This week's column answers questions about the Japanese nuclear reactor crisis. Check online for the latest information on this rapidly developing story.

What is the best source for information on the crisis, from a scientist's perspective?

The Nuclear Information and Resource Service has an excellent, timely, and continuously updated expert-quality fact sheet on its website. Some details might be a bit technical. The Great Beyond blog from the scientific journal Nature also provides insightful and accurate coverage with (somewhat) less technical language.

Why are these reactors melting down? I thought they underwent emergency shutdowns immediately after the earthquake struck.

Nuclear reactors generate heat to boil water by two mechanisms: primarily, by the chain-reaction fission of uranium atoms and, secondly, by the spontaneous decay of various radioactive waste elements produced during the plant's operation. The control rods inserted in the reactor cores shortly after the quake successfully stopped the chain reaction but couldn't stop the decay of the waste elements. Thus, even with the reactor shut down, coolant water must still be circulated to carry away the heat generated from these waste elements. The coolant systems of these plants failed due to earthquake damage, and over time, the heat from these decaying waste elements was sufficient to first boil off the remaining coolant water and then partially melt the fuel rods in two reactors.

What are the health risks from this accident? What can I do to protect myself?

The workers on-site, now desperately trying to bring the situation under control, have the highest health risks. At the peaks of radiation leakage so far, someone working at the plant would receive more radiation exposure in an hour than one should receive in a year. Some of these workers might come down with acute radiation sickness—with failures of the blood- and gut-regenerating systems, resulting in death. (I'm deeply grateful for the duty and bravery of these workers as they struggle to protect us all.)

Some of the waste elements generated by nuclear fission—known to be released into the environment by this disaster—carry health risks. Radioactive iodine, strontium, and cesium from the plant are capable of replacing nonradioactive iodine, calcium, and potassium in the human body. Once integrated into the body, these radioactive replacements can cause organ damage, cancers, and other health problems. The best defense—beyond leaving the contaminated areas and avoiding eating or drinking contaminated substances—is to supplement yourself with the nonradioactive variants, flooding your body with the safe versions to prevent the uptake of the radioactive alternatives. Cesium has been detected in the region surrounding these plants in Japan. The people who live around them are being given potassium iodide by emergency workers.

For now, in Seattle, 4,500 miles away from the reactors, there is almost no risk of exposure from the released radioactive elements. People living within the region (over about a thousand-mile radius) should consider taking a daily multivitamin as a precaution. (Do not overdose; taking too much potassium can kill you.)

Overall, despite the magnitude of this accident so far, the health risks to the general population are very low—lower than those posed by atmospheric atom bomb tests in the 1950s and '60s and lower than that from medical imaging doses. Don't panic.

Could something like this happen here, in the United States? Can nuclear power ever really be safe?

The type and specific model of reactor involved in this accident has been heavily criticized for having a relatively unsafe design—dependent upon active cooling in an emergency situation and with a weak secondary containment building. (The Columbia Generating Station in Hanford, Washington, is a slightly updated version of the reactor design that partially melted down in Japan.) Even though these reactors have redundant backup cooling systems, the systems failed—admittedly, in the face of one of the largest earthquakes in recorded human history—and the weakness in the reactor design came to the fore. Modern reactor designs rely on passive emergency cooling, with a designed ability to dissipate the residual heat generated after an emergency shutdown with no functional cooling system.

For perspective, the routine operation of a coal-fired power plant releases more radiation into the environment than a nuclear power plant—thanks to highly radioactive elements found in coal and coal ash. In a hundred years of operation, all of the coal-fired plants in the world can be estimated to release over two million tons of radioactive thorium and 800,000 tons of uranium into the air. Even with nuclear disasters factored in, nuclear plants release far less radioactive material. Similarly, the mining of rare earth elements to make touch screens (like those in iPhones, iPads, and the like) generates vast waste pools of thorium—mostly uncontrolled and uncontained in any manner.

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