The Nuclear Regulatory Commission (NRC) issued a bulletin to all nuclear power plant licensees requesting information about their electric power system designs and alerting them to a potential design vulnerability that could affect the operation of key safety equipment.
The NRC issued Information Notice 2012-03 on March 1 to inform licensees of the loss of one of three phases of the offsite power circuit, including an event at Byron nuclear power plant in Illinois on January 30. A loss of off-site power happened at the 1,136 MW Unit 2 due to an unbalanced voltage entering the onsite power distribution system from the transmission network. The plant’s electric power system’s protection scheme was not designed to sense the loss of one of three power phases and automatically trip circuits to isolate the degraded outside power source and switch to emergency backup power. The degraded offsite power source could have damaged the plant’s emergency core cooling system, NRC said in a statement. The unit was brought back online Feb. 7.
NRC regulations and plant technical specifications require reliable off-site and onsite power systems with sufficient capacity and capability to operate safety-related systems. Therefore, the NRC staff is seeking information to verify compliance with existing regulations and plant-specific licensing bases. The staff will use the information it receives to determine if further regulatory action is needed.
The bulletin requests licensees to provide information on their electric system designs within 90 days. It applies to all 104 currently operating commercial power reactors and the four combined licenses for new reactors issued earlier this year.
To read the bulletin, click here.
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