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Worrall, A.

Publications and source records attributed to Worrall, A..

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Sensitivity and Uncertainty Quantification of Transition Scenario Simulations

This report documents the first collective attempt at developing and applying capabilities to quantify uncertainties, assess parametric sensitivities, and optimize multiple parameters and metrics in fuel cycle simulations generated by the SA&I Campaign. To do this, external codes that were designed to perform sensitivity analysis and uncertainty quantification (SA&UQ) needed to be coupled to the SA&I Campaign’s nuclear fuel cycle simulators (NFCS). In FY20, two approaches were pursued: 1) coupling Cyclus to an ORNL-internal code called MOT (Metaheuristic Optimization Tool) and 2) coupling DYMOND to the opensource SA&UQ tool kit Dakota. The primary objective of having these NFCS/SA&UQ coupled capabilities is to better inform DOE-NE and other stakeholders on the results generated from the NFCS. For a given set of fuel cycle strategies, policies, and technology assumptions that make up a fuel cycle scenario, these NFCS have traditionally been used by the SA&I Campaign to provide quantitative answers in terms of year-by-year mass flows, infrastructure requirements, costs, etc. With these newly developed coupled capabilities, the SA&I Campaign can now efficiently simulate hundreds or thousands of these scenarios, sample large ranges of parameters and assumptions, and use the unique features of the SA&UQ tools to process the data. This enables providing answers with known and propagated uncertainties, determining the sensitivity of important metrics to different parameters and assumptions, quantifying how much fuel cycle and technology parameters impact each other, and producing optimized fuel cycle strategies for single and multiple variables. To demonstrate these new capabilities, the Cyclus/MOT was used to model several scenarios ranging from simple fleet retirements to transitions to advanced reactors. Specifically, for a transition scenario from LWRs to SFRs and advanced LWRs, uncertainty quantification, sensitivity analysis, and optimization studies were applied to cases involving single and multiple parameter (input) and single and multiple metric (output) variations. In addition, a similar transition scenario was modeled to demonstrate how to optimize the reprocessing capacity parameter to minimize two performance metrics while taking into account uncertainties from two other parameters. Lastly, a depletion module based on SCALE/ORIGEN was added in Cyclus to simulate the third scenario that was designed to quantify the impact of the modeling assumption that all LWR used nuclear fuel have the same burnup. The newly developed DYMOND/Dakota capability was also applied to a transition scenario from the existing fleet to small modular reactors and fast reactors. This particular scenario involves not only explicit isotopic depletion via ORIGEN-2, but also includes multirecycling and utilizing the criticality search feature to determine the fresh fuel composition of recycled fuel, a feature unique to the DYMOND NFCS. A large database of simulations were run with 4 main parameters that were sampled: start date of reprocessing, reprocessing capacity, energy demand growth rate, and advanced reactor share of the fleet. The 4 main metrics were uranium consumption, enrichment requirements, waste generation, and levelized cost of electricity using data from the Cost Basis Report. The demonstrated SA&UQ results include those that inform on how to choose parameters to avoid “failed” scenarios, Sobol’ indices that inform on the importance of various parameters individually and synergistically, and Analysis of Variance (ANOVA) studies that decompose parameter ranges into groups and informs on whether variations are statistically significant.

Feng, B.↗
DOE OSTI2017

Two-Dimensional Neutronic and Fuel Cycle Analysis of the LEU-Fueled Transatomic Power Molten Salt Reactor

