I am not an expert but I do not think one plant having a meltdown would poison the entire pacific ocean. If that were the case no environmentalist group would ever have let these plants ever be built near water.
Generally if a meltdown occurs, the fuel rods get so hot they melt through the bottom of the containment vessel and burn themselves deep into the ground. They go down vertically. Not out to sea.
Ahhhhh, thanks for the info. That’s pretty scary. How far to they go before they stop? Do they keep getting hotter? Or do they reach a certain temp and began to cool? I don’t know much of anything about nuclear power, except I’m not a fan...lol