Also, I'll repeat that throwing away valuable nuclear material just because it's called a "waste" product is stupid. Paying a lot of money to throw it into space is even dumber.
Used nuclear fuel in those flasks are not transported trough air. Always by land or sea. On the sea they are transported in purpose-built ships.
Small amounts of highly radioactive nuclear fuel are transported trough air but they be in extremely secure type C containers that survive crash from cruising altitude. Creating similar containers that survive crash from space launch would make launching very expensive. Most of the payload would be just the container and only small amounts would be radioactive material.
It's 1000 times cheaper to recycle nuclear fuel make nuclear reactors that use nuclear waste than shoot it into space. France does it in La Hague. The rest can be buried into the ground.
The thing is, we transport nuclear waste over sea or air all the time, don't we? I believe the spent fuel is put into "casks" which is then loaded onto ships or jumbo jets and flown around the world.
Planes crash and ships sink, but we judge the risk (with proper pre-cautions) to be low enough when transporting radioactive waste. To me this shows that people generally accept transporting nuclear waste when the danger of catastrophe is low enough - importantly this signals that the risk only has to be low enough, it doesn't actually have to be 0.
Presumably as rocket technology advances we will eventually enter a stage similar to that in air travel, where the risk of a crash is measured in 1-per-billions rather than 1-per-hundreds or 1-per-dozens.
At that point, would we accept launching radioactive waste into space?