Image: 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
Nuclear Meltdown: Cutting Through the Fukushima Myths
Written by Andrew Karam, Radiation Expert
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.
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 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.
That wasn’t the end of the immediate danger. High-temperature chemical reactions between the zirconium fuel cladding and water created hydrogen. Over the next several days, the hydrogen escaped the reactor plant and collected in the support buildings. Some of these pockets exploded in the days to come, damaging the support buildings.
As a result of these radioactivity releases to the environment, the Japanese government ordered the evacuation of everyone living within 20 km (12 miles) of the site; this included a number of hospitals. Japan also banned produce from the area around the reactor site to reduce radioactivity entering the food supply. When I was there, about a month after the accident, I heard daily radio announcements in Tokyo (in English!) informing people of the radioactivity concentrations in the drinking water. We were also told that people who remained in the “shelter-in-place” region close to Fukushima were having problems finding food at the stores because truck drivers were reluctant to enter the area. We ate a lot of meals at 7-11 stores, which somehow remained well stocked. Some things you can count on!
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 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?”
Although all these products are present in reactor fuel, not all are released equally when the fuel is compromised like it was at Fukushima. For example, cesium and iodine are volatile, and these are far more likely to be released into the atmosphere than elements like plutonium. The elements that are more soluble—cesium and iodine are among those—are more likely to dissolve into reactor cooling water and escape into groundwater or seawater if the reactor coolant leaks out. What this means is that the elements we’re most likely to see in the air, on the ground (because they settled out from the air), or in the water are the elements that are volatile or soluble.
Given this, it’s not surprising that scientists detected airborne iodine and cesium throughout the Northern Hemisphere in the aftermath of Fukushima. Radioactivity from the airborne plume over the nuclear plant settled onto the ground—aerial and ground surveys by the Japanese and American governments confirmed this in the weeks and months following the accident. I visited Japan shortly after the accident, measured elevated radiation levels, and identified some of these volatile nuclides on the ground in the few places we visited, including I-131, Cs-134, and Cs-137. The highest radiation dose rates I measured were clearly elevated, but were also too low to cause short-term or long-term health risks.
“Radioactivity escaping into the environment” sounds scary no matter how small the levels, which probably explains why there was so much bad information put out about the environmental impact of Fukushima’s radioactive releases. For example, it’s true that radioactive cesium (Cs-134 and Cs-137) was measured in tuna caught in the Pacific Ocean. But it’s not true that this cesium posed any risk to people eating this tuna. I interviewed the scientist who made these measurements and he pointed out that the radioactivity of the cesium was lower than the radioactivity content of the natural potassium in the fish.
Likewise, there were claims that dissolved radioactivity from Fukushima was entering the ecosystem and causing massive die-offs of marine life. This claim was refuted by oceanographers who studied the matter extensively. As for claims that the collapse of the Unit 4 spent fuel pool might render the American West Coast uninhabitable? I calculated that dissolving all of the fuel of all three operating reactors, plus the entire contents of all of the spent fuel pools at Fukushima into the waters of the northern Pacific would still give a person swimming in the ocean off Hawaii, Alaska, or California about one billionth the amount of radiation dose needed to cause any harm. In the words of oceanographer Miriam Goldstein, radioactivity from this accident in seawater is “detectable but not hazardous.” I had no qualms about eating sushi when I was in Japan the month after the accident, as well as in later trips to the West Coast.
Here’s the thing: There are demonstrably high levels of radioactivity in the seafloor sediments in the vicinity of the Fukushima site. But the question to ask is not “Is there any radioactivity present?” but rather, “How much radioactivity is present, and is it enough to be harmful?” Despite the very serious nature of the Fukushima calamity, the answer to the latter question isn’t as worrying as you might have been led to believe.
In the case of the seafloor around the Fukushima site, radioactivity concentrations are elevated, but not dangerously so. Samples of seafloor sediments show that the highest Cs-137 concentrations in sediments near to the Fukushima site measured 73,000 Becquerels (Bq) per square meter, a unit of measuring concentrations of radioactivity. Now, this is a very high reading. Most such seafloor samples show Cs-137 present at less than 100 Bq. On the other hand, the EPA says that each Bq per square meter will give us a radiation dose of about 3×10-19 Sieverts per second (the Sievert is a measure of radiation dose). Do the math and you find that this one very contaminated location would expose a person (or aquatic organism) to a radiation dose of less than 1 mrem annually. To put this in perspective, we receive this amount of radiation every single day from natural sources; I received more than this on the 14-hour flight from New York City to Japan.
Read more at www.popularmechanics.com
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