Establishing Risk-Informed Non-Fixed Surface Contamination Limits for Spent Fuel Transportation Casks

Current limits for non-fixed surface contamination on spent fuel casks are the same as for other transportation package types: 4 Bq cm- ² [110 pCi cm- ²] for beta and gamma emitters and low toxicity alpha emitters, and 0.4 Bq cm- ² [11 pCi cm- ²] for all other alpha emitters. These limits have been called into question in recent years, particularly with regard to spent fuel casks, because they are based on conditions, practices, and radiation dosimetry of the 1950s; they are not optimized with regard to the total doses received from spent fuel casks by workers and members of the public; and the radionuclides considered in their derivation do not include the generally dominant sources of activity on cask surfaces. In 2001 the International Atomic Energy Agency (IAEA) initiated a Coordinated Research Project (CRP) to reexamine limits for non-fixed contamination on all types of packages. This paper provides an update on the results of the CRP as they apply to limits for contamination on spent fuel casks. Because the CRP’s proposed limits are radionuclide-specific, much of the discussion is concerned with identification of radionuclides likely to be present on cask surfaces.