Japan has approved a revised 40-year roadmap to clean up the wrecked Fukushima nuclear plant, but many questions remain.

The plan, endorsed Friday by key Cabinet members and officials, delays the start of a key initial step — the removal of spent fuel in storage pools at each of the three melted reactors — by up to three years due to earlier mishaps and safety problems at the plant.

Three of the plant's six reactors melted following the 2011 earthquake and tsunami.

Despite the delay, experts need to locate and study melted fuel inside the reactors and develop robots to start debris removal within six years as planned.

Radiation levels at the reactors remain high and the plant is still hobbled by the massive amount of contaminated water.