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DOE OSTI2020

Tapsolver: A Python Package For The Simulation And Analysis Of Tap Reactor Experiments

TAPsolver is a python package, which automates TAP simulation and analysis routines. TAPsolver is built around the python packages FEniCS and Dolfin-Adjoint, which help take advantage of model adjoints to provide automatic derivatives. TAPsolver is flexible, with reaction mechanisms and rate constants that can be set through input files that allow users to take advantage of the different functionalities, which include sensitivity analyses, parameter optimization and uncertainty quantification.

Yonge, Adam↗

DOE OSTI2020

Tapsolver: A Python Package For The Simulation And Analysis Of Tap Reactor Experiments

Kunz, MatthewR.↗

DOE OSTI2021

TAPsolver: A Python package for the simulation and analysis of TAP reactor experiments

Not Available

Yonge, Adam↗

DOE OSTI2023

Simulating Catalysis with Realistic Pellet Geometries Using Mesoflow: A Case Study of Catalytic Propane Dehydrogenation

We present a case study of catalytic propane dehydrogenation with our open-source multiphysics solver, Mesoflow. The solver was developed to simulate reactive flow coupled to heterogeneous catalytic reactions and deactivation in the context of complex, mesoscale geometry. The method leverages cartesian block-structured adaptive mesh refinement to capture realistic catalyst microstructural features acquired directly from X-ray computed tomography data. A kinetic model for propane dehydrogenation and catalyst deactivation was developed based on temporal analysis of products (TAP) reactor experiments. The TAP reactor experiments allow for precise characterization of intrinsic kinetic reaction steps which are implemented into Mesoflow simulations to model the spatial and temporal evolution of reactants, products, and catalyst active sites. The short-term and long-term deactivation behavior is studied by using XCT data collected from fresh and aged catalyst pellets, which exhibit different microstructural features. This study employs time-splitting algorithms to connect disparate reaction and flow timescales, enabling the simulations to achieve realistic deactivation timescales on the order of minutes while the flow time-scales for small particles (100 microns) are several milliseconds. We also introduce a flexible automated python script that writes the necessary files to construct a Mesoflow simulation from user-created chemical mechanisms. We will also introduce a few new features that are added to Mesoflow such as higher order schemes, implicit chemistry integrators and the ability to run on AMD and NVIDIA graphics-processing-units.

AMReX↗

DOE OSTI2023

Internal calibration of transient kinetic data via machine learning

The temporal analysis of products (TAP) reactor provides a vast amount of transient kinetic information that may be used to describe a variety of chemical features including residence time distributions, kinetic coefficients, number of active sites, reaction mechanism, etc. However, as with any measurement device, the TAP reactor signal is convoluted with noise and drift is common. In order to reduce the uncertainty of the kinetic measurement and any derived parameters or mechanisms, proper preprocessing must be performed prior to any advanced type of analysis. This preprocessing includes baseline correction, i.e., a shift in the voltage response, and calibration, i.e., a scaling of the flux response based on prior experiments. The traditional methodology of preprocessing requires significant user discretion and reliance on separate calibration experiments that may drift over time. Herein we use machine learning techniques combined with physical constraints to understand the noise and drift that is being generated within and between experiments for enhancement of the chemical kinetic signal. As such, the proposed methodology demonstrates clear benefits over the traditional preprocessing approach by eliminating the need for separate calibration experiments or heuristic input from the user.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Quantifying the impact of temporal analysis of products reactor initial state uncertainties on kinetic parameters

The temporal analysis of products (TAP) reactor, a transient kinetic tool, provides users with information as the catalyst state evolves. However, the state of the art for TAP uncertainty quantification only considers the experimental noise present in the outlet flow signal. Additional sources of uncertainty, including, but not limited to, initial surface coverages, the catalyst zone location, the inert void fraction, and the gas pulse intensity and pulse delay, are not included. For this reason, a framework for quantifying all uncertainty sources present in TAP experiments is presented and applied to a carbon monoxide oxidation case study. Herein, two methods for quantifying these sources of uncertainty are introduced. The first utilizes initial state sensitivities to approximate the parameter variances, as well as to provide insights into the structural certainty of the model. The second generates parameter confidence distributions through an ensemble-based sampling algorithm. This initial state covariance matrix can ultimately be merged with the experimental noise covariance matrix, providing a unified description of the parameter uncertainties for a single TAP experiment.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Transient kinetic insights into selective propene oxidation over industrial bismuth molybdate catalysts

