CANDU-6 reactivity devices optimization for advanced fuel cycles - Part I: Adjuster rods optimization

We develop a method to optimize the adjuster rods of CANDU-6 reactors for pre-selected thorium-based cycles. The objective is to ensure that the reactivity devices requirements of the natural uranium cycle during normal and accidental situations are maintained with minimal modifications to the reactor regulating system, while maximizing the fuel management advantages of advanced cycles. An equivalent approach, based on DRAGON and DONJON simulations, is used to match the compensation period offered by the nominal devices after a reactor trip or during a fueling machine breakdown. A constrained geometrical approach combined with cadmium doping of the rods is coupled with a time-average fuel management method to optimize the average exit burnup of the cycles under these constraints. The results demonstrate that our approach is efficient for increasing or decreasing the adjusters reactivity worth, while achieving excellent fuel management performances.