Is Japan's Fukushima Power Plant Still a Threat?

Part 2: Radiation experts test Pacific Ocean waters surrounding the plant for signs of unsafe levels.
3:00 | 01/09/14

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Transcript for Is Japan's Fukushima Power Plant Still a Threat?
We're back with our exclusive look inside the still damaged fukushima nuclear plant. Here agains abc's cecila vega. Reporter: We shouldn't be doing interviews in a hot spot like that. Workers here are racing to contain the damage after that massive tsunami triggered one of the worst nuclear disasters in history. But what if mother nature strikes again. During our trip, a typhoon made land fall near fukushima. These winds are up to 90 miles an hour. You can't even walk. You have to hold on to this railing. There's a serious concern this torrential storm could do even more damage to the already crippled plant. The plant's operator, tepco assures the world that this time it can defend against the next natural disaster. They beefed up defenses with new technology that will ensure backup power and supply water to cool reactors during an emergency. But how will nature fair against the threat from fukushima? This summer, the company admitted that even after the accident, radioactive water had seemed into the ocean. And many scientists fear the plant still leaks every day. But how bad is the damage? To find out, we're venturing to the power plant, with us a team of japanese scientists. Our rented fishing boat transformed into a mobile lab that can detect radiation in the water and the ocean floor. We're so close, you can hear them working. This is about half a football field away essentially. This is as close as we can get to collect samples without tepco permission. Ed a radiation detectors climb, the team has to work quickly to limit our exposure. Now they're going to lower this device down into the ocean, measuring the water to find out how much contamination there is. On shore, just behind the plants, there are more than 1,000 temporary tanks holding over 100 million gallons of highly radioactive waste water. Tepco admits some of them have leaked. They want to measure the full extent of the damage. It doesn't take long. The team says it finds evidence of radiation. A lot of cesium you found? He says it's just what he suspected. Even though the radiation levels he says he measured fall within the legal limb fit for swimming and drinking, they're still 1,000 times higher than before the meltdown and the effects for long-term exposure for people and the environment are still unknown. Can the damage that's been done be repaired here? Or is it too late? It's not too late, he says. But japan can't do it alone. We need help from the rest of the world. We've seen them trying. It's just not working. Reporter: We meet ken bessler. He studied the fallout from the world's largest nuclear disaster in chernobyl 26 years ago and now he's come here to help survey the damage. How long will it take to work through from the land to the ocean, the power plant into the sea life. And across the pacific. Reporter: The government claims radiation from fukushima is contained in this small harbor outside the plant. But on expeditions into the pacific, bessler and his team of scientists say they med sured radiation linked to fukushima more than 70 miles away. Some of that radiation is predicted to reach american shores early this year. The le are expected to be very low. I think the fear of what's happening outside the local area is a bit exaggerated. For americans to worry about swimming on our beaches when i can swim here I think is overblown. Reporter: What does concern him is how this unprecedented amount of migrating raildiation will affect the food chain. I try get as much as possible. Reporter: Some fish tested positive for radiation levels low enough to make them legally safe to eat. The japanese isn't taking any chances. This is one of the countries that consumes the most fish in the world. Now they've got to convince everyone that these fish are safe to eat. Even fish caught miles outside of fukushima are inspected before they can be sold at markets. They are required to test every batch. Trace amounts of radiation linked to the power plant have been detected in blue fin tuna as far away as california. Still, experts say americans shouldn't worry. Dangerous radiation dilutes as fish migrate to the u.S. To end our trip, we visit tepco's headquarters in tokyo. A spokesperson for this embattled company assures us tepco will keep testing the ocean surrounding the plant and publicly report the results. Does the fukushima daiichi power plant pose any kind of threats to the public today? He says people can feel safe. There is no threat to the general public. Why should the public trust tepco now. The only way to restore trust, he tells me, is to decommission the plant safely and explain the process to the public. Our journey may be over, but the clean- goes on. Closing the fukushima daiichi power plant will cost an estimated $15 billion and take 40 years to complete. And then there's the damage we can't see. Radiation on land and in the ocean that could be japan's invisible enemy for generations. Our thanks to cecilia vega for her remarkable work on that

This transcript has been automatically generated and may not be 100% accurate.

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