Junk Plant Waterford 3: A Disgraceful Scram And Resultant Latent Deficiencies Discovered

These guys got too many LOCAs in recent times. All the latent defects sitting around to show themselves upon a triggering event is a disgrace. 

Considering: 

PREVIOUS OCCURRENCES

CR-WF3-2015-3566:  Failure of ‘B’ Fast Dead Bus Transfer during Plant Scram on June 3, 2015.  (Reported under  LER 2015-005-00 and 2015 005-01.

It is amazing they didn't catch these latent defects. It is very unprofessional. 

Licensee Event Report (LER) 2017-002-01 Automatic Reactor Scram due to the Failure of Fast Dead Bus Transfer Relays to Automatically Transfer Station Loads to Off-Site Power on a Main Generator Trip     Waterford Steam Electric Station, Unit 3 (Waterford 3)

On July 17, 2017, at 1606 CDT, Waterford 3 experienced an automatic reactor scram due to a loss of forced circulation, which was the result of a loss of off-site power to the safety and non-safety electrical busses.  Prior to the scram, plant operators manually tripped the main turbine and generator due to overheating of the isophase bus duct due to the failure of a shunt assembly connection in the duct to Main Transformer 'B'.  The automatic electrical bus transfer did not occur due to relay failures in the fast dead bus transfer system.  Both 'A' and 'B' Emergency Diesel Generators started and loaded as designed to re-energize the 'A' and 'B' safety busses.  The loss of off-site power caused a loss of both Main Feedwater pumps, resulting in an automatic actuation of the Emergency Feedwater system.
 
The Root Cause of this event was the design change procedure used for modifications to the fast dead bus transfer circuitry did not include guidance to detect the susceptibility of the relays to DC coil inductive kick.  The faulty relays in the fast bus transfer circuit were replaced prior to plant startup.