A recent Third Way report detailing $1.3 billion in private investment in advanced reactor technology includes several liquid-fueled molten salt reactor (MSR) concepts. Interest in these MSR concepts is driven by the enhanced safety, economic, and promising fuel cycle benefits of these advanced reactor concepts. The US Department of Energy (DOE) Office of Nuclear Energy established the Gateway for Accelerated Innovation in Nuclear (GAIN) to provide private companies pursuing innovative nuclear energy technologies with access to the technical support necessary to move toward commercialization. GAIN activities in 2016 included competitive selection of projects for vouchers to fund applicant-specific work at national laboratories. One of these GAIN small business voucher awards was to Transatomic Power Corporation (TAP) to work with Oak Ridge National Laboratory (ORNL) to perform neutronic and fuel cycle analysis and design of TAP's innovative MSR concept. The initial phase of this project is to perform two-dimensional (2D) analysis with ORNL-developed tools to verify TAP-calculated metrics and to develop an understanding of the effects of fuel feed and isotopic removal rates to prepare for the more complex three-dimensional (3D) analysis in coming phases. Design information was based on the TAP white papers wherever possible. This summary discusses the results of this initial phase of the collaboration between ORNL and TAP.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

Fuel cycle impacts of accident tolerant fuels

This paper discusses the impact of several accident-tolerant fuel (ATF) options on the fuel cycle performance of once-through LWRs compared to current uranium oxide-Zircaloy fueled commercial LWRs. Desirable characteristics of proposed ATF concepts include higher thermal conductivity, enhanced fission product retention, and reduced reaction kinetics and hydrogen generation in loss of coolant conditions. ATF concepts that have been proposed target changes to the fuel and/or cladding. Broadly speaking, the options can be summarized as follows: -) UO{sub 2} pellet fuels with increased thermal conductivity to lower temperatures, -) high-density pellet fuels (e.g., nitrides and/or silicides), -) fully ceramic microencapsulated (FCM) fuels, -) metallic fuel with high fissile density and high thermal conductivity, -) coatings on Zircaloy cladding, -) total elimination of the Zircaloy as cladding and replacement with a ceramic, and -) composite cladding including for instance layered Zircaloy and SiC and molybdenum. We can draw 4 conclusions. First, other than SiC, the other cladding options will result in a reactivity penalty requiring either thinner cladding or increased fissile loading. Secondly, silicide fuels have a higher density than UO{sub 2} and can allow longer cycle lengths for the same enrichment or a reduction in the enrichment for a given cycle length. Thirdly, while the pellet fuels yield very similar results, the FCM fuel is dramatically different due to the low fuel loading. Fourthly, we have to note that in order to achieve the maximum benefit from a particular fuel-clad combination, it requires consideration of the characteristics of each. For example, a cladding with a relatively high absorption (e.g., FeCrAl) would benefit from a high density fuel such as U{sub 3}Si{sub 2}.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Reactor Physics Analysis of Transitioning to a Thorium Fuel Cycle with Molten Salt Reactors

Commercial power reactors operating in the United States are light-water reactors (LWRs) fueled with low-enriched uranium (LEU) in a once-through fuel cycle; the important fissile isotopes are {sup 235}U, {sup 239}Pu, and {sup 241}Pu. In a thorium fuel cycle, the fertile isotope {sup 232}Th is converted into {sup 233}U, a fissile isotope that is not naturally occurring. In transitioning from the once-through fuel cycle to the thorium fuel cycle, the availability of man-made {sup 233}U presents a challenge: without it, the initial fissile material fueling the first reactors built in this transition is not the fissile isotope that the reactor is breeding. The transition requires an alternate fissile material until enough surplus {sup 233}U is available to start up additional reactors. In liquid-fueled molten salt reactors (MSRs), the fuel is dissolved into molten salt, which is continuously circulated through the core, simultaneously undergoing irradiation, chemical treatments and separations, and feeds. MSRs are an attractive technology in which the thorium fuel cycle can be deployed, as the {sup 233}U bred from {sup 232}Th is continuously being recycled back through the core. The bred fissile material is immediately available to fuel the core without processing or fuel fabrication. After start-up, only a fertile {sup 232}Th feed is necessary to sustain criticality in the MSR. But, in single-fluid MSRs, the initial fissile and fertile materials are mixed into the same molten fuel salt, complicating separations of initial and bred fissile materials. In solid-fuel systems, these materials are often separate. This analysis herein builds on previous work modeling thorium-fueled MSR start-up. It is based on unit cell representations of the graphite-moderated, 2250 MWt Oak Ridge National Laboratory (ORNL) Molten Salt Breeder Reactor (MSBR). This paper discusses the start-up of the first MSR in the transition to a thorium fuel cycle and identifies challenges and limitations of fuel cycle deployment with this reactor technology. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Transition to Uranium-Based Fast Reactor Fuel Cycle Options

