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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