Selective oxidation of propene to acrolein over industrial multicomponent bismuth molybdate (BMO) catalysts significantly depends on reaction conditions that include operating parameters and catalyst state. Here, this work investigates selective propene oxidation in the intrinsic kinetic paradigm of Temporal Analysis of Products (TAP) reactor by systematically varying catalyst redox state, temperature, and oxygen-to-propene feed ratio. A 93 % propene conversion with an acrolein yield of 80 % is achieved at elevated temperatures (450 °C) on oxidized catalysts under oxygen-rich conditions (O 2 :C 3 H 6 = 10). However, these conditions diminish acrolein-to-CO 2 selectivity due to enhanced total oxidation to CO 2 . In contrast, a reduced catalyst state, moderate temperature (350 °C), and lower oxygen feed (O 2 :C 3 H 6 = 1) nearly doubles the acrolein to-CO 2 selectivity, albeit at a lower acrolein yield (33 %). Transient kinetic studies together with a kinetic model that simplify the major product formation pathways in lumped non-elementary forms reveal that the availability of surface oxygen species plays a pivotal role in governing reaction pathways. Additionally, density functional theory (DFT) calculations on pure BMO catalysts inform the role of surface redox states on propene and oxygen activation barriers. Lattice oxygen at acrolein-selective sites drives both acrolein and CO 2 formation, while adsorbed oxygen at activation sites favors unselective CO 2 generation. This work establishes a critical relationship between transient product selectivity and surface oxygen availability, which is strongly influenced by catalyst redox state, feed ratio, and reaction temperature. These insights underscore the importance of dynamic reactor operation strategies and offer a foundation for designing next-generation propene oxidation processes with tunable acrolein selectivity.

42 - ENGINEERING↗

DOE OSTI2025

Statistical distributions for transient transport

Here, this paper introduces the use of statistical distributions based on transport differential equations for clear distinction of transport modes within transient kinetic experiments. More specifically, novel techniques are developed for the transient data obtained through the Temporal Analysis of Products (TAP) reactor and are applicable to experiments where pulse response into a gas flow is used. The methodology allows distinguishing between two domains of diffusion transport in heterogeneous catalytic systems, i.e., Knudsen and non-Knudsen diffusion, using statistical fingerprints, and finding the transition domain. Two distribution parameters were obtained that directly result in coefficients that correspond to the concentration and the rate of transport. Using a linear relationship between the rate and concentration coefficients, Knudsen diffusion is revealed when the rate of transport is constant and non-Knudsen diffusion is confirmed when the rate of transport coefficient is a function of the concentration coefficient. As a result, accurate transport information can be extracted from experimental data even in the presence of comprising instrument drift or noise particularly when analyzing higher pressure pulse responses with complex transport. This enables more direct investigation of experiments influenced by gas-phase reactions.

TAP reactor↗

DOE OSTI2021

Formation of Surface Impurities on Lithium–Nickel–Manganese–Cobalt Oxides in the Presence of CO 2 and H 2 O

Surface impurities involving parasitic reactions and gas evolution contribute to the degradation of high Ni content LiNi x Mn y Co z O 2 (NMC) cathode materials. The transient kinetic technique of Temporal Analysis of Products (TAP), density functional theory, and infrared spectroscopy have been used to study the formation of surface impurities on varying nickel content NMC materials (NMC811, NMC622, NMC532, NMC433, NMC111) in the presence of CO 2 and H 2 O. CO 2 reactivity on a clean surface as characterized by CO 2 conversion rate in the TAP reactor follows the order: NMC811 > NMC622 > NMC532 > NMC433 > NMC111. The capacity of CO 2 uptake follows a different order: NMC532 > NMC433 > NMC622 > NMC811 > NMC111. Moisture pretreatment slows down the direct CO 2 adsorption process and creates additional active sites for CO 2 adsorption. Electronic structure calculations predict that the (012) surface is more reactive than the ($10\bar{1}4$) surface for CO 2 and H 2 O adsorption. CO 2 adsorption leading to carbonate formation is exothermic with formation of ion pairs. The average CO 2 binding energies on the different materials follow the CO 2 reactivity order. Water hydroxylates the (012) surface and surface OH groups favor bicarbonate formation. Water creates more active sites for CO 2 adsorption on the ($10\bar{1}4$) surface due to hydrogen bonding. The composition of surface impurities formed in ambient air exposure is dependent on water concentration and the percentage of different crystal planes. Different surface reactivities suggest that battery performance degradation due to surface impurities can be mitigated by precise control of the dominant surfaces in NMC materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Time-Gated Raman Spectroscopy (Intern Final Report)

