Modeling delayed thermal runaway in nitric acid-soaked cat litter mixed with radioactive waste

Journal Article · Mon Jan 15 00:00:00 EST 2024 · Journal of Thermal Analysis and Calorimetry

DOI:https://doi.org/10.1007/s10973-023-12818-6· OSTI ID:2999064

Hobbs, Michael L. ^[1]; Britt, Phillip F. ^[2]; Hobbs, David T. ^[3]; Kaneshige, Michael Jiro ^[1]; Minette, Michael J. ^[4]; Mintz, Jessica ^[5]; Pennebaker, Frank M. ^[3]; Parker, Jr., Gary R. ^[6]; Pierce, Robert ^[3]; Rosenberg, David M. ^[1]; Schwantes, Jon M. ^[7]; Williams, Audrey M. ^[5]

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1. Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
2. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
3. Savannah River National Laboratory (SRNL), Aiken, SC (United States)
4. Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
5. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
6. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
7. Pennsylvania State Univ., University Park, PA (United States)

Thermal ignition of radioactive waste within a 55-gallon drum was simulated by using a pressure-dependent waste decomposition model (Hobbs et al. in Process Saf Environ Prot https://doi.org/10.1016/j.psep.2022.09.047, 2022) calibrated with data from full-scale drum experiments (Parker et al. in The thermolytic response of a surrogate RNS waste mixture at the drum scale. Los Alamos National Laboratory Report LA-UR-16-21760, 2016) and validated with experiments from multiple laboratories (Hobbs et al. in Thermal analysis of aged nitric acid-soaked kitty litter in TRU waste drums-23370.WM2023 Conference, Phoenix, AZ, 2023). The acceleration of nitric acid chemistry reacting with an organic cat litter leading to thermal ignition was likely triggered by a restricted vent in the drum. Here, we address whether the form of the rate equation in (Hobbs et al. in Process Saf Environ Prot https://doi.org/10.1016/j.psep.2022.09.047, 2022) is sufficient to extrapolate thermal ignition within aged drums of similar content that have been stored in Texas for over nine years by investigating four different reaction rate forms for waste decomposition. A critical reaction rate reduction analysis is performed on each of these models to determine if delayed thermal runaway within vented aged waste is possible after nine years. We found that a pressure-dependent first-order rate expression not only predicted the accidental ignition of the waste drum, but the form also matches multiple experiments from different laboratories. Even though the waste composition decreases over time, the model predicts that acceleration leading to thermal runaway is possible if the waste is confined, even after 9 years. In conclusion, waste containing oxidizers such as nitric acid should not be mixed with organic adsorbents, especially if the waste is confined.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: NA0003525
• OSTI ID: 2999064
• Alternate ID(s): OSTI ID: 2998315
• Report Number(s): SAND--2025-13359J; 1792046
• Journal Information: Journal of Thermal Analysis and Calorimetry, Journal Name: Journal of Thermal Analysis and Calorimetry Journal Issue: 19 Vol. 149; ISSN 1388-6150; ISSN 1588-2926
• Publisher: Springer
• Country of Publication: United States
• Language: English

Related Subjects

cookoff
safety analysis
thermal hazard
waste behaviour
waste characteristics