When Japan announced on Tuesday that the nuclear calamity at Fukushima is now a Level 6 on the International Nuclear Event Scale (INES), just behind Chernobyl at a Level 7, they finally admitted what many experts had already understood by late last week -- Fukushima was far, far worse than the Level 5 accident at Three Mile Island. In fact, it is already a Level 7.
Just because the Chernobyl accident has been the only nuclear accident (thus far) to be awarded the dubious distinction of being a Level 7 does not mean that it is the only type of Level 7 possible. That is why the often heard statements to the effect of “Fukushima can’t be another Chernobyl” may be technically true but ultimately misleading.
Yes, Chernobyl and Fukushima have many differences: each disaster’s causes, their reactor designs, the way in which they disperse radiation -- with an explosion of the radioactive core at Chernobyl and none seemingly likely at Fukushima.
Consider other differences: Chernobyl involved one exploding reactor. Fukushima involves at least three reactors and four spent fuel ponds that have lost their coolant. Chernobyl’s core burned and melted for ten days. Fukushima has been belching radiation for nearly three weeks, and with no end in sight. Chernobyl seriously affected larger parts of the globe -- some British farmers still can’t sell their sheep because of it. Fukushima may be more localized. Chernobyl exploded chunks of core around the inner area, including a good deal of plutonium. Fukushima may release more biologically active isotopes such as I131 and Cs137. Chernobyl had serious health effects. Fukushima probably won’t – except for the heroic plant workers -- because of timely evacuations.
That said, pointing out those differences is misleading. Events can be totally different yet equally bad. That is why INES uses a scale of 1 to 7 – where 1 is the most benign and 7 is the worst – to assess a variety of ways in which an accident can affect people and the environment, radiological barriers and controls, and defense in depth.
You can even ignore the last two concepts to understand why Fukushima is already a Level 7 disaster. A disaster is rated by the highest level it gets on any one of INES criteria. If an event is Level 7 because of the amount of radiation it releases, it is a Level 7 “major accident” even it is only Level 2 in the number of people injured.
The Japanese have not been very informative about radiation levels around the nuclear plant, and especially near the reactor cores and spent fuel ponds. The number 1000 milliSievert is often bandied about, though it surely underestimates the true levels. Reportedly, the plant’s measuring devices can only give a maximum reading of 1000 milliSievert. They can’t measure anything higher. In Chernobyl, too, it took days to bring in military devices that could measure the deadly radiation levels expected during nuclear war – rather than the sensitive instruments that measure the trace levels expected during a nuclear power plant’s operations.
Nevertheless, some of that radiation is being detected by the global array of radiation monitoring stations used to detect above ground nuclear tests. Using data from California and Japan, scientists in Vienna have estimated that in just the just first three days, Fukushima released 20 percent of the radioactive iodine as the total released by Chernobyl and as much as 60 percent of the radio-cesium. Fukushima has been emitting a good deal of radiation since then, so the total could be much more. But even the Viennese estimates already make it a Level 7.
The tipping point from a Level 6 into a Level 7 radiation release is ‘tens of thousands of terabecquerel” of Iodine-131. You don’t have to understand what a Becquerel is to know that a “tera” is a 1 followed by 12 zeros or 1012. “Tens of thousands” adds four zeros to 1012, making it 1016. More than that is Level 7.
So, what did the Viennese scientists find? For Iodine-131, the amount measured at 1017 or ten times as much as 1016. Since the INES defines a Level 7 radiation release as the equivalent of “several tens of thousands of terabecquerels”, any number of Becquerel with a 1017 next to it exceeds that significantly. Radioactive cesium estimates are even higher, and more worrisome, because it is so long-lived.
If the Viennese scientists are correct – and no authoritative voices have disputed them – Fukushima is already a Level 7 nuclear disaster that will rival Chernobyl as the worst on record and will surely meet the same fate: entombment and encirclement with a no-man’s land too radioactive for people to safely live. It may become an accidental wildlife refuge like Chernobyl – if it is left alone – but declaring a no-man’s land will come at a high price for a small island nation like Japan.