Left:
An illustration showing the key characteristics of the MARVEL reactor Source: DOE
chain and with fabricators that have kept us from starting actual fabrication of the components. We expect that sometime within the next several months.” MARVEL is comprised primarily of 316 H stainless steel,
a high temperature variant 316 stainless. Jackson explains: “Some of the larger forgings have very long lead times. We are also having trouble identifying a fabricator that can meet all our needs. People haven’t built advanced reactors of this size in the past so there’s a lot of learning associated with it. The supply chain is an issue and resolving typical issues associated with identification of a fabricator that’s suitable and is the best for our needs.” Construction start is dependent on how quickly INL
can resolve the fabrication issues and how quickly the components can be fabricated. Nonetheless, research work has begun on the Primary Coolant Apparatus Test (PCAT), an electric-powered full-scale replica of MARVEL. PCAT will be used to collect data on system’s temperature and coolant flow to validate MARVEL’s modeling and simulation tools. At 4 metres tall and weighing almost a tonne, the PCAT has been loaded with sodium-potassium and lead-bismuth coolants and has been installed at a manufacturing facility at New Freedom in Pennsylvania by Creative Engineers Inc. Jackson says: “The primary coolant apparatus is the
electrically heated surrogate for MARVEL that came online initially on September 19th, 2023. The purpose of the primary coolant apparatus test is not for connection to a micro grid but is more for validation of the MARVEL micro reactor itself by measurement and validation of modelling and simulation tools through the natural circulation of the primary coolant and the secondary coolant demonstration of power conversion.” He continues: “Under initial operation we did measure primary coolant flow and power output but we only took it up to 200 degrees Celsius whereas the reactor will operate at somewhere around 400 to 450 degrees Celsius. The reason we stopped the testing at 200 degrees Celsius had to do with the Stirling engines and their internal coolant. This is a glycol mixture that cools the sterling engines and there was some uncertainty with respect to its cooling capacity and measurement of its flow. So, in order to protect the overall system, we stopped and reassessed and we’re just about ready to restart it and take it up to full temperature and validate the MARVEL modelling and simulation tools.”
Research outcomes With an anticipated two-year lifespan, MARVEL will offer experimental capabilities that are not currently available at US national laboratories and will allow R&D to be conducted on fundamental features, operations, and behaviours of
microreactors. It will also be connected to the lab’s first nuclear microgrid. Kurt Meyers, Lead for Microgrids at INL, outlines the
microgrid elements of the MARVEL programme: “Our microgrid system that we already have at INL is actually a relocatable deployable microgrid. Our initial thoughts are to deploy that after MARVEL has gone through its initial testing. It already has pretty sizable energy storage with lithium iron phosphate grid-forming inverter systems and a full microgrid control system. We also have renewables, solar and wind, that we can couple with it so we can start to demonstrate some of those controls and couplings between microreactor and other energy input and storage systems.” Todd Knighton, Lead for Nuclear Applications under INL’s
Integrated Energy Systems arm, highlights how MARVEL will potentially tie in with some of the other major research programmes underway at INL: “We want to close the carbon cycle. Our plan and our research with Integrated Energy Systems is to use a nuclear reactor and instead of sequestering carbon use carbon from industry, use it as a chemical building block to produce synthetic fuels and chemicals that could drop-in to the existing economy and infrastructure. We need a large energy input and that’s where nuclear energy comes in. Near term, we’re looking at a lot of heat uses for advanced nuclear reactors. There’s industry out there already that can use that heat and we can substitute advanced nuclear reactors and decarbonise that heat source very easily. Once you get the nuclear actor on the ground, the process of getting to the heat is easy. Nuclear reactor heat can be very competitive on a cost basis with natural gas, especially once carbon carbon credits are taken into account. It could be a very clean and viable direct heat option for industry versus the more costly method of using electricity to provide process heat using solar or wind. That heat from electricity would come at a much higher cost just because of the conversion efficiency from heat to electricity and back to heat. As far as integrated energy systems use of advanced reactor heat, MARVEL is the vanguard system that will enable future advanced nuclear reactor companies to bring their prototypes and demonstrations to INL for future integration with IES such as hydrogen, chemicals, and synthetic fuels production. A co-electrolysis system demonstration by GE is already planned at INL.”
Jackson picks up on the theme of anticipated
outcomes from MARVEL: “For the reactor itself, along the themes of supporting accelerated demonstration and deployment of commercial microreactor concepts we’re studying things like start-up transient, zero power, physics testing, and operational characteristics of the
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