As workers struggle to contain Japan's nuclear disaster, a vast cleanup task lies ahead.

THE GIST:

- The cleanup of radioactive contaminants from the Japan nuclear crisis is a huge task that could have impacts for decades to come.

- Burning coal and other combustion products for energy is responsible for 20,000 to 50,000 premature deaths in the United States.

- Chernobyl, the world's worst nuclear disaster, will ultimately be responsible for about 5,000 fatalities.

What could be more daunting than a 9.0-magnitude earthquake, a killer tsunami and leaking nuclear power plants? Cleaning up all that radioactive contamination.

Thomas McKone, a senior environmental scientist at Lawrence Berkeley National Laboratory, says cleaning things up from Japan's crippled nuclear power plants will be a complex, expensive task.

"It's happening at slow enough motion that we can take actions. But the actions we have to take to prevent people from being exposed are enormously expensive and complicated," McKone told Discovery News.

"Once this is all taken care of, now you've got this mess. You just can't go in and clean it up like a chemical spill or something, and it's not like the oil (spill) where it disburses," he said.

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After primary and backup cooling systems failed in the wake of Friday's earthquake and tsunami, officials resorted to using seawater to keep Japan's most vulnerable reactors from melting down. That water is now contaminated, and needs to be contained.

"It's very radioactive," McKone said. "Designing a cleanup operation for this plant is probably as hard as designing a nuclear plant to begin with."

McKone pointed out that teams are going to have to come up with step-by-step procedures, test them out, think about the risks and consider alternatives every step of the way.

"I see this as an enormous engineering challenge over the next decade. It's going to cost more than the nuclear power plants cost to build. It's going to cost billions," he said.

As a precaution, Japan evacuated tens of thousands of people who live within 12 miles of the Daiichi nuclear plant in Fukushima, 150 miles north of Tokyo. Those within 19 miles were told to stay indoors.

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At one point, radiation in Tokyo, home to 13 million, was 10 times above normal levels, though still not considered a threat to human health.

Because radiation can be measured so precisely, its impact overshadows far more widespread health risks, such as pollutants from combustion products.

"I've spent a lot of time looking at particulate matter from combustion sources -- not radiation -- and it's responsible for a lot of premature deaths in the United States. We did a study a couple of years ago with the National Research Council and it's 20,000 to 50,000 early fatalities in the United States, just from combustion for energy," McKone said.

In comparison, the World Health Organization estimates that the 1986 Chernobyl nuclear disaster will ultimately be responsible for 5,000 deaths, a figure that includes workers killed in the accident, people directly exposed to the highest levels of radiation and longer-term cancer fatalities.

"I can't imagine that this (situation in Japan) could ever get to the scale of a Chernobyl," McKone said. "There, the reactor burned and all the fission products wafted up. There was no containment, nothing to slow it down. Here, there are still so many defense levels in place. Even if it melts, they have a lot of defense that will mitigate and slow the release down."

"The dangers are real," added Massachusetts Institute of Technology nuclear scientist Dwight Williams. "But fortunately, the dangers have been studied in great detail over time, so we're able to protect ourselves."