Time-gated Raman spectroscopy is a powerful tool for rapid non-destructive analysis of chemical compounds, particularly when combined with other investigative methods. Time-gating the signal obtained from a sample during Raman spectroscopy allows for the removal of background emission and black body radiation, improving clarity and accuracy of scans. The main objectives of this project were to prove the lab’s time-gated Raman spectroscopy system works as proof of concept and to make select improvements to the in-house LabVIEW software used to run the time-gated system. This time-gated system will be added to the CTK’s TAP reactors in the future, but this is out of the scope of this internship project. This research is important, as understanding the mechanisms behind catalysts leads to designing better systems/materials and the perfection of catalysts, and energy-efficient chemical manufacturing is key when designing a greener future. The research for this project was done with samples at both ambient conditions in sample holders and at operando conditions (i.e., high temperature, unsteady-state) inside a small-volume chemical reactor. Numerous spectro-kinetic scans of the catalysts were obtained, but the advanced dynamics of these systems are still being interpreted. There is data that demonstrates that the time-gated system is correctly rejecting emission from samples, and one can observe real-time changes in the signal from the sample, due to coking or changes induced by redox chemistry. Chemical manufacturers and the planet are the main beneficiaries of catalysis research, as better catalysts will reduce carbon emissions.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Transient Catalytic Reaction Analysis Through Signal Defragmentation

The Temporal Analysis of Products (TAP) pulse response technique provides valuable insights into catalytic function and reaction kinetics. However, complex fragmentation patterns in the TAP mass spectrometry signals can complicate precise quantification, particularly when analyzing transient gas flux data typical of TAP experiments. This work demonstrates a standard defragmentation method that deconvolves transient TAP signals while maintaining the temporal resolution of the experiment. First, the integrals of calibration gas fluxes are used to determine the fingerprint fragmentation pattern and construct a fragmentation matrix. This matrix is then used to defragment experimental flux data at each recorded time point via a non-negative least squares regression. The effectiveness of this method is demonstrated using virtual data and control experiments with a TAP reactor system. The defragmentation is then applied to the more complex propane dehydrogenation reaction on a chromia/alumina catalyst, which can contain up to ten significant gas species in the reactor outlet. Initial propane pulsing reveals an induction period during which propane is fully oxidized to CO2, followed by partial reduction to CO. Afterwards, there is a transition in chemistries towards coking and propylene production. Our example illustrates a practical method for the accurate determination of the time-dependent reactant/product concentrations and rates for a thorough analysis of the propane dehydrogenation kinetics. This approach can be broadly applied to any transient mass spectrometry experiment for a better understanding of catalyst-reaction dynamics.

36 - MATERIALS SCIENCE↗

DOE OSTI2023

Chemical looping conversion of CH4/CO2 to syngas on 5wt.%Ni@Ce0.6Zr0.4O2 catalyst: Impact of dynamic accumulation of surface carbon and oxygen vacancies

