Eventually we'll just burn the "spent" fuel in breeder reactors. Anything else doesn't make much sense.

I think you also missed where I'm advocating for DGRs for non-nuclear material too. I think you underestimate how some materials don't have a halflife at all and are still dangerous (e.g. heavy metals never become less dangerous over time).

Dirty bombs aren't an issue. You might want to ask yourself why we've never seen one used, especially if you understand how easy it is to obtain the necessary materials. IIRC we've only caught a handful of devices (none exploded). Also we have to consider when it explodes, it just doesn't make enough radiation. It is pretty difficult to generate enough radiation that would actually cause an increase in cancer rates (bombs disperse the radiation quickly, though it does aerosolize it). And then that cancer hits in 20+ years. It just isn't an effective weapon. Sure, it makes for a scary pipe bomb, but at the end of the day it is far more dangerous for the maker and greatly increases the complexity of the terrorist attack (also greatly increasing the likelihood that you get caught before you can deploy).

So a terrorist just gets a slight increase in fear factor, but it doesn't increase deadliness of the weapon, requires a lot more work, greatly increases the chance that they get caught, puts them in more danger, and so they just don't do it. There's too many downsides for only a minor upside. Why do it when you could just make a dozen pipe bombs and put them in trash cans around the city?

Really just think if you were a terrorist and wanted to do damage. There's a lot of things you could do (bunch of rusty nails on the I-5) that just don't happen. They are easy to accomplish, can do a lot of damage, but just don't. Why? Different objectives and just terrorism is extremely rare in the first place. And I'm pretty sure a drilling through feet of concrete and metal in a likely highly monitored site is too big of a hurdle when you can just go to home depot and get some stump remover and some steel pipes.

Coal plants are like aerosolized dirty bombs operating 24/7, so the trade-off is still good even with that (irrational, IMO, but for the sake of argument let's consider it probable) factor.

Terrorists are going to break into a government facility, go a mile deep, retrieve massive concrete cylinders, and transport them back to base. Just to get access to low level nuclear material? If they want to poison people en-masse there are way better options. Uranium is a relatively slow killer. And we test our water supply for it because it's a heavy metal like lead. So any real attempt to poison people with it will get detected pretty promptly.

Groups that have the expertise to covertly retrieve spent fuel could probably just buy guns and shoot up a stadium. And that would cause more damage. The relative risk presented by nuclear waste is trivial.

The "highly radio active" material that is dispersed is mainly radioactive by contamination and unsuitable for any bomb. In La Hague, uranium and plutonium are recycled. The part that could be used for a dirty bomb (other fission products) does not leave La Hague. It is called "glass storage" if you do a google search. This storage is the origin of the old logo of cogema.

Pulverised fuel ash seems a much more effective component for a dirty bomb. It mixes good with air, is much more harmful to humans both long term and short term, is also very radiactive, and mixes well with fresh water supplies. It also much easier to find and is likely much less guarded, and if stolen less likely to be tracked.

The only reason I can see why no one has used that already is that chemical weapons designed for the purpose are more effective.

It also just isn't a lot of waste. It sounds like a lot, but consider that the US produces 100 million tons of coal waste per year (2014). Hell, solar has ~30ktons of waste a year (just PV panels). 11ktons over 60 years just is astronomically tiny. That's 138 tons a year, 150x less than solar and 500000x less than coal. They just don't compare.

Ironically, most waste is radioactive. Obviously not as radioactive or we wouldn’t be having this discussion, but turns out almost everything is at least a bit.