Japanese nuclear regulators trusted that the reactors at the Fukushima Dai-ichi nuclear power plant 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 Dec. 19, 2001, document — one double-sized page obtained by The Associated Press under Japan’s public records law — Tokyo Electric Power Co (TEPCO) 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 (NISA), had asked plant operators for assessments of their earthquake and tsunami preparedness. They did not 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 Japanese text, boxes and numbers. It also has a tiny map of Japan indicating where historical earthquakes are believed to have struck. TEPCO considered five quakes, ranging from magnitude 8.0 to 8.6, in northeastern Japan, and a magnitude 9.5 earthquake across the Pacific near Chile, as examples of possible tsunami-causing temblors.
In the next nine years, despite advances in earthquake and tsunami science, the document gathered dust and was never updated.
When TEPCO finally did revisit 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 towering 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. Workers have yet to bring the plant under control more than two months later.
Ishibashi said the problem with the plant’s tsunami preparedness did not lie with the limitations of science back in 2001. The problem was that TEPCO and regulators did not look at risk factors more carefully.
“It is critical to be prepared for what might happen even if the possibilities are small,” he said.
NISA’s request for tsunami risk assessments did not have the force of law and thus the operators’ responses technically were voluntary, but in Japan’s often-informal regulatory structure, regulators would expect such a request to be obeyed.
TEPCO’s memo was titled “The Assessment of Effects Related to the Japan Society of Civil Engineers’ ‘Guidelines on Tsunami Assessment for Nuclear Power Plants’ — Fukushima Dai-ichi and Dai-ni Nuclear Power Plants.”
The company said it used measures for expected earthquakes and other “parameters” to calculate that water would not surpass 5.7m at Fukushima Dai-ichi.
The waters set off by the March tsunami reached 14m above sea level, according to TEPCO.
One big reason for the underestimate: TEPCO’s experts asserted that the biggest earthquake that the nearest fault could produce was magnitude 8.6. At magnitude 9.0, the quake that struck was four times more powerful than that.