Carl Stoots | Idaho National Laboratory (original) (raw)

Papers by Carl Stoots

Energy Conversion and Management, 2013

ABSTRACT Advanced reactor designs offer potentially significant improvements over currently opera... more ABSTRACT Advanced reactor designs offer potentially significant improvements over currently operating light water reactors including improved fuel utilization, increased efficiency, higher temperature operation (enabling a new suite of non-electric industrial process heat applications), and increased safety. As with most technologies, these potential performance improvements come with a variety of challenges to bringing advanced designs to the marketplace. There are technical challenges in material selection and thermal hydraulic and power conversion design that arise particularly for higher temperature, long life operation (possibly >60 years). The process of licensing a new reactor design is also daunting, requiring significant data collection for model verification and validation to provide confidence in safety margins associated with operating a new reactor design under normal and off-normal conditions. This paper focuses on the key technical challenges associated with two proposed advanced reactor concepts: the helium gas cooled Very High Temperature Reactor (VHTR) and the molten salt cooled Advanced High Temperature Reactor (AHTR). Published by Elsevier Ltd.

The Department of Energy (DOE) requested that he INEL perform experiments to study the thermal fa... more The Department of Energy (DOE) requested that he INEL perform experiments to study the thermal failure characteristics of a simulated Savannah River Site nuclear reactor safety rod and its surrounding thimble assembly. An electrically heated stainless steel rod simulated a reactor safety rod located eccentrically or concentrically within a perforated aluminum guide tube or thimble. A total of 37 experiments were conducted for a range of power levels and safety rod/thimble relative orientations. Video tapes were made of the four failure tests that were conducted to the melting point of the thimble. Although the primary emphasis of the experiments were to characterize the melting of the thimble qualitatively, experimental transient measurements included heater voltage and current, heater surface temperatures, aluminum thimble temperatures, and ambient temperature. Numerical studies were also performed in support of the experiments and data interpretation. Two finite element models were created to model the heat conduction-radiation between the stainless steel heater and thimble. The predicted temperatures were in good agreement with the experimental results.

A research program is under way at the Idaho National Laboratory to assess the performance of sol... more A research program is under way at the Idaho National Laboratory to assess the performance of solid-oxide cells operating in the steam electrolysis mode for hydrogen production over a temperature range of 800 to 900ºC. The research program includes both experimental and modeling activities. Selected results from both activities are presented in this paper. Experimental results were obtained from a ten-cell planar electrolysis stack, fabricated by Ceramatec 1 , Inc. The electrolysis cells are electrolyte-supported, with scandiastabilized zirconia electrolytes (~140 µm thick), nickel-cermet steam/hydrogen electrodes, and manganite air-side electrodes. The metallic interconnect plates are fabricated from ferritic stainless steel. The experiments were performed over a range of steam inlet mole fractions (0.1 -0.6), gas flow rates (1000 -4000 sccm), and current densities (0 to 0.38 A/cm 2 ). Hydrogen production rates up to 90 Normal liters per hour were demonstrated. Stack performance is shown to be dependent on inlet steam flow rate. A three-dimensional computational fluid dynamics (CFD) model was also created to model high-temperature steam electrolysis in a planar solid oxide electrolysis cell (SOEC). The model represents a single cell as it would exist in the experimental electrolysis stack. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT 1 . A solid-oxide fuel cell (SOFC) model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, Nernst potential, operating potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Mean model results are shown to compare favorably with the experimental results obtained from the ten-cell stack tested at INL.

We have significantly greater renewable energy resources than can effectively be utilized by the ... more We have significantly greater renewable energy resources than can effectively be utilized by the electric grid due to intermittency and remoteness of the resources from large load centers. A further barrier to greater exploitation of renewable energy is that in some locales it may be competing with very low cost generation resources. For example, in many regions off-peak nuclear power is available at very low cost. Of much more urgent concern than electricity generation is the cost and assured availability of transportation fuels. Developing a means of storing intermittent renewable energy and off-peak nuclear energy as liquid transportation fuels offers improved economic prospects and a solution to the energy security of our transportation fuels while simultaneously reducing net CO2 emissions. Many countries are now considering taxing CO2 emissions, which will increase the cost of products that are associated with those emissions. The most common method currently considered for dea...

