A radioactive plume of water in the Pacific Ocean from Japan's Fukushima nuclear plant, which was crippled in the 2011 earthquake and tsunami, will likely reach U.S. coastal waters starting in 2014, according to a new study. The long journey of the radioactive particles could help researchers better understand how the ocean’s currents circulate around the world.
TEPCO estimated that between 20 trillion and 40 trillion becquerels (units of radioactivity representing decay per second) of radioactive tritium have leaked into the ocean since the disaster, according to the Japanese newspaper Asahi Shimbun. The Fukushima plant is still leaking about 300 tons of radioactive water into the ocean every day, according to Japanese government officials.
The Fukushima plant is leaking much less contaminated water today compared with the immediate aftermath of the nuclear meltdown in June 2011 — a period when scientists measured 5,000 to 15,000 trillion becquerels of radioactive substances reaching the ocean.
The biggest threat in the contaminated water that flowed directly from Fukushima's reactors into the sea in June 2011 was huge quantities of the radionuclide called cesium. But the danger has changed over time as groundwater became the main source for leaks into the ocean. Soil can naturally absorb the cesium in groundwater, but other radionuclides, such as strontium and tritium, flow more freely through the soil into the ocean.
California’s coast may receive just 10 to 20 becquerels per cubic meter from 2016 to 2025
About 10 to 30 becquerels (units of radioactivity representing decay per second) per cubic meter of cesium-137 could reach U.S. and Canadian coastal waters north of Oregon between 2014 and 2020.
A large proportion of the radioactive plume from the initial Fukushima release won't even reach U.S. coastal waters anytime soon. Instead, the majority of the cesium-137 will remain in the North Pacific gyre — a region of ocean that circulates slowly clockwise and has trapped debris in its center to form the “Great Pacific Garbage Patch” — and continue to be diluted for approximately a decade following the initial Fukushima release in 2011. (The water from the current power plant leak would be expected to take a similar long-term path to the initial plume released, Rossi said.)