Usually, the information I send out is from Nuclear Regulatory Commission Event Reports, which are published on the NRC website the first working day following an incident. However, the NRC also has a category of reports called Preliminary Notifications, which are “brief descriptions, generated by NRC regions when needed, of matters that are of significant safety or safeguards concern or have high public interest. PNs are used to promptly inform the Commissioners and others in NRC and Agreement States with new and current information.”
PN’s usually indicate that there is additional information that the NRC needs in order to properly evaluate nuclear incidents, particularly when there might be reason for additional corrective action. PN’s tend to be more detailed.
On November 30, 2011, the NRC posted a Prelimary Notification on the turbine trip at the South Texas Nuclear Project. There are a couple of details in the PN that were not in the Event Report. The reactor shutdown was not without complications.
“… there were a few equipment anomalies associated with the trip.
At 3:10 a.m., on November 29, 2011, Unit 2 operators received a stator cooling water system trouble alarm. The Stator, which is the stationary piece of the generator, has its own cooling system. Automatic protective features for the main generator caused the main generator to go offline, causing a turbine trip and a reactor trip per design at 3:29 a.m. Followint the reactor trip, a main condensor steam dump valve stuck open resulting in a cool down of the reactor coolant system. Operators manually isolated the affected steam dump valve to stop the cooldown.
In addition, a water seal associated with the stator cooling water system voided, releasing hydrogen gas from the main generator into the turbine building. The licensee vented the turbine building to provide additional air flow and purged the main generator with carbon dioxide to dissipate the hydrogen gas.
Here’s a link: http://pbadupws.nrc.gov/docs/ML1133/ML113340450.pdf