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Now we take you to a place that garnered headlines around the world three years ago, but has hardly been seen since, because it's so dangerous.
NewsHour science correspondent Miles O'Brien is our guide.
Three years after the meltdowns, the road to Fukushima is still a gauntlet of roadblocks and strict security checks.
And inside the exclusion zone, it remains a post-apocalyptic landscape of abandoned towns, frozen in time. We were on our way to one of the most hazardous places on Earth, the Fukushima Daiichi nuclear power plant. The Tokyo Electric Power Company, TEPCO, granted the NewsHour permission for a rare tour inside the plant, where three nuclear reactors melted down after the great Tohoku earthquake and subsequent tsunami on March 11, 2011.
In the seismically isolated and radioactively protected emergency response center, we met the man in the hottest seat of all here, superintendent Akira Ono. He runs an unprecedented decommissioning project that will not be done for decades. He prefers not to call it a cleanup.
"After all, if you are just cleaning up after an accident," he told me, "there is a lack of quality, meaning speed is the only concern. I feel that isn't enough. We need to look ahead, 30 to 40 years."
To see it firsthand, we had to suit up. We must also wear a full face mask and respirator for good measure, resembling astronauts on the way to a fully fueled rocket. We donned special shoes and hardhats, then boarded a bus that would get us as close to the meltdowns as the laws of physics and common sense would allow us.
Fukushima Daiichi or, number one, was a complex of six boiling water reactors designed by General Electric. They were built on sloping terrain, sandwiched between a mountain ridge and the Pacific Ocean. The nuclear cores are between 600 and 800 feet from the harbor.
Three of those cores are now melted down, still steaming hot, their steel containment structures breached. Engineers believe some of the nuclear fuel has melted right through the steel containment vessels on to a concrete basement floor, where it is exposed to groundwater.
As the ground water passes through the plant, it gets mixed in with the contaminated water that is used to cool the melted-down cores. The result is an awful lot of water that needs to be captured, or else it ends up in the ocean.
Each and every day, about 100,000 gallons of fresh groundwater seeps into the basements of the plant, where it becomes contaminated with a witch's brew of radionuclide. TEPCO is furiously trying to keep pace with the water. They finish a new quarter-million-gallon holding tank here about every other day.
But the hastily built tanks have been leaking, prompting a switch to a welded design, buttressed by gutters, dikes, trenches and water sealants. Regardless, no one disputes the plant is steadily leaking radiation-tainted water into the sea.
"When you go out to the open ocean, there is very little contamination found," says superintendent Ono. "Basically, the contamination is limited to the port."
At the port, they are bolstering the last line of defense. This water-shielding wall should be complete in September. Behind it is a system that injects a chemical into the ground that turns water into a viscous gel, stemming the flow to the sea. The company is also testing an idea to bury cooling pipes near the melted reactors to freeze the ground, making impermeable ice plugs in walls that would keep the clean and contaminated water apart.
But all of this is clearly not sustainable. In about three years, they will run out of space for new water holding tanks. Then what?
Masayuki Ono, no relation to the superintendent is general manager of TEPCO's nuclear power division.
"We can't solve this problem by simply increasing the number of tanks," he told me. "We need to solve the fundamental issue of underground water coming in."
And TEPCO is also investing a lot in this sophisticated radiation water-filtering technology. In trial runs, the advanced liquid processing system, ALPS, has cleaned up 12.5 million gallons of water. ALPS removes cesium, strontium and 60 other radioactive nuclides, but not tritium. There is no practical way to factor out this isotope of hydrogen.
"It is hard to remove tritium with scientific methods," he says. "But given its biological properties, it is a radioactive substance with a very limited risk."
Nuclear engineer Lake Barrett worked for the U.S. Nuclear Regulatory Commission at Three Mile Island in the wake of the meltdown there in 1979. He is now a special adviser to TEPCO's president.
LAKE BARRETT, TEPCO special advisor: When you combine all the water on the site with the tritium, the tritium levels will be so low at Fukushima that they would meet the international drinking water standards.
TEPCO has no authorization from the Japanese government, local residents or fishermen to discharge any water at all, including what is leaking, from the Fukushima Daiichi site.
But a release of millions of gallons of water tainted with tritium into the ocean seems inevitable.
You can release it into the ocean, in a normal controlled release, which is what I personally believe they ought to do. But they have to work through the fishermen and all the governors and all the social issues that have to be addressed with that.
The long-term solution here is to remove and secure the nuclear fuel. At unit four, they have begun that process. This reactor was shut down for maintenance when the tsunami hit. And so the fuel had been moved into this storage pool.
Even though the reactor wasn't running, during the worst of the crisis, hydrogen gas accumulated in the reactor buildings, causing a series of explosions. Debris rained down into the pool, landing on top of the stored fuel assemblies. Workers have now carefully plucked away the pieces and have begun removing the 1,533 fuel assemblies stored here.
"It is assumed that some debris fell through the gaps," engineer Takashi Hara told me. "So far, we don't think it is anything that will cause the fuel to get stuck. However, it could be the case in the future, so we're proceeding very slowly."
The fuel assemblies are transported in casts that will be stored in a more seismically secure common storage pool. If all goes as planned, this process will be complete by the end of this year.
But removing the melted fuel from units one, two and three is another matter entirely. The radiation levels are simply too high for humans to ever get close enough to clean up. Even so, TEPCO is vowing to have the fuel debris removed from one of the reactors by mid 2020. But how? The only way to do that is to invent robots that can do the job. And that is precisely what they're trying to do.
They're probably the most robotic society, you know, there is on earth. Now you have to take it to another level, you know, to work in the high radiation field and to do things that they have never done before.
There are many things that will have to be done here that have never been done before in order to decommission this plant.
"We will need to incorporate more and more new things," superintendent Ono told me. "You can't brood on the past for answers. I want to take on the various challenges with a constructive attitude."
Before we left, they carefully scanned all of us and checked the dosimeters that we carried along the way. During our four-and-a-half-hour tour, we absorbed as much radiation as we would have in a single chest X-ray. It was dark when we rode the bus out of the exclusion zone. It was a quiet ride, as we all processed the magnitude of the mess.
Three years after the meltdowns, the crisis has not ended here. In some ways, it is still unfolding.
Next Wednesday, Miles will have a report on the Fukushima meltdown's effect on fish in the surrounding waters.
And we want to note, these stories were produced before Miles' trip to the Philippines, where an accident led to the loss of his left arm. As we said earlier this week, we, his NewsHour colleagues, are in awe of his courage.
There is more information about what happened, and a link to Miles' blog, on our Web site.
Due to a transcription error, an earlier version of this post incorrectly described the route of the groundwater that mixes in with contaminated water used to cool the melted-down cores. As Miles O'Brien says correctly in the report, the groundwater passes through the plant, not the pump.