New Chernobyl "extremely unlikely" in Japan

As alarming as developments may sound at a nuclear plant damaged in Friday's disaster in Japan, a radiation release similar to the one in the 1986 tragedy at Chernobyl is "extremely unlikely," a nuclear energy expert said on "The Early Show" Tuesday.

An explosion rocked the No. 2 reactor at the Fukushima Daiichi plant Tuesday, the third blast at the facility in four days.

"The last 24 hours have been a particularly bad time for even this dreadful crisis," James Acton, an associate in the Nuclear Policy Program at the Carnegie Endowment and a Stanton Nuclear Security Fellow, observed to co-anchor Erica Hill. "We've seen two explosions already in units one and three, but this third explosion, unlike the other two, was actually inside the containment building that surrounds the reactor. And that's significant, because it's going to make it harder to prevent the release of radioactivity. And the spent fuel, the used nuclear fuel sitting in the pools, the fact that that has caught fire, is also serious, because it now means that there is another pathway to reach the environment."

Blanket Coverage: Disaster in Japan

Still, Acton said, "I think a catastrophic release of radiation on the scale of the Chernobyl accident is extremely unlikely. But containing smaller releases of radiation that are nonetheless very serious is becoming increasingly hard."

Authorities are asking people who haven't evacuated a wide area around the plant to stay indoors, Hill noted. How long can that go on?

"We have to remember throughout all of this that Japan was hit by the largest earthquake in its history, a massive tsunami," Acton pointed out."And that entire region at the moment is in absolute turmoil, as people don't have houses. So, this is not a food or water -- this is not a crisis that the Japanese government can manage in any perfect way. There is no good solution to this and, to some extent, the authorities are being forced to make it up as they go along, given the extraordinary challenges they're facing right now."

Acton said he doesn't know whether authorities are telling the public all they know and he's "been frustrated, as many other people have, about the amount of information coming out. But let me say this, which is ... there's been this massive earthquake, this massive tsunami. The (nuclear plant) operators probably all have their own personal tragedies to deal with in a crisis of unprecedented magnitude. So, there's going to have to be an investigation. We're going to have to find out who knew what, when, and how much was revealed to the public. But I think, at this stage, given the extraordinary challenges the Japanese authorities are under, it's too early to criticize right now."

What about the 50 or so workers still in the plant - how long can they stay inside?

"It's going to depend a lot on the exact level of radiation within the plant. ... But it's worth emphasizing that, in these kinds of nuclear accidents, the heroes of this crisis are the people who decide to stay in the plant at very significant personal risk to themselves in an effort to prevent a much larger tragedy. ... There can be no doubt whatsoever about the personal danger they are in."