NPPs at low power and shutdown conditions

Events occurring during shutdown operational modes represent a significant contribution to the NPP risk due to the fact that both preventive and mitigative capabilities of the plant can be degraded, e.g. by  

Extensive maintenance work together with a large number of people present due to refueling, preventive and corrective maintenance, modifications, surveillance testing and in-service inspections can increase considerably the likelihood of an inadvertent event. Due to an inherent belief that the unit is in a safe shutdown mode the operating personnel may be unaware of the potential for higher risk during various shutdown conditions. 

The number of events occurring during LPS conditions is considerably higher than might be expected compared to the number of events occurring during power operational modes. In many cases higher probability of an LPS event is partially compensated for by the slowly 

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