The U.S. had repeatedly warned Japan about vulnerabilities at its nuclear plants in case of a Sept. 11-style terror attack. It turned out Washington was right about the soft spots, but wrong about the enemy that would strike them.
When nature unleashed its own fury on Japan last year with a devastating tsunami, a list of U.S. recommendations proved highly prescient. The elements Washington identified as most vulnerable in an attack _ spent fuel pools, cooling systems, backup electricity _ were the ones worst hit in Japan's disaster.
Tokyo had ignored the recommendations, which were implemented at U.S. nuclear sites, because Japanese officials thought the chances of terrorist-flown aircraft striking its plants were remote.
But as leaders from around the world head to Seoul for a major summit this week on nuclear security, Japan's disaster at its Fukushima plant has provided a salient example of how solid protections against terrorist attacks go hand in hand with protections against natural disasters.
The summit is primarily about ways to keep nuclear materials out of the hands of terrorists, but the Japanese government plans to propose a series of Fukushima-inspired measures to enhance emergency power backup systems and advocate a closer link between anti-terror security and general safety issues.
"We have to imagine the unimaginable," Kensuke Yoshida, the director of the arms control and disarmament division of Japan's Foreign Ministry and a member of Japan's delegation, told The Associated Press.
"Once an incident happens, the consequences will be extremely grave, whether caused by a natural disaster or terrorists," Yoshida said.
Japan had been slow to make that connection.
Documents made public since Japan's nuclear crisis began last year suggest the scenario that played out in Fukushima was by no means unforeseeable _ it was simply ignored.
After the 9/11 attacks, the U.S. Nuclear Regulatory Commission issued a number of directives to the domestic nuclear industry based on a review of what might happen if an airliner hijacked by terrorists was crashed into an atomic plant.
It expressed concern that such an attack could cripple a plant's power system, and proposed portable diesel-driven pumps, portable power supplies and hoses be made readily available so that reactor cores can be kept cool to prevent them from going into dangerous, radiation-spewing meltdowns. It also suggested measures to provide backup cooling water to the vulnerable spent fuel pools.
The suggestions were passed on to Japan several times, but Tokyo dismissed them because it regarded the recommendations as a terrorism issue and did not think it faced a significant terrorist threat, according to Tetsuya Endo, a former diplomat and vice chairman of the Atomic Energy Commission of Japan.
"The agency that got the recommendations just put them in their pocket. No one else knew anything about it," said Endo, who is on an independent fact-finding commission that recently released a scathing review of Japan's response to the crisis.
"We are an island nation with an island mentality. We see ourselves as free from the possibility of terrorist attack," he said.
Last year's March 11 earthquake and tsunami devastated the very systems that the NRC had found to be weakest. Fukushima experienced the electrical blackout that it warned of, and three of its reactors went into meltdowns, forcing tens of thousands to evacuate as plant workers struggled to find ways to keep them cool.
In recent testimony before a parliament-appointed investigative panel, Haruki Madarame, a nuclear physicist and head of Japan's Nuclear Safety Commission, acknowledged that Japan should have taken the U.S. findings more seriously.
"Even though we were aware of the issue and knew that they were taking steps, we didn't do anything," he said. "When other countries were discussing the problems, we only wasted time trying to find excuses why we didn't have to do it."
Edwin Lyman, a nuclear terrorism expert with the Union of Concerned Scientists, said Japan's crisis is a good case-in-point for experts who have long warned that anti-terrorism measures need to be enhanced.
"The Fukushima accident has certainly illustrated the dependence of nuclear plants on electrical power supply, both off- and on-site, and how core damage can occur solely as a result of a prolonged loss of power in the absence of timely intervention," he said.
But he said the disconnect between policymakers who are primarily concerned with anti-terror measures and those focused on mitigating natural disasters continues to be a major problem.
Lyman said the United States' post-9/11 recommendations, which were made public in May to support the NRC's argument that the U.S. was prepared for a Fukushima-type event, reflected that imbalance.
"The measures were specifically intended to help plants survive the impact of a single aircraft, and not to survive other types of initiating events, like earthquakes and floods," he said. "In fact, the U.S. guidance specified that such equipment did not have to be seismically qualified."
Because of the Fukushima example, he said, the NRC is now updating its measures to take into account a wider variety of challenges.