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