Huge plant: Grand Gulf's reactor is the most powerful in the United States, with a core power of 4408 MWth[1] yielding a nominal gross electrical output of about 1500 MWe.
Grand Gulf Station, a supplemental inspection team is being chartered - White PI for Unplanned Scrams per 7000 Critical Hours
by Bob Meyer
June 12, 2014, The NRC Director's office sent out a memorandum to Jim Drake, Senior Reactor Inspector, Plant Support Branch 2, Division of Reactor Safety designating him as the team leader for the Supplemental Inspection Team.
Since December 29, 2012 to March 29, 2014, the station experienced six unplanned scrams.
As a result of the licensee experiencing three unplanned scrams between December 29, 2012, and January 14, 2013, the Performance Indicator for “Unplanned Scrams per 7000 Critical Hours,” crossed the threshold into White. The following are the descriptions of each of these scrams:
December 29, 2012 - Scram from 100% due to phase A unit differential signal resulting in a main generator lockout and turbine trip
January 4, 2013 - Scram from 94% power due to a phase A unit differential signal resulting in a main generator/turbine trip. Returned to 100% power on January 11
January 14, 2013 - Scram from 100% power due to a turbine generator trip caused by a generator neutral time overcurrent relay tripping. Commenced startup activities on January 27
The licensee had originally indicated that they were prepared for the IP 95001, “Supplemental Inspection for One or Two White Inputs in a Strategic Performance Area,” to be performed in August 2013. However, the licensee experienced another reactor scram (below), which resulted in their request to delay the inspection while they evaluated this new event against the planned actions that they had developed for the previous events.
July 30, 2013 - Scram from 100% power due to high reactor pressure. Cause was a failure of the B turbine stress evaluator (TSE) transmitter
On February 28, 2014, the licensee notified the NRC that they were ready for the IP 95001 inspection.
Subsequently, the licensee experienced two more reactor scrams.
March 17, 2014 - Operators inserted a manual scram from 41 percent thermal power due to a steam leak in the turbine building
March 29, 2014 - Scram from 87% power due to a main generator load reject, resulting in a turbine control valve fast closure
As a result, the licensee contracted an outside firm to perform an independent evaluation of these events and the licensee’s proposed corrective actions.
This supplemental inspection is being performed to obtain a better understanding of each of the referenced events; to assess the licensee’s understanding and response; and to assess whether all underlying contributing causes were appropriately considered and evaluated in the development of the licensee’s corrective actions.
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