Tokyo: Radioactive water has apparently leaked from another underground storage tank at the crippled Fukushima Daiichi power plant, Tokyo Electric Power Co (Tepco) said on Sunday. The volume of the latest leakage was believed to be small, it said. On Saturday, it said as much as 120 tonnes of radioactive water may have leaked from another nearby storage tank. The plant’s seven storage tanks are lined with water proof sheets meant to keep the contaminated water from leaking into the soil. The power company has faced a range of problems with leaks and with the plant’s cooling system. Tepco said on Friday it lost the ability to cool radioactive fuel rods in one of the plant’s reactors for about three hours, the second cooling system failure at the plant in three weeks. Nuclear fuel, even after use, has to be kept cool to prevent it from overheating and beginning a self-sustaining atomic reaction that could lead to meltdown. The 9.0 earthquake that shook Japan on March 11, 2011 triggered a 15m tsunami that struck the plant and set off the chain of events that caused its reactors to start melting down.