TOKYO >> Japan’s wrecked Fukushima nuclear power plant said it began releasing a second batch of treated radioactive wastewater into the sea on Thursday after the first round of discharges ended smoothly.

Plant operator Tokyo Electric Power Company Holdings said workers activated a pump to dilute the treated water with large amounts of seawater, slowly sending the mixture into the ocean through an underground tunnel.

The plant’s first wastewater release began Aug. 24 and ended Sept. 11. During the 17-day first release, TEPCO said it discharged 7,800 tons of treated water from 10 tanks. About 1.34 million tons of radioactive wastewater is stored in about 1,000 tanks at the plant.

The water has accumulated at the plant since it was crippled by a massive earthquake and tsunami in 2011.

In the second discharge TEPCO plans to release another 7,800 metric tons of treated wastewater into the Pacific Ocean over 17 days.

TEPCO and the government say the wastewater is treated to reduce radioactive materials to safe levels, and then is diluted with seawater to make it much safer than international standards.

They say discharging the water into the sea is unavoidable because the tanks will reach capacity early next year and space at the plant will be needed for its decommissioning, which is expected to take decades.

The wastewater discharges, which also are expected to continue for decades, have been strongly opposed by fishing groups and neighboring countries including South Korea, where hundreds of people staged protest rallies. China banned all imports of Japanese seafood, badly hurting Japanese seafood exporters.

Japan’s government has set up a relief fund to find new markets and reduce the impact of China’s ban.