Some radioactive substance was detected Thursday in filter at the No. 7 reactor of the Kashiwazaki nuclear power plant, after a series of incidents occurred there due to a major quake, Kyodo News said.
According to the ministry of economy, the level of iodine detected will do no harm to the environment and will not constitute a nuclear fuel leakage.
Some 50 incidents related with the earthquake have been confirmed by Tuesday evening at the Kashiwazaki Kariwa nuclear power plant in Niigata prefecture, the world's largest nuclear plant.
The incidents included a fire, leakage of water containing radioactive material, detection of a small quantity of radiation from a ventilation filter and toppling of drums containing low-level radioactive waste, according Tokyo Electric Power Co., which managed the nuke plant.
The nuke plant, located at the coast of the Sea of Japan, is designed to withstand an earthquake caused by an unknown active fault up to a magnitude of 6.5., which is below the 6.8 magnitude of Monday's quake.
