Nuclear data sensitivity and uncertainty analysis of effective neutron multiplication factor in various MYRRHA core configurations

Abstract

A sensitivity and uncertainty analysis was carried out to estimate the uncertainty in the neutron multiplication factor keff and to identify the most important nuclear data for neutron induced reactions for criticality calculations of the latest MYRRHA designs. Sensitivity profiles, i.e. sensitivity to the nuclear data as a function of incoming neutron energy, were derived for both a critical and sub-critical core. They were calculated using codes that are based on different methodologies including stochastic and deterministic calculations (i.e. SCALE, MCNP and XSUN). The neutron induced nuclear data sensitivity analysis outlined the following quantities to be of special importance for the MYRRHA reactor concept: 239Pu(n,γ) both in resonance and fast energy region, (n,f) fast, χ and ν fast; 238U(n,n′) fast, (n,γ) resonance and fast, (n,n) resonance and fast; 240Pu ν fast; 238Pu(n,f) both resonance and fast; 56Fe(n,γ) both resonance and fast. Differences of less than 4% between codes were obtained for these quantities, with few exceptions (238Pu(n,f), 238U(n,n) and 56Fe(n,γ) reactions). Nuclear data covariance matrices of different libraries (SCALE-6, COMMARA-2 and JENDL-4.0m) were used to derive the uncertainty in keff based on the calculated sensitivities. This study reveals that the largest contributions to keff uncertainty result from the uncertainty in the average prompt neutron fission multiplicity of 239Pu, in the 238U inelastic scattering cross section and 239Pu fission cross section, using the covariances from SCALE-6, COMMARA-2 and JENDL-4.0m, respectively.