Human failure or natural disaster. Slowness and opacity compared to fast measurements. Location on land or on the coast.
The nuclear accidents at Chernobyl (Ukraine, April 26, 1986) and Fukushima (Japan, March 11, 2011) were very different, but the only ones in history that reached level 7, the highest, on the scale that measures these disasters.
These are eight keys that differentiate them and keep the accident in Ukraine as the worst in history, according to a report issued on Tuesday in Vienna by the UN Scientific Committee on the Effects of Atomic Radiation (Unscear)
1. Causes. On April 26, 1986, a chain of nuclear reactions during a security check caused a steam explosion that melted the fuel at the Chernobyl plant, which exploded and burned for ten days.
On March 11, 2011, a tsunami, caused by an earthquake, destroyed the power of the cooling system of the Fukushima plant, which triggered a radioactive leak that lasted 12 days.
1. Design. Fukushima had a primary source that prevented the release of many radionuclides, while at Chernobyl the reactor core was directly exposed to the atmosphere.
The Soviet reactor released 85 petabecquerels (PBq) of Celsius 137 and 1,760 petabecquerels of Iodine 131, compared to 10 and 120 at Fukushima, respectively.
2. The fire at the Chernobyl reactor had to be extinguished quickly to minimize the risk of flames spreading to other reactors, exposing hundreds of workers to high levels of radiation. Up to 134 suffered from acute radiation syndrome and 28 died. There were no deaths among rescue teams in Fukushima.
3. 80% of coastal radiation from Fukushima went to the Pacific Ocean, while inland Chernobyl was deposited in Ukraine, Belarus, Russia and part of the north and center. Europe.
4. The Chernobyl incident took place closer to the agricultural harvest season, which contaminated more food, along with fewer restrictions taken in the Soviet Union than in Japan.
Moreover, the level of radionuclides allowed in food was much lower in Japan than in the Soviet Union, where the population was not properly warned about which foods to avoid.
5. In Fukushima, a high level of security measures has been maintained: from a larger evacuation radius (118,000 people within a radius of up to 30 kilometers, compared to 116,000 evacuees from Chernobyl within a radius of 20 km). kilometers), until the distribution of about one million meals of iodine among all those under the age of 40 (in Chernobyl were distributed only among evacuees and emergency personnel).
In addition to those evacuated immediately after the accident, there were another 220,000 people in Ukraine who were transferred between 1989-1992 to other areas further away from the incident.
6. Japan benefited from the breeding of most of its animals in barns, rather than on open pastures, as was the case in the Soviet Union, which prevented the transfer of higher levels of radionuclides into animal milk and meat.
7. Contaminated food in the Soviet Union has led many people – children at the time of the incident – to develop long-term thyroid cancer.
In addition, the medical equipment used in Japan, 35 years after Chernobyl, was more modern and therefore more sensitive to the detection of thyroid abnormalities, which facilitated the immediate treatment of patients.
The level of iodine-131 absorbed by evacuees in Chernobyl was also much higher than that of evacuees in Fukushima, being between 50 milliGray (mGy) and 5 Gray (Gy) in the Soviet case, compared to 1-15 mGy in the Soviet case. Japanese case.
8. As far as the biosphere is concerned, in an area of four square kilometers around Chernobyl all the trees were killed and in a larger area they suffered almost lethal damage, while in Fukushima no damage was confirmed. adjacent forests that can be attributed to the incident.
Similarly, Chernobyl radiation reduced the number of invertebrates (such as insects, snails or worms) by 30% within a radius of three to seven kilometers, and the number of rodents decreased.
In Fukushima, the animal population was not affected, although it caused genetic damage to some invertebrates.