The Evaluation of Battery Capacity Availability by Applying DC Load Shedding and Management for WH1000 NPP

Following Extended Loss of AC Power (ELAP) event, the station batteries are the only source of electrical power. The station batteries supply the DC busses and the AC vital instrument busses. Since AC emergency power is not available to charge the station batteries, battery power supply must be conserved to permit monitoring and control of the plant until AC power can be restored. The purpose of this paper is to prolong essential equipment and control DC power supply by shedding and management DC loads from the DC busses as soon as practical. To meet this requirement, the effect of load shedding of equipment loads from the DC busses and of instrumentation from the AC vital busses have been reviewed. The proposed operation strategy provides actions to establish DC loads and time at which they should be shed and switch. The plant specific availability of the class 1E batteries evaluated considering load shedding of equipment loads from the dc busses and instrumentation from the ac vital busses. In addition to review load shedding possibility of detail load characteristics, every plant has to be prepared specific procedure according to the shedding and switching strategy of DC loads in order to conserve and prolong the station battery power supply. This result of evaluation also supports plant response to near-term actions to address the effects of an ELAP in response to the Fukushima Daiichi Event and Stress Test.