A new radioactive leak has been found at the Fukushima Daiichi nuclear power plant in Japan, a day after the Tokyo Electric Power Company admitted up to 120 tons of contaminated water may have seeped into the ground out of a holding tank.

"We have determined that a minimal amount of water was feared to have leaked from the tank although there was no decline in the level of water inside the tank," TEPCO said in a statement of the latest leak, according to AFP.

On April 5th, a system that helped to keep nuclear fuel rods cool malfunctioned, while the 120 ton leak was reported on April 6th — polishing off a rough weekend for the severely damaged Fukushima plant.

The holding tanks are used to cool down reactors, notes Al Jazeera, and the water contains some nuclear material, although the majority of the nuclear cesium has been removed.

The 120 tons of water that leaked into the ground contained an estimated 710 billion becquerels of radioactivity, notes Kyodo News, which added that it's the largest radioactive leak since December 2011, after the March 2011 tsunami.

TEPCO is currently pumping water out of the damaged tank into other tanks, though the process will take a while and the utility warns that 47 more tons of irradiated water could potentially leak out before it's finished, added Kyodo.