TOKYO (AP) — Japan on Friday revised a roadmap for the tsunami-wrecked Fukushima nuclear plant cleanup, further delaying the removal of thousands of spent fuel units that remain in cooling pools since the 2011 disaster. It’s a key step in the decades-long process, underscoring high radiation and other risks. The government and the plant operator, Tokyo Electric Power Co., still keep a 30- to 40-year completion target. A look at some of the challenges: More than 4,700 units of fuel in pools More than 4,700 units of fuel rods remain inside the three melted reactors and two others that survived the 2011 earthquake and tsunami.