As the spectre of nuclear fallout threatens Japan, New Zealand scientists are assuring New Zealanders that radioactive material will not reach their shores.
GNS Science senior scientist Bernard Barry said even in the "worst possible event" of radioactive fallout at the stricken Fukushima plant, the southern hemisphere would not be affected.
No environmental contamination would reach New Zealand because the atmosphere's circulation around the equator formed a natural barrier.
Dr Barry said the most common long-term consequence of the type of radiation exposure that Japanese residents were at risk of was thyroid cancer.
Providing non-radioactive iodine to the population should prevent that. "Even if the reactor cores were to melt and remain within the reactor vessel, consequences for the general population would be minimal."
Although there had been a release of radioactive material in excess of acceptable levels, it would be "minor" compared with the fallout from the Chernobyl disaster and would not pose a significant public health risk.
"For New Zealanders in Japan, the only significant risk will be to people in the local area if a reactor explosion, with loss of integrity of the reactor containment, did occur."
Moving away from the plant was the most important precaution people could take, he said. "Moving 10 times further away will, on average, reduce radiation exposure 100 times."
GNS Science research manager Chris Kroger said the Fukushima No 1 plant operated boiling water reactors that used fresh water for cooling, to provide steam to the turbines, and to slow neutrons so they could be captured for sustainable nuclear fission.
The reactors could not sustain nuclear fission after water was removed from around the fuel rods.
"This was a fundamental difference to the design of the Chernobyl plant, which allowed an uncontrolled nuclear fission chain reaction to take place after an increase in the steam-liquid water ratio."
If an explosion caused damage to the containment vessel around the nuclear reactor vessel, nuclear fallout from fission products could occur "in the vicinity of the power plant and beyond".
However, such an explosion would not rival that of Chernobyl because nuclear fission had stopped days ago.
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