“We still have the possibilities that the tsunami height exceeds the determined design height due to the uncertainties regarding the tsunami phenomenon,” Tokyo Electric researchers said in a report reviewed by Reuters.
The research paper concluded that there was a roughly 10 percent chance that a tsunami could test or overrun the defenses of the Fukushima Daiichi nuclear power plant within a 50-year span based on the most conservative assumptions.
But Tokyo Electric did nothing to change its safety planning based on that study, which was presented at a nuclear engineering conference in Miami in July 2007.
Meanwhile, Japanese nuclear regulators clung to a model that left crucial safety decisions in the hands of the utility that ran the plant, according to regulatory records, officials and outside experts.
Among examples of the failed opportunities to prepare for disaster, Japanese nuclear regulators never demanded that Tokyo Electric reassess its fundamental assumptions about earthquake and tsunami risk for a nuclear plant built more than four decades ago. In the 1990s, officials urged but did not require that Tokyo Electric and other utilities shore up their system of plant monitoring in the event of a crisis, the record shows.
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