JUDY WOODRUFF: We learn more now on the latest discoveries at Japan's crippled Fukushima Daiichi nuclear plant from James Acton. He's a physicist in the Nuclear Policy Program at the Carnegie Endowment for International Peace.

Thank you for being with us again.
JAMES ACTON, Carnegie Endowment for International Peace: My pleasure.
JUDY WOODRUFF: What is significant to you in this new information?
JAMES ACTON: Well, the new information today adds to a growing picture that we have been seeing over the last month that suggests that this crisis was much more serious much more quickly than anybody realized at the time.
In fact, information that NISA -- that's the Japanese regulator -- released on Monday suggests that the fueling unit one melted down within five hours of the earthquake on March the 11th, which is pretty astonishing, actually.
JUDY WOODRUFF: So, walk us through what happened that we didn't understand before.
JAMES ACTON: Well, you know, at an early stage of this crisis, the first few days of this crisis, if you think back all the way to the immediate time after March the 11th, you know, a lot of analysts, including myself, were talking about, there's the risk of a fuel meltdown.
In fact, we now know that that had already happened. The majority, the -- probably all the fuel in units one, two and three melted at a much earlier stage. And because the severity of the crisis is at an earlier stage, the remediation and the cleanup I think is going to be that much harder now.
JUDY WOODRUFF: So -- and the amount of radiation out there is how much worse than what was thought?
JAMES ACTON: It appears to be -- you know, NISA has increased their estimate by about a factor of two. I think that's largely a reflection of how difficult it is to estimate the amount of radiation being released from the plant. I mean, this is a very, very difficult calculation. And it is a calculation, actually, rather than a measurement.
JUDY WOODRUFF: So, how do you account for the difference in what we were told in March, when this happened, with what we're learning now? Is it that it's just been harder to get to the bottom of what happened, or do you think the information was deliberately withheld?
JAMES ACTON: I think the main reason is the -- is the astonishing difficulty of understanding what is going on inside reactors under these extreme circumstances.
You know, there's intense radiation inside these reactors by design. So, you can't just kind of pop the lid in and have a look inside. So, a lot of the new information we have been seeing is the Japanese utility, TEPCO, the regulator, NISA, finding out more information, better computer models.
There clearly needs to be an investigation to find out whether information was withheld deliberately. But I think the -- almost -- I mean, the main reason is the utility and the operators themselves are getting new information for it.
JUDY WOODRUFF: How much does it matter that we either had erroneous or incomplete information in the early weeks?
JAMES ACTON: In any major disaster -- and this was an enormous disaster -- you're never going to have perfect communication.
Information that you believe to be true is going to turn out not to be true. And that's the nature of the crisis. I think the crucial thing is that communication is honest, that it's done in good faith, that information that -- you only say what you know to be true.
And I think the key question is whether information was withheld and whether everything that was said was known to be true at the time.
JUDY WOODRUFF: So, based on what we know now, James Acton, what about the safety of people who are living anywhere near the area right around these reactors?
JAMES ACTON: Well, there isn't really anybody living around the reactors anymore. As the feed up to this segment showed, there's this exclusion zone.
JUDY WOODRUFF: But I mean right outside that area. How much certainty can they have that they're safe?
JAMES ACTON: Well, statistically, levels outside the plant are such that there is likely to be a very small increase in long-term cancer rates.
There are a few places around the plant now where the levels of radiation are significantly -- significantly above background. But I -- you know, I think it's worth emphasizing that 14,000 people died in the tsunami and the earthquake; 10,000 more people are still unaccounted for. The number of casualties from the nuclear crisis is going to be orders of magnitude smaller.
JUDY WOODRUFF: And we -- you're right. We are often setting that aside, when the death toll was much greater.
James Acton, what about what the government of Japan, what the Tokyo Electric Power facility should be doing now to make sure that safety is at its maximum around these plants?
JAMES ACTON: This accident was a failure of regulation, rather than a failure of operation. This plant was simply not designed to withstand the size of the earthquake, and particularly the size of the tsunami that hit it.
So, I think the key question this asks about, you know, the future safety of this particular plant, of nuclear plants in Japan, indeed, around the world, is whether the size of hazards that might befall them has been correctly predicted.
JUDY WOODRUFF: And how close do you think we are now to knowing all that there is to be known about what has happened here?
JAMES ACTON: Oh, probably quite a long way.
I mean, for instance, with Three Mile Island, it was only -- I believe it was five years after the accident when the lid of the reactor was finally opened. A huge amount of new information, the extent of the fuel melting, was discovered.
We know a lot more about this accident than we did three months ago. But I have no doubt that the investigation which has just started in Japan and future investigations in the weeks and the months and the years ahead are going to discover more information that is simply not known or knowable at the moment.
JUDY WOODRUFF: So, for you, again, what are the main questions that you have that are -- remain unanswered?
JAMES ACTON: I think the first question relates to, you know, this issue of regulation.
Were the -- was the Japanese government systemically failing to predict the size of hazards at reactors correctly? I think there's questions about emergency preparedness. Was -- emergency management is incredibly difficult at the best of times, but did the Japanese government do basically a good job under extraordinarily difficult circumstances, or were there serious errors that can and should have been avoided?
Was information deliberately withheld, or was knowingly incorrect information put forward? I think those are the key questions for me at this stage.
JUDY WOODRUFF: All right, James Acton, joining us again on this story that, as you say, continues to unfold, thank you very much.
JAMES ACTON: Thank you.