The operator of Japan's crippled nuclear power plant is still stumbling in its handling of the disaster 16 months later, by dragging its feet in investigations and trying to understate the true damage at the complex, investigators said Monday.

The Japanese government-appointed inquiry into the 3 Fukushima nuclear reactor meltdowns has raised doubts about whether other atomic plants are prepared for disasters despite new safety rules, and delivered a damning assessment of the regulators and the station's operator.

The report, the second this month about the disaster, could be seized upon by Japan's growing anti-nuclear movement after the restart of two reactors, and as the government readies a new energy policy due out next month.

The panel suggested post-Fukushima safety steps taken at other nuclear plants may not be enough to cope with a big, complex catastrophe caused by both human error and natural causes in a "disaster-prone nation" like Japan, which suffers from earthquakes, tsunami, floods and volcanoes.

"We understand that immediate safety measures are being further detailed and will materialize in the future. But we strongly urge the people concerned to make continued efforts to take really effective steps," said the panel, chaired by the University of Tokyo engineering professor Yotaro Hatamura.

Tokyo Electric Power Co (TEPCO), the operator of the Fukushima Daiichi plant, and regulators failed to plan for a massive natural disaster, the panel said, blaming them for being lulled by the same "safety myth" blasted by a parliament-appointed team of experts earlier this month.

"Both the government and companies should establish a new philosophy of disaster prevention that requires safety and disaster measures against any massive accident and disaster … regardless of event probability," the report said.

"The Fukushima crisis occurred because people didn't take the impact of natural disasters so seriously," Hatamura told a news conference.

"Even though there were new findings [about the risk of a tsunami], TEPCO couldn't see it because people are blind to what they don't want to see."

The decision by the prime minister, Yoshihiko Noda, to restart Kansai Electric Power Co's two reactors this month has energized the country's growing anti-nuclear movement, with more than 100,000 taking to the streets in Tokyo a week ago.

All of Japan's 50 reactors were shut down for safety checks after Fukushima. Critics say the two restarted reactors do not meet all the government's safety criteria announced this April.

Hatamura also said that because of time restrictions his panel was unable to address the concerns of residents, and the international community, who questioned whether the damaged reactors and the pool of used nuclear fuel at the No 4 reactor could withstand another earthquake.

"I now understand what people are worried the most about is the vulnerability of the No 4 spent fuel pool. I wish we had started an investigation on it much earlier," Hatamura said.

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