FUKUSHIMA'S RADIOACTIVE WASTEWATER IS BEING RELEASED IN THE PACIFIC.HERE'S WHAT YOU NEED TO KNOW

Treated and diluted but still slightly radioactive wastewater from the wrecked Fukushima Daiichi nuclear power plant is being discharged into the Pacific Ocean.

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The first batch being released over the next 17 days is a small part of the tons of water that have accumulated at the plant. But the Japanese government and the plant's operator say releasing the water is an unavoidable step in the decommissioning of the plant, which already will take decades. They say the water is treated and diluted to levels that are safer than international standards. But the plan faces opposition in and outside Japan. Here is a look at the controversy.

WHY IS THERE SO MUCH WASTEWATER?

The March 2011 earthquake and tsunami destroyed the plant's cooling systems, causing three reactors to melt. Highly contaminated cooling water applied to the damaged reactors has leaked continuously to building basements and mixed with groundwater.

The plant operator, Tokyo Electric Power Company Holdings, has taken steps to limit the amount of groundwater and rainwater entering the reactor area, and has reduced the increase in contaminated water to about 100 tons a day, 1/5 of the initial amount. The water is collected and partly recycled as cooling water after treatment, with the rest stored in around 1,000 tanks, which are already filled to 98% of their 1.37 million-ton capacity.

WHY IS TEPCO RELEASING THE WATER NOW?

The government and TEPCO say they need to empty the tanks and clear them from the plant complex to make room for the plant's decommissioning and prevent accidental leaks of the tanks.