The operator of the Japanese damaged Fukushima Daiichi nuclear power plant said contaminated water found in one of the plant’s tunnels is as highly radioactive as the water that leaked into the sea in April 2011, soon after the accident. Highly radioactive substances have been detected in coastal observation wells on the plant’s premises and in nearby seawater since May of this year, according to Japan’s (NHK WORLD) website. Tokyo Electric Power Company, or TEPCO, admitted that contaminated water was leaking into the sea but has not been able to identify its source. The firm says 2.35 billion becquerels of cesium per liter was detected in samples collected on Friday in a tunnel located near the plant’s Number 2 reactor and 50 meters from the coast. Contaminated water with a similar level of radioactivity leaked into the sea in April 2011, soon after the nuclear accident. The utility says contaminated water that accumulated after the accident is believed to have remained in the tunnel. The company said there may be other causes, but that it has not been able to identify them. TEPCO plans to continue to measure the concentration and level of contaminated water in coastal tunnels near the Number 2 and 3 reactors. It also intends to take measures to reduce the amount of contaminated water and prevent it from leaking into the sea.