ANALYSIS OF THE COOLANT DENSITY REACTIVITY COEFFICIENT IN LFRs AND SFRs VIA MONTE CARLO PERTURBATION/SENSITIVITY

The coolant density effect represents one of the main reactivity feedback in LFR and SFR. These reactivity feedback effects are often calculated via direct perturbation in Monte Carlo codes. This work presents a new approach for reactivity coefficient calculations based on Perturbation Theory. New methods were implemented in a extended Serpent version and are here verified against reference results for spatial coolant reactivity maps. In the paper, a detailed investigation of the effect of the calculation parameters and the applicability range of the perturbation calculations is presented. The main advantage of the present approach is the capability of providing, within a single Monte Carlo run, several reactivity coefficients. This feature is demonstrated via the reactivity feedback decomposition in energy, space, isotope and reaction in the ALFRED lead cooled reactor case. The obtained decompositions suggest that the reactivity coefficient is the result of large opposite effect. A preliminary uncertainty quantification analysis shows that 208-Pb cross sections uncertainties have a large impact on keff estimates in the ALFRED reactor.