Monday, March 14, 2011

Nuclear Power Plant Explosions Explained and the Public Health Risk

When Three Mile Island happened, the Disease Management Care Blog was attending medical school in the next town over. It not only remembers the contrast between the national ("worst accident in U.S. history") and local ("it's contained") news reports, but recalls the willingness of one hospital radiation physicist to wait out the accident on top of one of the cooling towers. His message: be of good cheer, students, the risk is very low.

While the experience may have biased the DMCB, its research has determined that the stricken Japanese reactors are of the circulating "light water" type. These use regular water (in contrast to heavy water, which has the added property of being able to also buffer radiation) to regulate the temperature of the radioactive rods at the core of a reactor. While the nuclear plants were apparently engineered to withstand the quake, the tsunami was a different matter. The water completely knocked out the circulating water pumps, permitting the temperature inside the reactors to climb to very high temperatures.

Enter "zirconium," a metal prized for its ability to inertly coat radioactive rods without interfering with the radiation that, in turn, creates the thermal heat that drives the steam turbines. With the loss of cool water, the contents of the superheated core partially melted, putting very hot zirconium in contact with standing water. At high temperatures, that metal chemically "strips" the oxygen out of the standing trapped steam/water leaving (remember "H2O?) hydrogen. That's the same highly flammable gas that was used to hold up the infamous Hindenburg airship and lifts the Space Shuttle into space. Given the combustible temperature inside the core, a hydrogen explosion was unavoidable.

Is this another "Chernobyl?" The DMCB learned there are two important differences: 1) that star-crossed nuclear plant used graphite (the same form of carbon that is inside pencils) in lieu of more expensive heavy water to buffer the radiation. When that core exploded, it was the graphite that caught fire, which burned uncontrollably, and 2) the location, which allowed the radioactive plume of smoke to spread over Europe. As noted above, the Japanese plants use water, so there is negligible "smoke." Until now, it's been radioactive steam and the prevailing winds are carrying it out to sea.

Is the radiation leak a threat to public health? Apparently the total amount of detectable radiation that's been released so far at the time of this writing has been very negligible. In an abundance of caution, iodide tablets have been distributed in some evacuation centers to prevent the eventual occurrence of thyroid cancer. While the amount of radioactive iodine in nuclear rods is small, release into the environment can allow children to ingest enough where it is concentrated in the thyroid gland. The iodide tablets saturate the thyroid with normal iodine, preventing uptake of the radioactive version. As for the risk of other types of cancer and malformations, the data are far less clear. It will take years to sort that out.

What is clear is that the news media seems to be again exaggerating the risk of a meltdown. Compared to the loss of life from the tsunami, the race to extract any survivors out of the rubble, the pressing need to restore basic services and the impact on Japan's and the world's economy, those crippled power plants are a relative side show.

Last but not least, it's not clear to the DMCB that, even with this latest catastrophe, that the health risk from nuclear power is that much worse than the respiratory illness and cancer associated with fossil fuels. The difference is that one happens in huge ugly spectacles, while the other kills one person at a time.

Neither of which is reason to be of good cheer.

March 15 Update: The New York Times is reporting that one of the plants has caught fire, which is now producing radioactive smoke, not steam. Since the plume is made up of particulate matter laced with radioactivity, concern has appropriately grown. Fortunately, prevailing winds appear to be heading east, toward the Pacific Ocean.

1 comment:

Zoltán Dani said...

Good post; very informative.

Appreciate it.