By Mike Mulvihill
The massive earthquake and tsunami that have devastated Japan also rocked the nuclear power world. Powerful explosions at two of three nuclear reactors at Fukushima have generated much media coverage suggesting comparisons to Three Mile Island and Chernobyl (see photo), by far the world’s worst nuclear accident affecting a 30 km radius around the site. Media reports suggest a catastrophic core meltdown is in process. And, today the financial markets logged in – alternative energy stocks were up and anything involved with nuclear power was down.
To put things in perspective, Chernobyl and Three Mile Island were really very different from one another. According to David Brenner, a professor of radiation biophysics at the Center for Radiological Research at Columbia University, “… Chernobyl was roughly the equivalent of a million Three Mile Islands” in terms of the amount of radiation released. The explosions at Fukushima are markedly different from the Chernobyl blast, which sent huge amounts of radiation into the atmosphere. Explosions at the Fukushima plant didn’t do that. One reason is that in Chernobyl, the nuclear reaction itself was out of control. But in Japan, all three reactors shut down once an earthquake warning was sounded. This is important because upon shutdown, decay heat is about 7 percent of the heat produced while running, and this falls to about 0.3 percent after 10 days. (And runaway heat created by exposed nuclear fuel rods is the root cause of a catastrophic core breech.)
Secondly, Chernobyl had no containment vessel around the core (something virtually all nuclear plants have in place.) At the Three Mile Island accident, explosions happened outside the containment vessel as at Fukushima. This caused a malfunction in the cooling system, which exposed the nuclear fuel rods resulting in about half of the fuel melting in the reactor, but the containment vessel remained intact. (In a complete meltdown, the nuclear fuel ends up in a molten mass hot enough to burn its way right through the concrete and steel pressure chamber surrounding the core.)
According to bravenewclimate,there was and will not be any significant release of radioactivity. “By significant, I mean a level of radiation of more than what you would receive on – say – a long distance flight, or drinking a glass of beer that comes from certain areas with high levels of natural background radiation.”
The Fukushima reactor does not have a combustible core made of graphite like RBMK-type (Chernobyl-type) reactors do and the Japanese Nuclear Safety Agency has said that damage to the reactor vessel is minimal. It is currently rated at Level 4 on the International Nuclear Event Scale (INES), making it less significant that the Level 5 Sellafield fire in the UK in 1957.
It is worth noting that this is the first nuclear emergency ever declared in Japan, a country that produces more nuclear energy than any other country except the USA and France. The March 11 earthquake, at a magnitude of 9.0, was the most powerful ever to strike Japan and the fourth largest since records began. The energy released in a magnitude 9.0 quake is equivalent to nearly 900,000 times the energy released by the Hiroshima and Nagasaki nuclear attacks combined.
It is a tribute to Japanese engineering and building codes that damage has not been more severe. The Fukushima plant has survived at least 10 previous earthquakes and had the earthquake not been followed by a tsunami, the shutdown would have been far less problematic.
If you’re interested in an excellent Nuclear Power 101 primer, go to boingboing. If you want a good scare, watch your nightly news.