Edward J. Hnetkovsky

Performance of metal and polymeric O-ring seals during beyond-design-basis thermal conditions

This paper summarizes the small scale thermal exposure test results of the performance of metallic and polymeric O-ring seals typically used in radioactive material transportation packages. Five different O-ring materials were evaluated: Inconel/silver, ethylene-propylene diene monomer (EPDM), polytetrafluoroethylene (PTFE), silicone, butyl, and Viton. The overall objective of this study is to provide test data and insights to the performance of these Oring seals when exposed to beyond-design-basis temperature conditions due to a severe fire. Tests were conducted using a small-scale stainless steel pressure vessel pressurized with helium to 2 bar or 5 bar at room temperature. The vessel was then heated in an electric furnace to temperatures up to 900 °C for a pre-determined period (typically 8 h to 9 h). The pressure drop technique was used to determine if leakage occurred during thermal exposure. Out of a total of 46 tests performed, leakage (loss of vessel pressure) was detected in 13 tests.

Investigation of Surrogate Smoldering Ignition Sources for Testing Soft Furnishings

The introduction of cigarette ignition propensity standards has led to a reduction in the availability of high ignition propensity commercial cigarettes. Since high ignition propensity cigarettes are needed for soft furnishing flammability tests, a standard reference cigarette, SRM 1196, was developed. The current supply of SRM 1196 cigarettes is limited, and so the feasibility of a surrogate ignition source was examined. The surrogate ignition source should be repeatable, sustainable, relatively inexpensive, and should have a similar ignition propensity to the SRM 1196 cigarette on a broad range of substrates. A literature review identified several potential surrogate ignition sources including cartridge heaters, hot slugs, and materials that can smolder, such as charcoal, cotton plugs, and cotton rope. Experiments quantified the heat transfer characteristics and ignition propensity of the SRM 1196 cigarette as a baseline for evaluating candidate ignition sources. In particular, thermocouples were used to measure the temperatures at the interface of the cigarette and the substrate for both reactive and inert substrates. Screening experiments were performed to estimate the ignition propensities of the candidate surrogate sources. Analysis of and experiments with these sources found that cartridge heaters are impractical for routine testing and that commercial versions of the combustible materials do not show appropriate or repeatable values of ignition propensity. The use of hot slugs would require additional testing in which the materials, dimensions, shape, and mass were all systematically varied. Extensive testing to identify fabrics which, when supported on a foam slab, would lead to some, but not 100 % ignitions did not find enough fabrics to demonstrate equivalence to the SRM 1196 cigarette. Because of the unlikelihood of success, it is recommended that these tests not be performed and that the National Institute of Standards and Technology (NIST) order another supply of SRM 1196 cigarettes.

Spent Nuclear Fuel Transportation Package Seals in Beyond Design Basis Temperature Excursions

The US Nuclear Regulatory Commission (NRC) is studying the performance of seals in spent nuclear fuel (SNF) transportation packages exposed to fires that could exceed the hypothetical accident condition fire described in Title 10 of the Code of Federal Regulations, Part 71, such as the Baltimore Tunnel Fire that occurred in 2001, or the MacArthur Maze fire that occurred in 2007. The performance of package seals is important for determining the potential for 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 the containment barrier between the environment and the radioactive package contents. The NRC Office of Nuclear Regulatory Research contracted the National Institute of Standards and Technology to conduct small-scale thermal testing to obtain experimental data of the performance of seals during extreme temperature exposures. The experimental testing consisted of several small-scale pressure vessels fabricated with a modified ASME flange design and tested metallic and polymeric seals, similar to those that might be used on an actual SNF transportation package. The vessels were heated in an electrical oven to temperatures as high as 800°C (1472°F), exceeding the rated temperatures of the seals in question. This paper will provide a summary of the testing conducted and present test results and conclusions. BACKGROUND

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.