This paper presents the technical case for high-temperature nuclear hydrogen production. A genera... more This paper presents the technical case for high-temperature nuclear hydrogen production. A general thermodynamic analysis of hydrogen production based on high-temperature thermal water splitting processes is presented. Specific details of hydrogen production based on high- temperature electrolysis are also provided, including results of recent experiments performed at the Idaho National Laboratory. Based on these results, high-temperature electrolysis appears to be

A three-dimensional computational fluid dynamics (CFD) model has been created to model high tempe... more A three-dimensional computational fluid dynamics (CFD) model has been created to model high temperature co-electrolysis of steam and carbon dioxide in a planar solid oxide electrolyzer (SOE). A research program is under way at the Idaho National Laboratory (INL) to simultaneously address the research and scale-up issues associated with the implementation of planar solid-oxide electrolysis cell technology for syn-gas production from CO 2 and steam. Various runs have been performed under different run conditions to help assess the performance of the SOE. An experimental study is also being performed at the INL to assess the SOE.

Idaho National Laboratorys (INL) high temperature electrolysis research to generate hydrogen usin... more Idaho National Laboratorys (INL) high temperature electrolysis research to generate hydrogen using solid oxide electrolysis cells is presented in this paper. The research results reported here have been obtained in a laboratory-scale apparatus. These results and common scale-up issues also indicate that for the technology to be successful in a large industrial setting, several technical, economical, and manufacturing issues have

The Idaho National Laboratory (INL) has been researching the application of solid-oxide electroly... more The Idaho National Laboratory (INL) has been researching the application of solid-oxide electrolysis cell for large-scale hydrogen production from steam over a temperature range of 800 to 900ºC. The INL has been testing various solid oxide cell designs to characterize their electrolytic performance operating in the electrolysis mode for hydrogen production. Some results presented in this report were obtained from cells, initially developed by the Forschungszentrum Jülich and now manufactured by the French ceramics firm St. Gobain. These cells have an active area of 16 cm2 per cell. They were initially developed as fuel cells, but are being tested as electrolytic cells in the INL test stands. The electrolysis cells are electrode-supported, with ~10 µm thick yttria-stabilized zirconia (YSZ) electrolytes, ~1400 µm thick nickel-YSZ steam-hydrogen electrodes, and manganite (LSM) air-oxygen electrodes. The experiments were performed over a range of steam inlet mole fractions (0.1 to 0.6), gas flow rates, and current densities (0 to 0.6 A/cm2). Steam consumption rates associated with electrolysis were measured directly using inlet and outlet dewpoint instrumentation. On a molar basis, the steam consumption rate is equal to the hydrogen production rate. Cell performance was evaluated by performing DC potential sweeps at 800, 850, and 900°C. The voltage-current characteristics are presented, along with values of area-specific resistance as a function of current density. Long-term cell performance is also assessed to evaluate cell degradation. Details of the custom single-cell test apparatus developed for these experiments are also presented. NASA, in conjunction with the University of Toledo, has developed another fuel cell concept with the goals of reduced weight and high power density. The NASA cell is structurally symmetrical, with both electrodes supporting the thin electrolyte and containing micro-channels for gas diffusion. This configuration is called a bi-electrode supported cell or BSC. The electrodes are made by freeze-casting, a modified tape casting technique which creates the many micro-channels in the YSZ electrode green tape. This report presents results of the INLs testing of this new solid oxide cell design as an electrolyzer. Gas composition, operating voltage, and other parameters were varied during testing. Results to date show the NASA cell to be a promising design for both high power-to-weight fuel cell and electrolyzer applications.

Syngas components hydrogen and carbon monoxide may be formed by the decomposition of carbon dioxi... more Syngas components hydrogen and carbon monoxide may be formed by the decomposition of carbon dioxide and water or steam by a solid-oxide electrolysis cell to form carbon monoxide and hydrogen, a portion of which may be reacted with carbon dioxide to form carbon monoxide. One or more of the components for the process, such as steam, energy, or electricity, may

