The only application of uranium in airliners I have heard of is rudder balance on the CV-990. (We are of course talking about U-238, not the 235 variant).
I think that it was chosen as a substitute for lead because the rudder was larger than the CV-880 rudder. With this substitute some substantial redesign of the CV-880 fixed fin was prevented. Uranium is much heavier than lead.
U-238 is a toxic heavy metal just like lead which is widely used on all types of aeroplanes. When talking about U-238 disadvantages compared to lead, then there is probably only one really serious one, the price! Lead is so much cheaper.
It is not pleasant to have to work with heavy metals of any kind, not to mention having it spread in the environment when planes (military or civil planes) fall out of the sky. But that impact is really minor compared to the amounts of lead which gets spread all over from hand weapons - military and civil - wars, hunters, murderers and whatever.
The obvious substitute for all toxic heavy metals is gold. It has the weight, but lacks the toxic properties. Gold just doesn't work in lead-acid batteries. But I doubt very much that we will ever fly on planes with gold balance weights.
Best regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs