Tokyo Electric Power Co (TEPCO)'s handout shows an image taken by a gamma ray camera showing the bottom of a ventilation stack standing between Fukushima Daiichi nuclear power plant's No 1 and No 2 reactors, where radiation exceeding 10 sieverts (10,000 millisieverts) per hour was found as shown in red, in Fukushima prefecture, northern Japan July 31, 2011, released by TEPCO August 2, 2011. [Photo / Agencies]

TOKYO - The operator of Japan's damaged nuclear power plant says an area where potentially lethal levels of radiation were detected has been sealed.

Tokyo Electric Power Co. said Tuesday radiation exceeded 10 sieverts at two locations near a duct connected to a ventilation stack between two reactor units at the Fukushima Dai-ichi plant.

TEPCO says no one has been injured. The area required no immediate work and was closed off.

It also said radiation levels around the complex were not rising. That's a sign the duct wasn't leaking.

TEPCO said melted fuel in the No 1 reactor might have collected inside the duct after leaking from the containment vessel during venting early in the crisis.

The plant was crippled by an earthquake and tsunami March 11.