Radioactive pollution in the ocean is nothing new. We've been loosing the stuff offshore since 1944. Here's how.1) Nuclear weapons tests2) Sinking of nuclear-powered submarines:
So far, eight nuclear-powered submarines have sunk or been scuttled: two American, four Soviet; two Russian. 3) Spacecraft and satellite failures, including: The launch failure in 1964 of an American navigation satellite with an onboard radioisotope thermoelectric generator. The failed Apollo 13 mission (1970) carrying its RTG with plutonium dioxide fuel. 4) Discharges from nuclear reprocessing and power plants: Due to accidents, chronic emissions, and overflows at Sellafield, the nearby Irish Sea is deemed the most radioactive sea on Earth. The Hanford Site in Washington—home to the world's first plutonium production reactor—purposely released radionuclides... Dump sites for radioactive waste were created in the northeast Atlantic (1 site), off Europe (3), off the US eastern seaboard (1), and off the US Pacific coast (1). Between 1946 and 1970, the US dumped ~107,000 drums of radioactive wastes at its two sites, including some 47,800 in the ocean west of San Francisco. The exact location of most drums is unknown. At least some are corroding. The Hanford Site in Washington—home to the world's first plutonium production reactor—purposely released radionuclides down the Columbia River from the 1940s to the 1970s. The contamination travelled hundreds of miles into the Pacific Ocean. Today the radionuclides are used as markers by oceanographers tracking sediment movements on the continental shelf.
Of course the fallen satellites, the sunken submarines, the leftovers from nuclear bomb tests, and the dumped drums of waste are all subject to saltwater corrosion and the same destructive tectonic forces that triggered the March 11th Sendai earthquake and tsunami.