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Nuclear Car

G

GWestphal

Golden Member
This is a logistics question.

How much radioactive material would you need to run a radioactive car with equivalent performance of an A) smart car (100HP) and B) regular sedan (250 HP) and C) a heavy duty truck (600HP).

Take into account that you likely can't use weapons grade enriched uranium or plutonium? It would have to be somewhat stable as it would need to be safe and maintainable by auto technicians.
 
Curiosity has ~4kg of Pu238, and produces about 110 Watts. That's about 0.14 horsepower. But that's a thermoelectric generator.

Using the heat to boil water (or something) to run a turbine should be a lot more efficient.
 
Radioactive material produces heat, which isn't a great way to produce easily retrievable power for locomotion directly. Curiosity uses a thermocouple, but they are very inefficient and you'd get a lot of waste heat. The best way would be to have a steam turbine that generates electricity and then use the batteries to run an electric motor. At that point, why not just put the nuclear part in a power station and plug the car into a wall... Like we do now.

To get real power you'd need a nuclear reaction, not just passive decay heat.
 
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I always thought it would be neat for nuclear vehicles. It would drive a turbine which would then charge the battery. Basically the control rods with kick in/out based on the battery voltage.

The oil industry would never allow this to happen though, as a single "charge" would last way too long. Some of the stuff they're sending out in space is no bigger than a regular size SUV and has enough power for like 10+ years. I think the mars rover has like 5ish years, possibly more. It's nuclear powered as I think solar power is not efficient enough on mars due to the dust storms. (I don't know if this is why, just my guess)
 
Neat, but talk about over engineering. The fuel cell can already do what needs to be done and without the annoyance of fissionable materials. As it stands the only real hurdle with fuel cells is the expense and that is improving all the time. 🙂
 
Not only is the weight of the containment a concern but also the high possibility of Radio Active contamination in the event of an accident was the reason they cancelled the Nuclear Bomber.
 
Z15CAM said:
Not only is the weight of the containment a concern but also the high possibility of Radio Active contamination in the event of an accident was the reason they cancelled the Nuclear Bomber.
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It was the weight of the shielding to protect the flight crew which made the atomic bomber impractical.

To answer the OP's question, for a fission reactor with high enriched uranium, the amount of fissionable material required is not very high - in the tens of kilograms. The power output of the reactor is entirely dependent on the design of the engine itself and how much heat it can carry away. The power density of a fission reactor can be arbitrarily high.
 
My initial calculation said you need about 15KG of pure Uranium-235 for a K=1 sustainable reaction. A power plant can convert about 30% of the energy density to energy out on the line say 15% in a car we might be looking at about 88Kw * 0.15 = 13.2 Kw from 15KG of Uranium. That is calculated on the basis of the half life of the material and its energy density from a decay perspective (ignoring its by products which also decay and produce heat).

Given that and the numbers from Gibsons we would get about 16.8 bhp. You would get that for 700 million years though!!! In the first few years it would be quite a bit higher, that is the average (the 300 million year mark).

Don't think that is a particularly practical design.
 
BrightCandle said:
My initial calculation said you need about 15KG of pure Uranium-235 for a K=1 sustainable reaction. A power plant can convert about 30% of the energy density to energy out on the line say 15% in a car we might be looking at about 88Kw * 0.15 = 13.2 Kw from 15KG of Uranium. That is calculated on the basis of the half life of the material and its energy density from a decay perspective (ignoring its by products which also decay and produce heat).

Given that and the numbers from Gibsons we would get about 16.8 bhp. You would get that for 700 million years though!!! In the first few years it would be quite a bit higher, that is the average (the 300 million year mark).

Don't think that is a particularly practical design.
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You are confusing two completely separate concepts. Fission rate has nothing to do with half life.

A 500 HP engine = 373 kW. Let's say the engine has a thermal efficiency of 20%. So the thermal output is 1865 kW. A typical commercial nuclear power reactor contains about 32000 fuel rods 12 ft long producing 3000 MW which means a power density of ~ 8 kW/ft. So this 500 HP engine would need ~230 ft of fuel. 230 1-foot fuel rods can fit into a volume of about 1 cubic foot. The reactor would need to be high enriched uranium and probably reflected in order to be critical with this volume but it is physically possible. Then all you need is the heat exchanger, pump, and turbine to produce the power. Again, the main problem with small nuclear powered vehicles is the weight of the required shielding.
 
I'm pretty sure an all electric car charged off of electricity generated from a full blown nuclear power plant is going to be the most efficient "nuclear" car you can drive.

