Workers are pumping nitrogen into one of the reactors at Japan's damaged nuclear plant in an attempt to prevent an explosion caused by dangerously overheated fuel rods.
Wednesday's crisis at the Fukushima plant came after technicians finally stopped a leak of highly radioactive water from the power station that dramatically increased the amount of radiation found in nearby ocean waters.
Chief Cabinet Secretary Yukio Edano said the water leak stopped before 6 a.m. Wednesday local time. Until then, water samples in the vicinity had shown radiation levels up to 7.5 million times the allowable limit.
However, Edano said it is too early to say with confidence that the problem has been solved, and that officials from the Tokyo Electric Power Company are trying to determine whether radioactive water is leaking from any other location.
Radioactive water dumping continues
The government official apologized to neighboring countries for Japan's failure to notify them before it began pumping thousands of tons of low-level radioactive water into the sea near the plant - an issue separate from the water leak into the ocean.
Edano said the pumping will continue, possibly until Friday, in order to drain a storage area that will be used to hold much more dangerous water - up to 200,000 times as radioactive - from inside the reactor. He said steps have been taken to ensure better communication with nearby countries before such action is taken in the future.
The chief Cabinet secretary also said authorities are considering compensation payments for fishermen affected by the disaster, as well as whether to adjust the criteria for acceptable radiation levels within the 20-kilometer evacuation zone around the reactors.
After pumping began Tuesday to transfer 11,500 tons of lightly radioactive water from the number-two reactor into the sea, South Korea protested the action as a possible violation of international law.
Officials at TEPCO, which operates the Fukushima plant, said a dangerous hydrogen buildup is taking place at its number-one reactor. Japan's NHK television quoted officials saying hydrogen is accumulating inside the reactor's containment vessel - an indication that the reactor's core has been damaged.
Hydrogen explosions destroyed the outer housings of two of the plant's six reactors during the first days of the nuclear crisis that followed the earthquake and tsunami on March 11.
And highly radioactive water has accumulated in lower levels of several reactors, following weeks in which workers pumped in massive amounts of water to prevent fuel rods from overheating. The water needs to be removed before workers can complete repairs to the permanent cooling systems.
National police said Wednesday the confirmed death toll in the March 11 disasters now stands at 12,468, with more than 15,000 people still unaccounted for.
Some information for this report was provided by AP, AFP and Reuters.