The Nuclear Regulatory Commission today released details of an automatic shutdown of one of two units at the Susquehanna nuclear power plant on Dec. 19.

According to the release, the unit two reactor automatically shut down at 5:31 p.m. on Dec. 19 due to low reactor pressure vessel levels.

The cause of the loss of feed water flow and trip of the reactor recirculation pumps is under investigation, the report states.

As of 8:29 p.m., unit two returned to a stable mode of operation. Meanwhile, unit one was not affected and continued to operate at 99 percent power.

The shutdown was the second this week, with the first event ocurring on Dec. 16. That shutdown happened while performing testing on a control valve at about 1:56 a.m. A second shutdown signal at 2:10 a.m. was caused by low water levels, according to a separate release.