Chernobyl Exclusion Zone Radioactive Longer Than Expected

Dec. 20, 2009— -- Chernobyl, the worst nuclear accident in history, created an inadvertent laboratory to study the impacts of radiation — and more than twenty years later, the site still holds surprises.

Reinhabiting the large dead zone around the accident site may have to wait longer than expected. Radioactive cesium isn't disappearing from the environment as quickly as predicted, according to new research presented here Monday at the meeting of the American Geophysical Union.

Cesium 137's half-life — the time it takes for half of a given amount of material to decay — is 30 years, but the amount of cesium in soil near Chernobyl isn't decreasing nearly that fast. And scientists don't know why.

It stands to reason that at some point the Ukrainian government would like to be able to use that land again, but the 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 Jannick, nuclear scientist at Savannah River National Laboratory and a collaborator on the work. "It's going to be longer before they repopulate the area."

In 1986, after the Chernobyl accident, a series of test sites was established along paths that scientists expected the fallout to take. Soil samples were taken at different depths to gauge how the radioactive isotopes of strontium, cesium and plutonium migrated in the ground.

They've been taking these measurements for more than 20 years, providing a unique experiment in the long-term environmental repercussions of a near worst-case nuclear accident.

In some ways, Chernobyl is easier to understand than DOE sites like Hanford, which have been contaminated by long-term processes.

With Chernobyl, said Boris Faybishenko, a nuclear remediation expert at Lawrence Berkeley National Laboratory, we have a definite date at which the contamination began and a series of measurements carried out from that time to today.