The troubled No. 2 reactor of Japan 's Fukushima No. 1 nuclear power plant was still unstable hours after work resumed to pump weawater into it, the government said Tuesday morning, Xinhua reported.
The reactor "is not necessarily in a stable condition," Chief Cabinet Secretary Yukio Edano was quoted by Kyodo News as saying.
Tokyo Electric Power Co. (TEPCO) said the injection of seawater began early Tuesday morning to the reactor unit at the quake-hit Fukushima No. 1 nuclear power plant after a steam vent of the pressure container was opened.
The TEPCO said fuel rods were fully exposed again in the No. 2 reactor of the Fukushima No. 1 nuclear power plant as of 11 p.m. Monday.
Air pressure inside the reactor rose suddenly when the air flow gauge was accidentally turned off, operator TEPCO said, adding that this blocked the flow of cooling water into the reactor, leading to full exposure of the rods.
The nuclear plants shut down automatically due to Friday's massive earthquake, but the shortage of power and tsunami damage to back-up generators apparently crippled reactors' cooling systems.
Explosions created by "hydrogen bubble" blew apart the buildings housing the No. 1 and No. 3 reactors, but did not pierce the reactors' steel and concrete containment vessel.
Prime Minister Naoto Kan said earlier Tuesday morning that the government and TEPCO will set up an integrated headquarters headed by himself to address issues at the nuclear plant, according to a Kyodo News report.