10 Critical Questions About Japan's Nuclear Crisis

As Japan's nuclear crisis worsens at the Fukushima Daiichi plant 160 miles northeast of Tokyo more questions than answers have arisen about just how damaged the plant is and how much danger residents are in. This seesaw story has swung rapidly between peril and promise and back again, or as a colleague of mine once said, between no hope (catastrophe) and new hope (it's under control).

The challenge for the press and for government, seldom achieved in this crisis thus far, is to sound an appropriate alarm for those who are at greatest risk -- workers and local residents -- while calming those at little or no risk. (The challenge is intensified when instant global communication turns everyone into an observer, reporter, and worrier all at once.)

So how worried should we be about the unfolding disaster at Fukushima? Here are some key questions to ask in the hours and days to come.

1. What is the current state of damaged reactors at Fukushima Daiichi?

This has been a moving, and confusing, target and it's been hard to plot a trend line. Tokyo Electric Power Co. reported that fire had broken out again early Wednesday morning in Japan (Tuesday evening in the U.S.) in the building housing reactor 4. A hydrogen explosion had also occurred earlier at reactor 2. That brings the number of crippled units to four of the plant's six reactors. As with the pot that boils over on one burner of a stove when you're stirring another, the initial concerns focused on units 1 and 3, in which hydrogen explosions occurred over the weekend and had seemed somewhat more stable. But new concerns about reactor 3 containment have now arisen. Units 4, 5, and 6 were not operating at the time of the earthquake, but experts are now worried about storage of pools of spent nuclear fuel rods heating up.

2. Is this more like Three Mile Island or Chernobyl?

While the question is unavoidable (and I've been asking it myself, having covered TMI), we still can't answer it yet. The cascade of reactor crises, and uncertainty about bringing them under control, has increased the degree of concern that Fukushima could become a more serious catastrophe than it originally appeared. As Matthew Bunn of Harvard's Belfer Center for Science and International Affairs pointed out: "This is the worst nuclear accident since Chernobyl, and in some respects worse than Three Mile Island (TMI)."

At TMI, operators managed to avoid a hydrogen explosion and there was only a modest release of radiation as a result. In the case of Japan, there have been hydrogen explosions that damaged buildings at the plant and signs of significant radioactive releases (reports conflict about the amounts)., According to an international rating scale, Chernobyl (which involved a completely different type of reactor without a containment vessel and resulted in a significant radioactive release) was ranked 7 out of 7, while TMI was ranked 5. Initially, Japan's nuclear crisis was given a preliminary rating of 4, but this is sure to change over time once the outcome becomes more clear.

3. What do we know about possible "meltdowns" involving Fukushima's reactors?

The short answer is: very little. At least "partial" meltdowns (which occurred at TMI) may have occurred in several reactors. The key issue is the degree to which crucial containment vessels housing the nuclear fuel cores remain intact. There were fears that an explosion at reactor unit 2 may have damaged the containment vessel, which increases the risk of release of hazardous radioactive materials. While reactor 4 was shut down at the time the earthquake occurred, there is concern there and at the other reactors about the pools containing used or spent uranium fuel rods. Again, it is all about cooling and containment and it ain't over yet. Scientific American has a good online package, while this New York Times graphic shows what would happen in a meltdown.

4. What's happening with the water?

Ironically water--or lack of it--has been the real story at Fukushima for the past four days. The nuclear cores need water to cool them down, and the tsunami swamped Fukushima and initially cut off electricity powering the cooling systems. Then various backups failed, which forced plant operators to pump sea water into the reactors to try to cool them down. The Times initially reported that helicopters might be used to drop water on the pools of spent fuel that are too hot. (Later the idea was discounted.) In short: follow the water.

5. What do we know about current radiation levels inside the plant?

That's where the alarm bells went off on Monday evening (U.S. EDT) following a Japanese press conference in which a top official warned the situation was growing "very grave" and that there were new concerns about the release of radioactive materials that could pose human health risks. The bulk of the plant's workers were evacuated because of the increased radiation and health risk, with a bare-bones crew of 50 left to continue heroic efforts to contain the ongoing crisis. It is of course the workers who are at greatest risk of short-term radiation sickness and long-term health effects.

Beware of single reports of radiation level reports, since radiation levels can frequently fluctuate and it is not clear who is being exposed and for how long. The International Atomic Energy Agency (IAEA) confirmed today that elevated radiation ("dose rates up to 400 millisieverts per hour") had been reported at the plant. Falling radiation levels were also reported.

6. What about radiation levels outside the plant?

The degree of human health risk depends on several factors including: the type of radioactive material involved; the level of radiation in the environment; whether and how long individuals are exposed to the radiation; the cumulative amount or dose of radiation. Some individuals are more vulnerable than others, particularly pregnant women, young children and seriously ill patients. Reliable measures of levels outside the plant have not been available and won't be for the foreseeable future (some journalists and others are wearing radiation dosimeters which will keep track of their individual exposure).

7. Is enough being done to protect Japanese near Fukushima, and what about those who live farther away?

In order to reduce the amount of exposure by residents, the government increased evacuation area around Fukushima to 20 kilometers and asked those living up to 30 kilometers away to stay indoors to further protect them from radiation. (During the the Three Mile Island episode there wasn't a mass evacuation, but pregnant women and preschool children were urged to leave the area.) The TMI crisis was relatively short-lived (the immediate danger subsided after three days) and involved just one reactor. The Japan crisis is far larger and will clearly last far longer.

8. Which way is the wind blowing?

This is highly pertinent. The wind direction, should there be a plume containing radioactive material, determines whether fallout will land on populated areas or in the sea. One bright spot here -- dare I say "new hope," at least temporarily? -- is that the prevailing surface winds, which were blowing toward Tokyo, are now expected to head toward the Pacific. Because low-levels of airborne radiation dissipate over time and distance, officials have said they don't expect this to pose a significant health risk in Hawaii or the mainland U.S.

9. Should we believe the official sources of information?

Frustration continues to grow in about the confusing, often contradictory, information emanating from the Japanese government and the company running Fukushima (not to mention dueling experts in some of international media). Concerns have inevitably surfaced that some of the key players may be downplaying the situation (as was charged during TMI) and some finger-pointing about the company's handling has begun. But the situation is still so serious that it seems unlikely it's being downplayed at the moment by those in power. The primary source of information are Japanese government officials, the Tokyo Electric Power Company (TEPCO), and the International Atomic Energy Agency (IAEA).

10. How is the global media handling all of this?

Coverage by American news outlets has steadily improved, with more in-depth, informative updates replacing the limited, confusing weekend reports. You can get breaking news directly from Japan, including live USTREAM coverage on NHK WORLD TV, an English language 24-hour international news and information channel; NHK also has breaking online news in English; as does Kyodo News agency.

For more coverage of Japan's nuclear crisis see:

• What the Media Doesn't Get About Meltdowns

• A Japanese Three Mile Island?

• The Fog of Nuclear Emergency