TOKYO - The operator of Japan's crippled nuclear power plant says more radioactive water has leaked at the seaside complex.

The problem underlines the challenges facing Tokyo Electric Power Co. as it attempts to keep the Fukushima Dai-ichi nuclear plant under control. An earthquake and tsunami badly damaged the plant last March.

TEPCO says workers spotted a leak Friday at a water reprocessing unit which released enough beta rays to cause radiation sickness. It says no one was injured and the leak stopped after a tank was repaired.

TEPCO also found that 8.5 tons of radioactive water leaked earlier in the week after a pipe became detached at one of the six reactors.

Cold weather has also caused water inside pipes to freeze elsewhere at the plant, resulting in leaks of radioactivity.