Used Nuclear Fuel Transportation Package Seal Performance in Beyond Design Basis Thermal Conditions

The U.S. Nuclear Regulatory Commission (NRC) is evaluating the performance of seals in used fuel transportation packages during beyond-design-basis fires, similar to the Baltimore tunnel fire that occurred in 2001. The performance of package seals is important for determining the potential for a release of radioactive material from a package during a beyond-design-basis accident. Seals generally have lower temperature limits than other package components and are often part of the containment barrier between the environment and the cask contents. The NRC’s Office of Nuclear Regulatory Research (RES) funded the National Institute of Standards and Technology (NIST) to conduct small-scale thermal testing to obtain experimental data of the performance of seals during beyond-design basis temperature exposures. The experimental testing consisted of several small-scale pressure vessels fabricated with a modified ASME flange design, using commercial grade metallic seals, similar to those that might be used on an actual spent nuclear fuel transportation package. The vessels were heated in an electrical furnace for exposures up to 9 hours (hrs) at temperatures as high as 800°C (1472°F), which far exceeded the rated temperature of the seals in question. This paper will provide a summary of the testing completed as well as the preliminary results and conclusions of the experiments performed by NIST.