To keep the melted nuclear fuel from overheating, TEPCO has rigged a makeshift system of pipes and hoses to funnel water into the broken reactors. The radioactive water is then treated and stored in the aboveground tanks that have now developed leaks. But far more leaks into the reactor basements during the cooling process — then through cracks into the surrounding earth and groundwater.
About 1,000 tons of underground water from the mountains flows into the plant compound each day, of which 400 tons seep into the reactor and turbine basements and get contaminated. The remaining 600 avoids that area, but at least half of it is believed to eventually come in contact with contamination elsewhere before entering the sea, according to an estimate by Japan’s Agency for Natural Resources and Energy.
Scientists, pointing to stubbornly high radioactive cesium levels in bottom-dwelling fish since the disaster, had for some time suspected the plant was leaking radioactive water into the ocean. TEPCO repeatedly denied that until last month, when it acknowledged contaminated water has been leaking into the ocean from early in the crisis.
Even so, the company insists the seepage is coming from part of a network of maintenance tunnels, called trenches, near the coast, rather than underground water coming out of the reactor and turbine area.
“So far, we don’t have convincing data that confirm a leak from the turbine buildings. But we are open to consider any possible path of contamination,” said TEPCO spokesman Yoshimi Hitosugi.
The turbine buildings at the Fukushima Dai-ichi plant are about 150 meters (500 feet) from the ocean. According to a Japan Atomic Energy Agency document, the contaminated underground water is spreading toward the sea at a rate of about 4 meters (13 feet) a month.
At that rate, “the water from that area is just about to reach the coast,” if it hasn’t already, said Atsunao Marui, an underground water expert at the National Institute of Advanced Industrial Science and Technology who is on a government committee studying the contaminated water problem. “We must contain the problem as quickly as possible.”