As an "I just want the human race to make it through the next century w/o extinction" anarchist (no, that's not really a school of anarchist thought, I just made it up a moment ago based on my sentiments, shared by others of various, and no, adjectives), I think a lot on the practical matters of how one can safely transition out of this civilization (which I believe is in terminal collapse).
I believe the problem of nuclear materials will be one that must be handled locally, *irrespective of whether a government officially exists*, because I believe that the collapse of western civilization will eventually strip elites of their effective authority. Nuclear workers, assisted by local volunteers with relevant skills and abilities, will simply have to work the problem out on their own. Certainly they can't do worse than what we have right now. The problem as it is is being manufactured and aggravated, not resolved, by the decisions of our corporate and government masters.
Some solutions will turn out to be suboptimal (for example, disposing of waste where the geology simply can't handle it, for lack of a better solution), but it is unlikely that the persons involved would be making the kind of reckless decisions currently being made by persons who will never live downwind of the messes they create. People in those instances will have to dig the mess up and try again, just as governments have had to order already, on numerous occasions, with wastes (including the waste left behind from the very first nuclear reactor cp-1/cp-2).
My biggest concern is the possibility of plants simply being abandoned by workers under conditions where, for example, they have not been paid by their corporate masters for months, or where corporations decide to abandon plants and order compliant workers out without safely shutting the plants down. In such cases, local people with relevant skills (physicists, engineers) may need to take heroic measures to try to bring the plants into a state of stable cold shutdown.
I worry not at all about terrorists making bombs from nuclear waste. High level waste is so intensely radioactive that one would need some serious industrial capacity to safely (or even recklessly) separate fissionable material from spent fuel. In fact, in the absence of governments and corporations, there would be exactly ZERO bomb grade material on earth. If you look at all the current efforts to keep nuclear materials out of the hands of terrorists, they focus entirely on keeping government-manufactured fissionable material out of the hands of terrorists. The CIA and others assume, correctly, that only a government has the industrial capacity to refine fissionable materials.
You cannot possibly be made safer from a threat by clinging to the same people who create the threat in the first place.
That corporations and governments have created the stuff means that until we do clean it up, there will be some degree of threat from statist, and just plain psychopathic, terrorist groups who want to be our next government. But once the existing mess is cleaned up, the prospects for further nuclear proliferation are essentially zero. I don't know about you, but if Acme Terrorist Industries opened up a big industrial complex to refine nuclear materials in my neighborhood, I'd organize my neighborhood to shut them down before anything bad happened.
Of course nuclear accidents and nuclear weaponry are not the only threats talked about in the media. There us the 'dirty bomb' scenario, in which a terrorist spikes an ordinary bomb with radioactive materials. Would-be terrorists have already tried to build such devices, if we can believe the US government. But what the media doesn't tell you is that governments, including the US government, have examined such radiological weapons for use in battle for years. They were considered for use by both sides in WWII, and may even have been considered prior to WWII (I can't find the "history" of the dirty bomb concept, but there was enough radioactive material, and sufficient awareness of its hazards, much earlier than that). Why hasn't any government actually used such weapons (no, DU doesn't count, as the logic and methods of DU are different)? ***Because it turns out they don't work all that well*** Most of the damage is done by the explosives. The whole argument behind why a "dirty bomb" is to be feared, according to the War-On-Terrorists, is that such weapons will cause massive economic damage by scaring an ignorant public!
As to the whole notion that governments are needed to guard waste depositories, you should read up on how governments actually do it (and plan to do it in the future). In essence, they don't. The idea is to fill yje repositories, stick one or more carved rocks on top of them saying "warning, don't dig here for a very long time) in multiple languages and pictographs, and then just walk away. They know the hazards come from accidents, not terrorism, and so have no qualms about leaving such a place unguarded. But then, they also know the virtue of terrorizing the public with the specter of terrorism, so that frightened people will run to Daddy Authoritarianism and demand more of the very thing that has singularly created the danger in the first place.
(semi-disclaimer: I have a physics education and in a more deluded phase of life, imagined I wanted to be in the waste and hazard generation business).