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Published: March 25 2011 18:29 | Last updated: March 25 2011 18:29
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Those generators, located on the seaward side of the power station, were meant to keep coolant water circulating around the hot uranium fuel rods in the plant’s reactors and adjacent storage tanks. Within a day of the quake, some of that fuel had overheated, releasing hydrogen gas and radiation into the air.
Mr Okamura, director of Japan’s Active Fault and Earthquake Research Centre, told the Nisa meeting that a 1938 tsunami used as a reference by plant designers could be too small, citing evidence that a much larger tsunami had hit the area in the year 869.
When an attending Tepco official suggested that the 869 event had not been found to have caused much damage, Mr Okamura retorted that reputable historical sources had recorded that it “destroyed a castle”.
Tepco has not made any changes to Fukushima Daiichi’s concrete tsunami barrier since the plant opened four decades ago. Regulators last year approved a 10-year extension of the life of No 1 reactor, the plant’s oldest, which began operating in 1971.
In a telephone interview with the Financial Times, Mr Okamura said his warning about the possible scale of tsunamis in the area was based on models of the 869 tsunami created by his institute. Scientific surveys since 2005 had confirmed historical accounts of the disaster by analysing sediment left by the wave.
Mr Okamura said he was angry that Tepco had not acted on the evidence that tsunamis in the area could be bigger than their designs had allowed for. “I don’t know if all the damage could have been prevented, even if they had responded immediately when I pointed this out, but I do think they should have responded,” he said.