BS EN IEC 62855:2021

1   Scope

  [IEC 62855](/search?q=IEC%C2%A062855)
   provides the electrotechnical engineering guidelines for analysis of AC and DC electrical
  power systems in nuclear power plants (NPPs) in order to demonstrate that the power
  sources and the distribution systems have the capability for safe operation and shut
  down of the NPP, bringing it to a controlled state after an anticipated operational
  occurrence or accident conditions and finally reaching a safe state. 
The analytical studies discussed in this document provide assurance that the design
  bases are satisfied to meet their functional requirements under the conditions produced
  by the applicable design basis events. The studies provide assurance that the electrical
  power system is capable of supporting safety functions during all required plant conditions. 
Analytical studies validate the robustness and adequacy of design margins and demonstrate
  the capability of electrical power systems to support plant operation for normal,
  abnormal, degraded and accident conditions. 

    NOTE  The safety functions are described in IAEA Specific Safety Requirements SSR-2/1 related
     to the design of the nuclear power plants.. 

The analyses are used to verify that the electrical power system can withstand minor
  disturbances and that the consequences of major disturbances or failures do not degrade
  the capability of the electrical power systems to support safe shutdown of the plant
  and maintain the plant in shutdown condition. 
The analyses are performed with one or more of 

   
     ...