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Abstract not provided.

Abstract not provided.

Two major studies, one sponsored by the U.S. Department of Energy and the other by the U.S. Nuclear Regulatory Commission, were conducted in the late 1970s and early 1980s to provide information and source terms for an optimally successful act of sabotage on spent fuel casks typical of those available for use. This report applies the results of those studies and additional analysis to derive potential source terms for certain classes of sabotage events on spent fuel casks and spent fuel typical of those which could be shipped in the early decades of the 21st century. In addition to updating the cask and spent fuel characteristics used in the analysis, two release mechanisms not included in the earlier works were identified and evaluated. As would be expected, inclusion of these additional release mechanisms resulted in a somewhat higher total release from the postulated sabotage events. Although health effects from estimated releases were addressed in the earlier study conducted for U.S. Department of Energy, they have not been addressed in this report. The results from this report maybe used to estimate health effects.

System Certification is a regulatory concept which is intended to expand the scope of radioactive material transport regulations by allowing alternative means for proving compliance with the requisite standards of safety set out in transport regulations. In practice it may allow more stringent requirements in one aspect of the regulations to be substituted for less stringent application in other areas so long as the safety standard provided by regulation is preserved. The concept is widely perceived as the imposition of operational controls in exchange for relaxation of packaging standards, but that is only one possibility in the spectrum of potential actions under a System Certification provision in IAEA or national regulations.

It is likely that the ongoing process to produce the 1996 version of the IAEA Regulation for the Safe Transport of Radioactive Materials, IAEA Safety Series 6(SS 6) will result in a more stringent package qualification standard for air transport of large quantities of radioactive materials (RAM) than is included in the 1990 version. During the process to define the scope of the new requirements there was extensive discussion of their impact on, and application to, fissile material package qualification criteria. Since fissile materials are shipped in a variety of packaging ranging from exempt to Type B, each packaging of each type must be evaluated for its ability to maintain subcriticality both alone and in arrays and in both damaged and undamaged condition. In the 1990 version of SS 6 "damaged" means the condition of a package after it had undergone the "tests for demonstrating the ability to withstand accident conditions in transport," i.e., Type B qualification tests. These tests conditions are typical of severe accidents in surface modes but are less severe than air mode qualification test environments to be applied to Type C packages. As a result, questions arose about the need for a corresponding change in the 1996 SS 6 to define "damaged" to include the Type C test regime for criticality evaluations of fissile packages in air transport.

The source term for assessing events that involve the combustion of metallic plutonium (Pu) presents a continuing need in carrying out safety evaluations in support of DOE programs involving nuclear weapons. For production, storage, transport and decommissioning operations, an accident sequence that frequently must be evaluated involves metallic Pu being exposed in a fire environment. There are significant data on which to base an estimate for the source term which has been surveyed recently by Mishima et al (Mishima, 1993), but much of the surveyed work relates to well controlled laboratory experiments with relatively small amounts of Pu. One of the most relevant sources of information was the work by Stewart (Stewart, 1959) of the UK Atomic Weapon Research Establishment at Aldermaston. That work, referred to as the Vixen A Trials provides direct experimental data on the aerosolization and environmental releases from relatively large metallic Pu shapes immersed in a ``petrol`` fire. A new analysis of the air sampler data from the two Vixen A Trials experiments involving chunks of plutonium exposed to hydrocarbon fuel fires indicated a respirable release fraction (referenced to total plutonium involved) of 0.0001 to 0.0003 (1 E-4 to 3 E-4) depending on the parameters used in the atmospheric transport and dispersion model used. A value of 3 E-4 is recommended as an upper limit for use in safety assessment studies involving similar accident scenarios.