Even without damage, opening the vulnerable vents in the presence of a build-up of hydrogen gas was a known danger. In the case of Fukushima, opening the vents to relieve pressure was like turning on an acetylene torch and then watching the flame "shoot back into the fuel tank," said one expert with knowledge of Fukushima who asked not to be identified because of his commercial ties in Japan.
Tokyo Electric began venting the No. 1 reactor on March 12 just after 10 a.m. An hour earlier the pressure in the reactor was twice its designed limit. Six hours later the reactor exploded.
The same pattern held with reactor No. 3. Venting to relieve a dangerous build-up of pressure in the reactor began on March 13. A day later, the outer building - a concrete and steel shell known as the "secondary containment" -- exploded.
Toshiaki Sakai, the Tokyo Electric researcher who worked on tsunami risk, also sat on a panel in 2008 that reviewed the damage to the Kashiwazaki-Kariwa nuclear plant. In that case, Tokyo Electric safely shut down the plant, which survived a quake 2.5 times stronger than it had been designed to handle.
Sakai and the other panelists agreed that despite the successful outcome the way the ground sank and broke underground pipes needed for firefighting equipment had to be considered "a failure to fulfill expected performance".
Japanese regulators also knew a major earthquake could damage exhaust ducts. A September 2007 review of damage at the same Tokyo Electric nuclear plant by NISA Deputy Director Akira Fukushima showed two spots where the exhaust ducts had broken.
No new standard was put in place requiring vents to be shored up against potential damage, records show.
Masashi Goto, a former nuclear engineer who has turned critical of the industry, said he believed Tokyo Electric and regulators wrongly focused on the parts of the plant that performed well in the 2007 quake, rather than the weaknesses it exposed. "I think they drew the wrong lesson," Goto said.
The March 11 quake not only damaged the vents but also the gauges in the Fukushima Daiichi complex, which meant that Tokyo Electric was without much of the instrumentation it needed to assess the situation on the ground during the crisis.
"The data we're getting is very sketchy and makes it impossible for us to do the analysis," said David Lochbaum, a nuclear expert and analyst with the Union of Concerned Scientists. "It's hard to connect the dots when there are so few dots."
In fact, Japan's NSC had concluded in 1992 that it was important for nuclear plant operators to have access to key gauges and instruments even in the kind of crisis that had not happened then. But it left plans on how to implement that policy entirely to the plant operators.
In the Fukushima accident, most meters and gauges were taken out by the loss of power in the early days of the crisis.
That left a pair of workers in a white Prius to race into the plant to get radiation readings with a handheld device in the early days of the crisis, according to Tokyo Electric.
They could have used robots to go in.
Immediately after the tsunami, a French firm with nuclear expertise shipped robots for use in Fukushima, a European nuclear expert said. The robots are built to withstand high radiation.
But Japan, arguably the country with the most advanced robotics industry, stopped them from arriving in Fukishima, saying such help could only come through government channels, said the expert who asked not to be identified so as not to appear critical of Japan in a moment of crisis.
(Scott DiSavino was reporting from New York; Additional reporting by Kentaro Sugiayama in Tokyo, Bernie Woodall in Detroit, Eileen O'Grady in New York, Roberta Rampton in Washington; Editing by Bill Tarrant)
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