The BEAVRS benchmark problem describes detailed information such as the geometry and material specifications to construct a neutronic calculation model of a commercial Pressurized Water Reactor (PWR) core. The benchmark was modified several times; the main purpose of the current study is to investigate the effect of the modifications in the BEAVRS benchmark on sensitivities and uncertainties in cross section that in turn affect the multiplication factors and reactivity coefficients.
The sensitivity coefficients are calculated for keff due to perturbation in cross-sections using the KSEN card of MCNP6 code for the two cores, where all control rods are in and out. Since MCNP6 cannot calculate uncertainties, the NJOY2021 was used to compute the relative covariance matrices of the cross-sections data library, thereafter, a python script was developed to calculate the uncertainties of keff as well as sensitivities and uncertainties of reactivity due to the control rods insertion. The results indicate that the uncertainties in reactivities caused by control rods insertion for the BV2 model is greater than the BV1 model, due to the effect of using higher coolant density in the nozzle and support plate structures in addition to the effect of the burnable absorber designs in the BV2 model.