A security guard at the Sequoyah Nuclear Plant failed to conduct a required inventory of guns used by security personnel and then falsified records to try to cover up the error, according to Nuclear Regulatory Commission records released Tuesday.

The 2007 incident — uncovered by TVA and turned over to NRC investigators last year — violated federal security rules for nuclear plant safety, NRC spokesman Roger Hannah said. But in an order announced Tuesday, the NRC agreed not to impose a civil penalty against TVA if the utility adopts new controls over weapons inventory and guard practices at all three of its nuclear plants.

“In our opinion, the corrective action we took resulted in positive results for both us and the NRC,” TVA spokesman John Moulton said.

Mr. Moulton said TVA officials don’t discuss details of the security at its nuclear plants, but the agreement provides that TVA will improve its inventory practices and guard reviews at the Sequoyah, Watts Bar and Browns Ferry nuclear plants.

NRC records indicate that once TVA became aware of the falsified inventory records, the agency investigated the violation, updated its records and implemented new procedures to limit the chances of such an incident happening again.

TVA agreed to the changes shortly before the agency announced last September that it will terminate its use of a contract security company and bring nuclear plant safety under TVA employees in early 2009.

Pinkerton Government Services has provided most of the security around TVA’s three nuclear power plants for the past 11 years. TVA is transferring the 500 Pinkerton security officers to TVA’s payroll this year “to have more direct and effective management controls and lines of communication,” TVA Nuclear Chief Bill Campbell said.

In 2006, a government watchdog group — the Project on Government Oversight — disclosed another incident in which 30 M-4 assault rifles improperly were stored inside the Sequoyah plant. Peter Stockton, the group’s chief investigator, said the weapons “could have been delivered to an insider planning a hostage situation.”

The NRC also reported two incidences in 2007 in which Pinkerton guards were “inattentive” at the Sequoyah plant.

Mr. Hannah said federal regulators did not ask TVA to end its contract with Pinkerton. The NRC will continue to examine TVA’s nuclear security to ensure the agency meets its commitments, Mr. Hannah said.