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updated 3/29/2011 4:17:41 PM ET 2011-03-29T20:17:41

First the good news: Whatever damage has been done to the nuclear fuel rods at Japan’s crippled Fukushima Daiichi power plant is likely done and water for cooling has been restored.

Now the bad: It’s getting tougher to contain the radiation stemming from the damaged fuel rods. Worst-case scenario? Containment barriers fail and water and air laced with radioactive particles spew into the environment, raising health risks for people in the immediate area.

“There's a lot of radioactivity outside of containment barriers that's posing a threat to both workers and the public that needs to be addressed as the top priority,” said Dave Lochbaum, director of the Nuclear Power Project for the Union of Concerned Scientists, a Washington, D.C.-based advocacy group.

The plant’s cooling systems -- critical for keeping both the nuclear core and spent nuclear fuel rods from overheating -- failed following the 9.0-magnitude earthquake and killer tsunami that struck Japan on March 11. A last-resort decision to pump seawater into the reactors to keep their radioactive fuel rods from melting and spewing radioactive materials into the air bought time until other ways to deliver water for cooling could be found. Safely containing all the water used for cooling, which is now highly contaminated, is Japan’s latest pressing problem.

Radioactive water made its way into and around buildings housing the crippled reactors and experts don’t know how. Leaking pipes and rain that has picked up radioactive particles vented into the air are possible sources of contamination.

“The pathways for that material to get out are numerous,” Lochbaum said.

Lochbaum told reporters: “They need to get some control over that, some place to put it, some processing plant that can treat the water, remove as much radiation as possible from the water. They had to use the water -- I don't criticize the fact that they had to use that water to cool the spent fuel pools and the reactors -- but the legacy of that need has been a huge problem that they need to get their arms around quickly.”

Officials believe the containers holding the radioactive fuels remain intact, though they can't be certain.

“The problem is that you can’t look inside the reactor and see what state they’re in,” Thomas McKone, a senior environmental scientist at Lawrence Berkeley National Laboratory, told Discovery News. “At some point, they’re going to have to run in remote probes to see what’s happening with the core. Right now, their concern is to make sure it’s full of water.”

“Even if they have a larger radioactive release, I think the problems are going to be confined to Japan,” McKone added.

That's because over the distances the radioactive particles travel, they continually break down and dissipate. Radiation can be detected by individual atoms, just minuscule amounts, so the fact that sensors on the Eastern Seaboard of the United States, and other places, are picking up radioactive particles that migrated from Japan is not surprising, and the amounts are not close to any level that would raise health concerns, according to the Environmental Protection Agency.

Working in Japan’s favor: every eight days, the amount of radioactive iodine, one of the fission products generated by the nuclear fuel, decreases by 50 percent and the reactors themselves require less cooling to remain intact.

The crisis at Japan's stricken nuclear plant, where officials are working to stabilize four of six reactors, is more complicated than the situation 32 years ago at Three Mile Island in Pennsylvania, where one reactor experienced a partial core meltdown.

“Things could get worse,” Lochbaum said. “They could have some more equipment failures that lead to more damage ... but it seems like the fuel damage to date has already been done.”

© 2012 Discovery Channel

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