The announcement on 12 April 2011 of an increase of the Fukushima event from 5 to 7 – the highest level on the IAEA’s International Nuclear Event Scale (INES) – has given the misleading impression that it was as bad as the Chernobyl accident. This impression has been exploited in anti-nuclear propaganda. There is actually no possibility that the physical health consequences of damage to the Fukushima plants will get anywhere near those of Chernobyl.
The INES (illustration below, copied from Wikipedia
) divides nuclear incidents and accidents into seven levels, based on off-site effects, on-site effects, and degradation of the nuclear plant’s “defence in depth”. Before 12 April 2011, only one accident – at Chernobyl in 1986 – had been rated at Level 7. The accident at Three Mile Island in 1979 was rated Level 5.
The accident at Chernobyl was the worst that could happen: Safety and protection systems failed and there was a full core meltdown in a reactor that had no containment – which is an essential engineered safety feature in the “defence in depth” of nuclear power plants outside the former USSR. At Chernobyl:
· 237 workers were hospitalized with suspected acute radiation sickness (ARS); 134 cases of ARS were confirmed; 28 of them caused death; about 20 other workers have since died from illnesses considered to have been caused or aggravated by radiation exposure; 2 workers died from other causes at the time of the accident and another disappeared – presumed dead.
· It has been estimated that about 4,000 people will die (or may have died) from cancer, including workers exposed directly to radiation and members of the public exposed to the huge release of radioactive material from the reactor.
· About 4,000 cases of thyroid cancer (typically 5% fatal) have been attributed to inhalation and ingestion of radioactive iodine by children.
At Three Mile Island, emergency core cooling failed and the core melted. The reactor had a proper containment, which was not damaged. There were no radiation injuries and no radioactive release of any significance.
At Fukushima Daiichi, the reactors shut-down safely when struck by the fourth largest earthquake ever recorded, but they were then inundated by a much larger tsunami than had been anticipated in the design. This caused the protracted loss of all power supplies on the power station site, so that cooling systems could not function and the reactor cores in Units 1, 2 and 3 overheated. Fission products were released from the fuel and hydrogen was generated by chemical reaction between very hot fuel cladding and the water coolant. The reactor containments were partially effective, although they were damaged by hydrogen explosions and possibly by molten fuel. In this accident:
· There were no deaths attributable to radiation.
· Severe potential hazards have existed on the reactor sites due to high levels of radiation but health physics controls were mainly effective.
· Two workers received burns from beta-radiation. They were discharged from hospital after two days.
· Two workers incurred high internal exposures from inhalation of iodine-131, causing a significant risk of thyroid cancer.
· Doses incurred by about a hundred other workers have been high enough to cause a small risk of developing cancer after 20 or more years. About 25% of the population dies from cancer whether accidentally exposed to radiation or not. This rate might be increased by an additional one or two percent (say from 25% to 27%) for these workers.
· Exposures to radiation have been nowhere near high enough to cause ARS.
· There have been no radiation injuries to children or to other members of the public.
It is to be expected that every case of cancer that occurs in Japan over the next 40 years, starting now, will be blamed by those affected on radiation from Fukushima. And, probably, many other diseases also, ranging from heart failure to children’s nose bleeds – as they were at Chernobyl. This would be entirely understandable but will have no basis in science. As far as is known, no member of the public received a significant dose due to the Fukushima reactor emergency and no physical health effects of radiation should be expected.
As at Chernobyl, the major public health effect of the Fukushima accident has been psychological, due to the forced relocation of population and exaggerated fears about radiation. To a lesser extent, this applied also at Three Mile Island where evacuation was only advisory. Fortunately, the Japanese government is undertaking radiation monitoring and decontamination of the evacuated areas at Fukushima, and residents who were required to evacuate are already being allowed to return home for brief visits. At Chernobyl, relocation was permanent.
The INES was meant to aid public understanding of nuclear safety but has, in fact, made it more confused and has probably added to the mental anguish of the Japanese people. The accident at Fukushima became technically Level 7 on this scale a month after the tsunami, when the estimate of radioactive release was raised to a level which greatly exceeded the IAEA’s criterion for Level 7. However, the total release of iodine-131 from all the reactors at Fukushima was less than 10 percent of its release at Chernobyl, and the release of caesium-137 (the next most important fission product) was less than 15 percent.
Unless it is to be scrapped entirely, the INES should be substantially modified. One possibility is to divide Level 7 into several sub-levels. Perhaps a better option might be to base it on actual health effects, which would mean more to non-specialists than technical and scientific terminology.
Dr Don Higson is a Fellow of the Australasian Radiation Protection Society and Editor of the Society’s Newsletter; a Fellow of the Institution of Engineers Australia and Secretary of its Nuclear Engineering Panel; Vice President of the Australian Nuclear Association; and a member of the International Nuclear Energy Academy.