Engineering topics
Gregg, Robert
Publications and source records attributed to Gregg, Robert.
Modeling a fast spectrum molten salt reactor in a systems dynamics fuel cycles code
Molten salt reactor (MSR) concepts are being actively developed by several private companies, with some touting the fuel cycle benefits of this technology. Simulating the deployment of MSRs and their effect on fuel cycle transitions is the role of a system dynamics fuel cycles tool. However, many current fuel cycles tools have difficulty modeling MSR isotopic variations because they were designed for modeling existing reactors based on discrete fuel elements with batch fueling schemes (i.e., charge and discharge). This work presents ORION fuel cycle modeling results using a specific high power density fast spectrum MSR design. For code verification, a single-stage MSR fuel cycle was set up in ORION and results were compared with the results from the SCALE-based reactor physics model (ChemTriton). A transition scenario was set up in ORION from the current light water reactor fleet to a future fleet of MSRs to study the characteristics of an MSR that affect its performance during transition. Several transition scenarios were set with holds and delays in place that are representative of a sodium fast reactor as modeled in Evaluation Group 23 for the Fuel Cycle Options Campaign Evaluation and Screening Study. Several MSR characteristics lend to its high performance and ease in transition from the current fuel cycle: fissile material is only loaded at initial startup; all fissile material is available as it is bred due to online fuel processing; and fissile material recirculating through the core is briefly held in tanks for processing and has very minimal out-of-core time (on the order of a minutes to a few days). These characteristics are in contrast to a solid-fueled reactor, which requires discharge, cooling, and fabrication of fuel all of which could take a few months to a few years and repeated loading of fresh fuel assemblies. In conclusion, a solid-fueled reactor only discharges a fraction of a core every year.
Modeling a Fast Molten Salt Reactor with ORION
Molten Salt Reactors (MSRs) are being actively pursued by several private companies in the United States and elsewhere as a viable technology that can enable a low-carbon future. These companies have invested heavily in the design of different types of MSRs. This has led to a response from the US Department of Energy (DOE) to provide assistance in furthering R&D in this area by fostering collaboration between US national laboratories and industry through the Gateway for Accelerated Innovation in Nuclear (GAIN) initiative. With the renewed interest in MSRs, the full paper will focus on analyzing a single-stage MSR in a systems dynamics fuel cycles tool, ORION. Oak Ridge National Laboratory (ORNL) has chosen ORION, developed and maintained by the National Nuclear Laboratory (NNL) in the United Kingdom, to model fuel cycle scenarios. A single-stage MSR was set up in ORION using the ORIGEN reactor library for a fast MSR under analysis. The ORION results will be presented in this paper along with the results from the reactor physics model to compare the trends in various output of interest. The isotopic content of the salt evolves over time in an MSR. Certain MSR designs never reach equilibrium and continuously evolve over the entire life of the reactor. During the process of setting up the ORION MSR model, several assumptions had to be made to input parameters in ORION due to the current inability to account for certain behaviors inherent to MSRs. The model, these assumptions, and conclusions will be discussed in further detail in the full paper.
Value Added When Using Cross Sections for Fuel Cycle Analysis
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A US-UK Collaboration on Fuel Cycle Assessment
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Impact of Using Cross Sections Versus Recipes in Transition Fuel Cycle Analysis using ORION
ORION, a nuclear fuel cycle simulator developed at the UK National Nuclear Laboratory (NNL), is designed to simulate the operations of general nuclear fuel cycles, including once-through, limited recycle, and continuous recycle fuel cycle options. ORION can simulate the full range of nuclear-related facilities e.g. interim and long-term storage locations, fabrication and enrichment plants, reprocessing facilities, and reactors. It can track over 2,500 nuclides and can model decay and in-reactor irradiation. Based on ORION's ability to track the full isotopic mass flow between fuel cycle facilities (with or without decay), it is possible to model all of the necessary nuclide production and destruction routes. This is essential when calculating accurate spent nuclear fuel (SNF) compositions and associated metrics (e.g., decay heat and radioactivity). When modeling the transition from the current once through US fuel cycle to an alternative fuel cycle, it is important to accurately model the US pressurized water reactor (PWR) discharged SNF composition while minimizing the computational time. This paper discusses two rapid methods used to model the US PWR discharged SNF-fixed recipes versus cross sections-and it discusses the differences between the results from these two methods in relation to fuel cycle transition analysis. (authors)
Fuel Cycle Study to Developing a Viable Long Term Nuclear Power Scenario for the UK
