Abstract
The function of the electric power system of nuclear power plants (NPPs) is to provide safe and reliable electricity for the equipment both in normal operation and accident conditions, and to provide emergency power for nuclear safety-related systems to maintain the safety of NPPs. Station blackout (SBO) occurs when loss of offsite power (LOOP) happens concurrently with unavailability of the onsite emergency alternating current (ac) power. LOOP is a precursor of SBO which rarely occurs but contributes significantly to reactor core damage frequency (CDF). Collecting and analyzing all LOOP events in NPPs of China from 1993 to 2017, this paper summarizes the common features of the LOOP events, and identifies the weaknesses and lessons learned from these events. Conclusions and experience feedback suggestions are put forward for improving the reliability of the offsite power supply of NPPs in China.
Highlights
In normal operating conditions, the NPP electric power system sends the power generated by the main generator to the transmission grid through the main transformer and delivers the power to equipment through the step-down transformer
Two out of a total of 11 (18%) loss of offsite power (LOOP) events were due to procedure LTA, they are (1) loss of offsite AC power due to low-frequency trip of the transmission line (2001M) at Qinshan NPP; and (2) loss of two offsite power supply at Lingao Unit 2 NPP
In the LOOP event at Lingao Unit 2 NPP, the plant was powered by the 2GEV main transformer at the beginning, and automatically switched to 9LGR auxiliary power supply after the loss of main power, as the main coolant pump was powered by the main transformer and tripped, the operator decided to use auxiliary power through the 2LGB and 2LGA bus to start up the 2RCP003PO main coolant pump
Summary
A total of 11 LOOP events in China’s NPPs were collected from 1993 to the end of 2017 in the National Nuclear Safety Administration Experience Feedback System [2] (Table 1). Loss of all offsite power supply and unavailability of channel A EDG at Daya bay NPP. Loss of all AC power supply at Qinshan NPP due to transmission line (2001M) trip on low frequency. Reactor trip at Qinshan Phase III NPP (CANDU reactor) due to loss of offsite power supply. Loss of Level 4 power supply due to trip of standby transformer (SST1) causes Unit 1 trip at Qinshan Phase III Nuclear Power Plant. Loss of all offsite power supply on Unit 2, Daya bay NPP caused by Pinghe transmission line trip. Loss of offsite power supply on Unit 1 (VVER reactor), Tianwan NPP caused by activation of distance protection on Heyun 4911 transmission line.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
