This is the wrong question. The relevant question is "what is the political impact of dumping it in the ocean?" and the answer is "devastating".
No matter how scientifically sound the solution, "dump it all in the ocean" simply can't happen.
Headline: "State Government to dump contaminated water from nuclear plant in ocean"
Quote: "There may potentially be a risk to flora & fauna, but we don't know for sure."
That's all it takes to make the idea political suicide. I think that's obvious from a mile away, even if many of us here agree that diluting it in the ocean is likely to be environmentally and fiscally sound.
Since we're allowing impossible situations, it could also happen if we had a magic wand.