(Creative Commons)

TEPCO has struggled to contain the damaged reactors since the crisis began, and these latest reading, which were done by robots in reactor No.1, pose a threat to future containment efforts.

“Tepco must figure out the source of high radiation,” said Hironobu Unesaki, a nuclear engineering professor at Kyoto University. “If it’s from contaminated water leaking from inside the reactor, Tepco’s so-called water tomb may be jeopardized because flooding the containment vessel will result in more radiation in the building.”  

Radiation levels were as high as 1,120 millisierverts of radiation per hour, which is four times the allowed per year level for employees, TEPCO said Wednesday.

Four out of six of Fukushima's reactors were affected by the disaster, causing them to leak radiation into drinking and ocean water.

The utility company has received criticism for its handling of the disaster, which is the worst since the 1986 Chernobyl crisis. Critics have accused the company of being ill-prepared.

"The corporate nature of Tepco and its preparedness for the tsunami and loss of power should all be subject to investigation," said Goshi Hosono.

TEPCO has said that full containment of the reactors could take months. Reuters has more:

On April 17 TEPCO announced a timetable for its operations. Within the first three months it plans to cool the reactors and the spent fuel stored in some of them to a stable level and reduce the leakage of radiation.

TEPCO then hopes to bring the reactors to a cold shutdown in another three to six months.

But some experts said the process could take longer. TEPCO itself said constant aftershocks, power outages, high levels of radiation and the threat of hydrogen explosions were factors that could hamper its work.

In the meantime, radiation continues to contaminate ground and ocean water.