The Nuclear Regulation Authority said Sunday that an alarm went off at the Fukushima No. 1 nuclear plant signaling high radioactivity levels in drainage ditches.Australia's ABC news follows up:
According to the NRA and plant operator Tokyo Electric Power Co., the first alarm sounded at around 10 a.m., and another alarm 10 minutes later indicated much higher levels. Officials said contaminated water may have been discharged into the ditches.
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.
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.
Though contamination levels fell steadily throughout the day, the same sensors were still showing contamination levels about 10 to 20 times more than usual, a company spokesman said.
It was not immediately clear what caused the original spike of the contamination and its gradual fall, he said.