Tokyo Electric Power Co. predicted in 2008 that a tsunami could reach a height of more than 15 meters at the Fukushima No. 1 nuclear power plant, according to government sources.
The discovery of this prediction, made by the government's nuclear accident investigation and verification committee, contradicts TEPCO's assertions that the size of the March 11 tsunami was "unpredictable."
In the 2008 assessment, TEPCO predicted that a more than 10-meter-high tsunami could hit the nuclear plant. The March 11 tsunami at the plant was 14 to 15 meters high.
However, TEPCO did not incorporate its 2008 assessment in its countermeasures against tsunami, and only reported its findings to the Nuclear and Industrial Safety Agency on March 7 this year--four days before the March 11 disaster.
According to TEPCO, the assessment was made after the government's Headquarters for Earthquake Research Promotion released updated data on the probabilities of earthquakes in July 2002.
TEPCO made its 2008 assessment based on the premise that an earthquake of the same magnitude as the Meiji Sanriku Earthquake in 1896, which is believed to have been magnitude-8.3, would occur off Fukushima Prefecture. It calculated the height of tsunami that might hit the Fukushima No. 1 and No. 2 nuclear power plants in such an event.
The utility found that tsunami 8.4 meters to 10.2 meters high could strike near the Fukushima No. 1 plant's water-intake facility.
It also predicted that the water would move inland and could reach a height of 15.7 meters above sea level at the Nos. 1 to 4 reactors, and 13.7 meters at the Nos. 5 and 6 reactors.
After the assessment, in December 2008, TEPCO used study results from the National Institute of Industrial Science and Technology to calculate the damage tsunami might cause if an earthquake of the same magnitude as the 869 Jogan Earthquake occurred off Fukushima or Miyagi prefectures.
The Jogan Earthquake is believed to have been magnitude 8.4.
TEPCO's calculation indicated that tsunami 8.7 meters to 9.2 meters high could hit the No. 1 plant's water-intake facility, but TEPCO said the tsunami would not move inland.
It submitted this assessment to the nuclear safety agency in September 2009.
TEPCO had taken measures against tsunami on the premise of a tsunami 5.7 meters high at the No. 1 plant, but did not reinforce its defenses based on the two newer assessments.
Junichi Matsumoto, acting head of TEPCO's headquarters regarding nuclear plant locations, said at a press conference Wednesday, "[These figures] were the result of an extreme simulation that imagined the recurrence of the Meiji Sanriku Earthquake off Fukushima Prefecture.
"We judged that releasing the data was unnecessary and we didn't need to reflect the results in our facilities or management."
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Report reached vice president
Tokyo Electric Power Co.'s 2008 assessment that a tsunami more than 10 meters high could strike the Fukushima No. 1 nuclear power plant was reported to an executive vice president and other senior executives at the company, according to sources.
TEPCO officials who made the assessment reported the results to Sakae Muto, who was then an operating officer and deputy head of the company's headquarters regarding nuclear plant locations. Muto is now an adviser for TEPCO.
The findings were then reported to Ichiro Takekuro, at the time an executive vice president in charge of nuclear power plants. He is now a fellow in TEPCO.
However, TEPCO did not take any specific measures based on the report.
At a press conference Thursday, TEPCO officials said Muto received a report about the simulation results in June 2008, and approved a plan for TEPCO to ask the Japan Society of Civil Engineers to review its guidelines for calculating possible tsunami.
The simulation result was also reported to Takekuro by June 2010, but TEPCO's board of directors did not discuss the issue. Thus the company did not take such measures as relocating emergency diesel generators to higher places.
The Nuclear and Industrial Safety Agency said its officials instructed TEPCO to quickly implement measures, such as improving its facilities, when TEPCO reported the results of the 2008 assessment to the agency on March 7 this year.
However, TEPCO insists it did not receive instructions to improve its facilities or take other such actions.
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