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. 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.
But regulators and critics alike worry because the company, Tokyo Electric Power Co., 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 in an interview Tuesday.
The plant was already struggling to store hundreds of thousands of tons of contaminated water that flowed through the buildings housing three reactors that experienced meltdowns in 2011.
But the contamination in this new groundwater problem is from different sources, Tepco said.
Tepco had said the groundwater had remained relatively clean even after the accident because it is so deep, several meters 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.
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 like a dam that pooled the contaminated underground water behind it until it flowed over the top of the barrier toward the sea.
Experts agree with Tepco’s assessment that the amounts of radioactive material being 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.