On March 11, 2011, a tsunami over 40 feet high breached a protecting barrier on the coast of Japan causing a nuclear meltdown at the Fukushima nuclear power plant. This happened as a result of one of the most powerful earthquakes ever recorded. The tsunami cut off all electricity in the area and flooded the nuclear stations backup diesel engines preventing them from starting. As a result of the lack of any continual electricity generation capability, the station only had limited battery power. Once the stations batteries had run out, the radioactive decay of the fission products in the nuclear fuel continually dumped its heat into the reactor core with no means to remove that heat. With the heat being produced in the fuel faster than it could passively be removed, the core continued to increase in temperature until it reached the melting point. Chemical reactions from the resulting intense heat generated hydrogen gas which later ignited causing multiple explosions. A very bad day for public relations in the nuclear industry.
Besides this effect, the tsunami caused the death of around 20,000 people and caused approximately 500 billion dollars in damage. As a result of the nuclear power plant event, radioactive gasses were released into the environment which has left measurable traces around the world. With substantial measurement and evaluation having already been done, scientific evaluations of the health effects from the release are now being published by various international expert consensus committees.
The international committee UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) has evaluated the evidence for harm to all humans from the Fukushima event. The following is a direct quote from their recent report (GAOR, 67th sess., Suppl.No.46), “To date, there have been no health effects attributed to radiation exposure observed among workers, the people with the highest radiation exposures. To date, no health effects attributable to radiation exposure have been observed among children or any other member of the population“. This is profoundly significant in a way that might not seem so obvious (considering the measurable damage done by the tsunami). The reason is this, a common cold, a mild allergy or even spending an hour in the sun (if you are pasty white like me) all have observable health effects. Given that such small things can cause observable health effects, the fact that all the radiation emitted from the Fukushima event has not been able to produce a single observable health effect is worth repetition. The worst nuclear power plant accident of any kind in many decades has been unable to produce a single observable radiological health effect to date and may continue to do so indefinitely.
These findings are consistent with those found by another expert international committee, the World Health Organization (WHO). The WHO in their publication, “Preliminary dose estimation from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami”. The worst case bounding potential dose was for radioiodine intake by year old infants where the dose could theoretically produce a very small yet statistically significant increase (1%) in thyroid cancer (with this being a bounding worst case possibility). In general, the worst case doses applied to any member of the public in the Fukushima prefecture were bounded by the dose range of 1 to 5 rem. Currently 5 rem is the legal dose to a radiation worker in the United States. All other members of the public in Japan received doses less than 0.1 rem which is a legal dose in the United States for a member of the public in a nuclear facility. Natural background radiation is around 0.3 rem per year. In other words, most members of the public in Japan received doses which were small fractions of natural background from the Fukushima event.
Another conclusion of the UNSCEAR report was that evaluating small doses to large populations should not simply be used to predict cancer probabilities to populations. One possible simplified analogy would be like saying that taking the minimum amount of salmonella to get one person sick and distributing 1/10th of this to 10 people will get at least one of them sick. Although these are oversimplifications of the whole physics underlying the meaning here, the full interpretation requires a detailed understanding of uncertainties involved in these kinds of measurements but UNSCEAR clearly cautioned against these approaches which are often used when evaluating radiation effects to populations.