NASA and DARPA will Demo a Nuclear Thermal Rocket Engine in Space by 2027• https://www.nextbigfuture.com by Brian Wang
DRACO's proposed solid core nuclear thermal rocket temperatures could reach almost 5000 degrees fahrenheit, which will need new advanced materials. It will use high-assay low-enriched uranium (HALEU) fuel, rather than highly-enriched uranium, "to have fewer logistical hurdles on its ambitious timeframe". Highly enriched uranium has many restrictions to prevent diversion to make nuclear weapons.
The plan is to engineer the system so the engine's fission reaction will only turn on once it is in space. The goal is to test the nuclear thermal rocket engine enabled spacecraft in Earth orbit during 2027.
Nuclear thermal rocket could speed travel in space by about 2 to 5 times and reduce travel time. DARPA says that the nuclear thermal rocket offers a thrust-to-weight ratio 10,000 times greater than electric propulsion and two to five times greater efficiency than in-space chemical propulsion.