Description of BS EN IEC 62855:2021 2021

IEC 62855 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.

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

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.

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

• simulation tools (software and hardware) that have been verified and validated,

• hand calculations, and

• tests.

This document provides guidance on the types of analyses required to demonstrate that the plant's auxiliary power system can perform the required safety functions. This document does not provide specific details on how the analysis should be conducted.

This document does not cover digital controllers (such as controllers for rectifiers, inverters, sequencers and electrical protection devices) used in electrical power systems. IEC 61513 gives recommendations that apply to the electronic controls and protective elements of the electrical power systems.

This document does not include environmental conditions (i.e. temperature, humidity, etc.) or external events (seismic, flooding, fire, high energy electromagnetic pulse, etc.) that may impact equipment sizing or protection requirements. The external events lightning and geomagnetic storms are included.

This document does not cover additional or unique requirements for stand-alone power system, such as power supplies for security measures in NPPs. Pertinent clauses of this document may be used as a guideline for such systems.

Redundancy in the power system design can increase the availability of electrical power to critical plant equipment. Performing a probabilistic risk assessment (PRA) is a method of assessing system availability and optimizing design for high reliability. This document does not cover improving the reliability of NPP electrical power systems using statistical or diverse and redundant schemes.

Requirements for safeguards of personnel involved with installation, maintenance and operation of electrical systems and general personal safety are outside the scope of this document. General guidance for lightning protection of equipment is provided in relevant clauses of this document.

This document is intended to be used:

• for verification of the design of new nuclear power plants,

• for demonstrating the adequacy and impact of major modifications of electrical power systems in operating nuclear power plants, and

• where there is a requirement to assess and establish operating limits and constraints for existing plants.

Pertinent parts of this document can be used as guidance for decommissioning stages.

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