Interpretation of local flux measurements for reactivity prediction

The inverse point kinetic is usually used for the reactivity monitoring in nuclear systems due to its simplicity and easiness of use. Nevertheless, space and energy effects affect the reliability of these techniques based on a point-like behavior of the reactor; therefore it is necessary to improve the accuracy of reactivity predictions when large space effects are present. A method of impor- tance weighting on local flux signals has been recently developed to account for spatial effects and improve the accuracy of a reactivity reconstruction technique. A global signal can be obtained through an adjoint-flux-based weighting of local measurements and it is then used in the interpre- tation algorithm; it has been shown that the reactivity prediction can thus be improved, due to the richer information on the system provided by this global signal. To better evaluate the extent of the improvement in the reactivity prediction that can be attained with this technique, in the presentwork it is applied to the analysis of pulsed source transients simulated by MCNP for a lead-cooled fast subcritical system, considering detectors at various positions in the system. Transient signals from detectors are generated and then combined with the importance weighting, while the reactivity is reconstructed adopting the MArTA method.