An Evaluation and Screening (E and S) study of nuclear fuel cycle options was recently conducted for the U.S. Department of Energy to identify promising fuel cycle options with the potential for achieving substantial improvements compared to the current nuclear fuel cycle in the U.S. This study considered the entire fuel cycle, i.e., the complete nuclear energy system from mining to disposal including both once-through and recycle fuel cycles. The E and S study considered performance at steady-state when evaluating the potential benefits and challenges to achieving that eventual end state. Based on the steady-state findings from the E and S, a set of four fuel cycle options (FCOs) were identified as most promising, in terms of offering the most benefits compared to the current cycle. These FCOs have natural uranium (or existing stocks of uranium such as depleted uranium) as the makeup feed sent to the fast reactor (FR) fleet combined with two dimensions. The first dimension is whether the FR is a single-stage (produces just enough fuel resources to sustain operation and growth of the FR fleet) or a two-stage (produces additional fuel resources to also sustain a companion fleet of thermal reactors) fuel cycle. In all four cases, all of the uranium is continuously recycled. The second dimension is whether only the plutonium is co-extracted and recycled with the uranium (with minor actinides disposed as waste) or all transuranic elements are co-extracted and recycled. The four most promising options are: 1) single-stage FR recycling of U/Pu (EG23), 2) recycling of U/TRU in single-stage FR (EG24), 3) recycling of U/Pu in two-stage FR/thermal reactors (EG29), and 4) recycling of U/TRU in two-stage FR/thermal reactors (EG30). (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Transition Benefits of using Low Enriched Uranium Fuel in Fast Reactors

An Evaluation and Screening (E and S) study of nuclear fuel cycle options was recently conducted for the U.S. Department of Energy to identify a relatively small number of promising fuel cycle options with the potential for achieving substantial improvements compared to the current nuclear fuel cycle in the U.S. This study considered the entire fuel cycle, i.e., the complete nuclear energy system from mining to disposal including both once-through and recycle fuel cycles, and identified four options that were most promising, offering the highest benefits compared to the current cycle. The E and S study considered performance at steady-state when evaluating the potential benefits and challenges to achieving that eventual end state. Based on the steady-state findings from the E and S, a methodology was developed for extending the evaluation of the fuel cycle options over the period of transition from the current state of the U.S. fuel cycle to a completely new system. Such methods are being applied to a range of potential transition scenarios involving the aforementioned most promising options, with the goal of identifying issues and challenges associated with such transitions. For the first detailed analysis of transition, a single example scenario of transition was developed in order to implement the methodology. The timescales, assumptions, and specifications of this example scenario were chosen to be representative of a reasonable transition from the current state of the U.S. fuel cycle to a fuel cycle that will continuously recycle U/Pu in fast critical reactors (referred to as 'EG23'). The results represent just one transition pathway, but not necessarily the best or optimized solution for that specific scenario. These transition scenarios were modeled using nuclear fuel cycle systems codes in order to provide the time-dependent mass flows and inventories, reactor/facility capacities and throughputs, and system behavior that were used for performance analyses. These analyses of the example scenario identified a number of potential system issues that can be applied generally, but they did not consider the much broader transition space (scenarios involving various FR startup fuels, different cooling times, growth rates, recycling technologies, etc.). Therefore, additional studies were performed to inform over a broad range of these potential transition pathways. The main focus of this paper is on the results of these additional analyses for transition pathways that involve the use of low enriched uranium fuel as the initial startup fuel for fast reactors during transition. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