Nuclear Accidents: Determining Fukushima’s Health Consequences

Twenty-five years ago, the Chernobyl nuclear power station in Ukraine exploded killing 31 people, contaminating substantial areas of Ukraine, Belarus and Russia and sending shock waves around the world. We now face another global nuclear event: a “meltdown” at reactors at the Fukushima Daiichi nuclear power station in Japan.

Although officials and the public prepared to face the worst, the major immediate consequences at Fukushima turned out to be political, psychological and economic — not medical. This is made evident by a comparison of it with the Chernobyl accident. However, had medical intervention been necessary, techniques similar to those employed in Chernobyl are available that can counteract the effects of radiation. And, despite the lack of need for immediate medical intervention in Japan, a medical strategy is being formed to deal with future accidents, even with the likelihood that one will never be needed.

Fukushima vs. Chernobyl: Reactors

There are substantial similarities and differences between the Chernobyl and Fukushima-type reactors. The Chernobylreactor was a RBMK (bolshoy moshchnosty kanalny)-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 also are 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. And, although there are several other important technical differences between these reactors, they need not concern us here.

When comparing the Chernobyl and Fukushima accidents, several key variables need to be considered: 1) how much fuel is contained in the reactor; 2) what type of fuel it is: 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 are the physical-chemical forms of the released radionuclides; and 6) how much of the released radiation enters the environment where it affects biota, including humans.

Fukushima vs. Chernobyl: Health Consequences

When estimating the potential health consequences of radiological releases at Fukushima versus Chernobyl, fundamental differences in containment and the 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 U.S.

This Northern Hemispheric dispersion of radionuclides led to health consequences that were most easily detected in Ukraine, Belarus and Russia, where about 8,000 excess cases of thyroid cancer were detected, predominantly among young persons. These thyroid cancers were caused by 131-iodine in milk and dairy products (137-cesium also may have contributed). However, it is equally important to recall that there is, as yet, no convincingly documented substantial increase in leukemia or other cancers at 25 years post-accident. This is an adequate observation period for leukemias, but it is incomplete for solid cancers. Because leukemias are a harbinger of other cancers, the absence of a substantial 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 to 15,000 excess cancers over 50 years following the accident. This magnitude of increase is difficult to detect in the context of more than 40 million expected cancers 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.

These data estimates can be used to make some estimates of likely health consequences from the Fukushima nuclear accident. Assuming 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 less than Chernobyl. Finally, in contrast to Chernobyl, it has been possible to restrict consumption of contaminated milk and dairy products and to distribute nonradioactive iodine (potassium iodide) to block uptake of 131-iodine. Based on these considerations, we might expect few if any cases of thyroid cancer and about 200 to 1,500 leukemias and other cancers combined over the next 50 years. During this interval, about 20 million Japanese will develop cancer unrelated to Fukushima. Thus, the attributable risk of cancer from Fukushima should be less than 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 percent to 20 percent would result in a much greater reduction in cancer risk than the increase we can predict from the Fukushima accident. 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.

Fukushima vs. Chernobyl: Medical Intervention

At Chernobyl, the use of advanced medical techniques like sophisticated antibiotics and antivirus drugs, transfusions of blood components, genetically engineered hormones and bone marrow transplants were used to treat acute radiation syndrome. These types of techniques save about 85 percent of persons exposed to more than 1 gray (a unit of absorbed radiation dose of ionizing radiation) 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 170 mSv (the derived unit of dose equivalent radiation).

However, if there had been a need for a medical response at Fukushima, it is important to understand how medical techniques work to counteract radiation’s effects. There are three types of high-dose acute radiation syndromes: gastrointestinal, bone marrow and central nervous system. From a medical intervention perspective, bone marrow effects are the most important, and prompt, effective actions can save lives. People with gastrointestinal acute radiation syndrome will usually recover, whereas those with central nervous system effects will usually die.

Gastrointestinal. The effects of gastrointestinal radiation syndrome — nausea, vomiting and diarrhea — usually are treated symptomatically and with fluid replacement. It can be treated with molecularly cloned hormones, which accelerate recovery of the damaged cells of the gastrointestinal system; however, this treatment has not yet been tested in radiation accident victims. In addition, there are some recently developed drugs intended to mitigate radiation damage to the gastrointestinal tract when taken soon after radiation exposure, but whether these will work in an accident setting is unknown.

Bone marrow. Serious suppression of bone marrow function can cause bleeding, infection or both and can result in death within three to six weeks. Bone marrow suppression occurs at doses exceeding 1 to 2 gray. But bone marrow replacement may be needed after exposures exceeding 8 to 10 gray. Acute exposures exceeding 15 gray result in immediate symptoms, such as confusion, and then death from effects to the central nervous and cardiovascular systems. Because of the lethal consequences, the medical community’s focus is on mitigating the suppression of bone marrow function.

The medical approach to radiation-induced bone marrow failure is determined by the severity and the estimate of how long the blood cell production will decrease, including red blood cells (needed for oxygen transport), white blood cells (needed to prevent infections) and platelets (needed to prevent bleeding).

To respond to deficient bone marrow production of red blood cells — and to ultimately stimulate the production of these cells — cloned hormones can be used. It is more difficult to correct a reduced production of white blood cells, specifically granulocytes (needed to prevent bacterial and fungal infections). Antibiotics and antifungal drugs are typically given to prevent or treat infections. Ionizing radiation also can activate latent infections of DNA viruses, especially herpes viruses and cytomegalovirus; antiviral drugs, or sometimes antibodies, can be administered in such cases. In some accidents, intravenous immune globulin also is given to prevent or moderate infections. When platelet production is reduced, platelet transfusions and cloned hematopoietic growth factors, which stimulate platelet production, can be used.

Central nervous and cardiovascular systems. There is no effective medical intervention for these serious consequences of very high-dose acute radiation exposures.Though sedation and cardiovascular support are given, most victims die soon after exposure.

Fukushima vs. Chernobyl: Lessons Learned

The global concern over these accidents makes it clear that policymakers and the public should be educated on what radiation from an accident at a nuclear power station can and, more importantly, cannot do. For example, in the short-term, it is almost better to remain at one’s home or office (shelterin-place) than to evacuate. And, people should be made aware not to buy or take iodine tablets unless instructed by public health officials or their physician to do so. 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 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 also are 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 nations, especially in developing countries, where many nuclear plants plan to be, or are currently being, developed (like China and 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 usually political, psychological and economic — rather than 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.

Emergency Preparedness Is Key

Because of the recent accident at Fukushima, there is 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. And, we should not let one event, no matter how dramatic, 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. Needless to say, accident prevention is key.