TOKYO (Kyodo) — Tokyo Electric Power Co. estimated in 2006, using a new calculation method at the time, that the probability of a worst-case tsunami hitting the Fukushima Daiichi nuclear power plant was around 10 percent at the most over a span of 50 years, but the utility did not take measures based on the assessment, a nuclear energy expert at the company said Tuesday.
The expert told Kyodo News that the assessment showed the probability of a major tsunami hitting the plant in Fukushima Prefecture had “dramatically increased” and the company should have taken countermeasures as soon as possible.
Although the utility known as TEPCO describes the 2006 probability assessment as based on experimental analysis and says the figure was “small enough” in a draft report of an in-house panel investigating the nuclear crisis at the plant, experts at the utility as well as the central government are questioning TEPCO’s inaction.
The TEPCO expert who has long been involved in the field of nuclear energy said the 2006 assessment was only shared among people in the field and not disseminated to other relevant sections in the company.
The expert surmised that TEPCO did not take countermeasures because it did not want to spark concern among residents living near the plant and was worried about the possible impact on other electric power companies.
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.”
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.
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.
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.
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.
Junichi Matsumoto, acting head of TEPCO’s headquarters regarding nuclear plant locations, said at a press conference in August, “[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.”
Under the Probabilistic Safety Assessment method, the probability of a tsunami of more than 5.7 meters hitting the Fukushima Daiichi plant in 50 years — the general operating life of a nuclear reactor — was around 10 percent at most and the probability of a tsunami of more than 10 meters that could cause a nuclear meltdown striking the plant was less than 1 percent.
The latter probability far surpasses the International Atomic Energy Agency’s safety standards that say the possible occurrence of a nuclear meltdown should be less than once in 100,000 years.