Only because of political opposition. It's been consistently shown to be a very safe long term storage plan. Ironically, efforts to stop the Yucca proposal because of "safety" issues make it so that we must store much of our nuclear waste in metal barrels at the same nuclear power plants they were produced in.
Anti-nuclear activists are right when they say that nuclear energy is politically impossible but only because they're the ones making it politically impossible.
As usual experts do not judge it as simple as that.
Rust and corrosion will attack the strongest container – all they need are the right conditions and enough time to work. Not only that, but metals behave differently (and chemical reactions proceed more quickly) at higher temperatures – such as those produced by the decay of fission products. So the thermal effects also have to be factored in when designing the things.
So here’s the bad news about long-term disposal of spent reactor fuel – and the containers meant to hold it. Nobody knows how a container is going to hold up over even 100,000 years, let alone a million years (the time span required by EPA).
Who cares if the waste leaks out of the metal barrels? It's still going to be in Nevada, hundreds of miles from any human settlement for thousands of years.
https://en.wikipedia.org/wiki/Yucca_Mountain_nuclear_waste_r...