PARAMETER CHANGES IN CORE DESIGNS AND SAFETY ANALYSES DUE TO POWER UPRATE FOR KORI 34 AND YONGGWANG 12

摘要

Power uprate of 4.5percent is accomplished first for Kori 3&4 (KRN 3&4) and Yonggwang 1&2 (YGN 1&2) in Korea. This is categorized as a stretch power uprate, and generally the primary systems are not modified because it can be achieved by the originally possessed system margins, while the secondary systems or components are improved or replaced to accommodate the increased core power. Thus, investigation and evaluation of system, safety and operation parameters in the primary systems are one of the major tasks to achieve the stretch power uprate. This paper describes the parameter changes due to the power uprate of 4.5percent and evaluation efforts by core designs and safety analyses to implement it into KRN 3&4 and YGN 1&2. The power uprate of 4.5percent is determined through the feasibility study so that core power is increased from 2,775 to 2,900 MWt, while RCS pressure is maintained at 2,250 psia. Thermal design flow and RCS average temperature are reduced by 1.5percent and 2.5 deg F to compensate the degraded RCS flow rate and to keep the hot leg temperature the same, respectively. Physics design is carried out and the results show that most physics parameters are within typical variations at the current reload design. However, three input parameters to safety analyses such as most positive moderator density coefficient, F_(Q) at EOC, hot zero power for rod ejection accident and axial flux difference limit must be changed to accommodate the increased power. Thermal hydraulic design demonstrates that thermal hydraulic stability of the core can be maintained. DNBR is calculated using a statistical thermal design procedure and determines as 1.25 for design limit DNBR at the hottest rod, 1.45 for safety analysis limit DNBR and 2.53 for minimum DNBR at normal operation, which are decreased from 1.35, 1.71 and 2.66 respectively to accommodate the increased power. Evaluations of fuel rod and fuel assembly designs confirm that their performance and integrity are within related design criteria. Non-LOCA analyses are carried out using the current methodologies and all analyses results show compliance with the acceptance criteria even though they move in close to the limit due to the increased power. KREM which is a realistic evaluation model is newly applied to LBLOCA analysis and PCT is reduced from 2,091 to 2,032 deg F despite considering the power uprate conditions. SBLOCA and long term cooling analyses are carried out using the current methodologies and all results are within the criteria. Core designs and safety analyses are successfully completed and it is demonstrated that their results are appropriate and acceptable for power uprate of 4.5percent. And, electrical gains are 3.4percent for KRN 3&4 and 5.0percent for YGN 1&2 due to HP turbine diaphragm replacement and HP turbine retrofit, respectively.