Plutonium doesn't work, regardless of iteration. I tried it repeatedly.
While the multipulse system was active, plutonium charged depleted cells twice as fast, true; but it also scaled in efficiency at double the rate per neighbor, and as efficiency rises, heat generation scales exponentially. For one single putonium cell surrounded by 4 depleted cells, you were looking at 240 heat! That required so large of a cooling system to handle that you couldn't fit enough heat plating to get the temperature up, which slowed down the setup. A breeder with two uranium cells and eight depleted cells was running faster because it needed a lot less cooling and thus could reach a higher temperature.
And now that the multipulse system was retconned*, and we're back to 120 heat for a single plutonium cell with two neighbors, it's still not useful because it only charges at the same rate as uranium again. Or thorium. Which, now that the multipulse system was retconned, stopped being buggy and can once again be used to breed effectively.
* this was done in GregTech 3.07; I haven't checked the status quo since, based on Greg's statement that he's stopping to mess with nukes entirely until he can get around to implementing his own nuclear reactors.
So thorium now breeds at the same rate as uranium, but produces a lot less heat... Interesting...
So I guess it's back to the old thorium-powered breeders, then? Longer burn time than uranium plus less heat per tick (and thus less cooling, more heat plating) equals more breeding between refuels, correct?
Also, are thorium multicells more effective than single cells now?