The operator of the crippled Fukushima Daiichi nuclear power plant temporarily halted the discharge of treated radioactive water into the sea following a magnitude 5.8 earthquake that jolted northeastern Japan in the early hours of Friday.

Tokyo Electric Power Company Holdings Inc. shut down the discharge about 20 minutes after the quake hit Fukushima Prefecture at 12:14 a.m., in accordance with safety procedures. The release resumed 15 hours later after TEPCO confirmed there were no abnormalities in the function of the facilities.

It was the first time that TEPCO had halted the water release since the process started in August last year. The fourth batch of water release began late February and was ongoing when the quake struck, registering lower 5 on the Japanese seismic intensity scale of 7.

The water transfer facilities are equipped with two emergency isolation valves that automatically stop the discharge into the sea when problems are detected in the water pumps and flowmeters, according to TEPCO.

Additionally, workers can suspend the release remotely from a control room if a natural disaster occurs that could affect the water discharge facilities.

An earthquake registering lower 5 or above on the Japanese seismic intensity scale, tsunami alert, and high tide warning are among cases that will lead to such manual shutdowns. In response to the quake on Friday, TEPCO decided to manually suspend the release.

At the Fukushima plant, massive amounts of radioactive water have accumulated in the process of cooling nuclear fuel that melted in the 2011 accident. The water is processed to remove most radionuclides except tritium and diluted before being released into the Pacific Ocean.

A manual shutdown would also be undertaken if tritium above the permitted concentration level is detected in seawater near the plant.

==Kyodo

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