FUKUSHIMA, Japan—Twenty-five years ago, the Chernobyl nuclear power station in Ukraine exploded—killing 31 people and contaminating substantial areas of Ukraine, Belarus and Russia. It sent shockwaves around the world. We now face another global nuclear event: a potential meltdown at reactors at the Fukushima Daiichi nuclear power station in Japan.

There are substantial similarities and substantial differences between the Chernobyl and Fukushima-type reactors. The Chernobyl reactor was a RBMK-type boiling water reactor with a graphite moderator. Because of its huge size it was not possible to place it within a containment structure. RBMK-type reactors can produce weapons-grade plutonium as well as electricity, which accounts for their large size.

The Fukushima units are also boiling water reactors, but are much smaller, cannot produce weapons-grade plutonium (they do produce some plutonium as a consequence of fissioning uranium), and are within two containment structures: a steel vessel and a secondary containment building. There are several other important technical differences between these reactors but they need not concern us here. Consequently, in trying to compare these accidents we need to consider several key variables: (1) how much fuel is contained in the reactor; (2) what type of fuel—uranium, or a mixture of uranium and plutonium; (3) how much of the fuel is expended; (4) how much radiation is released from the reactor core; (5) what is the physical-chemical form of the released radionuclides; and (6) how much of the released radiation enters the environment where it affects biota, including humans.

In trying to estimate the potential health consequences of radiological releases at Fukushima versus Chernobyl, fundamental differences in containment and amount of radiation released are key.

Because the Chernobyl reactor core was not in a containment structure, and because the reactor had recently been refueled, a tremendous amount of radiation was released into the environment: predominately 131-iodine and 134- and 137-cesium (but also 90-strontium and 239-plutonium) were ejected into the lower troposphere and were spread by winds throughout the northern hemisphere (winds of the hemispheres do not mix). Rain was important in depositing the airborne radiation within the nuclear cloud throughout northern Europe. Eventually the radioactive cloud reached the US.

This northern hemispheric dispersion of radionuclides led to health consequences, most easily detected in Ukraine, Belarus and Russia, where about 6,000 excess cases of thyroid cancer were detected, mostly amongst young persons. These thyroid cancers were predominately caused by 131-iodine in milk and dairy products (137-cesium
may also have contributed). However, it is equally important to recall that there is, as yet, no convincingly documented increase in leukemia or solid cancers at 25 years post-accident. This is an adequate observation period for leukemias but is incomplete for solid cancers.

Because leukemias are a harbinger of other cancers, the absence of an increase in leukemia-risk is encouraging. If we use data of cancer-risk derived predominately from the atomic bomb survivors, we would estimate 2,000-15,000 excess cancer deaths over 50 years, following the accident. This magnitude of increase is difficult to detect in the context of 42 million expected cancer deaths in Europe and the ex-Soviet Union in this interval.

Other concerns, like genetic abnormalities and birth defects have, fortunately, not materialized. But there are many collateral effects, including the evacuation and relocation of about 300,000 people.

Turning to Fukushima, we can use these data to make some estimates of likely health consequences. Assuming (rather optimistically) there is no further radionuclide leakage, the Fukushima accident has released about 10 percent as much 131-iodine and 137-cesium as the Chernobyl accident. Also, the dispersion of the release is far smaller. Finally, in contrast to Chernobyl, it has been possible to restrict consumption of contaminated milk and dairy products and to distribute non-radioactive iodine (KI) to block uptake of 131-iodine.

Based on these considerations, we might expect few, if any, cases of thyroid cancer, and about 200-1,500 leukemias and other cancers combined over the next 50 years.

During this interval, about 20 million Japanese will die from cancer unrelated to Fukushima. Thus the attributable risk of cancer from Fukushima should be <0.1 percent. This is obviously below our level of detection in epidemiological studies. Raising the price of a pack of cigarettes in Japan by 10 to 20 percent would result in a much greater reduction in cancer risk than the increase we can predict from the Fukushima accident.

There is, however, an important caveat to the above discussion: the spent fuel assemblies stored atop each reactor at the Fukushima site. These fuel rods still contain radioactive materials and are stored under water to prevent excess heat production. There is no containment structure surrounding these pools.

Consequently, loss of water or a rupture in one of these pools could release radioactive materials directly into the environment and substantially alter the above calculations. I doubt this will happen. Another consequence of the accident is that about 120,000 people have been displaced, but many may be able to return within one to two years, if not sooner.

As for acute radiation syndrome, at Chernobyl the use of advanced medical techniques—like sophisticated antibiotics and anti-virus drugs, transfusions of blood components, genetically-engineered hormones and bone marrow transplants—save about 85 percent of persons exposed to more than 1 Gy of acute whole-body radiations.

This has led to recommendations for a medical strategy to deal with future nuclear accidents. Fortunately, there has been no need to test these recommendations until now. No worker so far at Fukushima has received a radiation dose greater than 250 mSv.

The global confusion and hysteria over these accidents makes it clear that policymakers and the public be educated on what radiation from an accident at a nuclear power station can—and, more importantly, cannot—do. For example, on the short-term it is almost all better to remain at one’s home or office (“shelter-in-place”) than evacuate. And people in the U.S. should not be buying and taking KI tablets. Response to such an event requires a solid, well-informed command and control structure and a panel of credible, independent medical experts to provide information and instructions and information to the public in settings where government credibility is often severely compromised.

Most accidents at nuclear plants involve few workers. There are extensive guidelines for dealing with these incidents that work reasonably well. There are also well-established command and control procedures and experienced personnel who rehearse potential incidents. Unfortunately the high standards, at least on paper, in most developed countries, like Japan, may not apply to all stations—especially those in developing countries, where many nuclear plants are planned or are currently being developed, such as in China or Indonesia.

Because an accident anywhere is an accident everywhere, developed countries should offer expert medical and accident-planning advice to their neighbors. This is being done by the International Atomic Energy Agency. As always, prevention of accidents at nuclear power stations is preferred to medical interventions.

The major issues with an event at a nuclear plant for the public are political, psychological and economic—not medical. As we have seen in Japan, a major natural disaster can disrupt the safety measures at almost all nuclear power stations. Are there adequate numbers of trained emergency personnel at nuclear power plants, especially those in geographically and/or politically unstable regions? In earthquakes of extraordinary magnitude, the widespread destruction, floods or tsunamis, fires and loss of life make the potential effects of a radiation release of less real impact.

In summary, there is suddenly renewed concern regarding potential accidents at nuclear power stations. Dealing effectively with these concerns requires diverse strategies, including policy decisions, public education, and as a last resort, a medical response. It is important to keep long-term risk-benefit ratios in mind.

As alarming as the news sounds, there are unlikely to be major health consequences of current events at nuclear power stations in Japan. Their magnitude will certainly be less than the consequences of continued dependence on fossil fuels for electrical generation. We should not let one event, no matter how dramatic, to alter our long-term calculus. On the other hand, we clearly need to increase our emergency preparedness at nuclear power stations if we want public acceptance of continued use or expansion of nuclear energy.