An ongoing project at Idaho National Laboratory involves generating hydrogen from steam using sol... more An ongoing project at Idaho National Laboratory involves generating hydrogen from steam using solid oxide electrolysis cells (SOEC). This report describes background information about SOECs, the Integrated Laboratory Scale (ILS) testing of solid-oxide electrolysis stacks, ILS performance degradation, and post-test examination of SOECs by various researchers. The ILS test was a 720- cell, three-module test comprised of 12 stacks of 60 cells each. A peak H2 production rate of 5.7 Nm3/hr was achieved. Initially, the module area-specific resistance ranged from 1.25 Ocm2 to just over 2 Ocm2. Total H2 production rate decreased from 5.7 Nm3/hr to a steady state value of 0.7 Nm3/hr. The decrease was primarily due to cell degradation. Post test examination by Ceramatec showed that the hydrogen electrode appeared to be in good condition. The oxygen evolution electrode does show delamination in operation and an apparent foreign layer deposited at the electrolyte interface. Post test examination by Argonne National Laboratory showed that the O2-electrode delaminated from the electrolyte near the edge. One possible reason for this delamination is excessive pressure buildup with high O2 flow in the over-sintered region. According to post test examination at the Massachusetts Institute of Technology, the electrochemical reactions have been recognized as one of the prevalent causes of their degradation. Specifically, two important degradation mechanisms were examined: (1) transport of Crcontaining species from steel interconnects into the oxygen electrode and LSC bond layers in SOECs, and (2) cation segregation and phase separation in the bond layer. INL conducted a workshop October 27, 2008 to discuss possible causes of degradation in a SOEC stack. Generally, it was agreed that the following are major degradation issues relating to SOECs: Delamination of the O2-electrode and bond layer on the steam/O2-electrode side Contaminants (Ni, Cr, Si, etc.) on reaction sites (triple phase boundary) Loss of electrical/ionic conductivity of electrolyte.

Nuclear Science, 2004

... of a conceptual design in order to identify the component needs specific to the nuclear produ... more ... of a conceptual design in order to identify the component needs specific to the nuclear production of ... The overall design of the HTE plant needs to be optimised within the context of electrical grid requirements, particularly with regard to peaking power, grid stability, and ...

Volume 15: Sustainable Products and Processes, 2007

ABSTRACT

Nuclear Science, 2010

This paper provides a status update on the high-temperature electrolysis (HTE) research and devel... more This paper provides a status update on the high-temperature electrolysis (HTE) research and development program at the Idaho National Laboratory (INL), with an overview of recent large-scale system modeling results and the status of the experimental program. System analysis results have been obtained using the commercial code UniSim, augmented with a custom high-temperature electrolyzer module. The process flow diagrams for the system simulations include an advanced nuclear reactor as a source of high-temperature process heat, a power cycle and a coupled steam electrolysis loop. Several reactor types and power cycles have been considered, over a range of reactor coolant outlet temperatures.

Nuclear Science, 2006

41st International Conference on Environmental Systems, 2011

SUMMARY NASA has been evaluating closed-loop atmosphere revitalization architectures that include... more SUMMARY NASA has been evaluating closed-loop atmosphere revitalization architectures that include carbon dioxide (CO2) reduction technologies. The CO2 and steam (H2O) co-electrolysis process is one of the reduction options that NASA has investigated. Utilizing ...

ECS Transactions, 2008

ABSTRACT The materials used in solid oxide fuel cells (SOFC) can be used to produce synthesis gas... more ABSTRACT The materials used in solid oxide fuel cells (SOFC) can be used to produce synthesis gas from inputs of carbon dioxide, steam, and electricity. Carbon dioxide can be recovered from concentrated sources, such as fossil power plants. The electricity should come from a non-carbon based energy source (i.e. nuclear, solar, wind, biomass, or hydropower). Ceramatec and the Idaho National Laboratory have demonstrated high temperature co-electrolysis of CO2 and steam to produce synthesis gas. If a source of high temperature process heat is available, the endothermic electrolysis reactions can utilize both thermal and electrical inputs such that the conversion efficiency within the solid oxide electrolysis cell (SOEC) is 100%. The synthesis gas produced at Ceramatec in a SOEC has been fed through a Fischer Tropsch reactor to produce hydrocarbon fuels. Widespread implementation of synthetic fuel production from CO2 will enable greater use of intermittent renewable energy sources.

ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 3, 2007

A three-dimensional computational fluid dynamics (CFD) model has been created to model hightemper... more A three-dimensional computational fluid dynamics (CFD) model has been created to model hightemperature steam electrolysis in a planar solid oxide electrolysis cell (SOEC). The model represents a single cell as it would exist in an electrolysis stack. Details of the model geometry are specific to a stack that was fabricated by Ceramatec 2 , Inc. and tested at the Idaho National Laboratory. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT 2 . A solid-oxide fuel cell (SOFC) model adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, Nernst potential, operating potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Mean model results are shown to compare favorably with experimental results obtained from an actual ten-cell stack tested at INL.