NZers should not panic about nuclear fallout - scientist

People in New Zealand do not need to worry about radiation poisoning should a quake-damaged nuclear power plant in Japan suffer catastrophic meltdowns, an expert says.

Should there be radioactive fallout from the facilities, it would not affect the southern hemisphere, GNS Science senior scientist Bernard Barry said.

Troubles at the Fukushima Daiichi plant in Fukushima province were set in motion when last Friday's magnitude 9 quake and tsunami in Japan's northeast knocked out power, crippling the cooling systems needed to keep nuclear fuel from going into full meltdown even weeks after a reactor shuts down.

There have since been three explosions at the plant, and a fourth reactor has caught fire.

However, even if the reactor cores were to melt and remain within the reactor vessel, consequences for the general population would be minimal, Dr Barry said.

There would be some release of radioactive material in excess of normally acceptable levels but it would be minor compared to the fallout from the Chernobyl, Ukraine, plant in 1986 and 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. People should follow the instructions of the Japanese authorities regarding evacuation. Moving some distance from the reactor site is the most important risk-minimising procedure.

"Moving 10 times further away will, on average, reduce radiation exposure 100 times," Dr Barry said.

The tsunami had caused the breakdown of emergency cooling, which in turn had the potential to cause core melting and explosions.

Such a potential explosion would not rival that of Chernobyl because nuclear fission stopped days ago, short-lived radioactive fission products had already had time to decay for several days, and containments were in place that would keep fallout inside the plant, or at least minimise external fallout, Dr Barry said.

The Japanese Government today warned anyone nearby to stay indoors to avoid exposure.

Officials say slightly elevated radiation levels have been detected in Tokyo but there is no health threat.

- NZPA