EXPLAINER: How dangerous is the Fukushima nuke plant today?

OKUMA, Japan (AP) — A decade ago, a massive tsunami crashed into the Fukushima Daiichi nuclear power plant. Three of its reactors melted down, leaving it looking like a bombed-out factory. Emergency workers risked their lives trying to keep one of history's worst nuclear crises from spiraling out of control.

Proper equipment has now replaced ragged plastic hoses held together with tape and an outdoor power switchboard infested by rats, which caused blackouts. Radiation levels have declined, allowing workers and visitors to wear regular clothes and surgical masks in most areas.

But deep inside the plant, danger still lurks. Officials don't know exactly how long the cleanup will take, whether it will be successful and what might become of the land where the plant sits.

Journalists from The Associated Press recently visited the plant to document progress in its cleanup on the 10th anniversary of the meltdowns and the challenges that lie ahead.

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WHAT HAPPENED 10 YEARS AGO?

After a magnitude 9.0 earthquake on March 11, 2011, a tsunami 17 meters (56 feet) high slammed into the coastal plant, destroying its power supply and cooling systems and causing meltdowns at reactors No. 1, 2 and 3.

The plant's three other reactors were offline and survived, though a fourth building, along with two of the three melted reactors, had hydrogen explosions, spewing massive radiation and causing long-term contamination in the area.

The plant's operator, Tokyo Electric Power Co., says the tsunami couldn't have been anticipated, but reports from government and independent investigations and recent court decisions described the disaster at the plant as human-made and a result of safety negligence, lax oversight by regulators and collusion.

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WHAT'S INSIDE THE MELTED REACTORS?

About 900...