Early Thermal Testing of Type B Radioactive Material Packages in the US to Environments beyond the Regulatory Package Thermal Test Standards

Three separate fire test programs exposing casks beyond the regulatory thermal test requirements were performed by Sandia National Laboratories during the late-1970s and mid-1980s. The results of these test programs can be used to assist in addressing the adequacy of the regulatory thermal test of fully-engulfing exposure at 800oC for 30 minutes and how that test might relate to real accident thermal environments. The test programs were undertaken on obsolete and new casks on behalf of the U.S. Department of Energy, the U.S. Department of Transportation, and the Japanese Power Reactor and Nuclear Fuel Development Corporation (currently known as the Japan Atomic Energy Agency). Two of the tests involved exposure of casks in damaged transport vehicles to fully engulfing fires for 72 to 125 minutes, and the other test involved four exposures of a cask to torch environments for 30 minutes. Much of the original documentation regarding these tests and their results is no longer readily available. The documents relating to these tests have been surveyed; this paper presents summaries from this survey of the tests and their results. Specifically, for the pool fire exposures, the temperatures measured in the flames of both exceeded the flame temperature required by the Transport Regulations; yet an obsolete 67- tonne cask endured 90 minutes of exposure before evidence of failure was detected, and a new cask endured the 72 minute exposure while retaining its containment integrity For the exposure of a modified obsolete cask to four different torch environments, the integrity of the cask was retained and the relative temperature increases within the cask were well within acceptable limits and were well below the values that could be expected if the cask were exposed to the Regulatory thermal test. A review of these three thermal test programs, establishes that the two older cask designs and one new cask design have the ability to survive environments that were different from (the torch environments) or more severe than the environment specified by the existing thermal test requirement in the Transport Regulations. These results can be extrapolated to apply to modern casks that generally have more robust designs as well as better quality assurance applied during the manufacturing process.