OMAHA, Neb. (AP) — Federal regulators have begun the detailed inspections that will determine whether the troubled Fort Calhoun nuclear power plant will be allowed to restart.

The Nuclear Regulatory Commission says teams of inspectors are checking out roughly 450 different concerns at the plant 20 miles north of Omaha that has been shut down since April 2011.

The NRC says will also evaluate a new concern related to the water pumps that supply cooling water from the Missouri River to the plant. The Omaha Public Power District reported in December that the bolts securing the pumps were shorter than required.

Regulators say the shorter 9-inch bolts could have let the pumps become inoperable in an earthquake. OPPD replaced the bolts with 16-inch ones.

Regulators say the plant won't restart unless it's safe.