Here's some scary science from Chernobyl:

[T]he scientists have calculated that what they call cesium’s “ecological half-life” — the time for half the cesium to disappear from the local environment — is between 180 and 320 years.

“Normally you’d say that every 30 years, it’s half as bad as it was. But it’s not,” said Tim Jannik, nuclear scientist at Savannah River National Laboratory and a collaborator on the work. “It’s going to be longer before they repopulate the area.”...

Scientists expected the ecological half-lives of radioactive isotopes to be shorter than their physical half-life as natural dispersion helped reduce the amount of material in any given soil sample. For strontium, that idea has held up. But for cesium the the opposite appears to be true.

The physical properties of cesium haven’t changed, so scientists think there must be an environmental explanation. It could be that new cesium is blowing over the soil sites from closer to the Chernobyl site. Or perhaps cesium is migrating up through the soil from deeper in the ground. Jannik hopes more research will uncover the truth.

The situation seems likely to be the same at Fukushima -- and Hanford. These are permanent national sacrifice zones -- don't let anybody kid you.