“Some tanks have automatic monitoring equipment and some don’t,” says Yo Koshimizu, a TEPCO spokesman. “We are currently determining whether to add such equipment to all of the tanks.”
Some 400 tons of cooling water are being collected in tanks each day. The growing fleet of storage tanks — which currently stands at about 1,000 — is a source of alarm for experts, who fear that huge amounts of contaminated water will eventually have to be dumped into the ocean. Worse still, some 300 tons of groundwater highly contaminated with caesium-137, which has a 30-year half-life, are thought to be flowing from beneath the destroyed reactors into the sea every day.
The potential for harm is huge, says Jota Kanda, an oceanographer at the Tokyo University of Marine Science and Technology who monitors radionuclide distribution in sediments and biota off Fukushima.
“The effects of one relatively small leak may be insignificant,” he says. “But there are huge amounts of radionuclides in these tanks and the water may have to be stored for a long time to come. If more leaks were to occur the consequences might be severe.”
The Fukushima nuclear accident resulted in the largest ever accidental release of radioactivity to the oceans. Some 80% of all the radionuclides released from Fukushima ended up in the Pacific. In some local fish, high residual levels of radioactivity were measured two years after the accident. Commercial fishing in the area is still banned.
But it is unclear how much residual radioactive contamination is still entering the sea from leaks around the Fukushima plant, says Scott Fowler, a marine ecologist at Stony Brook University in New York who has been involved in previous assessments of contamination levels in the ocean near Fukushima.
To track changes in coastal waters and predict when seafood species in the region may be safe to consume, it will be necessary to establish a ‘temporal data set’ — that is, to measure the levels and distributions of contaminant radionuclides at a given location over time, he says.
“Even if one assumes that leaks from the plant into the sea will eventually be stopped, residual contamination would continue to be present in the adjacent marine ecosystem for many years,” he says. “So the contamination of long-lived radionuclides in different organisms in the local marine food webs needs to be monitored continually.”