A New Reactivity Control Approach for Circulating Fuel Reactors

Molten Salt Reactors (MSRs) are nuclear power systems conceived to be working with a circulating salt-mixture, acting simultaneously as fuel and as coolant, providing safety and sustainability enhancements, other then improvements in the fuel cycle closure. The presence of a circulating fuel features not only the possibility of a continuous Fission Products (FPs) removal, but implies also the chance to perform tailored intervention on the fuel isotopic composition, adjusting the mixture as needed. These peculiarities prevent the adoption of commonly available simulation tools, which are designed for solid-fuelled reactors and lack in general the possibility to account for mass exchange processes within burn-up calculations. To overcome these limitations, a Serpent-2 extension is presented to couple depletion calculations and material transfer, thus featuring the capability to simulate FPs removal and continuous composition adjustments for both reactivity and eutectic control in MSR. The reactivity control is implemented with a new strategy allowing the independence from the chosen fuel treatment strategy and a limited impact on both the system mass and the eutectic proportions. The new implemented functionalities are verified and proven to work correctly, while the new reactivity control strategy is compared to an alternative one from previous studies, proving the superior performances of the new proposal