Note that it'd be a very heavy power plant system. RTGs are not wonders of power-to-weight ratio (I think the Cassini RTGs are about 300kg per kilowatt).

I'd take the electrical battery template, halve its load capacity, and ban the effects of superconductor drive and engine customization. Of course, fuel would be a non-issue.

As for converting RL power plants, SR/R3 is annoying in that the engines are poorly detailed from a weight and horsepower aspect. Those stats, and the overall weight/performance of the vehicle, are boiled down to speed, load capacity, etc. In GURPS Vehicles, it would be very easy to convert a RL power plant, mostly because it tries hard to model RL power plants and vehicle performance (it doesn't always succeed, but if you're careful, you can model a lot of RL vehicles quite accurately). But Rigger 3 is less "grounded" (and much simpler) than GURPS Vehicles.

Any conversion from RL to R3 would be, IMO, either on the vehicle scale ("this vehicle can do 0 to 60mph in 7 seconds...so it's acceleration would be X...") or the SWAG I did above for RTGs.

IIRC the Sowjets used RTG's to power some remote weather stations here on good ole earth. And who cares about shielding and mutations in SR.

Birdy

All them Injuns frown on the Anglos using power plants disrespectful to Mother Nature.

Yep, but those only needed a few hundred watts to operate.