Syngas, a combination of carbon monoxide (CO) and hydrogen (H2), is a precursor to many chemicals and fuels, contributing to the billion-dollar global hydrocarbon industry. Chemical looping reforming (CLR) of the greenhouse gases methane (CH4) and carbon dioxide (CO2) allows for energy-efficient production of syngas. 5wt.% nickel (Ni) on ceria-zirconia (5wt%Ni@Ce0.6Zr0.4O2) mixed metal oxide catalyst was investigated here to explore pathways for enhanced syngas production on sustainable earth-abundant transition metal supported catalysts. The role of reduction-oxidation (redox) state of the catalyst, and carbon formation on the catalyst surface during chemical looping is explored to drive superior reaction kinetics, conversions, selectivity, and syngas ratios (H2/CO). The bulk and surface structure of the catalyst, along with carbon deposition features were characterized by electron microscopy, X-Ray diffraction, and ex situ Raman spectroscopy. The dynamic evolution of catalysts under CLR reaction conditions and the intrinsic reaction mechanisms were probed with in situ Raman spectroscopy, in situ Fourier transform spectroscopy, dynamic oxygen storage capacity (DOSC), and the Temporal Analysis of Products (TAP) reactor studies. Intrinsic kinetics of syngas production via CLR was correlated to the redox state of catalyst and the participation of nickel-catalyzed multiwalled carbon nanotube (CNT) growth, allowing enhanced CLR reaction performance.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2025

Machine Learning-Assisted Recovery of Delicate Kinetic Information from Transient Reactor Experiments

Identifying active sites and their roles in chemical reaction steps remains a vital challenge in heterogeneous catalysis. Transient experiments offer a unique way to probe active sites and distinguish subtle kinetic features. Although physics-based analysis methods may be well-developed, they can be highly susceptible to experimental noise, and smoothing methods may erase or even distort important features; a smooth curve is not always the best curve. We demonstrate a new workflow for the direct interpretation of intrinsic kinetic information from exit flux curves measured in transient reactor experiments. This workflow contains three artificial neural networks (ANNs), including a noise reducer, a concentration predictor, and a rate predictor to analyze experimental data, followed by the virtual TAP (VTAP) physics-based reactor model and density functional theory (DFT) calculations of adsorption energies on specific sites. We use this workflow to analyze the data from experiments titrating Pt/Al 2 O 3 and Pt/SiO 2 catalysts with carbon monoxide (CO) in the temporal analysis of products (TAP) reactor. Our workflow separates the time-evolving chemical reaction and mass transfer information contained in the TAP pulse response. The existence of strong- and weak-binding sites on the Pt/Al 2 O 3 catalyst is observed in the catalyst titration experiment in the transient reactor. The structures of the strong- and weak-binding sites are then identified by using DFT calculations. We find that the Pt/SiO 2 catalyst has only strong-binding sites, which aligns with the inactive support effect of SiO 2 . We demonstrate how machine learning methods provide unique insights with high-resolution data analysis that cannot be achieved by using state-of-the-art physics-based methods.

Adsorption↗

DOE OSTI2022

Mechanistic pathways and role of oxygen in oxidative coupling of methane derived from transient kinetic studies

Oxidative coupling of methane (OCM) is a promising industrial process to upgrade natural gas to high value chemicals. In this study, Temporal Analysis of Products (TAP) and steady-state experiments were conducted to distinguish how the composition of surface and gas phase oxygen influence mechanistic details of the selective conversion of CH 4 to C 2 H 4 over the Mn-Na 2 WO 4 /SiO 2 catalyst. The results from TAP studies indicate that methane activation on this catalyst proceeds predominantly via a short-lived, transient surface oxygen species and there is a competition for this species to form either CO or methyl radicals on the surface. This active species has a total lifetime of 3 s and is identified to have a dioxygen (e.g. O 2 2- or O 2 -) form. We show that the concentration of the transient surface oxygen species significantly impacts the OCM performance. Oxygen attributed to the catalyst lattice (in a singular form e.g., O - ), is found to activate methane to a lesser degree, but exclusively forms CO 2 . Evidence for these surface pathways for methyl radical, CO and CO 2 formation identified by TAP are also validated through steady-state experiments. Finally, by distinguishing different catalyst oxygen species and their role in selective/nonselective pathways, important screening criteria have been identified for the advancement of superior catalyst formulations.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Fermi-Based Kinetic Model for the Sabatier Reaction: Sabatier Principle and Beyond It

