I understand that Plutonium 239 is produced when fast neutrons bombard the U-238 in the fuel rods of a breeder reactor. Does the plutonium immediately start producing neutrons to increase the controlled nuclear reaction, or do the rods have to be removed and processed for future use? Also, do breeder reactors theoretically have a longer lifespan than conventional power plants, or does the deterioration of materials limit the lifespan to the current 40 plus years? In other words, do they produce more fissionable material, but it has to be moved to a new power plant in order to be used? Is it possible to build nuclear plants that have virtually unlimited lifespans, and if so, which components would periodically require replacement?