Just over a year ago, the Trump Administration issued an executive order meant to accelerate the development of nuclear power in the US. While an entire startup ecosystem has developed around the use of different—and typically smaller—reactor designs, only one of them has been fully licensed so far, and there are no plans to actually build any instances of that design.
The executive order directed the Department of Energy to have three different reactor designs reach criticality in a bit over a year. On Thursday, a startup called Antares announced that a test reactor it had placed at the Idaho National Laboratory had reached criticality, making it the first new design to cross this threshold. Criticality means that the nuclear reactions inside the hardware had become self sustaining; it does not mean the reactor had started to generate power.
Antares is one of a number of companies that is basing its design on a new fuel system called TRISO that takes some of the complexity and safety out of the reactor design and places them in the fuel design. The fuel design is based on tiny pellets with a uranium oxide core. The pellets are surrounded by several layers of carbon that can moderate the energy of both the neutrons and lighter nuclei that are released by fission reactions. All of that is encased in a hard ceramic shell that's designed to withstand the highest temperatures that can be produced by the encased uranium.
