TODAY   |  March 17, 2011

What happens if nuclear rods melt down?

James Acton, a nuclear expert at the Carnegie Endowment for International Peace, talks about the potential consequences of the nuclear crisis in Japan and discusses the ways in which fuel rods can release radiation.

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This content comes from a Full-Text Transcript of the program.

MATT LAUER, co-host: Chuck Todd , thank you very much . James Acton is a nuclear expert with the Carnegie Endowment for International Peace . James , good to see you again. Good morning.

Mr. JAMES ACTON (Carnegie Endowment for International Peace): Good morning, Matt.

LAUER: Let's start with what seems to be the most serious of several serious situations at the Fukushima plant in the building housing reactor number 4 . According to reports the pool that is holding these spent fuel rods, the water in it is gone, and these rods are now either completely exposed or almost completely exposed, thus bleeding radiation. Is this the worst case scenario ?

Mr. ACTON: No, Matt , this isn't. This is -- this is extremely serious, but it's certainly not the worst case scenario . The water that filled those swimming pool -like structures serves two purposes. It both is a shield of radiation and it keeps those rods cool. Now, in the immediate term, perhaps the biggest danger comes from the lack of shielding because these highly radioactive fuel rods are now going to be irradiating the area around it, making it much harder for workers. In addition, it actually turns out that the expert community is divided upon whether if you lose water those fuel rods can start burning. And our lack of knowledge about what might happen in this situation is also a source of significant concern.

LAUER: Well, why wouldn't people know if those -- if those rods are exposed, whether they can start burning? Shouldn 't that be scientific fact?

Mr. ACTON: Well, it's -- it ought to be, but one of the things we're learning about this crisis is when you're so far out of the playbook, when you have so little experience of an accident of this scale and conditions this extreme, then actually there's significant uncertainty scientifically about what might happen.

LAUER: Right. You know, I -- we've all seen images now over the last 24 hours , James , of helicopters flying over that damaged building dropping loads of water. I mean, I guess the idea is that, through fractures in the roof, they're hoping some of that water gets down into that pool that's holding these spent fuel rods. From a complete novice point of view, James , it seems like an extreme long shot. What's your opinion of it?

Mr. ACTON: Well, my understanding is that the helicopters have been bombarding unit 3 rather than the spent fuel pond in unit 4. So it is an attempt to try and keep the reactor cool. And I think the operators will probably acknowledge this is a long shot. But as I've said before, we're a long way out of the playbook here. And, you know, it's necessary to improvise.

LAUER: And going back to unit 4 then for a second and this pool with the spent fuel rods, if in fact the water is gone from that pool, do we assume that it's gone because it leaked after the earthquake or explosions or because the heat of those rods has forced it to evaporate?

Mr. ACTON: Well, some of the analysis that I've read, and I haven't had a chance to do any calculations myself to try and confirm this, has suggested that the evaporation rate would be relatively slow. Now, if that's the case...

LAUER: So then that pool is damaged?

Mr. ACTON: I -- very hard to say, but that would be the tentative conclusion at this point.

LAUER: I want to ask you about something. Everywhere I go and we talk about this story I get -- I get the same comments, and that is about these 50 workers. You've got -- you've got 50 or so people who are trying to stand between what is already a serious situation and a desperate situation. We've heard reports of extremely high levels of radiation at that plant right now and headlines have blared this, but I'm just going to ask you, have they -- is it likely they have already been exposed to levels of radiation where their survival is doubtful?

Mr. ACTON: I haven't seen the latest data for the levels of radiation on site. When that radiation was at its highest, a number of hours of exposure, four hours or 10 hours, and you'd start to feel the onset of radiation sickness . Now, the levels have been fluctuating. I'm talking about when the levels were at their highest. And those brave workers who are on site are also not just out in the open, at least most of the time, they are in shielded structures. So we don't know how much they've been exposed to. But what's clear is those brave men and women know that they are at great personal risk to themselves in this situation.

LAUER: And finally, James , 104 nuclear reactors in this country, some in areas that are at risk for earthquake, others near high population centers in this country. Do we need to, in the wake of what's happening in Japan , re-examine the procedures at these plants, or the designs of these plants?

Mr. ACTON: I think the key thing we need to examine, Matt , is the following: The reason why we have had this accident in Japan is because it was hit by a bigger earthquake and particularly tsunami than it was designed to withstand. I think what we need is a wholesale review to ask whether all plants across the world are capable of withstanding the full range of accidents, both natural and manmade, to which they might be subject.

LAUER: James Acton with the Carnegie Endowment . James , thank you so much for your time this morning.

Mr. ACTON: Thank you, Matt.