U-238 should not spoil

[rmunn]

Currently all uranium isotopes from 232 to 240 spoil into uranium oxide in 50 minutes (which was bumped up from 5 minutes in commit pyanodon/pyalternativeenergy@d213cc1). It seems to me, though, that U-238 (which in real life has a half-life of 4.5 BILLION years) should not decay. Maybe game balance reasons require all uranium isotopes to decay at the same rate, but it just seems wrong to me to have U-238, the most stable isotope of uranium, decaying at all. Within the timeframe of a typical game of Pyanodon's, you might see one or two ATOMS of U-238 decaying, but certainly not any measurabe quantity.

Of course, if you want to go with realistic half-lifes, then U-235 (half-life of 700 million years) should also not decay within the timeframe of a single playthrough. So perhaps game balance reasons still require them to decay, and the unrealistic nature of that decay can be handwaved by saying "This isn't the same uranium as in real life, but a different element that we're calling uranium for convenience". (Reminiscent of the old line "The Odyssey wasn't written by Homer, but by another man of that name.") Thoughts?