG 1556, Volume 3 "Applications for Sealed Source and Device Evaluation and Registration," also provides a more general description of NRC's approach to evaluating SS&D registration applications. In particular, Appendix F "Standard Reference Materials," lists various reference documents typically used during the evaluation process. The NUREG 1556 series is available on the NRC Web site. Volume 3 and Volume 8 are also available on the NRC Web site.

Keith Dinger, CHP