MARVEL, a creative acronym meaning Microreactor Applications Research Validation and EvaLuation, is a trail blazing reactor development program designed to help the Idaho National Laboratory (INL) and the nuclear industry remember how to build and operate small nuclear reactors for testing and demonstration. The program was initiated in 2020 and has created many opportunities to learn and improve.
The current MARVEL program lead, Dr. Abdalla Abou-Jaoude, joined me for Atomic Show #348 to talk about the program and its historic accomplishments. Even though the MARVEL reactor has not yet been completed, he and his team – both superiors and subordinates – consider the program to be a research and development success story.
MARVEL is a micro reactor designed to produce 85 kilowatts of thermal energy. Using Stirling engines, it will be able to produce approximately 20 kilowatts of electricity. That’s about the same generating capacity as a whole house generator for a 4,000 square foot American suburban home.
The reactor uses uranium-zirconium hydride (UZrH) fuel rods with uranium enriched to less than 20% U-235 (HALEU). They are similar to those used in Triga research reactors. The reactor coolant is NaK (sodium potassium eutectic) that is naturally circulated through the reactor core and the system heat exchangers.
The early system design concept included directly-connected Stirling engines to convert reactor heat to electricity. That configuration was proven to be unworkable during a non nuclear thermal testing program called PCAT – Primary Coolant Apparatus Test. The Stirling engines vibrated enough to put the rest of the system at risk of rapid deterioration, so the design was changed to include a secondary, non radioactive NaK loop that then transferred its heat to a tertiary molten salt loop.
This choice allows the Stirling engines and the heat conversion system to be placed outside of the building. That design change had the added benefit of making it easier to use the MARVEL reactor system to test various direct heat applications; with the directly mounted engines, it would have been difficult to extract any product other than electricity.
A major benefit of a government funded research and development program like MARVEL is that it can provide widely accessible lessons learned. For a variety of commercial reasons, private sector programs are less likely to share what they have learned from their mistakes or dead end choices.
Private sector participants can be hesitant to be the first to move, especially in a field where everyone knows that the existing government approval process is a major barrier that needs to be improved. A government funded program has the ability to approach and overcome the barriers without incurring the risk that they are simply making the path easier and smoother for their competitors. The cliche “don’t fight city hall” applies; it’s a somewhat easier battle when you are part of the city hall machinery.
Abdalla explained how the MARVEL program leaders are happy to see how later projects are moving more quickly and even passing it to reach certain key development milestones. MARVEL leaders feel like they did their job by helping to exercise and improve the processes of review and approval. The program has also helped to give dozens of engineers more experience in the process of moving component and system designs off of computer screens and into real life fabrication.
Numerous entities from universities, governments and the private sector are queuing up to use MARVEL to test various concepts for taking advantage of nuclear fission heat. Some of the potential uses include desalination (especially produced water from oil and gas wells), hydrogen production, micro grids, remote operations and training AI for reactor control.
MARVEL is currently scheduled to achieve dry criticality in 2026. It should achieve full power operations in 2028. It is classified as a non capitalized asset, which limits its projected operating life to about 2 years. It has sufficient fuel to last longer if the decision is made to extend it past the two year point. Even if it operates a little longer, the plan is still to have it reach the decommissioning phase quickly enough to serve as a barrier breaker for that important life cycle phase.
You are sure to enjoy the show and to learn something in the process.
