Consistent modelling of material weight loss and gas release due to pyrolysis and conducting benchmark tests of the model—A case for glovebox panel materials such as polymethyl methacrylate

PLOS ONE RESEARCH ARTICLE Consistent modelling of material weight loss and gas release due to pyrolysis and conducting benchmark tests of the model—A case for glovebox panel materials such as polymethyl methacrylate a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 Takuya Ohno ID*, Shinsuke Tashiro, Yuki Amano, Naoki Yoshida, Ryoichiro Yoshida, Hitoshi Abe Japan Atomic Energy Agency, Tokai, Japan * Abstract OPEN ACCESS Citation: Ohno T, Tashiro S, Amano Y, Yoshida N, Yoshida R, Abe H (2021) Consistent modelling of material weight loss and gas release due to pyrolysis and conducting benchmark tests of the model—A case for glovebox panel materials such as polymethyl methacrylate. PLoS ONE 16(1): e0245303. https://doi.org/10.1371/journal. pone.0245303 Editor: Giuseppina Luciani, University of Naples Federico II, ITALY Received: October 19, 2020 Accepted: December 25, 2020 Published: January 28, 2021 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pone.0245303 Copyright: © 2021 Ohno et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the manuscript. It is necessary to consider how a glove box’s confinement function will be lost when evaluating the amount of radioactive material leaking from a nuclear facility during a fire. In this study, we build a model that consistently explains the weight loss of glove box materials because of heat input from a flame and accompanying generation of the pyrolysis gas. The weight loss suggests thinning of the glove box housing, and the generation of pyrolysis gas suggests the possibility of fire spreading. The target was polymethyl methacrylate (PMMA), used as the glove box panel. Thermal gravimetric tests on PMMA determined the parameters to be substituted in the Arrhenius equation for predicting the weight loss in pyrolysis. The pyrolysis process of PMMA was divided into 3 stages with activation energies of 62 kJ/ mol, 250 kJ/mol, and 265 kJ/mol. Furthermore, quantifying the gas composition revealed that the composition of the pyrolysis gas released from PMMA can be approximated as 100% methyl methacrylate. This result suggests that the released amount of methyl methacrylate can be estimated by the Arrhenius equation. To investigate the validity of such estimation, a sealed vessel test was performed. In this test, we observed increase of the number of gas molecules during the pyrolysis as internal pressure change of the vessel. The number of gas molecules was similar to that estimated from the Arrhenius equation, and indicated the validity of our method. Moreover, we also performed the same tests on bisphenol-A-polycarbonate (PC) for comparison. In case of PC, the number of gas molecules obtained in the vessel test was higher than the estimated value. Introduction When assessing the amount of radioactive material leaking from a nuclear facility during a fire, it is critical to consider how the containment function of the glove box will be lost. For example, if a fire is stopped early, radioactive material leakage will be minimized because the PLOS ONE | https://doi.org/10.1371/journal.pone.0245303 January 28, 2021 1 / 16 PLOS ONE Funding: This study was performed under the research entrusted by Secretariat of Nuclear Regulation Authority. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. Consistent modelling of material weight loss and gas release due to pyrolysis of glovebox panel materials containment barriers, such as the glove box, will still perform well in the early stages of the fire. Therefore, it is necessary to understand how containment barriers to radioactive material are lost as the fire progresses. The glove box is one such containment barrier in many nuclear facilities. Therefore, this study models the process by which the containment function of the glove box is lost during a fire. Research on glovebox fires has been carried out vigorously from the 1960s to the 1970s. Overview of these studies have been summarized in a literature review by Hart [1]. The literature review suggests that research on glovebox fires has focused primarily on material selections and glovebox designs [2] or initial fire extinguishing in the event of a fire [3, 4]. In other words, research on how to prevent fires is the mainstream, and little research has been done on what kind of effects will occur in the event of a fire. Some studies have addressed the effects of fire, but the focus have been primarily on the thermal effects of combustion on the surroundings [5, 6]. On the other hand, recently, studies on how glove box fires progress were conducted by conducting actual combustion tests on full-scale glove boxes [7, 8]. In these studies, for example, one glove box was burned to investigate the release amount of heat and soot to examine how it affects the facility. However, the studies did not consider when the containment function of the glove box was lost. The Japan Atomic Energy Agency (JAEA) modeled the pyrolysis behavior of materials used in glove box panels by conducting thermogravimetricdifferential thermal analysis (TG-DTA) tests and differential scanning calorimetry (DSC) tests [9–11] to estimate when the containment function of a glove box was lost. For example, the weight loss of the panel materials in TG-DTA tests is a reduction in the thickness of the glove box barrier during a fire. As an extension of JAEA’s studies, this study was conducted. In this study, we consider a scenario of a glovebox fire (Fig 1). We assume that the fire occurs outside the glove box in a process room, and the inside of the glove box is filled with an inert gas such as N2, and the process room is filled with air. The fire heats the glove box. When the temperature of the glove box rises because of heating, the constituent materials of the glove box, especially polymers, such as organic glass and rubber, can be pyrolyzed, reducing the thickness of the glove box barrier. An indicator of this barrier thickness is the weight of the polymer. As the pyrolysis progresses, the weight of the polymer decreases, which is equivalent to making holes in the glove box during a fire. The mass lost by pyrolysis is released to the outside and inside of the glove box as a flammable pyrolysis gas. On the outside, the pyrolysis gas Fig 1. Schematic of glovebox fire. This study models the reduc (...truncated)