Correction appended.

Twenty-eight of 66 U.S. nuclear plants reviewed by federal inspectors include procedures for managing severe accidents in their plant safety procedures and 40 of the plants conduct drills to simulate a damaged reactor core, the Nuclear Regulatory Commission said in a report released today.

"While overall we believe plants are safe ... we are concerned that our inspectors found many of the plants have work to do in either training their staff on these procedures or ensuring the guidelines are appropriately updated," said Eric Leeds, director of NRC's Office of Nuclear Reactor Regulation.

At issue are "severe accident management guidelines," steps to be taken after a reactor's fuel has been damaged during an emergency and the operator is attempting to limit radioactive releases. Such safety guidelines are voluntary, NRC said.

The agency's on-site inspectors found that almost all plants are keeping copies of the guidelines in technical support centers, plant control rooms and emergency operation facilities. They found that staff at 92 percent of the plants received initial training on the guidelines.

NRC is conducting short- and long-term safety reviews of U.S. nuclear plants in the wake of a March 11 earthquake and tsunami that heavily damaged Japanese nuclear power plants.

Rep. Ed Markey (D-Mass.) said the findings show NRC has allowed dust to gather on emergency response guidelines instead of ensuring that employees are properly trained and drilled on their use.

"We must not wait until a nuclear incident in this country to ensure that the guidelines in place to respond to an emergency are up-to-date and consistently applied," Markey said in a statement. "The commission should not give the go-ahead to any new reactors, new designs or relicense applications for operating reactors until we have incorporated the lessons of the Fukushima meltdown into our regulations."

The original version of this story offered an incorrect tally of the plants reviewed by federal inspectors.