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Comment by thomasedwards | Hacker News Reader

I really wanted this to be about Rolls-Royce Motor Cars Limited rather than Rolls-Royce Holdings plc. A nuclear-powered Rolls-Royce Phantom would be incredibly boss.

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Actually, several American car manufactured experimented with this idea in the 50's. Most notably Ford with the Nucleon [0], but also other brands such as Packard and (I believe) Cadillac were also designing nuclear powered cars.

Eventually it was concluded that the shielding of the reactor would make a nuclear powered passenger car impractical, as it would make the vehicle too big. And of course there were the obvious safety concerns.

There is an good documentary on this subject on youtube [1].

[0] https://en.wikipedia.org/wiki/Ford_Nucleon [1] https://www.youtube.com/watch?v=kR5gefU87TY

Maybe that "too big" argument should be revisited in light of recent standard sizes.

It's probably the only possible successor to that surprisingly standard looking Merlin powered Phantom II someone did a few years ago.

I'm still waiting for my Mr. Fusion.

Would a nuclear powered EV ever need refuelling?

I remember Toshiba having a decay-based laptop battery in development (at least 10 years ago, maybe 20). You wouldn't have to charge, ever. Now that would be something!

When I was five or so, I had a watch with a radium dial.

I read in a kid's science book that if you went to bed and waited until your eyes were adjusted to the dark, and then held the watch dial against your closed eyelid, you would be able to see the sparks as individual radium atoms decayed.

I did this, and it worked! I could see each spark!

Radium is primarily an alpha emitter. Alpha won't cross through the glass of the watch face, or even your skin. Maybe you were seeing the much more rare beta decays.

I doubt it was from the betas, they are all fairly low energy for typical radium. It was probably from the gammas produced by Ra-226. Ra-226 produces a 186 keV gamma in 3.3% of decays. Cherenkov radiation flashes in the eye are observed by patients undergoing clinical radiation therapy (see this interesting paper where this was explored and tested: https://www.redjournal.org/article/S0360-3016(19)33947-1/ful... ). The test done in the paper was with much higher energy gammas, but it is feasible that the 186 keV lines could cause the same effect.

I've never observed this when working with radium, but then I don't stick it in my eye.

I remember reading some witness accounts who saw nuclear explosions and they described being able to see through their eyelids (when closed) and in some cases even through their hands. Pretty wild when you think about how bright and forceful a nuclear explosion is.

Ball watches use Tritium in glass tubes for some really incredible lume https://shop.ballwatch.ch/en/

Well Doc Brown had to put in banana peels and some flat beer, so I'd say yes:

* https://www.youtube.com/watch?v=ptlhgFaB89Y

If it were a radioisotope thermoelectric generator, then probably yes.

I don't think that would generate enough power for a car. See maximum output of some here: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

Sure it would. Couple it with a lion - battery as a buffer. A tiny pellet gives 60 watts of heat. A heat cycle engine could recover maybe 10 watts of that. Put 500 pellets in there and you could get 5kw or so electric charge, all the time.

Of course the pellets are insanely toxic in just about every way.

Are you sure? If I'm reading the "Terrestrial" table on that Wikipedia page right, 5kW of electrical power would need an RTG weighing many tonnes, significantly more than a bus.

The problem with the related 25 KW of 24x7 waste heat is that'll eventually melt the very heavy several inches of lead unless very carefully cooled or distributed.

Even 20 watts will eventually melt small quantities of metal, think of every soldering iron. The authorities are not going to approve a reactor that melts its own armor if someone accidentally throws a quilt on top or equivalent.

So most designs do some kind of incredibly heavy passive cooling where the required very large surface of the armor only emits a fraction of the heat you'd see from sunlight. Now sunlight as an engineering 1 sig fig estimate is about a kilowatt per sq meter, so your 25 KW of waste heat would require some multiple of 25 square meters of surface area for passive safety cooling. A cube 5 meters on a side of solid copper and lead would have a surface area of 150 square meters, which will be warm to the touch but not as warm as it would get laying in the sun all day.

The problem with a cube of lead and copper 5 meters on a side is that is 125 cubic meters. And metal, again to one sig fig, weighs about ten thousand kilos per cubic meter. So that shielding would weigh quite a lot.

Its the old problem of the ratio of surface area to volume that comes up in so many engineering problems. Yeah I'm strong enough that I could pick up a small space craft RTG and walk around with it, for several reps at the gym anyway, but the scaling factors are such that a car charger would be immensely heavy.

I'm not sure, on a daily basis, what you'd do with 125 kilowatt-hours of car charge anyway. A gallon of gas is about 25 KW-hr (to one sig fig) so that's five gallons of gas. That would be 150 miles of driving per day, around here that would be something like 3 to 5 hours of driving per day, which sounds like a horrible way to live. Unless you're a bus driver, or delivery guy, or similar, LOL of course. Still, I don't think a five meter on a side bus or car is in our future.

> I'm not sure, on a daily basis, what you'd do with 125 kilowatt-hours of car charge anyway. A gallon of gas is about 25 KW-hr (to one sig fig) so that's five gallons of gas. That would be 150 miles of driving per day, around here that would be something like 3 to 5 hours of driving per day, which sounds like a horrible way to live

I’d have my car mine bitcoin when it’s not being used :)

It'd probably need to replenish the liquid (e.g. water) used for reactor cooling/energy extraction.

I don't know about the thermal efficiency of a small nuclear reactor, but I imagine you could probably make that a closed loop system. Just as you would on an internal combustion engine, with a radiator to cool/condense the heated coolant.

Even in an ICE, you have to replenish/change the oil and cooling fluid; I'd expect a closed-loop small nuclear reactor to be similar in this regard. Still, replenishing something every couple months is much better than refueling or recharging.

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