Within the UK a closed fuel cycle has been in operation for decades but with the introduction of a new build programme to create 16 GWe capacity using LWR technology and with the closure of the UK's reprocessing industry, an open fuel cycle will be implemented beyond 2020. However, it is expected that 16 GWe nuclear capacity will not be enough for the UK to curb greenhouse gas emissions through increased demand for low carbon electricity, and tackle energy security. As such further nuclear expansion scenarios are being considered between 40 and 75 GWe by 2050. This study evaluates a viable 40 GWe UK nuclear scenario, evaluating the extent to which key drivers can impact a future UK nuclear energy strategy, including; the ability to sustain a relatively high nuclear capacity, fresh uranium availability, accumulation of spent fuel at decommissioning nuclear reactor sites and capacity requirements of future GDF host sites. The thermal reactor open fuel cycle is the de-facto standard around the world for many reasons including the reliance on extremely mature technology, significant operational experience and most importantly a relatively low cost. However, the premise that a thermal reactor open fuel cycle is the correct one to adopt long term is dependent on the notion that large quantities of UO{sub 2} spent fuel can eventually be disposed of in a geological disposal facility and the future availability of fresh uranium. The total amount of available uranium is unknown and if extraction from seawater proves to be economic and practical then any future concerns regarding supply disappear. Spent fuel disposability on the other hand has never been performed on a commercial scale and there is some uncertainty when and whether this can be achieved. This paper will follow from previous work already presented in 2013 [REF] which examined UK fuel cycles involving the transition to a closed fast reactor fleet by the end of this century. The revised scenarios now assume fast reactors are required later in the scenario, in-line with other countries. In addition, the new study has used physics methods originally developed by SKB to assess the physical size of the repository required to dispose of all intermediate and high level waste whilst ensuring temperature limits imposed by the engineered barriers and surrounding geology are adhered to. The disposition of less Am-241 in the repository will no doubt lead to a reduction in GDF footprint. However, this may not be important to GDF design and economics. The purpose of this paper is to also critically review the importance of and put into perspective a smaller GDF footprint and lower fissile inventory. (authors)
Generating Cross Sections for ORION Fuel Cycle Models
Abstract was accepted and this is final paper.
Impact of Using Cross Sections Versus Recipes in Transition Fuel Cycle Analysis using ORION
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Effectiveness of actinide management in fast reactors over a finite recycling period - 15123
Long-lived nuclear waste primarily consists of transuranic (TRU) isotopes. Full recycling of TRU isotopes can, in theory, lead to a reduction in repository radiotoxicity to reference levels in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. However, over a limited time frame, the radiotoxicity of the 'final' core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. In this paper, the fuel cycle code ORION is used to model the recycle of light water reactor (LWR)-produced TRUs in sodium-cooled fast reactors (SFRs). With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance. Break-even SFRs are much less effective from a point of view of reducing waste radiotoxicity. Thorium (Th)-burner fuel cycles are found to result in slightly lower radiotoxicity than U-burner fuel cycles for the same number of generations. Closed break-even Th fuel cycles require ∼3 generations of operation before their waste radiotoxicity benefits result in decay to the reference level in ∼1000 years, provided that Pa is recycled. While this is a very long time frame, it is substantially better than the time frame required by other strategies. The integrated decay heat over the scenario time frame is substantially higher for break-even Th-SFRs than break-even U-SFRs as a result of much higher {sup 90}Sr production. As decay heat affects repository sizing, this weakens the argument for the Th cycle. (authors)
Transition Analysis of Promising U.S. Future Fuel Cycles Using ORION
The US Department of Energy Office of Fuel Cycle Technologies performed an evaluation and screening (E&S) study of nuclear fuel cycle options to help prioritize future research and development decisions. Previous work for this E&S study focused on establishing equilibrium conditions for analysis examples of 40 nuclear fuel cycle evaluation groups (EGs) and evaluating their performance according to a set of 22 standardized metrics. Following the E&S study, additional studies are being conducted to assess transitioning from the current US fuel cycle to future fuel cycle options identified by the E&S study as being most promising. These studies help inform decisions on how to effectively achieve full transition, estimate the length of time needed to undergo transition from the current fuel cycle, and evaluate performance of nuclear systems and facilities in place during the transition. These studies also help identify any barriers to achieve transition. Oak Ridge National Laboratory (ORNL) Fuel Cycle Options Campaign team used ORION to analyze the transition pathway from the existing US nuclear fuel cycle—the once-through use of low-enriched-uranium (LEU) fuel in thermal-spectrum light water reactors (LWRs) —to a new fuel cycle with continuous recycling of plutonium and uranium in sodium fast reactors (SFRs). This paper discusses the analysis of the transition from an LWR to an SFR fleet using ORION, highlights the role of lifetime extensions of existing LWRs to aid transition, and discusses how a slight delay in SFR deployment can actually reduce the time to achieve an equilibrium fuel cycle.
Fuel Cycle Assessment: Evaluation and Analyses using ORION for US Fuel Cycle Options
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