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.