Publications

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Several Department of Energy (DOE) facilities have nuclear or hazardous materials stored in robust, welded, stainless-steel containers with undetermined fire-induced pressure response behaviors. Lack of test data related to fire exposure requires conservative safety analysis assumptions for container response at these facilities. This conservatism can in turn result in the implementation of challenging operational restrictions with costly nuclear safety controls. To help address this issue for sites that store DOE 3013 stainless-steel containers, a series of five tests were undertaken at Sandia National Laboratories. The goal of this test series was to obtain the response behavior for various configurations of the DOE 3013 containers when exposed to various fire conditions. Key parameters measured in the test series included identification of failure-specific characteristics such as pressure, temperature, and leak/burst failure type. This paper describes the development and execution of the test series performed to identify these failure-specific characteristics. Work completed to define the test configurations, payload compositions, thermal insults, and experimental setups are discussed. Test results are presented along with corresponding discussions for each test.

Certification of radioactive material (RAM) packages for storage and transportation requires multiple tiers of testing that simulate accident conditions in order to assure safety. One of these key testing aspects focuses on container response to thermal insults when a package includes materials that decompose, combust, or change phase between-40 °C and 800 °C. Thermal insult for RAM packages during testing can be imposed from a direct pool fire, but it can also be imposed using a furnace or a radiant heat system. Depending on variables such as scale, heating rates, desired environment, intended diagnostics, cost, etc., each of the different methods possess their advantages and disadvantages. While a direct fire can be the closest method to represent a plausible insult, incorporating comprehensive diagnostics in a controlled fire test can pose various challenges due to the nature of a fire. Radiant heat setups can instead be used to impose a comparable heat flux on a test specimen in a controlled manner that allows more comprehensive diagnostics. With radiant heat setups, however, challenges can arise when attempting to impose desired nonuniform heat fluxes that would account for specimen orientation and position in a simulated accident scenario. This work describes the development, implementation, and validation of a series of techniques used by Sandia National Laboratories to create prescribed non-uniform thermal environments using radiant heat sources for RAM packages as large as a 55-gallon drum.

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Fire suppression systems for transuranic (TRU) waste facilities are designed to minimize radioactive material release to the public and to facility employees in the event of a fire. Currently, facilities with Department of Transportation (DOT) 7A drums filled with TRU waste follow guidelines that assume a fraction of the drums experience lid ejection in case of a fire. This lid loss is assumed to result in significant TRU waste material from the drum experiencing an unconfined burn during the fire, and fire suppression systems are thus designed to respond and mitigate potential radioactive material release. However, recent preliminary tests where the standard lid filters of 7A drums were replaced with a UT-9424S filter suggest that the drums could retain their lid if equipped with this filter. The retention of the drum lid could thus result in a very different airborne release fraction (ARF) of a 7A drum's contents when exposed to a pool fire than what is assumed in current safety basis documents. This potentially different ARF is currently unknown because, while studies have been performed in the past to quantify ARF for 7A drums in a fire, no comprehensive measurements have been performed for drums equipped with a UT-9424S filter. If the ARF is lower than what is currently assumed, it could change the way TRU waste facilities operate. Sandia National Laboratories has thus developed a set of tests and techniques to help determine an ARF value for 7A drums filled with TRU waste and equipped with a UT-9424S filter when exposed to the hypothetical accident conditions (HAC) of a 30-minute hydrocarbon pool fire. In this multi-phase test series, SNL has accomplished the following: (1) performed a thermogravimetric analysis (TGA) on various combustible materials typically found in 7A drums in order to identify a conservative load for 7A drums in a pool fire; (2) performed a 30-minute pool fire test to (a) determine if lid ejection is possible under extreme conditions despite the UT-9424S filter, and (b) to measure key parameters in order to replicate the fire environment using a radiant heat setup; and (3) designed a radiant heat setup to demonstrate capability of reproducing the fire environment with a system that would facilitate measurements of ARF. This manuscript thus discusses the techniques, approach, and unique capabilities SNL has developed to help determine an ARF value for DOT 7A drums exposed to a 30-minute fully engulfing pool fire while equipped with a UT-9424S filter on the drum lid.

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The Pipe Overpack Container (POC) was developed at Rocky Flats to transport plutonium residues with higher levels of plutonium than standard transuranic (TRU) waste to the Waste Isolation Pilot Plant (WIPP) for disposal. In 1996 Sandia National Laboratories (SNL) conducted a series of tests to determine the degree of protection POCs provided during storage accident events. One of these tests exposed four of the POCs to a 30-minute engulfing pool fire, resulting in one of the 7A drum overpacks generating sufficient internal pressure to pop off its lid and expose the top of the pipe container (PC) to the fire environment. The initial contents of the POCs were inert materials, which would not generate large internal pressure within the PC if heated. However, POCs are now being used to store combustible Transuranic (TRU) waste at Department of Energy (DOE) sites. At the request of DOE's Office of Environmental Management (EM) and National Nuclear Security Administration (NNSA), SNL started conducting a new series of fire tests in 2015 to examine whether PCs with combustibles would reach a temperature that would result in (1) decomposition of inner contents and (2) subsequent generation of sufficient gas to cause the PC to overpressurize and release its inner content. In 2016, Phase II tests showed that POCs tested in a pool fire failed within 3 minutes of ignition with the POC lid ejecting. These POC lids were fitted with an all-metal (NUCFIL019DS) filter and revealed that this specific filter did not relieve sufficient pressure to prevent lid ejection. For the test phase discussed in this report, Phase II-A, the POCs are exposed to a 30-minute pool fire, with similar configurations to those tested in Phase II, except that the POC lids are fitted with a hybrid metal-polyethylene (UT9424S) filter instead. This report will: describe the various tests conducted in Phase II-A, present results from these tests, and discuss implications for the POCs based on the test results.

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Sandia National Laboratories (SNL) conducted in the summer of 2017 its third fracture challenge (i.e., the Third Sandia Fracture Challenge or SFC3). The challenge, which was open to the public, asked participants to predict, without foreknowledge of the outcome, the fracture response predictions of an additively manufactured tensile test coupon of moderate geometric complexity when loaded to failure. This paper outlines the approach taken by our team, one of the SNL teams that participated in the challenge, to make a prediction. To do so, we employed a traditional finite element approach coupled with a continuum damage mechanics constitutive model. Constitutive model parameters were determined through a calibration process of the model response with the provided longitudinal and transverse tensile test coupon data. Comparison of model predictions with the challenge coupon test results are presented and general observations gleaned from the exercise are provided.

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