While I'm not certain about this system, it sounds like the fuel pellets they've designed for it have no graphite in them. It sounds like they've gone for an in

While I'm not certain about this system, it sounds like the fuel pellets they've designed for it have no graphite in them. It sounds like they've gone for an intrinsically safe design where the maximum safe temperature of the fuel composites is higher than the maximum temperate an uncontrolled reaction could reach.