Design of nuclear power plants against damaging effects from lightning strikes. Version 2022-11

In accordance with Sec. 2.4 SiAnf ("Protection concept against internal and external hazards as well as against very rare human induced external hazards"), protection measures are required with respect to natural external events. Appendix 3 SiAnf specifies the extent of required lightning protection measures in so far as stating that equipment-related protection measures shall be taken against this event. This is achieved by properly designing the lightning protection of the plant and by installing suitable lightning protection systems. The present safety standard is established under the presumption that the requirements from conventional standards and regulations (e.g., building regulations of the individual German states, the German Accident Prevention Regulations, DIN standards and VDE regulations, EN standards, IEC standards) are observed taking the nuclear power plant specific safety requirements into consideration. This safety standard specifies additional requirements for the lightning protection of nuclear power plants. The objective of this safety standard is to specify these additional requirements regarding the Exterior and the Interior Lightning Protection System such that the influence of lightning strikes on electrical facilities will not lead to impermissibly adverse effects on plant safety. The foundation of the present safety standard is based on a) deriving, and then specifying, lightning strike characteristics from the measurement results of actual lightning strikes, b) evaluating specific experiments with pulse generators that simulate lightning strikes by inducing voltage pulses into cables and conductors of existing nuclear power plants which were already protected by defined and relevant lightning protection measures, c) specifying analytical procedures for determining that portion of the lightning current that must be considered for the voltage induction, d) evaluating results from analytical and numeric procedures regarding the lightning-based voltage induction into cables of cable ducts and into buried cables (cf. Appendix F). The general requirements regarding quality assurance are specified in safety standard KTA 1401. The present safety standard specifies the protection measures against lightning-strikes required in accordance with Secs. 4.1.2.3 and 4.2.2 of safety standard KTA 3501. The present safety standard does not specify any analytical procedures regarding the induction of lightning strike based voltages into the instrumentation and control circuitry inside the power plant buildings. Various analytical procedures have been published in technical literature relating to the calculation of induced voltages in buildings of power plants. However, due to the differences between power plants with respect to geometric arrangement of the electrical equipment and the instrumentation and control equipment and due to the various induction possibilities, no single easily applicable analytical procedure is available that would suit all individual cases. Note: Further information on the voltages coupled into buildings can also be obtained from measurements of building shielding effectiveness and measurements on models (cf. Appendix E).