Okay, first off...
I'm in general opposed to nuclear power and have been very critical in the Fukushima thread. But let's stop and think for a moment. The stuff that's leaking is 8.000.000 times the safe drinking level, right? Okay. But the Pacific ocean is 187.000.000.000.000.000.000 gallons. And of course the Pacific isn't isolated, all of the world's oceans are connected, leading to a total of 326.000.000.000.000.000.000 gallons. That means that to render the Pacific ocean at having levels of radioactivity that would be unsafe to drink *as your sole source of water every day*, you'd have to dump 40.000.000.000.000 (40 trillion) gallons of that stuff in. Needless to say, there is not 40 trillion gallons of it stored at Fukushima, nor 40 billion, or even 40 million. Not to mention that it would take so long to cross the pacific that it would be far less radioactive on the other side.
People hear about "scientists detecting radiation in the US". But you wouldn't believe the lengths they have to go to be able to detect it. It's like saying, "scientists detect a magnitude 1 earthquake in Los Angeles from San Francisco". The level of stuff they're detecting is dwarfed by natural radioactive substances millions to billions of times over.
But if that's not enough for you, consider this: The Soviets had horribly lax nuclear controls, especially in the early days, and there are rivers in Russia that even *today* continuously dump high levels of radioisotopes into the arctic. They've ditched whole nuclear reactors in the oceans (the US never has admitted to, but who knows). There've been nuclear powered satellites that have crashed into the oceans. Again, we're talking *entire reactors*, not just cooling water from years after the reactor was shut down. And of course, should I bother bringing up that both sides detonated hundreds of nuclear bombs *in the atmosphere*, changing the atmosphere's isotope ratio so much that future scientists will no longer be able to reliably carbon date artifacts from the 20th century?
Nuclear accidents really, really suck.... near where the accident occurs. But as much of a concentrated punch that radioisotopes pack, the world is really, really, REALLY big.
Okay.... now, all that said.
The most widely recognized dietary substance for fighting radiation is iodine. This works because there's several radioactive iodine isotopes associated with nuclear accidents and the body tends to store iodine; however, if you've already consumed enough iodine, your body won't store any more. Caveat: if you're getting your idione from food, it's generally from seafood products, especially seaweeds and the like, which are not unlikely to be produced in... wait for it.. .Japan
So it's better to go with simple iodine supplements. Of course, even ignoring the massive dilution problem, the fact is that radioactive iodine is generally a short-term problem, not a long-term one. The different isotopes have different lifespans, but in general the iodine threat is primarily in the days-to-weeks after the accident timeframe.
For acute exposure, vitamin E is thought to have the same benefit for radiation burns as for regular burns. But of course, we're not talking about acute exposure here. Actually, we're not even talking about any exposure here, really.
There's a wide range of other isotopes besides iodine that can cause problems - of strontium, of cesium, etc. In general, "cause problems" means get stored in your body. An atom outside your body has very little odds of breaking down when you're near it, but if it's in you, you're near 100% guaranteed to get the damage from its decomposition, so what gets stored in the body is orders of magnitude more dangerous. If a person has high levels of stored radioisotopes in their body, the current standard medical treatment is indeed chelation therapy. However, not with just random chelators, but targeted chelators - prussian blue, DTPA, etc. The problem here is that you *don't* want to be taking them unless you have high levels of radioisotopes in your body. Even the more selective chelators still will bind with and remove minerals you *don't* want removed from your body.
Going whole-hog on trying to consume things for radiation treatment when you're not exposed is sort of like taking chemotherapy when you don't have cancer - "just in case".