The fuel rods of the first reactor of Japan's troubled Fukushima-1 nuclear power plant have melted down completely. The total meltdown took place because the rods were not covered with water fully.
To all appearance, the melted mass is currently resting on the bottom of the reactor, under the water. The mass is being cooled, TEPCO officials said Thursday.
TEPCO acknowledged the total meltdown of nuclear fuel in one of the three damaged reactors of Fukushima-1 nuclear power plant. The biggest danger now is the possibility of hydrogen explosion inside the reactor. However, both the operation of the nuclear plant and experts evaluate the danger as insignificant.
The external surface of the reactor shell remains relatively "cool" - from 100 and 120 degrees Celsius.
Yoshiaki Oka, a nuclear engineering professor at Tokyo's Waseda University, said that workers pump nitrogen into the reactor to prevent a hydrogen explosion. The probability of explosion is extremely low, the professor told reporters.
It became possible to find out what happened in the reactor after ventilation equipment in the first reactor reduced the content of radioactive particles in the air. The equipment was installed last week. Afterwards, workers could enter the building and install gauges there.
It became known that the water level in the first reactor is five meters low than required. It means that four-meter red-hot fuel rods were not cooled by water. As a result, the rods have already melted down completely. There is still some water on the bottom of the reactor: the water cools the melted mass, expert said.
TEPCO specialists previously said that the rods in the first reactor had been 55 percent destroyed. The company currently pumps eight tons of water an hour between the reactor shell and its external steel surface. This will create a water sarcophagus to cool the system.
The situation in the second and in the third reactor of the nuclear power plant is not completely clear either. TEPCO experts said that 30 or 35 percent of the fuel rods at those reactors may have been destroyed. In the second reactor, it is highly likely that the steam condensate pool of the reactor has been damaged. Radioactive water leaks through the damaged pool.
Extremely high temperatures have been registered in the third reactor. The fourth reactor of the nuclear power plant had been shut down for technical servicing before the tsunami and the quake. There was no fuel in the fourth reactor. The fifth and the sixth reactors have not been damaged much. They have been shut down and remain stable.