Sensitivity and uncertainty calculations in support of the noise analysis of the TAPIRO reactor

In the framework of an assessment of the application of neutron noise methodologies to the TAPIRO reactor, sensitivity and uncertainty analyses on impacting nuclear data for this experimental reactor have been performed using the Serpent Monte Carlo code. Integral parameters relevant to the noise analysis of TAPIRO have been investigated, namely the effective multiplication factor, the effective delayed neutron fraction, the effective generation time and the prompt neutron decay constant. The nuclear data uncertainty has been assessed using different data libraries (ENDF/B-VIII.0 and JEFF-3.3), different energy grids (ECCO-33 and XMAS-172) and different techniques (Generalised Perturbation Theory and Unscented Transform). A ranking of the most impacting nuclides (235U, 63Cu, 65Cu and 238U) and reactions (elastic scattering, fission, radiative capture and fission neutron yield) in terms of uncertainties has been performed, pointing out that the impact of nuclear data uncertainties on the responses is non-negligible and must be taken into account when the noise analysis of the reactor is performed. In particular, the uncertainty on the value of the prompt neutron decay constant due to effect of the nuclear data uncertainties is larger than 100%, especially when the system under study is close to criticality.