As long as your reactor can keep the Triso pellets contained, there should be no risk of melting or even release of the most dangerous isotopes resulting from the reactions. There are still some safety concerns, as neutrons will still escape and potentially convert some of the surrounding material into unstable isotopes. But the Antares design surrounds TRISO with a graphite sheath, which slows down most of these neutrons.
To minimize non-radioactive risks, the Antares design uses sodium to take heat from the reactor to a heat exchanger. The heat is transferred to pressurized nitrogen, which then drives a turbine in a closed Brayton cycle setup.
At the moment, Antares is only testing the Mark 0 reactor, which is not involved in the power generation part. Instead, it is being used to validate modeling of physical conditions in the company’s reactors and to generate safety data that can be used during licensing applications. Efforts to run the entire system, including power generation, are expected next year.
While the work was done at the Department of Energy laboratory, the company is working with the Department of Defense’s Project Pele program to develop a mobile nuclear reactor. The company has also received support from NASA.
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