![]() All are potentially hazardous, but they decay at different rates. Some of the most abundant radionuclides released in the disaster were iodine-131, cesium-134 and cesium-137. (Photo by Ken Kostel, © Woods Hole Oceanographic Institution) Over the past decade, scientists, technicians, and members of the public have collected samples of water, sediment, and marine life from the ocean near the power plant to the West Coast of Canada and the U.S. The first international research expedition in June 2011 traced the spread of radionuclides from the coast near Fukushima Dai-ichi to more than 300 miles offshore. This water also picked up radionuclides and overflowed into the ocean or seeped into the ground, carrying those isotopes to the ocean. Over following days, three hydrogen explosions at the plant sent even more radioactivity skyward, much of it eventually settling in the ocean.Įmergency crews desperately sprayed the overheating reactors with water cannons and firehoses, and military helicopters dropped hundreds of gallons of water from above. This gas carried radioactive isotopes, also known as radionuclides, into the atmosphere, but this was not enough. To relieve the pressure building up in the reactor cores, plant workers vented the gas several times over the next few days. At the same time, water in the reactors turned to steam and began reacting with the metal fuel rods, generating volatile hydrogen gas. The fuel rods inside the reactors started to overheat and melt, exposing the uranium fuel and damaging their containment vessels. When the cooling systems failed, the temperatures in the reactor cores began to rise. They flooded the facility and destroyed the backup generators. But the tsunami waves that hit that day measured between 37 and 50 feet high. The maximum expected height of a tsunami in that area was around 20 feet, Kanda said. The nuclear plant was constructed on a cliff which had been excavated down to 30 feet above the ocean. The facility switched over to its backup generators to continue pumping the water needed to cool the fuel rods. "You have to keep cooling by water for quite a long period." "Even if the fission reaction stops, the radioactive material continues to generate heat," said Jota Kanda, a professor at Tokyo University of Marine Science and Technology who has led several research expeditions off the coast of Fukushima. But shutting off a nuclear reactor isn't as simple as turning off the lights. When the violent shaking damaged utility lines and cut off the plant and its six reactors from the power grid, the three active reactors shut down automatically. The Fukushima Dai-ichi nuclear plant had systems in place to cope with an earthquake. Irradiated groundwater and cooling water flowed into the ocean, some collecting in beach sands and seafloor sediment, some building up in fish and other organisms, and the rest spreading with currents across the Pacific. The earthquake knocked out power at Fukushima Dai-ichi and the tsunami flooded back-up generators, causing three of the six reactors to overheat and generating hydrogen gas that later exploded. "It seems very important to look back and take stock of where we're at."Ī decade after Japan's triple disaster, Buesseler joined researchers around the world for a remote discussion of the events at Fukushima, what they've learned over the past decade, and how the situation continues to evolve. "Fukushima Dai-ichi was an unprecedented event for the ocean, in terms of the amount of radioactivity going in to the ocean from a disaster of this nature," said Ken Buesseler, a senior scientist at the Woods Hole Oceanographic Institution. Even more radioactivity was washed into the ocean or deposited there from the atmosphere. In the following days, explosions rocked the facility and more than 150,000 people were forced to evacuate the surrounding area to avoid potential radioactive fallout. The Fukushima Dai-ichi nuclear power plant had also been damaged. Entire towns were destroyed by the three-story wall of water and nearly 16,000 people were killed. Tsunami waves, generated as the seafloor thrust upwards, hit the closest parts of the Japanese coastline less than half an hour later. The 9.0-magnitude quake lasted as long as six minutes and shifted the main island eight feet to the east. Japan experiences hundreds of earthquakes every year, but the Great Tohoku Earthquake was the most powerful the country had ever recorded. Nearly 16,000 people died and the releases of radioactive water from the plant continue today. On March 11, 2011, a magnitude 9 earthquake 80 miles east of the Japanese city of Sendai generated a towering tsunami that slammed into the coastline and critically damaged the Fukushima Dai-ichi nuclear power plant.
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