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Answer to Question #2098 Submitted to "Ask the Experts"Category: Policy, Guidelines, and Regulations — Radiation Safety Issues The following question was answered by an expert in the appropriate field: Q
I have a question about shipping surveys. 49 CFR 173 specifies the shipping survey be averaged over a 300 cm2 smear, but gives authorization to use alternate methods if the alternate method is at least as efficient as the prescribed method. Has anyone qualified using large area wipes (such as muslin cloth) when shipping materials with a large surface area? If not, how would you recommend qualifying the use of large area wipes to meet the shipping regulations?
A
Your question appears most related to 49 CFR 173.443(a)(2), that pertains to the efficiency of a wipe in removing surface contamination. That subparagraph is needed because the Department of Transportation's (DOT) contamination limit is established for the wipe used to determine package surface contamination, rather than for the surface itself. DOT set the wipe limit to 10% of the International Atomic Energy Agency (IAEA) package surface contamination level, based on the assumption that the wipe is only 10% efficient in removing contamination from the surface. Thus DOT's wipe limit of 0.4 Bq cm-2 is effectively the same as IAEA's package surface contamination limit of 4 Bq cm-2, provided the wiping efficiency is 10%.
Of course, 0.4 Bq cm-2 is not much activity on a wipe, so DOT allows greater wipe activity, provided the wiping efficiency is demonstrated to be proportionately greater, up to 4 Bq cm-2, which is reached at 100% wiping efficiency. The qualification of a contamination averaging area of greater than 300 cm2 is beyond the intent of DOT's provision permitting the use wiping efficiencies greater than 10%. In answer to your question, to our knowledge, no one has "qualified large area wipes, such as muslin cloth." Note that contamination limits are expressed as a maximum area concentration averaged over 300 cm2. For example, if you had a single cm2 on a package surface with 1200 Bq on it, that's okay, provided the surrounding 299 cm2 has no removable surface contamination, because the average contamination for that 300 cm2 is 4 Bq cm-2. Keeping the same 4 Bq cm-2 limit but increasing the averaging area to say 60 m2 (i.e., the area of a spent fuel cask) would increase the maximum permissible hot-spot activity to 1,440,000 Bq. The U.S. Nuclear Regulatory Commission (NRC) does not endorse this approach. John Cook Cynthia G. Jones, PhD
Answer posted on 9 April 2003. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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