So far the problem lies in the low operating voltage, although the capacity is impressive and astonishing. Until recently, it was unattainable. It remains to connect them in series to increase the supply voltage.
I believe that spent nuclear fuel is too dangerous to use anywhere, although the temptation is great! Any significant failure in it will cause contamination, whether it be in the orbit of the Earth or directly our Planet. The search for a good battery/capacitor must continue, but safety considerations must come first. There are two possibilities, either the nuclear cell will fall to the Earth, or it will be directed into space together with the satellite. However, I bet on the first possibility due to the shortage of fuel or its lack! I cordially greet you.