The last line connecting the plant to the Ukrainian electricity grid was cut on Monday, leaving the plant without an outside source of power.
The loss of power to the plant is a major concern since a disruption of electricity supply could knock out cooling systems.
The 10th anniversary of the disaster will be in March next year.
The operator of the wrecked Fukushima nuclear plant for the first time is removing fuel from a cooling pool at one of three reactors that melted down in the 2011 disaster.
A nuclear test reactor that can melt uranium fuel rods in seconds is running again after a near quarter-century shutdown as U.S. officials try to revamp a fading nuclear power industry with safer fuel designs and a new generation of power plants.
The owner of Three Mile Island, site of the United States' worst commercial nuclear power accident, says it will shut down the plant in 2019 without a financial rescue from Pennsylvania.
President Obama is defending his high-stakes nuclear accord with Iran as a sign of American leadership that will make the world safer. And he says that critics of the plan should consider the alternatives.