The author has given the ship a reactor pile, so the uranium, plutonium, or thorium split into lead. Unless he meant a fusion reactor pile, even though reactor pile is specific to fission; it’s doubtful any fission reactor which could fit in one of those shuttles would have the energy density to allow it to reach orbit.
Li2 is pretty light stuff, but turning to lead would seem to imply something transuranic.
Enter the Enterprise?
The author has given the ship a reactor pile, so the uranium, plutonium, or thorium split into lead. Unless he meant a fusion reactor pile, even though reactor pile is specific to fission; it’s doubtful any fission reactor which could fit in one of those shuttles would have the energy density to allow it to reach orbit.
Or perhaps he meant it figuratively.