Optimization of dynamic terms in core overtemperature delta-T trip function

The characteristics of the core overtemperature Delta-T (OT Delta-T) dynamic terms are investigated for various time constants. In addition, the effects of the dynamic terms on the OT Delta-T trip setpoint in case of the uncontrolled RCCA bank withdrawal at power transient are studied by using the NLOOP and the PUMA code. Based on the above study, the procedure in determining the optimal dynamic term is suggested and the time constants of the OT Delta-T dynamic terms are optimized for the KORI 3 and 4 transition core. It reveals that the most improtant one in the OT Delta-T dynamic terms affecting the minimum DNBR thorugh the system transient is the vessel average temperature lead-lag term, and the optimized time constants are 21 seconds for lead and 4 seconds for lag. By this optimization, the core operation region is expected to be improved without changing the core safety limits. (Author)