NRC SPENT FUEL TRANSPORTATION RISK ASSESSMENT METHODOLOGY

In the approximately 30 years since the Final Environmental Statement on the Transportation of Radioactive Material by Air and Other Modes (NUREG-0170) [1], there have been many changes in the shipment of spent fuel and the ability to analyze normal conditions and accident events that have a profound impact on calculated risks. Sandia National Laboratories is in the process of conducting a new spent fuel transportation risk assessment for the U.S. NRC. Unlike previous generic spent fuel risk assessments, this assessment will include certified cask designs and will also evaluate the effects of using welded or bolted inner canisters on spent fuel transport impacts. The intended result of the study is an updated assessment of the risks associated with the transport of spent fuel. This new risk assessment, which will be published as an NRC document, will be submitted to a peer review group and will be published for public comment. This paper will discuss the general analysis plan to be used in performing the risk assessment. Included will be the development of new event probability distributions for both truck and rail transport, the choice of real cask designs to be used in the study, the types of analyses to be performed, the analytical methodologies that will be used, and the schedule for completion of the study. A criticism of recent risk assessments has been that accident probability numbers are too old and do not represent the current transportation environment. The updated event probability distributions will address this concern. Parameters that influenced the cask selection included: type of wall construction, shipment mode, and whether or not a canister was used. Both structural and thermal response will be determined with detailed 3-D finite element calculations for a number of hypothetical accident conditions. The finite element analyses of the casks will be used to determine the presence or absence of any release pathways and analyses of the spent fuel contents will determine the source term available for release. Release information will be coupled with environmental and route factors to calculate risks using the computer code RADTRAN [2].