The Tokyo Electric Power Company, or Tepco, said it was ready Thursday to inject boric acid into one of its most heavily damaged reactors after it found steam emanating from the reactor building, The New York Times reported.
The measure would prevent a sustained nuclear reaction in the reactor's damaged core, Tepco officials said, stressing such reactions were very unlikely.
No signs of criticality, or sustained nuclear reactions, were detected, the company said, but it announced a halt to all work removing debris from the top floors of the reactor building as a precaution.
The nuclear plant is still presenting problems more than two years after an earthquake and tsunami knocked out its cooling systems, causing multiple meltdowns in its reactors.
Recently radioactive cesium and tritium were detected in the groundwater at the coastal plant, raising concerns the groundwater could be leaking into the Pacific Ocean.
After steam was seen escaping from the top of the No. 3 reactor's primary containment structure Thursday, workers stood ready to inject water containing boric acid into the reactor from the outside if there were any signs of a rapid rise in temperature or radiation levels, Tepco said.