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{sup 2} for beta and gamma emitters and low toxicity alpha emitters, and 0.4 Bq/cm{sup 2} for all other alpha emitters. These limits have been called into question in recent years, particularly with regard to spent fuel casks, for several reasons. For example, 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 (Pu-239 and Sr-90) 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 nonfixed contamination on all types of packages. The CRP reviewed the scientific basis for current surface contamination limits and developed a model to estimate doses to workers and members of the public due to package surface contamination. The 'CRP Basic Model' is described in IAEA TECDOC-1449, 'Radiological aspects of non-fixed contamination of packages and conveyances'. The full paper provides an update on themore » results of the CRP and subsequent international efforts to apply these results in establishing dose-based contamination limits. The effects of applying these limits to spent fuel casks are examined, including the effects on overall worker and public doses.« less