Tokyo Electric Power Co. has detected high levels of cesium in test wells near damaged reactors, and the head of Japan's new nuclear regulatory body believes they provide further evidence that radioactive contaminants from Fukushima Daiichi have made their way into the sea.

Developments in the last week related to the plant severely damaged following Japan's 2011 earthquake and tsunami include:

Contamination High in New Test Wells

New test well at Fukushima Daiichi. Source: TEPCOAfter detecting high levels of strontium and tritium in a test well between units 1 and 2, TEPCO drilled additional wells to monitor potentially contaminated groundwater. On Wednesday, TEPCO reported cesium-134 in one of the new holes was measured at 11,000 becquerels per liter and cesium-137 was detected at 22,000 becquerels per liter. Both concentrations had increased from tests two days earlier.

TEPCO maintains the contamination is limited to plant grounds and suggested the high readings might have been caused by dust in the samples. But the head of Japan's new Nuclear Regulation Authority said Wednesday he thinks radioactive water has reached the sea. The Asahi Shimbun and other outlets quoted Shunichi Tanaka as saying he believes contaminated groundwater might have been leaking into the ocean since the accidents, and he also suggested the NRA gather its own data on the contamination instead of relying on TEPCO.

Leader of "Fukushima 50" Dies

The plant manager who led the group of TEPCO workers who manned the plant at the height of the crisis died Tuesday after an unrelated fight with cancer. Masao Yoshida became a household name in Japan for heading the so-called "Fukushima 50" – workers who stayed behind to manage overheating reactors and spent fuel pools during the worst station blackout in the history of nuclear power. At one point during the crisis he defied an order to cease pumping salt water into unit 1, potentially averting even worse damage to the reactor. As a leader in TEPCO's nuclear operations, he was also criticized for not doing more in advance to protect reactors from tsunamis. Yoshida was diagnosed with esophageal cancer in late 2011 and died in Tokyo this week at 58, TEPCO said in a release. The cancer's onset so soon after the accidents indicates it was not caused by radiation exposure during the crisis.