Indeed, it’s not just how much radiation that matters, but also what kind, how far it travels, and how long it persists. In the Chernobyl accident, radioactive material exploded into the air. “The plume went across many countries, traveling at 60,000 feet,” Kelly Classic of the Health Physics Society says. About 5 percent of the reactor core actually went up into the air and was carried along the jet stream, allowing the radioactive material to spread across Europe.
So far, the explosions at Fukushima have not been great enough to skyrocket material to the heights observed during Chernobyl. That’s because Fukushima uses water as a coolant and as a way to slow down neutrons unleashed by the fission process, thereby slowing the process itself. The Chernobyl plant was designed to use graphite to control the nuclear reaction instead, and when the accident happened, the graphite caught fire. “When the graphite burned, it was like a campfire, and carried away parts of the nuclear fuel rods,” explains Barry Brook, professor of environmental sciences at the University of Adelaide.
Good info to know.