Greenpeace International claimed Wednesday that a defective nickel-based alloy has been in use in core parts of South Korean nuclear power plants, exposing the country to the risk of massive leaks of radioactive water from the plants.

"Inconel-600" is currently in use at 14 local nuclear reactors throughout the United States, but various other countries stopped using it four decades ago due to the material's serious problem with durability.

Manufactured by an American company, the nickel-chromium alloy had been used worldwide for building key parts of nuclear power plants such as steam generators and nuclear reactors that require resistance to corrosion and high temperatures.

The environmental group, during a news conference in Seoul, said any corrosion or cracking of the nuclear reactors made of the alloy could cause massive leaks of radioactive materials at any time, similar to those that occurred in the Fukushima or Chernobyl disasters.

Noting that six of the 14 nuclear reactors in South Korea were already found to have cracking, with problems at Hanbit reactors No. 3 and No. 4 the most serious, the group urged the Seoul government to immediately stop the operation of the two reactors and of other reactors in turn.

It also urged the Korea Water Resources Corp., a state-run company that operates the nation's atomic power plants, to launch a full-scale inspection into the use of the alloy at nuclear power plants in the country. (Yonhap)