Electrical and other support systems ES

ISSUE TITLE Reliability of off-site power supply (ESI) 

Offsite power supplies are required to be available to have sufficient capacity and capability to ensure that the fuel and reactor boundary are maintained within specified acceptable limits and core cooling, containment integrity, and other vital safety functions are maintained during accident conditions. 

The main concerns with the offsite power supplies are as follows  

In a multi-unit nuclear power plant, it is questionable whether one set of two startup transformers can provide enough power for normal shutdown of two or even tiiree plant units, as would be required after a loss of power from the main offsite grid. Furthermore, there is a concern about the electrical system failures spreading simultaneously to several units through their common startup transformers. 

Reliable offsite power supplies are essential to avoid challenging the emergency power supplies whose potential failure is one of the main contributors to the overall core damage frequency, as quantified by most of the performed PSA. Degraded voltage conditions can impair the operation of the equipment without producing a transfer to onsite power supplies. 

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