Japan Nuclear Plant Rocked By Second Blast

The second hydrogen explosion in three days rocked a stricken Japanese nuclear plant Monday, sending a massive cloud of smoke into the air and injuring workers.

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RENEE MONTAGNE, host:

We turn, now, to NPR science correspondent, Joe Palca, who's here in our studio, to talk about the events surrounding those troubled nuclear power plants in Japan.

Good morning.

JOE PALCA: Good Morning.

MONTAGNE: So, Joe, we just heard that there was a second explosion at the Fukushima power plant. What was the cause?

PALCA: Well, like the first explosion, people think the cause is a build up well, hydrogen gas, that was released from the containment vessel where the nuclear reaction was taking place. Now, the nuclear fission reaction has been shut down, but the fuel rods - which are contained in a zirconium metal canisters, essentially - they are heating up and it's possible, when they get hot or if they get compromised, that hydrogen gas can be given off.

Subsequently, that's vented from the control from the chamber where containment is, into the building outside the containment chamber, and that's what exploded. So it's not inside the reactor core, but outside in this building.

MONTAGNE: Is the situation under control?

PALCA: Well, no, I think is the short answer. It there are signs that it may be getting there. The key is keeping these fuel rods cool and intact. And to do that you need to pump water into them cool water or water that can cool off. And, um, there's indications now, that all three of these reactions reactors have had seawater pumped into them. That would cool them off, it would also probably it has, in fact, most people say, ended their useful life, because the seawater is corrosive and it will just eat away at the parts inside the reactor. But if they can be kept cool, then the problem will cease in a few days.

MONTAGNE: What is the risk for people who are near these reactors and possibly exposed to whatever radiation is coming out?

PALCA: Well, it all depends on dose. Some radiation has come out, it's been detected. How much, what kind of intensity, that's where the questions all are. And we just don't know yet. I mean, the measurements for environmental radiation release have not come out in any kind of coherent way.

MONTAGNE: And you just spoke about the fuel rods what does it mean when people talk about a meltdown within these reactors? I mean, when we think of meltdown, many people think of Chernobyl.

PALCA: Right. Well, they're very different reactors, first of all, so the Chernobyl reactor didn't use water to control the nuclear reaction, it used graphite or carbon and the carbon rods are capable of catching fire, which is, in fact, might seems to be what happened, because the fire sent radioactive material up into the sky. The other problem in Chernobyl was there was no containment vessel, so things just went you know, once they started burning, up they went.

Um, the meltdown refers to fuel melting.

MONTAGNE: Melting...

PALCA: Right. Well, in any scenario, when there's a meltdown, something is melting. The question is: is it a little bit, or is it going to be released into the environment? At this point, there doesn't seem to be any indication that any of the fuel material will leak, in major amounts, into the environment.

MONTAGNE: And partly, again, because there's containment in these Japanese reactors they're just that much better made.

PALCA: Right.

MONTAGNE: Much, much better made.

PALCA: Well, they're made with a different philosophy, and yes, they seem to be controlling the release of material.

MONTAGNE: Japan relies on nuclear power for a lot of its electricity, what does all this mean for the country's power?

PALCA: Well, there apparently have already been power outages, on purpose this is the power company trying to allocate what electricity it has to the country in some equitable way. And so, that means that some areas won't get power at certain times.

MONTAGNE: So, now, officials in Japan are warning of a strong aftershock from this earthquake last week. Aftershocks, really, are another name for more earthquakes.

PALCA: Right. This is just another big earthquake that they're warning about. It hasn't happened. Predicting earthquakes is tricky business, but this is the concern that that could be. Of course, if you're an optimist, it's a 30 percent chance that it won't occur, and a 70 percent chance it will if you're a pessimist. That's what they're saying.

MONTAGNE: That's what they're saying, 70 percent chance of a strong aftershock?

PALCA: Correct.

MONTAGNE: NPR's science correspondent, Joe Palca. Thanks very much.

PALCA: You're welcome.

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