Parameter changes in core designs and safety analyses due to power up-rate for Kori 3 and 4 and Yonggwang 1 and 2

A power upgrade of 4.5%, which is categorized as a stretch power upgrade is applied first to Kori 3 and 4 (KRN 3-4) and Yonggwang 1 and 2 (YGN 1-2) in Korea. The power upgrade of 4.5% is determined through the feasibility study so that core power is increased from 2,775 to 2,900 MWt, while the reactor coolant system (RCS) pressure is maintained at 2,250 psia. Thermal design flow and RCS average temperature are reduced respectively by 1.5% and 2.5 F degrees to compensate the degraded RCS flow rate and to keep the hot leg temperature the same. Physics design is carried out and shows that most physics parameters are within typical variations at the current reload design except 3 input parameters: moderator density coefficient, FQ at EOC (hot zero power for rod ejection accident analysis), and axial flux difference limit. The thermal stability of the core can be maintained. Fuel rod and fuel mechanical evaluations confirmed that their performances can meet the related design criteria. Non-LOCA analyses results show compliance with the acceptance criteria even though they approach the limit due to the increased power. within the criteria. Core designs and safety analyses are successfully completed and it is demonstrated that their results are appropriate and acceptable for power upgrade of 4.5 per cent. Electrical gains are 3.4% for KRN 3-4 and 5.0% for YGN 1-2 due to HP turbine diaphragm replacement and HP turbine retrofit, respectively