A Wall Street Journal analysis of safety and maintenance practices released Monday alleges how the plant's age, structure and work procedures threatened to spin the situation at the nuclear reactor out of control.
The Japan Nuclear Energy Safety Organization, a mostly government-funded group monitoring safety and conducting inspections, reported Daiichi had the highest accident rate of any big Japanese nuclear plant. The data shows Daiichi's workers were exposed to more radiation than their peers at most other plants, the Journal reported.
Since 2005, the Daiichi plant has had 15 accidents, the most of any Japanese plant containing more than three reactors with maintenance problems as the leading cause.
TEPCO, the company operating the reactor, said overall the Daiichi plants operated safely and the plant's age accounted for the higher rate of accidents, all of which were relatively minor until March 11 when Japan was hit by a 9-magnitude earthquake and tsunami, the Journal said.
All of Daiichi's reactors came online in the 1970s.
"(Since) Fukushima Daiichi has older reactors, it requires more frequent repairs and checks than new nuclear plants." Because the plant is of an old design, "radiation tends to be higher," said Teruaki Kobayashi, head of TEPCO's nuclear-plant-management section.
"When we carry out major improvements or checks, inevitably people are more likely to receive radiation," Kobayashi said. "That's because some tasks can only be done by human hands."
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