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 distribut

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.