An Optimization of ASI Operation Band in KSNP

A power level dependent ASI LCO (Limiting Condition for Operation) is developed for the Korea Standard Nuclear Power Plant to improve the plant operability in the low power range and to gain the additional thermal margin in the high power range. The ASI LCO for COLSS (Core Operating Limit Supervisory System) in the low power range between 20% and 40% is relaxed to ±0.57 from ±0.27 so as to enhance the plant operability especially during the fast return-to-power maneuvering after trip. In contrast, the ASI LCO in the high power range between 80% and 100% is tightened to ±0.17 from ±0.27 to recover unnecessarily eroded thermal margin that could otherwise be easily utilized for enhancing capacity factor like the power up-rating. In addition to the COLSS ASI optimization, the CPC ASI range trip set point is expanded from ±0.5 to ±0.7 to allow the COLSS LCO change and to enhance the plant operability for power range below 20% by virtually eliminating the possibility of ASI range trip. Safety evaluations for the limiting accidents of concern have been carried out to demonstrate that the power dependent ASI LCO does not cause any un-compliance with safety criteria and provides considerable thermal margin gain in the high power range. Thermal margin evaluation to date indicates that ±0.1 ASI reduction near full power level can lead to ∼2% overpower margin gain and more than 85 K gain in LOCA PCT. (authors)