New Leaks Into Pacific at Japan Nuclear Plant

Kyodo, via Reuters

Members of a Fukushima panel inspecting the construction of a barrier that is meant to stop contaminated water from leaking.

TOKYO — Tons of contaminated groundwater from the stricken Fukushima nuclear plant have overwhelmed an underground barrier and are emptying daily into the Pacific, creating what a top regulator has called a crisis.

The water contains strontium and cesium, as well as tritium, which is considered less dangerous when released into the ocean. Despite increasing alarm among regulators in recent weeks, the plant's operator says it does not yet pose a health threat because levels of the contaminants are still very low in the open ocean, beyond the plant's man-made harbor — a contention even critics support.

But regulators and critics alike are worried because the company, the Tokyo Electric Power Company, or Tepco, has been unable to stop the flow of the contaminated water, which appears to have started between December and May. The company has also not yet conclusively identified the source of the contamination, compounding fears.

"Tepco lacks a sufficient sense of urgency for this crisis," Shinji Kinjo, a high-level official at the country's nuclear regulatory watchdog, said Tuesday in an interview.

The plant was already struggling to store hundreds of thousands of tons of contaminated water that flowed through the buildings housing three reactors where meltdowns occurred in 2011. But the contamination in this new groundwater problem is from different sources, Tepco said.

The releases of information in recent days on the latest problem followed a familiar pattern, with the company providing very technical data in bits and pieces without context, making it difficult to judge its significance.

Tepco had said that the groundwater, which flows downhill from mountains behind the plant and into the sea, had remained relatively clean even after the accident because it is so deep, several yards below the surface. But in May the company reported detecting a sharp increase in the amounts of radioactive tritium in groundwater beneath the plant.

Tepco now says the groundwater is emptying into the plant's man-made harbor at a rate of 400 tons a day — enough to fill an Olympic swimming pool every week. While the company did not specifically say how much of the water was contaminated, it offered a calculation for the amount of tritium being released that assumed all of the water was contaminated.

To halt the flow of contaminated water, Tepco built an underground barrier along the shoreline in front of one damaged reactor in June by injecting chemicals into the soil to harden it. But the operator has told regulators that it believes the barrier failed to stop the water, instead acting as a dam that pooled the contaminated underground water behind it until it flowed over the top of the barrier toward the sea. Mr. Kinjo, the regulator, warned that if the water kept rising, it could soon come to the surface, increasing hazards for the plant's already hard-pressed workers.

The company has admitted that it failed to respond quickly enough to the latest groundwater contamination, saying it was preoccupied with more pressing issues like cooling the damaged reactors.

"Tepco appears overwhelmed in dealing with what is a very serious problem," said Akio Yamamoto, a professor of nuclear engineering at Nagoya University, who serves as outside expert for the Nuclear Regulation Authority, Japan's nuclear watchdog. "It cannot do everything on its own."

Mr. Yamamoto and other experts agree with Tepco's assessment that the amounts of radioactive material released into the Pacific have been too small to pose a risk to human health. Still, some critics contend that the plant has emitted far more radioactive materials than it is saying, based in part on levels of contaminants discovered in the harbor, which are well above safe levels in some places.

Regulators said they were waiting for Tepco to take additional steps to slow the flow of contaminated groundwater into the sea. These include construction of more chemical barriers as well as pumping out about 100 tons per day of the water to keep it from overflowing the barriers. This, however, will create a new problem, as the water must then be stored on the grounds of a plant that is already crowded with more than 1,000 large tanks filled with contaminated water siphoned from the reactor buildings.

Matthew L. Wald contributed reporting from Washington.

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