Effect of Reactor Model Modifications on the Sensitivity and Uncertainty of Keff and Reactivity

Mohga Hassan, Basma Foad

Abstract: In nuclear reactor physics models, a major source of uncertainty is cross sections uncertainties, which is dependent upon model specifications. The main objective of this work is to the study the effect of change in some reactor model details on the sensitivity and uncertainty of keff and reactivity. Modifications considered for keff sensitivity and uncertainty estimations are change in coolant density and burnable absorber design. Reactivity sensitivity and uncertainty is affected by control rod design modification. The KSEN card of MCNP6 code is used to calculate the sensitivity vectors for of 235U, 238U, and 1H, in two PWR cores with differences in design. NJOY2021 was used to compute the relative covariance matrices of the cross-sections data library. A python script was developed to read the MCNP and NJOY outputs, and to calculate the uncertainties of keff as well as sensitivities and uncertainties of reactivity due to the control rods insertion.

Keywords: Sensitivity, Uncertainty, NJOY, MCNP6