Some headway has been made in the massive decommissioning effort at Tepco’s wrecked Fukushima No. 1 nuclear plant over the past year, an inspection team from the International Atomic Energy Agency said on Tuesday — but there are still a number of challenges, including what to do with a huge amount of contaminated water stored at the facility.

To deal with the massive amount of tritium-tainted water, the team repeated the same advice it gave during the last visit in 2013: analyze the possibility of “controlled discharges to the sea” after reducing the concentration to below the legal limit.

“Japan has made significant progress in several areas since our last visit in November and December 2013,” said Juan Carlos Lentijo, director of the IAEA division of nuclear fuel cycle and waste technology and head of the inspection team.

Lentijo cited the removal of all spent fuel rods from the cooling pool in the reactor 4 building, reinforcement of the water treatment systems to process tainted water, and a reduction in workers’ exposure to radiation.

However, “the situation remains very complex at the site, with a number of challenging issues,” according to a preliminary summary report released by the team, which consists of 15 experts.

One issue is the toxic water. About 300 tons of groundwater is seeping into the reactor buildings daily and mixing with highly radioactive water used to cool the reactors.

While Tepco has been processing the contaminated water, the treatment systems can’t remove tritium. Water laced with tritium has been accumulating in hundreds of tanks packed into the site.

“The IAEA team considered the current practice of storing contaminated water a temporary measure and highlighted the need for a more sustainable solution,” the report says.

The team said that the utility should analyze how discharging the tritium water into the sea would improve the situation. And if the discharge is to be implemented, it will also be necessary to research the environmental impact and to convince local residents, it added.

A government panel is currently trying to figure out how best to deal with the contaminated water.

Other issues highlighted by the team team include drafting a long-term plan to manage radioactive waste, as well as completing the removal of spent fuel rods and melted fuel from the other reactor buildings.

This is the third time the IAEA team has assessed the situation at the Fukushima No. 1 plant at the request of the central government.

The decommissioning effort at Fukushima No. 1 is expected to take 30 or 40 years.

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