A Historical Review of the Safe Transport of Spent Nuclear Fuel
|Enhanced safety record report - final public release.pdf (3.87 MB)||3.87 MB|
This report is a revision to M3 milestone M3FT-16OR090402028 for the former Nuclear Fuels Storage and Transportation Planning Project (NFST), “Safety Record of SNF Shipments.” The US Department of Energy (DOE) has since established the Office of Integrated Waste Management (IWM), which builds on the work begun by NFST, to develop an integrated waste management system for spent nuclear fuel (SNF), including the development of a large-scale transportation system for the safe transport of SNF to storage or disposal facilities. The US does not currently operate a large-scale transportation system for SNF, but there is extensive experience worldwide in transporting SNF safely. This report contains a review of publicly available information on SNF transportation worldwide. Estimates were developed to ascertain the number of fuel assemblies, the number of tons of SNF shipped, and the number of shipments made between 1962 and 2016 worldwide. Data are not available for all countries, and statistics are also incomplete for many of the countries that have supplied information, so all quantities shown are lower bounds. However, from this review, it can be concluded that: • At least 25,400 shipments of SNF have been made worldwide, but likely more than 44,400. It is likely that significantly more cask shipments have been made for all forms of SNF considered. The shipments within and into the US account for approximately 10 to 17 percent of this total. • The quantity of SNF shipped worldwide to date is at least 87,000 metric tons of heavy metal (MTHM) and likely more than 109,000 MTHM. This is considered a lower bound since many of the data sources did not report on the heavy metal quantities shipped. Of the quantities reported here, the US accounts for only about 5 to7 percent of the total. Additionally, the study identified that at least 130 cask shipments of vitrified high-level radioactive waste (HLW) containing more than 2,350 canisters of HLW have been reprocessed at the plant in La Hague, France, and shipped back to the countries where the SNF originated. Review of the data sources shows that all of these shipments were undertaken without any injury or loss of life caused by the radioactive nature of the material transported. In general, there have been few transportation accidents worldwide in the history of transporting SNF, and none have had significant radiological consequences. This report investigates incidents in SNF and HLW transportation for which information could be found. These incidents may be classified as transportation accidents, instances of equipment contamination which occurred during transport of SNF, problems with or failure of conveyances, or disruptions to the transport of radioactive material. Accidents have been infrequent in SNF and HLW transportation, and most have been minor accidents such as low-speed derailments or minor traffic accidents. Instances of radioactive contamination on SNF and HLW casks and the vehicles that carry them have occurred more frequently than transportation accidents, but these instances were still infrequent when compared to the overall number of shipments which were made in several countries over the years. Contamination was found on shipments within the US in the 1970s and 1980s and in Europe in the 1990s. After many studies, improvements in operating procedures at nuclear facilities, and enhanced regulatory oversight and enforcement of contamination limits, instances of radiological contamination of equipment have become less frequent. Although uncommon, disruptions to shipments have occurred recently in Germany. Thousands of people have attended nonviolent and violent protests, resulting in shipments being delayed. Although there have not been any radiological effects as a result these protests, injuries have occurred, shipments have been delayed, and millions of dollars in extra costs have been incurred. There have been very few incidents in the history of SNF transportation due to (1) the robust regulatory requirements in place for SNF shipping packages, commonly called casks, and (2) the high degree of expertise of the package designers, manufacturers, and SNF shippers. However, a cask’s performance during a transportation accident, including its ability to contain radioactive contents and to provide adequate shielding and criticality safety, has always been a subject of concern to shippers, regulators, and the general public. This report examines an actual accident involving a loaded SNF cask that occurred during a shipment in the US in 1971. It was a severe accident in which a truck overturned and then the cask being transported on the truck separated from the trailer. To the knowledge of the authors, it was the most severe accident ever to occur during a shipment of SNF. However, the cask was only superficially damaged; it succeeded in containing all of the radioactive material, and furthermore, the SNF element inside the cask was undamaged. Photographs of the accident scene, the cask damage, the recovery of the cask from the accident site, and the SNF element are included in this report, along with a photograph of the cask upon its return to service after inspection and refurbishment. Following the case study of the accident involving SNF, this report presents a review of the US Nuclear Regulatory Commission (NRC) documents analyzing the risks inherent to SNF transportation. The NRC has conducted four studies attempting to quantify the risks in transporting SNF using the best available data, assumptions, and models. In every reinvestigation of SNF transportation risk assessment undertaken by the NRC, the radiological risks of SNF transportation have been estimated to be low in comparison to the risks inherent in truck and rail transportation. Furthermore, the collective dose received by the general public from SNF and HLW shipments is four orders of magnitude smaller than the naturally occurring background dose received by the same population in the same period of time. As computational analysis methods have improved, estimated risks of SNF transportation have decreased. In the earliest risk assessment reports, it was assumed that casks would rupture in accidents and release all of their contents since the mechanisms for cask failure could not be modeled. As methods improved, it became possible to model strains on cask components and SNF rods, as well as the effects of high temperatures on containment seals and cask shielding. As more detailed and realistic simulations were performed, it became possible to reduce the uncertainty associated with risk analysis, thereby providing more reliable estimates of the actual risks involved in transportation. Since the first investigation of SNF transportation risk by the NRC, regulations on casks have always been found adequate to protect the health and safety of the public in the event of a transportation accident. The hypothetical accident conditions described in the regulations are, in fact, much more severe than the majority of potential transportation accidents. This report shows that transportation of SNF has been accomplished routinely and safely in many countries around the world, including the US, for decades.