The operator of the disaster-hit Fukushima No. 1 nuclear power plant has found that a coolant solution, used to create an ice wall halting the seepage of groundwater into reactor buildings, has leaked from two storage tanks.

The leakage has had no impact on the wall or the environment, said Tokyo Electric Power Company Holdings Inc. (Tepco).

Still, it underscores the unpredictable challenges in the clean-up of the site, nearly 11 years after an earthquake and tsunami ravaged Japan's northeastern coast, causing the world's worst nuclear incident since the Chernobyl disaster in 1986.