SMALL BREAK LOCA ANALYSIS FOR OPTIMIZATION OF SAFETY INJECTION SYSTEMOF KOREAN STANDARD NUCLEAR-POWER-PLANT

The Ulchin Nuclear Power Plant Units 3 and 4 (UCN 3&4) design was base d on ABB-Combustion Engineering's (ABB-CE's) standardized 3800 Mt Nucl ear Steam Supply System (System 80). Despite the 25% core power differ ence between the two plants (3800 MWt for System 80, 2815 MWt for UCN 3&4), several design features have not been changed, especially the ca pacity of Safety Injection System (SIS). Focusing on this fact, the se nsitivity study for UCN 3&4 SIS capacity on the behavior of the postul ated small break Loss of Coolant Accident (LOCA) was performed to opti mize the SIS capacity. Firstly, the sensitivity study for Safety Injec tion Tank (SIT) capacity on the postulated small break LOCA was perfor med by changing the size of SIT from 100% to 60% (100%, 85%, 75%, 60%, respectively) for the 0.5 ft(2) (465 cm(2)) pump discharge leg break. Secondly, the sensitivity study of High Pressure Safety Injection (HP ST) pump capacity on the behavior of small break LOCA was investigated by reducing its discharge flow rate of UCN 3&4 to 50% (100%, 85%, 75% , 70%, 60% and 50%, respectively) for the 0.05 ft(2) (46.5 cm(2)) pump discharge leg break. Finally, the spectrum analysis was performed usi ng the acceptable results of these two studies, i.e., the reduced SIT size and HPSI pump capacity to 70% of UCN 3&4 to retain sufficient mar gin for the small break LOCA. The results of this spectrum analysis sh ow that the peak cladding temperature (PCT) and peak local cladding ox idation (PLO) for the limiting break size of 0.05 ft(2) (46.5 cm(2)) p ump discharge leg break were 1459 degrees F (793 degrees C) and 0.486% respectively, which are in compliance with the Emergency Core Cooling System (ECCS) acceptance criteria of 2200 degrees F (1204 degrees C) and 17% specified in 10 CFR 50.46. The results of this sensitivity stu dy can be adapted to the optimal design of SIS for the future 2815 MWt Korean Standard Nuclear Power Plant and be contributed to the increas e of economical gain. (C) 1998 Elsevier Science Ltd.