5 ms·

Almost all space reactor concepts have fresh fuel at takeoff and then start-up once they're launched. You can hold fresh nuclear fuel in your hand with very lit

Almost all space reactor concepts have fresh fuel at takeoff and then start-up once they're launched. You can hold fresh nuclear fuel in your hand with very little hazard. It's only once you start splitting atoms that the radiation levels get high. So you launch the fresh and mostly inert reactor to avoid this risk. RTGs, on the other hand, are radioactive from the get-go, but are usually quite small. The USA did run a reactor in space (SNAP-10A) and the Soviets did a few dozen.

nickelpro 5y ago
SNAP was a scaled up RTG, as are the soviet examples. You can call these reactors if you want but then we're just playing a semantics game. I tried to head this off by saying "traditional naval reactor or anything that resembles one". Also the problem isn't running the reactor on the launch pad, the problem is if the launch vessel explodes and the fuel load gets spread out over your launch area. The enriched uranium used in naval-style propulsion is absolutely not "safe to hold in your hand" and the weight requirements for using natural uranium, which is safe, would be prohibitive for use in space.
- cameldrv 5y ago
  The odd numbered SNAPs were RTGs. The Even numbered ones were reactors. SNAP-10A was the only reactor from that program to fly.
- acidburnNSA 5y ago
  Most SNAPs were RTGs but SNAP-10A was an honest to goodness fissioning nuclear reactor [1]. [1] https://en.wikipedia.org/wiki/SNAP-10A https://en.wikipedia.org/wiki/SNAP-10A Highly enriched uranium is still barely radioactive, very similar to natural uranium. The half-life of U-235 is 703 million years. As half-life approaches infinity, atoms approach stability. The dose rate of holding navy nuclear fuel is modest compared to the hazards of fission products.
  - nickelpro 5y ago
    Again this is a semantics game, SNAP 10A was still driving a thermo electric converter, thus "scaled up RTG", nothing resembling a traditional naval reactor. The on-contact for a HEU billet is over 10mrem/hour. You and I have very different ideas about nuclear safety apparently and I presume you haven't worked professionally in the field with that attitude.
    - mumblemumble 5y ago
      Frankly, it seems to me that you're the one trying to make it a semantics game, by trying to define what is and is not a nuclear reactor based on how you collect power from the device. According to that Wikipedia article, SNAP 10A was centered on a device that created and maintained a controlled, sustained nuclear fission reaction. I would call that a "nuclear reactor" even if no attempt were made to harvest the power. I think that the rest of the world is probably with me on this. The Chicago Pile 1 is widely regarded as the first nuclear reactor, and nobody particularly cares how it generated electricity. What they care about is that it demonstrated a controlled, sustained nuclear fission reaction.
      - deleted 5y ago
        [deleted]
    - ceejayoz 5y ago
      10 mrem/hour seems to confirm the "barely radioactive" argument; the CDC says (https://www.cdc.gov/nceh/radiation/air_travel.html https://www.cdc.gov/nceh/radiation/air_travel.html) that a cross-country flight exposes you to 3.5 mrem. No one's saying you should hold said uranium in your hand for weeks at a time; they're saying the risk of chucking some around after a (very rare) spacecraft crash is pretty minor, especially as it'll be launched over water.
    - ClumsyPilot 5y ago
      >"Again this is a semantics game, SNAP 10A was still driving a thermo electric converter, thus "scaled up RTG"" You are getting the absolute basics wrong, so you have no standing to question the OP's atittude. Nuclear reactor runs a nuclear chain reaction, hence the name, RTG does not. There is no scope for debate here. The difference is night and day and is obvious if you look at fuel, power to weight ratio, or do physics 101. RTGs run on decay heat and use plutonium 238, they cant be turned off, their power slowly drops off over decades. Reactors use U235, have active control and starting/stop procedure and 10-100x higher power to weight

nickelpro 5y ago

SNAP was a scaled up RTG, as are the soviet examples. You can call these reactors if you want but then we're just playing a semantics game. I tried to head this off by saying "traditional naval reactor or anything that resembles one". Also the problem isn't running the reactor on the launch pad, the problem is if the launch vessel explodes and the fuel load gets spread out over your launch area. The enriched uranium used in naval-style propulsion is absolutely not "safe to hold in your hand" and the weight requirements for using natural uranium, which is safe, would be prohibitive for use in space.

cameldrv 5y ago
The odd numbered SNAPs were RTGs. The Even numbered ones were reactors. SNAP-10A was the only reactor from that program to fly.
acidburnNSA 5y ago
Most SNAPs were RTGs but SNAP-10A was an honest to goodness fissioning nuclear reactor [1]. [1] https://en.wikipedia.org/wiki/SNAP-10A https://en.wikipedia.org/wiki/SNAP-10A Highly enriched uranium is still barely radioactive, very similar to natural uranium. The half-life of U-235 is 703 million years. As half-life approaches infinity, atoms approach stability. The dose rate of holding navy nuclear fuel is modest compared to the hazards of fission products.
- nickelpro 5y ago
  Again this is a semantics game, SNAP 10A was still driving a thermo electric converter, thus "scaled up RTG", nothing resembling a traditional naval reactor. The on-contact for a HEU billet is over 10mrem/hour. You and I have very different ideas about nuclear safety apparently and I presume you haven't worked professionally in the field with that attitude.
  - mumblemumble 5y ago
    Frankly, it seems to me that you're the one trying to make it a semantics game, by trying to define what is and is not a nuclear reactor based on how you collect power from the device. According to that Wikipedia article, SNAP 10A was centered on a device that created and maintained a controlled, sustained nuclear fission reaction. I would call that a "nuclear reactor" even if no attempt were made to harvest the power. I think that the rest of the world is probably with me on this. The Chicago Pile 1 is widely regarded as the first nuclear reactor, and nobody particularly cares how it generated electricity. What they care about is that it demonstrated a controlled, sustained nuclear fission reaction.
    - deleted 5y ago
      [deleted]
  - ceejayoz 5y ago
    10 mrem/hour seems to confirm the "barely radioactive" argument; the CDC says (https://www.cdc.gov/nceh/radiation/air_travel.html https://www.cdc.gov/nceh/radiation/air_travel.html) that a cross-country flight exposes you to 3.5 mrem. No one's saying you should hold said uranium in your hand for weeks at a time; they're saying the risk of chucking some around after a (very rare) spacecraft crash is pretty minor, especially as it'll be launched over water.
  - ClumsyPilot 5y ago
    >"Again this is a semantics game, SNAP 10A was still driving a thermo electric converter, thus "scaled up RTG"" You are getting the absolute basics wrong, so you have no standing to question the OP's atittude. Nuclear reactor runs a nuclear chain reaction, hence the name, RTG does not. There is no scope for debate here. The difference is night and day and is obvious if you look at fuel, power to weight ratio, or do physics 101. RTGs run on decay heat and use plutonium 238, they cant be turned off, their power slowly drops off over decades. Reactors use U235, have active control and starting/stop procedure and 10-100x higher power to weight