ATHENS — For almost a month, from Aug. 17 to Sept. 15, earthquake monitoring equipment at Browns Ferry Nuclear Plant was not working, according to a report TVA filed with a regulatory agency.

Tennessee Valley Authority reported that the malfunction could have hampered Browns Ferry's ability to declare and respond to an earthquake, "because the declarations would be based on personnel feeling an earthquake."

The unavailability of the seismic monitoring instrumentation also could have hampered the Limestone County nuclear plant's ability to determine whether an earthquake required a shutdown, TVA said in its Sept. 20 report to the Nuclear Regulatory Commission.

TVA said it fixed the problem when it discovered it on Sept. 15.

An earthquake and a related tsunami caused a meltdown of reactors in Japan last year, leading to heightened regulatory scrutiny of U.S. nuclear preparedness in the event of an earthquake.

All three Browns Ferry reactors are under increased scrutiny by the NRC. Unit 1 is is operating under a "red" finding, the most severe safety rating short of a mandatory shutdown.