Tokyo Electric Power Co. said it started injecting nitrogen early Thursday into reactor 1 at the Fukushima No. 1 nuclear plant to purge the hydrogen inside and prevent an explosion, and the process went smoothly in the afternoon.
Tepco meanwhile said it believes 25 percent of the fuel rods in reactor No. 3's core were damaged as of March 15, with their casings ruptured or melted from earlier overheating caused by temporary loss of coolant water. The damage could lead to the release of strong radioactive materials from the reactor's core.
Tepco said earlier that an estimated 70 percent of the fuel rods in the No. 1 reactor and 30 percent in the No. 2 reactor were damaged as of March 15. This was the first time the utility issued an estimate for reactor 3's core.