Comparison of LCO's due to difference in accident analysis methodology

Variations of Limiting Conditions for Operation (LCO's ) were evaluated according to accident analysis methodologies of Combustion Engineering Inc., which uses Core Operating Limit Supervisory System (COLSS ) for monitoring state parameters, and Westinghouse which treats state parameters statistically off-line to determine Design Safety Analysis Limit DNBR. Yonggwang Nuclear Units 3 and 4 (YGN 3 and 4) are used as a base plant of the comparison. For the generation of possible operating axial shapes, FLAIR code was used. Complete loss of flow event was analyzed using CESEC-III and CETOP-D codes. The results show that the CE's methodology using the monitoring system of COLSS gives more flexible operation than the Westinghouse