It doesn't have to be contained. Dumping it into the ocean would cause exactly zero harm to anyone or anything.
But it is required to be contained because the regulations are based on fear, not fact.
And a dry cask is a permanent storage solution. You just need to transfer the material to a new one every few centuries, which is easy to do.
The claim that nuclear waste has no permanent solution is bunk - nuclear waste is the only industrial waste for which a permanent solution exists, and one of very few for which even a short term solution is attempted. Most toxic wastes (such as those produced in the manufacturing of wind turbines and solar panels) are just dumped into the environment; and unlike nuclear waste, which decays over time, these chemical toxins remain hazardous forever.
It's a good article that goes through exactly what has occurred and continues to occur relative to decontamination. It mentions safe levels of radiation in sieverts, areas that are safe areas that are still unsafe, soil having to be removed, food supplies, etc. It's a thorough article and worth the read.
It also mentions how at Chernobyl and also Fukishima how people were not informed properly of the danger. In Chernobyl they were expressly lied to. In Fukushima the people seem to be so afraid of radiation that they keep themselves misinformed and absolutely do not trust what the government tells them. They even obtain their own test equipment.
They've had to remove and continue to remove tons of topsoil to the depth of about a meter to get the radiation to a safe level. In all it is quite a disaster. The contaminated water seems like the smallest problem they have but the radiation certainly has to be contained and dealt with safely. It did happen and all the effort and expense isn't attributable to fear but genuine danger from radiation imho.
Again, they didn't
have to do any of these things. The Japanese have set their official 'safe level' based on the pre-existing background radiation levels - and Japan has some of the world's lowest background radiation levels. The 'safe level', that has "required" the expensive and disruptive removal of topsoil, and the declaration of some areas as "dangerous", are less than the natural background radiation levels in many parts of the world where people have lived for centuries without any detectable harm befalling them.
The Japanese "safe" levels are even more insanely low than those used elsewhere in the world, which are still based on the discredited and frankly insane LNT hypothesis. No other industry is constrained to keep contamination below one percent of the amount that causes measurable consequences. If you exposed a million people to ninety times the "safe" level of radiation as defined by the Japanese, for their entire lives, you wouldn't find a higher incidence of illnesses in any of them. Indeed, this has been done - Ramsar, a town on the Iranian Caspian Sea coast, naturally has radiation levels that high - and residents have
lower levels of most cancers than the global average.
The risk to human life and health from these measures is demonstrably greater than the risk of doing nothing.
This is the most frustrating tactic of the anti-nuclear lobby - they invent a problem that doesn't exist, and than bang on about how it hasn't been solved, or that it's costing a fortune to solve it.
The correct and safe response to slightly elevated radiation levels in a place that started with very low levels is to ignore them. But if you pull a random very low number out of your arse, declare it to be the "safe level", and then insist that people move heaven and earth to decontaminate everything down to that level, you can very effectively cripple an industry.
There's nowhere outside the power plant perimeter fence at Fukushima Daiichi that ever needed to be evacuated or decontaminated for the protection of human life or health - indeed, the evacuations caused a number of fatalities that could easily have been avoided by not evacuating anyone.
There was never any environmental or public health need to store the tritiated water that's currently on site.
The death toll from radiation at Fukushima Daiichi is, and will remain, nil. Regardless of any efforts to reduce that number.
The Japanese people are right not to trust their government and officials - those people are fearmongers who are making things worse by panicking over nonexistent threats. If people want a real hazard to worry about, they should be looking at dioxin contamination post the Tōhoku Earthquake and Tsunami - that's a far more significant threat, and nobody seems to give two shits about it. Because it doesn't make for sufficiently scary headlines.