¡¡KASHIWAZAKI, Japan, July 18 (Xinhua) -- Frequent minor incidents from the world's largest nuclear plant after Monday's major earthquake have raised increasing concerns over the safety of the Kashiwazaki-Kariwa nuclear power facility in Niigata, Japan.

    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. The magnitude 6.8 quake on Monday, apparently, has led to troubles unforeseeable.

    Some 50 trouble cases related with the earthquake have been confirmed by Tuesday evening at the Kashiwazaki Kariwa nuclear power 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.

    "We did not assume an earthquake of this magnitude at the time of designing the nuclear power plant," an official from the company was quoted as saying.

    Besides, the plant probably sit right on the fault line that caused the major quake, expert analysis showed.

    The epicenter of the magnitude 6.8 quake was around 9 km northeast of the nuclear plant and some 17 km underground. Aftershocks have been observed in a 15 km-wide, 30 km-long strip southwest of the epicenter. The fault line is believed to be descending underground from a Sea of Japan area toward the shore. "After looking at aftershock location data, we have come to realize a fault lies right below the nuclear power plant," the company official said.

    Aside from doubts over plant site selection, local media also raised questions over the safety management of the nuclear plant.

    When an electric transformer caught fire at the No. 3 reactor of the plant, only several untrained personnel were there to handle the issue before the firefighters came two hours later, local reports said.

    Tokyo Electric Power Co. was also rapped for not releasing related information as soon as possible. Chief Cabinet Secretary Yasuhisa Shiozaki told reporters Wednesday that building nuclear plant on solid rock layers should be a basic principle. He urged the operator to have the public informed about any incidents happened in the nuclear plant.

    Prime Minister Shinzo Abe Tuesday criticized the operator Tokyo Electric Power for being "too slow" in reporting the incidents and said it must ensure that top priority is given to the public's safety.

    On Wednesday, an incident of incorrect report of radiation level was released. The radiation leak in water discharged into the sea from the plant was initially put at 60,000 Bq and later found to be 90,000 Bq. It was accounted for as "computation errors" and the company said it would not cause a safety problem.

    Mayor of Kashiwazaki, where the plant is located, issued an order Wednesday to Tokyo Electric Power Co. to suspend the operation of the nuclear plant.

    In Kuala Lumpur, chief of the International Atomic Energy Agency Mohamed ElBaradei said Wednesday that the UN nuclear watchdog will be ready to join Japan in investigating the incidents at the Kashiwazaki-Kariwa nuclear power plant.

    "Japan needs to go into full investigation of the structure, of the systems, of the components of the reactor," he told reporters during a visit to Malaysia.

    No direct harm to humans or the environment has been confirmed till now. However, for those 19 households living about a kilometer away from the nuclear power complex, the risk of a nuclear leak has become something like a taboo, which they would rather avoid mentioning at all.