The CO 2 methanation reaction (aka the Sabatier reaction) is one of the important carbon utilization technologies to reduce atmospheric greenhouse gases. In this study, kinetic modeling of the Sabatier reaction proceeding via the CO route has been presented by considering weak and strong chemisorption concepts rooted in electronic theory. Based on the single-route mechanism of the Sabatier reaction, the dependence of the reaction rate on the position of the catalyst Fermi level with respect to the antibonding states of the reagent (CO 2 ) and the product (CH 4 ), is demonstrated with the classic Sabatier volcano-shape. Furthermore, the model was applied to explain experimental results of reaction rates for Ni- and Ru-based catalytic systems and to understand origin of enhancement of turnover frequencies established for dynamic catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Deciphering the Mechanistic Role of Individual Oxide Phases and Their Combinations in Supported Mn–Na 2 WO 4 Catalysts for Oxidative Coupling of Methane

Oxidative coupling of methane (OCM) is an attractive direct route for upgrading methane to valuable chemicals. In this study, Temporal Analysis of Products (TAP) and steady state experiments are conducted to understand the role of individual oxide phases and their combinations in supported Mn-Na 2 WO 4 /SiO 2 catalysts for OCM. The results from TAP transient kinetic studies indicate that Mn plays an important role in promoting gas phase oxygen activation, while NaO x /SiO 2 and WO x /SiO 2 are relatively inert towards gas phase oxygen and methane activation. However, the supported catalyst combining Na and W in the form Na 2 WO 4 show enhanced gas phase oxygen activation exhibiting a much lower oxygen activation energy (148 kJ/mol) and enhanced activity toward methane activation as compared to the individual supported oxide catalysts. Addition of Mn to Na 2 WO 4 /SiO 2 further decreases the oxygen activation energy by 40 kJ/mol. Moreover, methane activation is also enhanced with CH 3 as the main intermediate but, with increasing Mn content, more CH 2 intermediates are observed. Different forms of oxygen (both dioxygen and atomic) are detected on the catalyst surface using isotopic pump/probe pulsing and their distribution is found to depend on the catalyst composition. An optimal Mn content in the Na 2 WO 4 /SiO 2 catalyst system is needed to enhance the amount of dioxide surface species (e.g., superoxide 16 O 2 - or peroxide 16 O 2 2- ) associated with the Na 2 WO 4 leading to high C 2 selectivity for OCM. When the Mn content is too high, the larger MnOx domains are shown to contribute to the formation of higher concertation of monoxide surface species that lead to nonselective OCM pathways. This insight from transient kinetic characterization using TAP combined with conventional steady state studies, provides a deeper understanding of the role of individual oxide phases and their combination on supported catalysts toward the formation of intermediate surface species and their impact on the OCM reaction mechanism. This knowledge is critical toward designing superior catalyst formulations for OCM.

10 SYNTHETIC FUELS↗

DOE OSTI2022

Distributed Fiber Optic Sensing to Identify Locations of Resistive Transitions in REBCO Conductors and Magnets

High-temperature superconductors such as REBa 2 Cu 3 O 7-x (REBCO, RE = rare earth) can generate strong magnetic fields that are promising for applications in particle accelerators and compact fusion reactors. Traditionally, voltage taps are installed in superconducting magnets to measure the voltage signals due to resistive transitions. The voltage-tap-based diagnostics is important for the development of magnet technology as it can help pinpoint the locations in the magnet windings that limit the magnet performance. The architecture of the multi-tape REBCO cable such as CORC wires, however, makes it difficult to apply the voltage-tap-based diagnostics to identify the locations of resistive transitions. Distributed fiber optic sensing (DFOS) has the potential to address this issue. In this paper, we report the measurements of thermal strain along a CORC wire based on optical frequency domain reflectometry with a maximum spatial resolution of 0.65 mm and a temporal resolution of 10 Hz. The optical fiber is co-wound with the CORC wire that is epoxy impregnated. During the test, current was increased until a resistive transition occurred in the conductor. The spectrum shift of the reflected light along the fiber was recorded. The results suggested that with proper thermal isolation from the cryogen, DFOS can be used to identify the locations of resistive transitions in CORC wires and magnets. In conclusion, the results will allow a better understanding of the causes of resistive transitions in REBCO conductors and magnets, which will help improve the REBCO magnet technology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

In-Sodium Testing of a Prototype Thermoacoustic Power Sensor for Sodium-Cooled Fast Reactors

