Allowing it to just accept nuclear fuel cells makes it's use time basically infinite, considering how long a stack of fuel cells lasts... I made changes to my personal copy to set the efficiency rate to 0.1.

I don't know if generator equipments can use efficiency rating at all, though, since it doesn't mention it any where in the tooltip.

Also, with adamo nuclear installed, do you think that the LEU fuel cells would be a better fit for it?

The choice of using HEU is purposeful. LEU is really a speciality product (I mean in real life) for only a very specific type of light-water reactor used in electrical infrastructure. Submarines use HEU. Basically everything that can use HEU does use it, because it's better.

I don't have trouble using up cells this way because I am also combining it with the use of large grids, like in the Dumptruck, which carries a LOT of equipment. It's basically a mobile construction vehicle. But I don't think this is unfair. Nuclear cells are expensive to make under Adamo Nuclear and thus, hey, here's one of the few rewards: the cell lasts a LONG TIME in the suit.