Vulnerability of Nuclear Power Plants to Voltage Sag Induced by Disturbances in the Transmission Grid: The Concept of Zone of Vulnerability for Voltage

Nuclear plants are particularly sensitive to events on the grid that may lead to undervoltage on the auxiliary or safety buses. Momentary voltage dips can cause separation from offsite power and operation of emergency diesel generator. Grid disturbances that occur in certain areas or “zones” in the surrounding network, may affect the operation of the nuclear plant, while disturbances from outside these zones may be cause no threat to the nuclear plant. A zone inside which a nuclear power station would be vulnerable to events on the surrounding grid can be defined as the Zone of Vulnerability (ZoV). Different types of ZoVs can be defined depending on the nature of the vulnerability being considered. This paper deals specifically with the Zone of Vulnerability associated with the risk of voltage sags in the safety and auxiliary for safety and auxiliary buses of nuclear plants induced by faults in the power grid. The paper first introduces the concept of ZoV_v and its importance for nuclear plants security. A methodology for determining the ZoV_v is then described.