Wired Science has a new post entitled Tour the Tomb of NASA’s First and Last Nuclear Reactor. The name is an apt description and there are a lot of photos.
What brought the post to my attention was their link to Frank's Technology Readiness post from November. Here's a taste of what he said about Marshall and nuclear research, but if you're interested in the topic, you should read the whole thing.
During the Constellation years, Marshall worked with the Energy Department on nuclear-power technology for a lunar outpost. While Los Alamos and other national labs handled the radioactive material, NASA experts used heating elements to simulate nuclear fuel and concentrated on power systems to generate electricity on the Moon.
That work continues, but it has expanded to encompass another technology goal of the new policy—advanced in-space propulsion. To test the way different materials react with the hydrogen at high temperature and pressure, a nuclear-thermal rocket environmental simulator flows gaseous hydrogen over heating elements that mimic different nuclear-fuel configurations.