JAPANESE nuclear regulators trusted that the reactors at Fukushima Dai-ichi were safe from the worst waves an earthquake could muster based on a single-page memo from the plant operator nearly a decade ago.
In the December 19, 2001 document — one double-sized page obtained by The Associated Press under Japan’s public records law — Tokyo Electric Power Co rules out the possibility of a tsunami large enough to knock the plant offline and gives scant details to justify this conclusion, which proved to be wildly optimistic.
Regulators at the Nuclear and Industrial Safety Agency, or NISA, had asked plant operators for assessments of their earthquake and tsunami preparedness. They didn’t mind the brevity of TEPCO’s response, and apparently made no moves to verify its calculations or ask for supporting documents.
“This is all we saw,” said Masaru Kobayashi, who now heads NISA’s quake-safety section. “We did not look into the validity of the content.”
The memo has a tiny map of Japan indicating where historical earthquakes are believed to have struck.
TEPCO considered five quakes, ranging from 8.0 to 8.6 magnitude, in northeastern Japan, and a 9.5 magnitude across the Pacific near Chile, as examples of possible tsunami-causing temblors.
Over the next nine years, despite advances in earthquake and tsunami science, the document was never updated.
When TEPCO finally revisited tsunami preparedness last year, it was the most cursory of checks. And the conclusion was the same: The facility would remain dry under every scenario the utility envisioned.
“There was an attitude of disrespecting nature,” said Kobe University professor emeritus Katsuhiko Ishibashi, who has sat on government nuclear safety advisory panels.
The waves unleashed by the magnitude-9.0 earthquake on March 11 destroyed backup generators for several reactors’ cooling systems, and nuclear fuel in three reactors melted in the worst such crisis since Chernobyl.
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