Nuclear power, like most power generation, becomes much more efficient when you start doing things in the large scale and electric cars are pretty efficient (somewhere between 70->80% efficient at converting whatever power comes into the system into motion).
 
Cogman said:
I'm pretty sure an all electric car charged off of electricity generated from a full blown nuclear power plant is going to be the most efficient "nuclear" car you can drive.

Nuclear power, like most power generation, becomes much more efficient when you start doing things in the large scale and electric cars are pretty efficient (somewhere between 70->80% efficient at converting whatever power comes into the system into motion).
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Electric motors are >90% efficient but that is separate from the thermal efficiency of the engine itself.
 
The reactor isn't even the worst part. Jay Leno made a turbine powered car and it was a complete mess. The turbine was not so great at slowing down so the engine had to be run at a really fast idle or risk going out. The ended up putting huge brakes on the car to counter act the excess of power.

I guess that is a different type of turbine but I bet the principle remains the same. Where does the power go when you don't need it?
 
Although slightly off topic, I thought I'd ask it since it's similar; how far off are we from a workable fusion reactor?
 
Ventanni said:
Although slightly off topic, I thought I'd ask it since it's similar; how far off are we from a workable fusion reactor?
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Depends on your definition of workable. We have reactors capable of producing fusion. Heck, even a Farnsworth fusor can do that. If you mean self-sustaining plasma, probably 10-20 years. If you mean greater than breakeven for commercial power, probably 30-50 years baring some massive government project to make it happen sooner.
 
lakedude said:
The reactor isn't even the worst part. Jay Leno made a turbine powered car and it was a complete mess. The turbine was not so great at slowing down so the engine had to be run at a really fast idle or risk going out. The ended up putting huge brakes on the car to counter act the excess of power.

I guess that is a different type of turbine but I bet the principle remains the same. Where does the power go when you don't need it?
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A road vehicle which requires constant power output changes is a poor candidate for being powered by a turbine directly. What would make more sense is an electric drive system with the turbine charging the batteries. Just like how diesel-electric locomotives work.
 
Fusion power is in use today all over the world. My son's new calculator is fusion powered! There is a huge fusion reactor in the center of our solar system, all we need to do is collect the free power.
 
Well, a fission reaction requires to maintain a lot of heat in order to remain critical and a fusion requires even more. Also, you need a certain density or area of radioactive material to keep it going(a few grams or single rod cannot sustain the reaction.
Then the biggest point is that you cannot just switch off and on such a vehicle. The reaction would need to be carried on 24/7*365 days. Here is the tricky part. You can't just leave such a reaction going on without any proper supervision and go to sleep in the night.

Also, so much heat all day would cut though your car/truck armor preety soon.
Not to forget the amount of radioactivity that would be spread in the areas where it will go. Even traces of radioactive particles is deadly.
 
Thromium is used because it needs much lower temperatures to remain critical. Also, is less radioactive then uranium or plutonium. Still several hundreds of degrees needs to be maintained. And thromium reaction is more difficult to start.
 
A Thorium reactor needs a neutron source to kick it off and maintain it, ie it needs a small uranium/plutonium starter in order to get and keep the reaction going. Its main advantage being its easy to shut off, block the source and the reaction slows until it stops. It thus requires less safety features from a power reactor stand point.

But to take thorium and put it into a car would be no less hazardous as the problem isn't the reaction itself, its getting hit or hitting other cars and obstacles which happens to millions of cars a year.
 
redhotiron2004 said:
Well, a fission reaction requires to maintain a lot of heat in order to remain critical
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No it doesn't. A reactor can be critical at zero power and cold.

Also, you need a certain density or area of radioactive material to keep it going(a few grams or single rod cannot sustain the reaction.
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Not really. You need a critical mass and critical geometry to have a fission chain reaction but the amount is not very much. A moderated volume of high enriched U can be critical with less than a kg in a sphere with a diameter of a few inches.

Then the biggest point is that you cannot just switch off and on such a vehicle. The reaction would need to be carried on 24/7*365 days. Here is the tricky part. You can't just leave such a reaction going on without any proper supervision and go to sleep in the night.
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No. Reactors can be started and stopped instantly using a variety of methods such as control rods or changing the geometry/moderation.

Also, so much heat all day would cut though your car/truck armor preety soon.
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No. A very small reactor would not produce a substantial amount of decay heat. It could be cooled by natural circulation of whatever cooling system is used.

Not to forget the amount of radioactivity that would be spread in the areas where it will go. Even traces of radioactive particles is deadly.
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No. Reactivity isn't spread around unless the reactor is damaged and exposed. Trace radioactive particles aren't necessarily deadly, it really depends on the type and duration of exposure.
 
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