Impact of Lightning Strikes on Nuclear Power Generating Stations

Electrical transients initiated by direct or indirect lightning strikes have caused reactor trips or misoperation of the equipment in nuclear power generating stations. The effects of lightning strikes on reactor trips or misoperation of the equipment were reviewed for the period 1984 through 1998. Based upon the review, it was found that in a number of cases, the overvoltage protection devices for the control rod drive system had operated due to the lightning strikes. There were also cases where lightning strikes had partially damaged the main/startup transformers, tripped the switchyard breakers or tripped the transmission lines and, thereby, impacted the availability of the required stable offsite power sources to the nuclear power generating stations. Since solid state circuitry designs including the digital instrumentation and control designs are being increasingly utilized in the reactor protection system and other systems, the chances of misoperation of low voltage equipment due to lightning strikes have increased. The low voltage circuitry may be more vulnerable now because of the integrated protection and microprocessor-based systems being used in the Simplified Passive Advanced Light Water Reactors which will be built into the next millennium.*