Link: http://www.popularmechanics.com/science/energy/a19871/fukushima-fiveyears-later/ This post contains excerpts. To see the full article, please go to the link above.
A lone tree sits on the tsunami scarred landscape, inside the exclusion zone, close to the devastated Fukushima Daiichi Nuclear Power Plant Getty - Christopher Furlong
Five Years Later, Cutting Through the Fukushima Myths Radiation expert Andrew Karam, who covered the disaster for Popular Mechanics in 2011 and later traveled to study the site, explains everything you need to know about Fukushima's legacy and danger five years later. page 1
Nuclear reactor accidents are so devastating and world-changing that you know them by one name: Three Mile Island (1979), Chernobyl (1986), and Fukushima. March 11, 2011 was a day of unimaginable tragedy in northern Japan, a tragedy exacerbated by the reactor meltdowns and release of contamination. But the nuclear part of this horrible day was, if the longest-lasting, certainly the least lethal event. Yet it's the part that still engenders so much fear. With the fifth anniversary of the Fukushima accident upon us this month, let's take a look at where things stand today with recovering from this calamity, and what might be happening next. What Happened You know the outline of the disaster by now: A powerful earthquake caused a massive tsunami that crashed into Fukushima Daiichi Nuclear Power Plant and caused multiple nuclear reactor meltdowns. But to really understand what happened at the nuclear plant that day, you need to know a little more. At the site of the earthquake, stress had been building up in the Earth's crust for decades. When it released, that stress caused one of the most damaging quakes on record. The earth moved more than 20 meters over a 500-mile zone and the resulting earthquake released as much energy as a 45-megaton hydrogen bomb (to put this in perspective, this is 30,000 times more powerful as the bomb that leveled Hiroshima). It was the fourth-strongest earthquake recorded since 1900 and the strongest earthquake to strike Japan in recorded history. The quake shifted the Earth's axis by somewhere between 4 and 10 inches, altering the length of a day by nearly 2 microseconds.
Then came the water. The moving rocks shoved a wall of water across the Pacific Ocean. The seafloor began rising towards the surface, and as the water ran into the shallower depths it piled up to a height of more than 40 meters (140 feet) before it swept over the land. The tsunami slammed into the coast of Japan, killing more than 15,000 people
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and destroying or damaging more than a million buildings. This was among the worst natural disasters to hit a nation known for natural disasters, and that was only the start. Near the city of Fukushima was a complex of six nuclear reactors capable of producing more than 4500 MW of electrical energy. When the earthquake hit there were three operating reactors (units 1, 2, and 3). Units 4, 5, and 6 were shut down, albeit with spent reactor fuel sitting in pools that required cooling. The quake itself caused the operating reactors to scram (shut down) as they were designed to do. With the electrical grid busted by the earthquake, Fukushima's emergency diesel generators kicked on and powered the site including cooling water pumps—again, as they were designed to do. But then the tsunami hit. Seawater climbed over the seawall and inundated the diesel generators, shutting them down. Lacking cooling water, the fuel—including the radioactive fission products—heated up and began to melt. As crews raced to contain the disaster, one of their biggest challenges was to add cooling water to the reactors and find a way to power pumps needed to circulate this water through the reactor cores and spent fuel pools. Ultimately, the answer was to bring in power barges to allow pumping seawater into the reactor plant to keep the core cooled. By the time this was accomplished, the core had already been damaged beyond repair. But it didn't matter. Once seawater has been introduced into a reactor plant, it will never operate again.
How Much Is Too Much? In the five years since the Fukushima accident there's been a lot of information put out about Fukushima – some is accurate but much is uninformed, hyperbolic, or worse. Let's take a look at what actually happened and what the science tells us. A fissioned uranium atom splits into two radioactive fission fragments. (Common fission products are Tc-99, Ru-106, I-131, Cs-137—isotopes of the elements technetium, ruthenium, iodine, and cesium respectively). These isotopes are contained within the fuel elements, but when those elements are compromised—by melting down, for page 3
example—they can be released. Heavier elements are also created in a reactor core when uranium that hasn't been fissioned captures neutrons (plutonium and americium are two of these). We call them neutron capture products. THE QUESTION TO ASK IS NOT "IS THERE ANY RADIOACTIVITY PRESENT?" BUT RATHER, "HOW MUCH, AND IS IT ENOUGH TO BE HARMFUL?" .. .. .. .. The Fukushima catastrophe did release a large amount of radioactivity into the environment—into the air, into the sea, and the ground. We can (or could) measure this radioactivity, though just because we can measure it doesn't necessarily mean that it's harmful (with the proper equipment I can detect radioactivity in my own body, in a bunch of bananas, and in virtually any natural air, water, or soil sample on Earth). But the scientific consensus seems to be that this radioactivity has not (and likely will not) cause long-lasting devastation on land or in the sea. This shouldn't surprise anyone who has studied the impact of the Chernobyl accident. While there was significant short-term impact in the areas close to the Chernobyl reactors—and the area right around the ruined reactor remains a forbidden zone where you just don't want to go—further afield the impact was fairly low. Numerous studies (summarized by the International Atomic Energy Agency in this 2006 report) concluded that the ecosystem in the exclusion zone around the Chernobyl site is among the richest ecosystems in Europe, teeming with large game as well as smaller animals, partly because there aren't any people there. .. .. .. page 4
.. The Japanese government recently compensated a worker who developed leukemia after receiving just under 20 mSv (about 2 rem) of radiation exposure from the accident. This leaves me with mixed feelings. On the one hand, leukemia is one of the first cancers to appear after radiation exposure, so if any cancer is going to show up after only a few years this is it. On the other hand, the dose the worker received is quite low and the probability that this low dose of radiation caused this particular cancer after only a few years is also very low—less than 1 percent. In fact, the Health Physics Society (America's radiation science professional organization) recommends against even performing this sort of calculation for any radiation exposure of less than 5 rem in a short period of time (or 10 rem over a lifetime) because of the great uncertainties in the epidemiological data at these low doses. In other words, when the radiation dosage is so low, it's hard to sort the signal from the noise—the actual risk could well be even lower. We've also heard a lot of stories about thyroid tumors in children—stories suggesting these are due to radiation exposure from the accident. Here's the hard truth: From a scientist's point of view, it's really, really tricky to know whether that's true. Because there was no comprehensive inventory of thyroid nodules before the accident, we simply don't know how many kids had growths on their thyroids before they were exposed to radiation, or how many of these nodules would have appeared even in the absence of radiation exposure. IT'S ENTIRELY POSSIBLE THAT THE EVACUATIONS MEANT TO GET THE PUBLIC TO SAFETY MIGHT HAVE BEEN DEADLIER THAN THE ACCIDENT ITSELF .. .. .. ..
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