Sensors at the Fukushima No. 1 nuclear plant have detected a fresh leak of highly radioactive water to the sea, the plant’s operator announced Sunday, highlighting continued difficulties in decommissioning the crippled atomic station.
Tokyo Electric Power Co. said the sensors, which were rigged to a gutter that drains rain and groundwater at the plant into a nearby bay, detected contamination levels up to 70 times greater than the already-high radioactive status seen on the plant grounds.
Tepco said its emergency inspections of tanks storing nuclear wastewater did not find any additional abnormalities, but the firm said it closed the gutter to prevent radioactive water from flowing into the Pacific Ocean.
The higher-than-normal levels of contamination were detected at around 10 a.m., with sensors showing radiation levels 50 to 70 times greater than usual, Tepco said.
The levels of beta ray-emitting substances, such as strontium-90, measured 5,050 to 7,230 becquerels per liter of water between 10:20 a.m. and 10:50 a.m. Tepco requires radioactivity levels of groundwater at the plant discharged into the sea to remain below 5 becquerels.
Though contamination levels had steadily fallen throughout the day, the same sensors were still showing contamination levels about 10 to 20 times more than usual, a company spokesman said later in the day.
It was not immediately clear what caused the original spike and its gradual fall, he added.
“With emergency surveys of the plant and monitoring of other sensors, we have no reason to believe tanks storing radioactive wastewater have leaked,” he said.
“We have shut the gutter (from draining water to the bay). We are currently monitoring the sensors at the gutter and seeing the trend,” he said.
The latest incident, one of several that have plagued the plant in recent months, reflects the difficulty in controlling and decommissioning the plant, which suffered a triple-meltdown and explosions after being battered by a giant quake and tsunami in March 2011, sparking the world’s worst nuclear disaster in a generation.
Tepco has been unable to effectively deal with an increasing amount of contaminated water, which is used to cool the crippled reactors and molten fuel inside them and is kept in large storage tanks on the plant’s vast spread.
Adding to Tepco’s headaches has been the persistent flow of groundwater from nearby mountains traveling under the contaminated plant before flowing into the Pacific Ocean.
The International Atomic Energy Agency recently said Tepco has made “significant progress” in cleaning up the plant, but suggested that Japan should consider ways to discharge treated wastewater into the sea as a relatively safer way to deal with the radioactive water crisis.
Since the drainage ditches are connected to the port of the No. 1 plant, the NRA has instructed Tepco to shut the gates there, officials said.
Tepco confirmed that no leaks from tanks containing radioactive water were found, but said it was investing further.