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I am using the BattleTech universe for my stories, which has nuclear fusion powered cars. My assumption is that they work similarly to an EV, but with an onboard power plant. So, they'd still be run by electrical traction motors, and have a battery to provide juice to start the reactor up and run small accessories. The reactor would work in much the same way that a power plant does, using heat to generate steam that drives electrical dynamos.

So, I hop into my Rotunda and press the start button. I think I'd be hearing the humming of the reactor's magnetic containment, the rumble of the reactor coolant pumps, and perhaps the whining of the steam turbines as well. The instrument cluster looks similar to that of a 21st century car, but has some additional gauges like temperature gauges for the reactor and the drive motor coolant. The speedometer still works the same, but the RPM gauge instead watches the dynamo turbine's speed. I'd have the same instant torque that an EV has, and more then enough horsepower to go around.

One thing that I'm still trying to figure out is the fuel--from BattleTech, a fusion reactor in a BattleMech is used in much the same way to generate power, and is efficient enough that it only has to be refueled very infrequently, about once every few decades or so. The game states that coolant wears out and has to be replaced much more frequently, so would coolant top-off and refresh stations become the new gas station?

Other then that, there may be many more things I haven't though of, so tell me your thoughts below--what experiences, costs, and maintenance procedures would come with owning a nuclear car?

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    $\begingroup$ i doubt a pocket sized fusion plant would work via steam turbines. you'd need to have some more direct heat to electricity conversion. and if you had turbines, why go the detour through electricity instead of driving the wheels directly? also, you'd need to take on water like steam locomotives. $\endgroup$
    – ths
    Commented Aug 14, 2020 at 21:25
  • $\begingroup$ @ths: you wouldn’t use an open system. Taking on water (or more likely a specific heat transfer fluid) would be a rare thing to do. $\endgroup$
    – Joe Bloggs
    Commented Aug 14, 2020 at 21:42

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Given how complex a fusion reactor would have to be and the need for safety to be built into it's very design:

It's a black-box

Your fusion engine will be a single piece blackbox with computer wires in and power wires out. The reactors would be designed to scram (shut down in a safe way) if any tampering or crashes are detected or if any internal sensor readings start to fall outside acceptable parameters. Fail-safe shutdowns (even at the expense of destroying the reactor) are favourable to blowing up when you're using a vehicle that contains a decades-worth of stored energy, so the last line of defence will be hardware controlled procedures for safely dumping the heat and stopping the nuclear reaction. This may literally include the reactor melting down and out of your car (as long as this won't cause the fuel to ignite).

When it comes to maintenance a civilian-use reactor would probably be best designed to be completely replaced when serviced, with a brand-new factory fresh unit installed each time and the old unit sent back to a factory for reconditioning and (rigorous) testing. Perhaps you would have licensed operators performing coolant changes and refuelling (which should only happen infrequently) but even then the reactor itself would be in charge of deciding if it was happy with the new coolant/fuel, and if it wasn't it would shut itself down.

Any instrumentation exposed to the end-user should be very basic stuff, and mostly related to the vehicle and not the reactor. Like a hybrid car you would likely be interested in power draw for the motors and amount of power in battery or coming from the reactor/regenerative braking, but any diagnostic information for the reactor should be contained within the reactor. If a human is involved in the 'the reactor is getting too hot, shut down' decision process then you can expect a lot of small nuclear bombs going off across town, or at the very least a lot of slagged reactors where the physical failsafes have kicked in, and so to avoid this you just cut the human out of the loop. Make the reactor so it literally won't allow itself to run too hot. If the user needs more power? Sucks to be them. This is analogous to the way that internal combustion engines are designed to not explode under extreme conditions even though they could theoretically be made lighter and more efficient by doing so: You don't let the end user drive around town with a bomb under the bonnet.

Pretty much the only thing I can think of that the user would need to see is percentage of maximum power draw (mostly dictated by the vehicle), ready status (if the reactor needs time to start), and warnings to tell them to go to a licensed dealer for diagnostics (or pull to the side of the road and call a tow-truck). Everything else they should have no need to see or input over.

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  • $\begingroup$ Yeah, probably wouldn't be much of the inner workings of the reactor displayed to the customer, but I doubt it'd be anything like a nuke if one actually did explode--Fusion is hard to maintain, and 99% of the time if the containment failed the plasma would nearly instantly expand and harmlessly cool off against the shielding and the reaction would stop. The only real way to get a 'boom', one that wouldn't be nuclear, more or less a boiler explosion, is to precisely time the overload of the reactor and disable the containment. In effect, you'd have to deliberately wire it up as a bomb. $\endgroup$
    – Jazzyamx
    Commented Aug 14, 2020 at 13:58
  • $\begingroup$ @Jazzyamx: It doesn’t need to be anything like a nuke. The plasma cooling off against the inside of the containment vessel will (unless you’ve magic’d up cold fusion) be a Bad Thing for anyone inside the vehicle or even nearby. Even the super simple ‘boiler explosion’ scenario results in a cloud of scalding hot vapour enveloping the vehicle (or being vented into the passenger cabin). If you want some examples of how bad steam injuries can be I recommend researching early steam engines. They were... not fun. $\endgroup$
    – Joe Bloggs
    Commented Aug 14, 2020 at 15:58
  • $\begingroup$ @jazzyamx: Though I guess for commercial use you’ve got to have a low temperature reactor available. Nobody wants to have thousand degree radiator fins on their convertible... $\endgroup$
    – Joe Bloggs
    Commented Aug 14, 2020 at 16:02
  • $\begingroup$ Oh, I know--still very bad, but at least it isn't nuclear. It'd probably be a cloud not just enveloping the vehicle, but a cloud consisting of superheated steam, fire, and what used to be parts of the vehicle, being flung at silly velocities like a giant grenade. I'm kinda thinking that the inside of the reactor compartment would be lined with some light armor to stop at least a little bit of the shrapnel in the rare case that scenario did happen. The reactor compartment would probably be the most heavily built section of the whole vehicle. $\endgroup$
    – Jazzyamx
    Commented Aug 14, 2020 at 16:08
  • $\begingroup$ @Jazzyamx: Yeah. So the fewer places a human can get into the compartment the better!! $\endgroup$
    – Joe Bloggs
    Commented Aug 14, 2020 at 16:17

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