Continuing radiation from the physically damaged reactors at Japan's huge Fukushima nuclear complex (10 reactors) has created a media frenzy. Headlines like "Nuclear threat grips Japan" and "Nuclear threat escalates in Japan" have bannered newspaper and television stories everywhere.
Many of those stories suggest widespread health effects from nuclear radiation. There are apparently tens of thousands of deaths from Japan's earthquake and the resulting tsunami. But at this point, there is one known fatality from the "nuclear threat", a crane operator in Reactor No. 1, and a score of injuries. Additional workers have received significant radiation exposure.
Even though the energy producing fission process has been shut down in all Fukushima reactors, the radioactive fission product isotopes created by the fission continue to emit beta decay, releasing about 6% of full operation heat. This means that if this heat is not removed, the temperatures in the reactor core will rise indefinitely until some mechanism takes the heat away at the equilibrium rate. Normally this backup cooling is done by circulating water. This requires energy to drive the circulating pumps (usually diesel engines). At Fukushima, the diesel engine systems and the connecting pipework were both apparently damaged by the earthquake and tsunami. Future generation nuclear plants feature gravity based backup which doesn't depend on mechanical systems.
If all cooling water systems fail, the beta decay will heat the core, boiling the remaining water. This can separate the steam into hydrogen and oxygen, an explosive mixture. That happened at Chernobyl and now at Fukushima.
When they finally get emergency cooling water back into the reactors, there will be a lot of that dangerous hydrogen and oxygen mixture. In addition, the zirconium tubing containing the fuel pellets may be melted or ruptured. The soluble fission products will dissolve in the cooling water, which will be very radioactive. The next problem is what to do with this water—dump it in the sea or send it to the cooling towers, evaporating it, and sending out more radiation.
The primary public concern is the continuing release of radioactivity into the atmosphere from the damaged reactors. This can cause radiation sickness, fatal in severe cases, and cancers. Radiation levels at Fukushima are approaching curable radiation sickness levels. There is as yet no evidence that any of these releases are near the 300-500 rem exposure level which carries a high risk of fatal radiation sickness.
It is likely that cancer rates will rise in the vicinity of the nuclear complex. Iodine pills are being distributed to prevent a major concern, thyroid cancer from exposure to the isotope iodine 131. I-131 has a short half-life and tends to be gone in a few months. At Chernobyl, cows ate I-131-contaminated grass, and drinking their milk gave thyroid cancer to several thousand infants and children. A great majority of those children did recover.
The other serious cancer-causing releases at Fukushima are the longer-lived isotopes, cesium 137 and krypton 85, which can be a danger for decades. At this point, the cancer threat level is not clear, but prudent evacuations are continuing. Airborne radiation is diluted by distance and time, meaning little danger for US locations.
Widespread, unjustified panic after Three Mile Island helped end the growth of nuclear energy in the US, leaving the country with lots of polluting coal plants. There were no injuries from the Three Mile Island meltdown as the radiation was contained in the plant. Fukushima is closer to Chernobyl because containment structures are compromised. But let's wait on the results of the remediation effort before pushing the panic buttons.
Rolf E. Westgard
Member, American Nuclear Society,
American Association of Petroleum
Geologists
St. Paul, Minn.
(EDITOR'S NOTE: The writer will teach a spring-quarter class, "Nuclear energy: past, present, and future" for the University of Minnesota Lifelong Learning program.)
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