VIENNA — Tokyo Electric Power Co.'s claim that radioactive water leaking into the sea from the wrecked Fukushima nuclear plant is confined to the coast doesn't make scientific sense, according to a U.S. researcher who surveyed waters off the site last month.
Japan's government has supported the utility's statement that the irradiated groundwater flowing into the Pacific Ocean at a rate of some 400 tons a day remains in an area of 0.3 square kilometers (0.12 square miles) within the bay fronting the atomic station.
"These statements like a 0.3 square-kilometer zone are silly," Woods Hole Oceanographic Institution senior scientist Ken Buesseler said in an interview. "It's not true to the science," said Buesseler, who was on a Japanese research vessel 1 kilometer (0.6 miles) off Fukushima from Sept. 8 to Sept. 14.
The growing stockpile of radioactive water stored in tanks at the plant and leaks from the tanks into the sea is an increasing threat to ocean ecosystems, said Buesseler, who holds a joint Ph.D in marine chemistry from the Massachusetts Institute of Technology and Woods Hole. Founded in 1930, Woods Hole is the world's largest private non-profit oceanographic research institution, according to its website.
The Fukushima atomic station has more than 1,000 tanks holding more than 380,000 tons of water irradiated from contact with melted reactor fuel. Three hundred tanks are of a bolted variety, at least one of which leaked about 300 tons of water. Additional contaminated groundwater has been seeping into the Pacific Ocean and one of the tanks overflowed last week.
Each tank contains about 10 terabequerels, or 270 curies, of strontium-90, a radioactive element linked to leukemia that can enter the food chain by depositing into the bones of fish, Buesseler said. That is 100 times the amount of radioactivity dumped by Russia into the Sea of Japan in a 1993 incident that prompted international rules against ocean disposal.
"If only 10 of those tanks leaked it would equal all the strontium released in 2011" after the earthquake and tsunami, Buesseler said. "Once strontium gets into fish, it stays in them for months and years and it's going to be an additional reason why they won't be able to open up their fisheries."
"One hundred kilometers away I can measure isotopes of cesium that are coming from the reactor" in Fukushima, Buesseler said. "They're not at dangerous levels. The scientific question is are they at levels high enough to accumulate in the food chain and a cause for some of the fish to be above the legal limit."
Tokyo Electric's own monitoring data show radiation levels beyond the immediate area around the plant to be "limited," said spokesman Yoshikazu Nagai, who added that the company recognizes the importance of carefully managing contaminated water in storage at the site.
"We recognize that tank management is one of our most important issues so will continue making efforts to control contaminated water," he said.
Last month, South Korea banned imports of marine products from water off Fukushima and adjacent prefectures, citing public health concerns.
Japanese officials at the International Atomic Energy Agency in Vienna tried to assuage global concern over the impact of Fukushima's radiation last month.
"The effect of the contaminated water is limited to the 0.3 square kilometers just within the port outside of the plant," said Japan's science and technology minister, Ichita Yamamoto, on Sept. 16.
"The credibility problem is as great as the engineering solution," said Buesseler, who has traveled to Japan multiple times to assess Fukushima's impact on the ocean ecosystems. "There's a lack of trust that they keep reinforcing by saying things like 'beyond this 0.3 kilometers zone there's no release.'"
For Japan to reduce the risk of Fukushima's radiation entering the food chain, it may consider pumping effluent below 4,000 meters, said Stony Brook University marine biologist Nicholas Fisher in an interview. Before the practice was banned, the International Atomic Energy Agency developed best-practice guidelines for disposing of waste in deep water.
The International Maritime Organization has prohibited ocean dumping of radioactive material since 1996 after Russia pumped 900 tons of water with a reported 2.18 curies of radiation into the Sea of Japan three years earlier.
"There's certainly much more living stuff in surface waters than there is in deep waters around 4,000 meters," said Fisher, whose lab has sent scientists on three Fukushima ocean surveys. "There are no fisheries that are based on anything deeper than around 900 meters. If organisms became contaminated down around 4,000 meters, they may not ever appear in surface waters."
While most fish caught for food are safe and the amount of naturally-occurring radiation in the ocean exceeds the amount released by Fukushima, there is a risk that contamination could spread to larger sea creatures, he said.
Japan should also consider new storage alternatives, according to Buesseler and Robert Kelley, a U.S. nuclear engineer who was in charge of emergency response at the U.S. Los Alamos National Laboratory.
"A better solution would be to bring in tankage that already exists, such as a decommissioned very-large crude carrier," said Kelley, who worked for the Department of Energy for 30 years.
"These tanker ships can hold years worth of contaminated water and could be moored in the sea close to the site while they are being filled," he said. "It would be a cheaper and safer alternative to building hundreds of new tanks, possibly for years."
Because Japanese engineers were forced to build Fukushima storage tanks uphill and behind the damaged reactors, any leaks will complicate the clean-up process by creating new safety hazards for workers, Kelley and Buesseler said.
"There's a lot of radioactivity stored on site in tanks," said Buesseler, adding that he's concerned that even a small earthquake could trigger another crisis. "All of those tanks are connected by pipes to each other and those pipes and those fittings are not earthquake proof."
Lab results from his most recent visit should be published by February 2014, Buesseler said.
With assistance from Jacob Adelman in Tokyo.