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Now to Japan for an update on the troubled Fukushima Daiichi nuclear power plant. It was heavily damaged by an earthquake and resulting tsunami in March 2011, leading to several meltdowns. Then yesterday, the government estimated that some 300 tons of radioactive water are pouring into the ocean each day. Meanwhile, the plant's owner has unveiled plans to seal its reactors in a wall of ice. NPR science correspondent Geoff Brumfiel joins us now, and start by reminding us the basics here, I mean, how this water is actually getting contaminated.

GEOFF BRUMFIEL, BYLINE: Right. So to understand, you need to know the geography of Fukushima. There are three melted down reactors, and they're all right on the coast. To the west, you have mountains. To the east, you have ocean. And so what's happening is groundwater flows downhill. It flows down through the ruins of the plant and then flows out to the sea.

CORNISH: Now, we're talking about a lot of water here. I mean, 300 tons a day. How dangerous is this?

BRUMFIEL: Well, I mean, it is a lot of water. That's for sure. And it's certainly never a good situation when you have radioactive water flowing uncontained. It's a little hard to say just how dangerous it is. The seafloor around the plant already has a lot of radioactive contamination so that area has already been polluted, just like the land. And the Pacific Ocean is a big place, so this gets diluted very quickly. But certainly, it's not a good situation, and I think it's as much about public trust as anything else. It took TEPCO a long time to admit this leaking was happening. And I think people are fed up with them. And now that they have admitted it, now that the government's talking about it, they want this thing fixed.

CORNISH: So how do they do that?

BRUMFIEL: Well, they're trying to stop it any way they can. So the first thing that they tried was putting in some chemicals that would make the soil impermeable to water, to stop the water from flowing out. That worked in the short term. But what seems to have happened is the water built up behind that wall, and so now it's overflowing again, and this is where this new government figure comes from. So now, TEPCO has proposed literally creating a wall of ice around the plant. And what they're talking about is not a wall above ground, but freezing the ground around the plant to stop water from flowing in.

CORNISH: All right. Wait a second. So it's an underground ice wall. Like, how does that even work?

BRUMFIEL: So the basic idea is that they run piping into the ground and they put coolant in the piping and that freezes the earth around the pipes, and it all sort of gradually forms together into a wall. This is something that civil engineers see sometimes, but it's not that common. And certainly, the way they're talking about using it in Fukushima is unprecedented. This wall will be nearly a mile around according to TEPCO. It would require more than 2 million cubic feet of soil to be frozen. But if it worked, then it may be the only way to keep water from flowing into the plant and contaminated water from flowing out.

CORNISH: This sounds pretty incredible. I mean, can TEPCO actually pull it off?

BRUMFIEL: Well, this is why the government's getting involved. They clearly have started to lose faith in TEPCO a bit. Up until now, TEPCO has been taking the lead. They've been setting all the timelines and making all the plans for how to clean up this plant and the government's pledged financial support, but has largely stayed out of the way. Now, it looks like the government feels it needs to step in either to do this ice wall or something else.

CORNISH: NPR science correspondent Geoff Brumfiel. Thank you so much.

BRUMFIEL: Thank you, Audie. Transcript provided by NPR, Copyright NPR.