A United Nations nuclear expert says Japan’s nuclear disaster has been less serious than the Chernobyl accident in Ukraine in 1986. But Wolfgang Weiss, the head of the U.N. Scientific Committee on the Effects of Atomic Radiation, said Wednesday in Vienna that the disabled Fukushima Daiichi nuclear plant is a bigger problem than Three Mile Island in the United States which had an accident in 1979.
Workers on Wednesday began pumping nitrogen into one of the reactors at the damaged nuclear plant in an attempt to prevent an explosion in the containment vessels protecting over-heated fuel rods. They took that step after technicians had stopped a leak of highly radioactive water from the power station, which had raised radiation levels in the nearby ocean to 7.5 million times the legal limit.
Japan’s Chief Cabinet Secretary Yukio Edano said the leak had been stopped by 5:38 a.m. Wednesday.
Edano also 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. He said the pumping, which could continue until Friday, was necessary to make room in a storage area for water that is 200 thousand times more dangerous. But he said steps have been taken to ensure better communication with nearby countries before such steps are taken in future.
Chinese and South Korean authorities have complained about the release of radioactive water, and on Wednesday Chinese authorities said they had detected trace amounts of radioactive iodine in spinach grown in three areas. But the National Nuclear Emergency Coordination Committee said the amounts were well below legal limits.
In Washington Wednesday, an official from the U.S. Nuclear Regulatory Commission testified in Congress that his agency did not believe the core of Fukushima’s number two reactor had melted down. Earlier in the hearing, Democratic Congressman Edward Markey had said the NRC thought the core had probably melted through the reactor pressure vessel.
In Japan, Edano said the government is considering whether to change the criteria for acceptable levels of radioactive material in the 20-kilometer evacuation zone surrounding plant, which was damaged when an earthquake and tsunami hit Japan on March 11.
He said that with the nuclear crisis stretching into its third week, the government’s initial standards for exposure may need to be revised.
Officials at TEPCO, which operates the Fukushima plant, say hydrogen is building up in its number one reactor. Japan’s NHK television quoted officials as saying the dangerous buildup is occurring inside the containment vessel that keeps radiation from escaping into the atmosphere, an indication that the reactor’s core has been damaged.
Hydrogen explosions destroyed the outer buildings housing the number one and three reactors early in the crisis.
Highly radioactive water has accumulated in the basements of several of the plant’s reactors as workers pumped water into the reactors to prevent their fuel rods from overheating. The contaminated water needs to be removed before workers can complete repairs to the cooling system.
National police said Wednesday the confirmed death toll in the disasters now stands at 12,468, with more than 15,000 people still unaccounted for.