Concentration absolutely matters, and based on the figures I've seen coal fly ash - which is what the claims about radiation released from coal power plants are based on - is about as radioactive, kg for kg, as granite is. Which isn't nothing, but it's also not exactly nuclear waste. (Speaking of nuclear waste, the comparisons with coal often also get their numbers by ignoring it and only counting radiation intentionally released to the environment from a properly-working plant. Which is basically just a way of saying that if we could solve the nuclear waste disposal problem and the humans are too incompetent to build and run nuclear power plants problem it'd be a really clean form of power. That's probsbly true, but not realistic. Also, the comparison is generally based on really old and polluting coal power plants that mostly don't exist anymore.)
Nuclear waste can basically be safely solved by dumping sealed containers into the sea. We're talking about extremely small amounts of waste. A swimming pool can contain a year's supply of waste, and 20 ft of water is extremely effective radiation shielding. The ocean is so large that this would be totally negligible even if the worst happened.
It wouldn't be negligible. Dumping all our HWL waste (250,000 tons) would increase background radiation of the oceans by 10% if completely mixed, but of course oceans are not. We would simply end up with highly radioactive areas of ocean if and when the containment failed.
Just a throwaway idea, but instead of radiating the whole ocean evenly, why not dump it in the already highly radiated nuclear weapon test zone? The US blow around 100 nukes and I wonder if a few thousands of tons would actually do much worse compared to what already down there.
