The Atmospheric Factor in Nuclear Disaster

March 16, 2011 · 0 comments

The tense nuclear power plant situation in Japan after the recent earthquake has raised questions not only about safety for the calamity-stricken Japanese but also about the possibility that a release of radioactive gas might affect countries far away.

Such questions would seem natural for the U.S. West Coast, where aerosols from Asia have been detected in recent years, creating a media stir about potential health risks.  Nonetheless, the risks from a nuclear catastrophe in Japan are considered very, very low. Yesterday the San Francisco public radio station KQED aired an interview with atmospheric scientist Tony VanCuren of the California Air Resources Board about how a worst-case scenario would have to develop.

VanCuren emphasized that until an actual release is observed and measured, it’s very difficult to quantify risks, but he also made a few cautious speculative points:

It depends upon the meteorology when the release occurs.  If the stuff were caught up in rain then it would be rained into the ocean and most of the risk would be dissipated before it could make it across the Pacific.   If it were released in a dry air mass that was headed this way then more of it could make it across the Pacific.

VanCuren says that such transport would not happen with just any release of radioactive gas. There has to be a lot of push from a fire or other heat source, similar to what happened in Chernobyl in 1986:

If there were a very energetic release–either a very large steam explosion or something like that that could push material high into the atmosphere…a mile to three miles up in the atmosphere–then the potential for transport would become quite significant. It would still be quite diluted as it crossed the Pacific and large particles would fall out due to gravity in the trip across the Pacific. So what would be left would be relatively small particles five microns or less in diameter and they would be spread out over a very wide plume by the time it arrived in North America.

VanCuren noted that the difference between the older graphite-moderated Chernobyl reactor and the reactors in Japan makes such releases less likely now, and that findings from Chernobyl showed that the main health risks were confined to the immediate area around the reactor.

Japanese scientists were among those who took the lead after the 1986 Chernobyl release to simulate the long-range atmospheric transport of radiation. A modeling study in the Journal of Applied Meteorology by Hirohiko Ishikawa suggested that the westward and southward spread of low concentrations of radioactive particles found in Europe may have been sustained by resuspension of those particles back into the atmosphere.

Such findings recall the tail end of a whole different era in meteorology.

Decades ago, the tracking of explosively released radioactive particles in the atmosphere was a major topic in meteorology–see for example, this Journal of Meteorology paper (“Airborne Measurement of Atomic Particles”) that Les Machta et al. based on bomb tests in Nevada in 1956. (In 1992 in BAMS Machta later told the story of how meteorological trajectory analysis helped scientists identify the date and place of the first Soviet nuclear tests.)

One finds papers in the AMS archive about fallout dispersion, atmospheric waves, and other effects of nuclear explosions. Of course, radioactive particles in the atmosphere were not only of interest for health and national security reasons. These particles were excellent tracers for studies of then-poorly understood atmospheric properties like jet-stream and tropopause dynamics.

In 1955 there was even a paper in Monthly Weather Review by D. Lee Harris refuting a then-popular notion that rising counts of tornadoes in the United States were caused by nuclear weapons tests. However, since 1963 most nations have pledged to ban atmospheric, underwater, and space-based nuclear weapons tests, stemming the flow of research projects (but not the inexorable rise of improving tornado counts).

While the initial flurry of meteorological work spurred by the Atomic Age inevitably slowed down (a spate of Nuclear Winter questions aside), the earthquake and tsunami in Japan will undoubtedly shake loose new demands on geophysical scientists, and maybe dredge up a few old topics as well.