How Radioactive Is Japan’s Fukushima Nuclear Plant?

By Gavin Atkins

One of the frustrations of communicating nuclear science is a general lack of understanding of radiation. We are all surrounded by radiation, so hearing that someone has been exposed to radiation could be as trivial as meaning they have eaten a banana, or as serious as Japan’s worst civilian radiation accident at Tokaimura which killed two people following a deadly blue flash in 1999.

The latest news from the International Atomic Energy Agency is that radiation surrounding the plant now exceeds allowable levels. The big question is by how much does it exceed allowable levels?

Respected Australian nuclear expert, Dr Ziggy Switkowski tells us today:

Most of us are exposed to about 4 millisieverts (mSv) of mainly background radiation each year. Radiation workers are allowed 50mSv per year. At the current radiation level reported at the perimeter of the damaged Fukushima plant, an individual dose would exceed 50mSv after about a week’s continuous exposure. Measurable radiation poisoning occurs at a much higher level still.

Since local residents have been evacuated, this means that while the levels of radiation are concerning, they are not yet anything near levels that are life threatening. They are however, currently too high for people to live safely in the near vicinity for a long period of time.

To give some kind of idea, the highest level of natural radioactivity in the world occurs at Ramsar in Iran at a level of up to 260 mSv per year. These people show no ill effects. However, you would currently begin to get to this level if you stood at the border of Fukushima for about five weeks.

The good news is that this can be remedied quickly. As Dr Switkowski says:

Controlled venting of excess and mildly radioactive gases is happening, will result in some community exposure to radiation, but is very unlikely to have an effect on community health. At this time, only workers on site are likely to have had elevated radiation exposures. In the context of the general devastation from the earthquake and tsunami, any health or property damage arising from the affected reactors is likely to be small.

If core cooling can be satisfactorily restored, then in the best case local residents could return to their homes in days.