4 ms·
Whenever you're splitting Uranium atoms the results will tend to be radioactive. The results will build up in the fuel over time and eventually make the reacto
by Symmetry 7y ago
Whenever you're splitting Uranium atoms the results will tend to be radioactive. The results will build up in the fuel over time and eventually make the reactor stop working. Conventional reactors breed a bit of plutonium too as U238 captures neutrons but most aerospace reactors want to be as light as possible and so use highly enriched Uranium. So after your trip the engine will be quite radioactive but, as you point out, there's a lot of space and outside Earth's atmosphere and Van Allen belts it's moderately radioactive anyways.
Thankfully nuclear reactors aren't particularly radioactive until you turn them on, which is a big improvement on the radiothermal generators, RTGs, that we sometimes use in probes headed for the outer solar system where solar panels don't work. It's during launch, before this part gets turned on, that you have a risk of crashing and losing the reactor somewhere on Earth.
- BAReF00t 7y agoWho said anything about uranium? There are elements with far more favorable decay paths. Short decay + using that decay too = pretty much a clean nuclear reactor.
- Symmetry 7y agoWell, I'm no nuclear engineer but I'd hope that if you could make one of those that was light enough NASA would use that instead.
- greglindahl 7y agoIt's called an RTG, and they've been using them for decades.
- Symmetry 7y agoI'm not sure what you're talking about? RTGs don't have short decay paths, they have to have long decay paths to last through a mission. P238 is what we use for most probes and has a half life of 88 years. It decays to U234 which has a half life of 200,000 years, short enough to be dangerous but long enough to almost never go away. RTGs tend to produce on the order of 100 watts of electricity from 500 watts of heat. A good nuclear engine will want to use 100+ megawatts when in use. And more importantly RTGs don't put out nearly enough heat to make a usable nuclear thermal rocket. The important thing is being able to turn them on when you're doing a burn but then turn them off when you're coasting to your destination then turn them on again to stop there. RTGs can't do that.
- greglindahl 7y agoWhat was asked for sounded like an RTG to me. I wasn't saying it was a nuclear thermal rocket or that it could be used as one. As you point out, it's a constant power source.
- ianai 7y agoI’m increasingly of the opinion that nuclear for space should be mined and built in space. Just launch the infrastructure needed to bootstrap the process.
- Bud 7y agoUm, uh, um, uh...where to start? "Mined" from where? How?
- ianai 7y agoThe moon? Asteroids? Or even just ship up unrefined ore such that a catastrophic failure can’t threaten the population.
- cblades 7y agoWhat risks make that extraordinary cost worthwhile?
- mitchty 7y agoNeither of the first two are options... at all realistically, nither uranium nor thorium exist in anything below a large planetary size body in any quantity: https://www.quora.com/Do-uranium-and-thorium-exist-in-significant-quantities-in-our-solar-systems-asteroid-belt https://www.quora.com/Do-uranium-and-thorium-exist-in-signif... And shipping up unrefined ore is also a bit of a ludicrous idea for mass reasons and the rocket equation alone. You do realize you can isolate a nuclear reactor core from explosions on rockets right? What catastrophic failures are you attempting to design your solution of avoiding a nuclear reactor around?
- BAReF00t 7y agoThe moon's dust contains huge amounts of helium-3. Which apparently is an amazing power source. Also, why fission? We do have working fusion reactors. They are called hydrogen bombs. (The outer part, at least.) As long as you can keep the G forces low ...
- 7y ago