The ultimate goal of this project is to develop and demonstrate a thermoacoustic power sensor (TAPS) for Sodium-Cooled Fast Reactors (SFRs), with potential application also envisioned to other nuclear technologies such as Lead-Cooled Fast Reactors (LFRs), Molten Salt Reactors (MSRs), in addition to Light Water Reactors (LWRs). The project was led by Westinghouse Electric Company, LLC (Westinghouse) and carried out in collaboration with Argonne National Laboratory (ANL) and the University of Pittsburgh. A TAPS is a passive (self-powered), non-invasive (wireless) sensor envisioned for measuring key parameters, such as local temperature and neutron flux, in a nuclear reactor core. The sensor generates pressure waves (i.e., sound waves) with a frequency and amplitude dependent upon nuclear operating conditions (coolant temperature or power changes). The acoustic waves are able to travel through the core and associated structures, and reach to the sensor network placed outside and/or inside of the reactor vessel. These sensors require a very small amount of power which, during loss of power events, can be provided, for example, by harvesting gamma radiation energy, thus resulting in a monitoring system that can function both during normal operation and during loss of power events. Westinghouse and the University of Pittsburgh designed and fabricated TAPS prototypes for Argonne National Laboratory (ANL) to carry out in-sodium testing to evaluate the effects of sodium on the TAPS and the performance of the TAPS technique in sodium. Argonne received a TAPS prototype from Westinghouse, and the prototype was modified such that it can be installed into a test vessel and function in sodium at elevated temperature without potentially leaking. A water mockup test apparatus was constructed to validate proper working of the prototype. An instrumentation and control (I&C) system, running on the National Instruments (NI) LabView platform, was developed to: 1) operate both the water mockup test and the in-sodium test facility; and 2) process and analyze the received acoustic signals from an array of accelerometers and the Argonne sodium-submersible high-temperature acoustic sensor. The prototype was successfully tested in a water bath at different temperatures. Water mockup tests demonstrated that the TAPS prototype is working properly and its resonance frequency changes linearly with the coolant (water) temperature. A TAPS test apparatus was constructed and integrated with the upgraded Under-Sodium Viewing (USV) sodium test facility. The integrated USV-TAPS sodium test facility has been operational. The TAPS prototype and a high-temperature sodium-submersible acoustic sensor (SSAS) developed by Argonne were both installed inside the TAPS test vessel. Being operated within argon cover gas under ambient conditions, the TAPS prototype demonstrated that it was functioning properly with a resonance frequency at 1407.2 Hz, which was successfully detected by the accelerometers mounted on the external wall of the vessel and the high-temperature SSAS installed inside the vessel. After successfully transferring sodium into the vessel, in-sodium tests of the prototype were conducted. Tests of the TAPS prototype demonstrated that the resonance frequency of the TAPS changes linearly with respect to the temperature difference between the interior of the TAPS and bulk sodium. The early tests showed that the TAPS prototype could not establish a continuous and consistent resonance in sodium. The resonance diminished before the prototype reached its operating temperature. A signal postprocessor was added to the DAQ module latterly to isolate interferences, enhance signal conditioning, improve peak detection, and generate resonance frequency versus temperature plots. After testing in molten sodium and immersion at higher temperature for several weeks, the TAPS prototype was able to establish a continuous resonance. Performance evaluation of the TAPS prototype was then conducted in sodium. The tests included the investigation of 1) the effects of the temperature difference between the TAPS and bulk sodium, 2) the effects of sodium flowrate; and 3) the performance of the different sensor-receiver systems positioned inside or outside the vessel. Results of a test demonstrated that, with limited sodium circulation, a continuous and consistent resonance of the TAPS prototype was established occasionally. The tests also demonstrated that, because of the nature of detection principles and mounting methods, the high temperature SSAS is more affected by acoustic noise, while accelerometers are more affected by vibrations, in the test environment. It is unknown why the TAPS prototype only occasionally established a continuous and consistent resonance when the TAPS temperature reached its operating temperature in molten sodium, and why it ultimately failed to resonate at all. A failure modes assessment was conducted and a few potential causes of failure were identified. Different post in-sodium tests were conducted to obtain additional information potentially relevant to the cause of the failure. Nondestructive evaluation techniques are suggested to examine the internal integrity as well as the gas mixture of the prototype. If they prove inconclusive, the prototype should be cut open to conduct a thorough inspection of its internal integrity and determine the state of the gas mixture.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