5 ms·

Let me know when I can buy a nuclear car. No, electric cars aren't adequate. They don't do a damn thing but change the point of pollution so the driver can fee

Let me know when I can buy a nuclear car. No, electric cars aren't adequate. They don't do a damn thing but change the point of pollution so the driver can feel better about themselves. Electric power plants still mainly burning coal. Even if using a nuclear power plant for energy, still have the lithium and cobalt mining and then battery disposal. Also, wont fit my usecase of long haul towing and off road needs in frigid weather.

rascul 4y ago
I've been wondering for awhile now if a small reactor to power a car would be feasible.
- pjc50 4y ago
  The reactor is. The shielding is far too heavy to carry around.
  - rascul 4y ago
    How heavy would the shielding be? I'm clueless about this.
    - ben_w 4y ago
      When I ran the numbers for a nuclear powered engine for launching the space shuttle, the shielding ended up massing about the same as the fuel in the actual space shuttle. A car engine is less powerful than a spaceship, but radiation is your enemy. It's not just "Oh we need some shielding, slap some lead around it!" kind of enemy, it's "if your body absorbs ten joules per kilogram of body weight, then you die, it take a few days, and it hurts the whole time. Your modern car engine produces around fifteen thousand joules per second (and that's when it's cruising, multiply that by ten if you're accelerating as hard as you can). If you are in a crash and the shielding is breached, you die and so does everyone else nearby." - https://worldbuilding.stackexchange.com/questions/69576/practicality-of-a-thorium-powered-superheated-steam-car/69581#69581 https://worldbuilding.stackexchange.com/questions/69576/prac... The thickness of shielding needed to turn that radiation into safe heat is a bit challenging to calculate, but can be approximated with the mean free path, which for gamma rays at this per-photon energy level is in the order of 1cm. You need to reduce it by 1000 to not die immediately, a million to survive going to the shops once, a billion to regularly commute, and probably quite a lot more before regulators are happy. As it's an exponential, those correspond to (10, 20, 30) centimetres, all multiplied by some fudge factor because I'm handwaving a lot by saying the mean free path is 1 cm without giving a lot more specifics. 30 centimetre thick shell surrounding a 1 meter cube has a volume of about 3 cubic meters, massing much more than your car regardless of what you make it from. If you made it from lead, it would mass 34 tons. Unfortunately, the radiation shielding also has to cope with neutron radiation, and the best materials for neutrons are the light elements while the best for gamma is the heavy elements; and even more annoyingly, absorbing neutron radiation causes the emission of gamma radiation. This is also why we won't get a Mr. Fusion powered electric DeLorean even if someone figures out One Weird Trick That Makes Farnsworth Fusors Useful: fusion reactors are even worse than fusion for the instantaneous radiation output per unit energy, the advantage in this regard is (IIRC) that the radioactive waste from fusion is easier to deal with than the waste from fission.
      - rascul 4y ago
        Thank you. This was very informative.
        ben_w 4y ago
        You're welcome :)
galangalalgol 4y ago
Lithium isn't really an issue is it? It is the cobolt and nickel. If we had solid recycling for those or found alternatives, and electricity was mostly or all clean in your area, would that be sufficient?

rascul 4y ago

I've been wondering for awhile now if a small reactor to power a car would be feasible.

pjc50 4y ago
The reactor is. The shielding is far too heavy to carry around.
- rascul 4y ago
  How heavy would the shielding be? I'm clueless about this.
  - ben_w 4y ago
    When I ran the numbers for a nuclear powered engine for launching the space shuttle, the shielding ended up massing about the same as the fuel in the actual space shuttle. A car engine is less powerful than a spaceship, but radiation is your enemy. It's not just "Oh we need some shielding, slap some lead around it!" kind of enemy, it's "if your body absorbs ten joules per kilogram of body weight, then you die, it take a few days, and it hurts the whole time. Your modern car engine produces around fifteen thousand joules per second (and that's when it's cruising, multiply that by ten if you're accelerating as hard as you can). If you are in a crash and the shielding is breached, you die and so does everyone else nearby." - https://worldbuilding.stackexchange.com/questions/69576/practicality-of-a-thorium-powered-superheated-steam-car/69581#69581 https://worldbuilding.stackexchange.com/questions/69576/prac... The thickness of shielding needed to turn that radiation into safe heat is a bit challenging to calculate, but can be approximated with the mean free path, which for gamma rays at this per-photon energy level is in the order of 1cm. You need to reduce it by 1000 to not die immediately, a million to survive going to the shops once, a billion to regularly commute, and probably quite a lot more before regulators are happy. As it's an exponential, those correspond to (10, 20, 30) centimetres, all multiplied by some fudge factor because I'm handwaving a lot by saying the mean free path is 1 cm without giving a lot more specifics. 30 centimetre thick shell surrounding a 1 meter cube has a volume of about 3 cubic meters, massing much more than your car regardless of what you make it from. If you made it from lead, it would mass 34 tons. Unfortunately, the radiation shielding also has to cope with neutron radiation, and the best materials for neutrons are the light elements while the best for gamma is the heavy elements; and even more annoyingly, absorbing neutron radiation causes the emission of gamma radiation. This is also why we won't get a Mr. Fusion powered electric DeLorean even if someone figures out One Weird Trick That Makes Farnsworth Fusors Useful: fusion reactors are even worse than fusion for the instantaneous radiation output per unit energy, the advantage in this regard is (IIRC) that the radioactive waste from fusion is easier to deal with than the waste from fission.
    - rascul 4y ago
      Thank you. This was very informative.
      - ben_w 4y ago
        You're welcome :)

galangalalgol 4y ago

Lithium isn't really an issue is it? It is the cobolt and nickel. If we had solid recycling for those or found alternatives, and electricity was mostly or all clean in your area, would that be sufficient?