Evaluation of Reactor Physics Characteristics for the Modified CANDU6 Fuel

The regional overpower protection (ROP) system in CANDU6 reactor is to prevent OLD (Onset of Intermittent Dryout) caused by the slow loss of regulation (SLOR) and is performed at the evaluated ROP trip setpoint. The evaluated trip setpoint is getting lower as plant operating time goes on. Recently the modified fuel is being developed as one of solutions for lower ROP set point in CANDU6 reactor. The standard 37 element fuel bundle of CANDU6 has the same size fuel pins. The center pin of the modified fuel is smaller than the others in order to improve the operating and safety margin. In this study the main reactivity coefficients were calculated to evaluate the effect on reactor physics characteristics by the modifying diameters of center pin