In February, the World Health Organisation reported there would be no noticeable increases in cancer rates for the overall population. A third of emergency workers were at some increased risk. While infants in two localised hot spots were likely to have a 6 per cent relative increase in female breast cancer and 7 per cent relative increase in male leukaemia, WHO cautioned this was a small change. The lifetime risk of thyroid cancer, which is treatable, is only 0.75 per cent, so even in the worst-affected location it rose to only 1.25 per cent. Now the United Nations Scientific Committee on the Effects of Atomic Radiation has drawn on 80 scientists from 18 countries to produce a draft report that concludes: "Radiation exposure following the nuclear accident at Fukushima-Daiichi did not cause any immediate health effects. It is unlikely to be able to attribute any health effects in the future among the general public and the vast majority of workers." The committee has had two years to build a fuller picture of radiation dosages (measured as mSv) and impacts. It finds most Japanese in the first and second years were exposed to lower doses from the accident than from natural background radiation's 2-3 mSv a year. Also, "No radiation-related deaths or acute effects have been observed among nearly 25,000 workers involved at the accident site. Given the small number of highly exposed workers, it is unlikely that excess cases of thyroid cancer due to radiation exposure would be detectable."

Those workers, who were allowed a maximum short-term dose of 250 mSv, have been closely monitored. Of 167 exposed to more than the industry's recommended five-year limit of 100 mSv (a CT scan exposes patients to up to 10 mSv), 23 recorded 150-200 mSv, three 200-250 mSv and six up to 678 mSv, still short of the 1000 mSv single dosage that causes radiation sickness, or the accumulated exposure estimated to cause a fatal cancer years later in 5 per cent of people. So, not even one case of radiation sickness to report. A swift evacuation of 200,000 residents within a 20-kilometre radius of the plant helped protect them – WHO estimated most residents of Fukushima prefecture received doses of 1-10 mSv in the first year. By August 2011, however, the dose rate at the plant boundary was only 1.7 mSv a year. The rapid decay of most of the radioactive material (iodine-131, which reduced to a 16th of its original activity in a month) also means the evacuated area has not been permanently blighted. Many residents have returned, although some areas have restricted entry until radiation drops below the 20 mSv-a-year threshold, expected in 2016-17. Nor has the environment been devastated. The report says: "The exposures on both marine and terrestrial non-human biota were too low for observable acute effects."

The quake and tsunami damage is the real catastrophe. About 1000 deaths have been attributed to evacuations. About 90 per cent were people older than 66, who suffered from the trauma of evacuation and living in shelters. Sadly, those of them who left areas where radiation was no greater than in naturally high background areas would have been better off staying. Let's be clear, Fukushima was hit by a worst-case scenario: the world's fifth-most-powerful earthquake since 1900, a tsunami twice as high as the plant was built to withstand, and follow-up quakes of magnitudes 7.1 and 6.3. A Japanese commission of inquiry described it as a "man-made disaster" because of regulatory failure and lack of a safety culture. This "perfect storm" hit a nuclear plant built to a 50-year-old design and no one died. Japan moved a few metres east during a three-minute quake and the local coastline subsided half a metre, but the 11 reactors operating in four nuclear power plants in the region all shut down automatically. None suffered significant damage. (The tsunami disabled Fukushima's cooling system.) Yet such is the imbalance of dread to risk on matters nuclear that this accident was enough to turn public opinion and governments against nuclear power. Never mind that coal mining kills almost 6000 people a year, or that populations of coal-mining areas have death rates about 10 per cent higher than non-mining areas, or that coal emissions drive global warming.

And surely the fact that the more modern Onagawa nuclear plant was twice as close to the quake epicentre and shut down as designed, without incident, counts for something. Japan struggled without 30 per cent of its generating capacity for almost two years before electing pro-nuclear Prime Minister Shinzo Abe in December. About 50 reactors are expected to restart within a year. Worldwide, more than 60 plants are being built and 300 are in the licensing process, the strongest growth since the 1970s. Fukushima was serious, but it was not the end of the debate about nuclear power, nor should it be. And it's hardly an informed debate when the good news about smaller health impacts than anyone dared expect is so widely neglected. John Watson is a senior writer.