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Executive Summary
MARVEL stands for Microreactor Applications Research Validation and Evaluation. MARVEL is an 'open-source' microreactor design that is coming out of the Idaho National Laboratory. This 'open-source' idea is a response to commerical reactors such as eVinci from Westinghouse being closed-door endeavors. This isn't great, because it doesn't allow a place for everyone to communicate about designs. This is especially relevant for microreactors, where the low power model and economy-of-production model really benefits from common knowledge being out there.
MARVEL is a unique design that I haven't really seen before. First of all, coolant is by natural convection. This reactor system uses two coolant loops: the primary loop is sodium-potassium salt, while the secondary coolant is lead. These two fluids drive 'Stirling Engines', which are how the system generates power.
- [?] What are Stirling Engines? #MARVEL Stirling engines are heat engines that directly convert heat energy into mechanical energy. How they work is they have a piston that travels back and forth from a hot side to a cold side. When the cylinder travels over the hot side
Anyways, MARVEL also uses an interesting drum based system to do power control. They use one big central 'insurance' rod, but also have four drums around the cylindrical core. These drums have a poison side, whose angle of incidence on the reactor plays a large part in how much neutron fission is allowed to happen. These drums have a fail-close state, that if something were to happen to the controller, they would passively return to a shut position. To keep the poison faces from killing with the reactor, the controller must actively apply force to the drums to prevent them rotating.
These drum based control systems have a significant advantage that they don't create a longitudinal imbalance in reaction rate, compared to a typical control rod. Since they face / shy from the entire core equally along its length, they can probably be more efficiient, and take up way less space. The insurance rod is a typical rod however, as it would not be possible to put a rotating control drum in the middle of a cylinder. 🤷♂️