Michio Aoyama , a professor of radioisotope geoscience at the Institute of Environmental Radioactivity , has estimated Statement that 18,000 terabecquerel ( TBq ) of radioactive caesium 137 were released into the Pacific during the accident , and in 2013 , 30 gigabecquerel ( GBq ) of caesium 137 were still flowing Motion into the ocean every day .