GenZedong

Correct, but the water is processed to remove all the other radionuclides first. The really nasty stuff that causes all the horrible cancers and radiation burns and stuff is separated and stored/disposed of through other processes. That's the theory anyway, and based on the IAEA report seems to be the current practice as well. But this process is going to take years and since TEPCO is a publicly traded for-profit enterprise, concerns that cut corners and lax safety measures could lead to either untreated water or dangerous concentrations of tritiated water being released in the future aren't unfounded.

It makes me think of hydraulic fracturing. Pretty safe when done correctly, but profit-motivated corporations absolutely cannot be trusted to do things correctly. We can only hope that the ongoing IAEA oversight is enough. Or that the economic backlash is enough to convince the Japanese government to change course to a plan that it's neighbors can feel confident about.

I wish I could find a detailed study on this but I'm not having much luck unfortunately. Based on my knowledge of undergraduate physics and chemistry though, I think it goes something like this:

Tritium is an isotope of hydrogen. Water is H~2~O and the tritium here occupies some of those hydrogen atoms. This is why it can't be filtered out, because you're trying to separate water from slightly different but basically chemically identical water. If conducted properly, both options for diluting and releasing this stuff is quite safe.

But let's say some untreated waste water gets released. The water that has all kinds of unpleasant isotopes and toxic heavy metals. If that gets dumped into the ocean, it enters the food chain and gets carried around by ocean currents and ends up everywhere. Water vapor is different through because the tritium is chemically part of the water. Caesium, iodine, lanthanum, whatever the fuck else, isn't part of the water, it's dissolved in the water, and when you vaporize water, the other elements don't go with it (this is how distillation works). Highly toxic, really bad stuff, even if it was thrown into the air in a plume of steam or something, will tend settle out or get rained out near the source because it's, y'know, heavy. Furthermore, vaporizing water takes more time and energy than just dumping it in the ocean, so even in some catastrophic failure scenario the rate of release of the worst contaminants would probably be much, much slower with the vapor option meaning less damage done before the problem is detected and fixed.

China and Russia recommended the vapor release option, which seems to suggest that the tritiated water isn't their main concern, it ends up on their coasts regardless. I think that also is strong evidence that any articles or editorials focusing on tritium are sensationalist nonsense because if the tritium was the issue, China and Russia wouldn't have wanted a vapor release solution either.

Yeah. Theoretically, the water that's being released has been processed to remove all the nasty stuff though, all that remains is low concentrations of tritium. I don't know the precise details of Russia, China, and Korea's official concerns, but I suspect they're very concerned with the possibility that unprocessed wastewater could end up being dumped, intentionally or unintentionally.