This could be very expensive for the manipulators if they spend a fortune propping BC up, only for it to fall anyway, UNLESS the tethers they used were not paid for but were deliberately unbacked.
U235 has a half life of 700m years, and U238 1.4b years. Waste products we're worried about have half lives ranging from days to a few decades, so they're obviously much more radioactive than the original fuel.
I still like the idea of deep ocean burial. Even though the material will be radioactive the ocean is VAST and dilution will make the extra radiation immeasurable.
It is the same for the environment IF the hydrogen is produced with electricity, e.g. electrolysis. Unfortunately most H2 is produce from natural gas - so NO, unless you're careful about the source.
If the H2 is produced via electricity, its emissions depend on the electricity source, same as your battery.
A computer without COBOL and Fortran is like a piece of chocolate cake without ketchup and mustard.