The fault along which Monday’s magnitude-6.8 earthquake occurred appears to extend right beneath Niigata Prefecture’s Kashiwazaki-Kariwa nuclear plant, the world’s largest atomic power complex, an analysis of aftershock data by the Meteorological Agency showed Wednesday.
Also on Wednesday, Tokyo Electric Power Co., which runs the power station, said it underreported a radiation leak in water discharged into the sea from the Kashiwazaki-Kariwa nuclear power station after the earthquake, due to computation errors, but the utility reiterated that no danger to safety has been posed.
Rescue workers Wednesday found the body of a man among the rubble of a collapsed temple in Kashiwazaki, bringing the death toll in Monday’s earthquake to 10.
Police identified the man as Takashi Inomata, a 76-year-old resident of Kashiwazaki who has been listed as missing since the Monday quake.
The Kashiwazaki-Kariwa nuclear power station is designed to withstand an earthquake caused by an unknown active fault up to a magnitude of 6.5, casting into doubt the assumptions made about the strength of a possible temblor at the time the plant was planned.
An increase of 0.2 in magnitude translates into a roughly twofold increase in energy released. The latest quake registered magnitude 6.8.
On the underreported radiation leak Monday, a Tepco official said: “We are sorry for a simple calculation mistake, (but the amount of radiation still) falls below the safety standard set by the state and there is no safety problem.”
Tepco said the amount of radiation discharged totaled 90,000 becquerels, 50 percent more than the 60,000 becquerels it earlier reported in a revelation that came 12 hours after the quake struck.
The radiation-contaminated water is believed to have leaked from a container of spent nuclear fuel shaken by the earthquake.
The announcement came after Tepco said Tuesday a total of 50 cases of water leakage, fire and other problems had occurred at the plant, including the toppling of around 100 drums of low-level atomic waste, some of which broke open, and reactor exhaust pipes that shifted, possibly releasing radioactive materials.
Experts quickly criticized the government as well as Tepco for underestimating the earthquake threat.
“The troubles in the power plant by the latest earthquake revealed that the government’s safety checks as well as a Tokyo High Court ruling are not sufficient,” said Tetsuji Imanaka, associate professor at Kyoto University Research Reactor Institute.
In 2005, the Tokyo High Court rejected a lawsuit by local residents seeking to revoke a state permit on the installation of the No. 1 reactor at the seven-reactor power station.
The court rejected the plaintiffs’ argument that an active fault exists near the station, saying that what they claimed to be an active fault did not even amount to a fault and could not cause a quake.
“It is true that electric power companies don’t want to spend much money for earthquake-proof construction,” Imanaka said.
A Tepco public relations official said, “We did not assume an earthquake of this magnitude at the time of designing the nuclear power plant. After looking at aftershock location data, we have come to realize a fault lies right below the plant.”
The undersea focus of the quake was around 9 km northeast of the nuclear complex and some 17 km underground. Aftershocks have been observed in a 15-km-wide, 30-km-long strip southwest of the epicenter.
Some aftershocks, including the largest, a magnitude 5.8 quake, were focused in land areas.
Aftershocks are caused by parts of a fault that did not move in the initial major seismic movement.
IAEA urges checks
KUALA LUMPUR (Kyodo) International Atomic Energy Agency Director General Mohamed ElBaradei on Wednesday urged Japan to conduct a full and transparent assessment of damage to the nuclear power plant in Kashiwazaki, Niigata Prefecture, caused by this week’s powerful earthquake.
“Japan needs to go into full investigation of the structure, of the systems, of the components” of the reactors, he told a news conference during a two-day visit to Malaysia.
“I would hope that Japan would be fully transparent in its investigation of the accident,” ElBaradei said, adding the IAEA “will be ready to join Japan through an international team in reviewing that accident and drawing the necessary lessons.”
He said the Japanese authorities had told the agency that Monday’s quake was far stronger than what the seven-reactor Tokyo Electric Power Co. nuclear power station, the world’s largest in terms of output capacity, had been designed to withstand.
However, he said, it does not mean the reactors’ structural systems have been damaged.