Clarification of Several Aspects of Removable Radioactive Surface Contamination Limits for Transport Packages
See IE Information Notice No. 85-46 entitled as above and dated June 10, 1985. Clarification and guidance are provided on (1) averaging of wipe samples, (2) use of higher efficiency (>10%) wipe sampling methods, (3) wrapping of packages (casks), and (4) exclusive-use vehicle surveys for surface contamination.
AVERAGING OF WIPE SAMPLES:
The DOT regulations currently state in 49 CFR 173.443 (a) that "... the amount of radioactivity measured on any single wiping material when averaged over the surface wiped ..." shall not exceed the limits of 49 CFR 173.443, Table 10. Prior to the regulatory amendments by DOT in 1983 (Docket HM-169, 48 FR 10238, March 10, 1983), formerly applicable 173.397 (a) provided that wipe samples could be "... averaged over any area of 300 cm2 of any part of the package surface."
We understand that it was "not" DOT's intention to disallow such averaging and further that DOT will consider processing a future rule change to restore such a provision to 173.443. In the interim, until the text has been formally modified, we will continue to consider that averaging of multiple wipe samples over any 300 cm2 area of a package surface is an acceptable practice. [Note: Never changed in DOT 49 CFR 173.443 (a) (1). See 10 CFR 71.87 (h) (i) (1). NRC adopted DOT language.]
USE OF HIGHER EFFICIENCY WIPE SAMPLES:
49 CFR 173.433 (a) states: "Other methods of assessment of equal or greater efficiency may be used. When other methods are used, the detection efficiency of the method used shall be taken into account and in no case shall the nonfixed contamination on the external surfaces of the package exceed ten times the limits listed in Table 10." DOT considers that the statement "other methods of assessment of equal or greater efficiency may be used," also includes other wipe sampling methods wherein the efficiency has actually been demonstrated to be greater than 10%. Therefore, in effect, the wipe sample limits stated in 173.443 (a) and (b) and Table 10 therein, are limits "by default," which do not take advantage of utilizing an efficiency greater than 10%.
In evaluations of licensees' package surveys, NRC plans to accept assessments based on efficiencies which have been appropriately demonstrated to have an efficiency higher than 10%. The higher efficiency of the wipe sampling method must be documented and in no case may the removable levels exceed 10 times the values in Table 10 of 49 CFR 173.443.
WRAPPING OF PACKAGES (CASKS):
"Weeping" of contamination may occur on casks that have been immersed in spent fuel storage pools. The issue of whether exterior "wrapping" of casks can be used to achieve compliance with removable contamination limits has been raised on a number of occasions. The reply from DOT on this matter read as follows: "For both NRC-certified and non-NRC-certified packages, any wrapping must be addressed in the package design evaluation" (e.g., heat retention since the contents are a heat source). "For NRC-certified packages this would include specific mention in the certificate of compliance.
For DOT Specification 7A, Type A, packages, the shipper's package safety evaluation would have to document the ability of the wrapping to successfully pass the Type A tests" (e.g., the wrapping would maintain its closure integrity during normal conditions of transport).
EXCLUSIVE-USE VEHICLE SURVEYS FOR SURFACE CONTAMINATION:
For packages shipped as exclusive-use by rail or highway, the provision of 173.443 (b) provides that the removable (nonfixed) radioactive surface contamination at any time "during transport" may not exceed "10 times" the limits of 49 CFR 173.443 Table 10. At the "beginning" of transport, however, the levels may not exceed those stated above.
Further, pursuant to 173.443 (c), any transport vehicle in which packages are transported within the "factor of 10" higher values (e.g., above the Table 10 limits), must be surveyed with appropriate radiation detection instruments after each use and shall not be returned to service until the radiation dose rate is below 0.5 mrem/hr and the removable contamination is below the limits stated above (49 CFR 173.443, Table 10). An exception to this vehicle survey requirement is provided by 173.443 (d) for closed transport vehicles (highway) which are dedicated solely to the transport of radioactive material packages and are appropriately marked on the exterior of the vehicle. Also, in such cases the removable surface contamination on packages within such vehicles may be at the "factor of 10" limits at the "start" of transport.
Regulatory references: 10 CFR 71, 49 CFR 173
Subject codes: 7.6, 12.4, 12.17