Development of sensitivity calculation capability of Legendre moments of scattering angular distributions in NECP-MCX

The capability of sensitivity coefficients calculation of keff and reaction rate ratios to Legendre moment of scattering angular distributions based on a fully continuous method has been developed in the Monte Caro code NECP-MCX. The sensitivity calculation was based on Iterated Fission Probability (IFP) and Contributon-Linked eigenvalue sensitivity/Uncertainty estimation via Track-length importance Characterization (CLUTCH) method for k-eigenvalue sensitivity analysis and Generalized Adjoint Responses in Monte Carlo (GEAR-MC) method for generalized sensitivity analysis. The Jezebel and Flattop problems are analyzed and the sensitivity results calculated by NECP-MCX are compared with those by Serpent and ERANOS to demonstrate the accuracy of NECP-MCX. In addition, the CLUTCH-FC (CLUTCH coupled with forced collisions) method is implemented to reduce the variance of sensitivity coefficients of Legendre moment of scattering angular distributions with relatively small scattering cross sections. The numerical results indicate that 1) the sensitivity coefficients calculated by NECP-MCX agree well with those by Serpent and ERANOS, and 2) the CLUTCH-FC method is efficient in reducing the variance of sensitivity coefficients of Legendre moment of scattering angular distributions with relatively small scattering cross sections. The Figure of Merit (FOM) values of sensitivity coefficients calculated by the CLUTCH-FC method have increased by 1.9~306.0 times for Jezebel and Flattop problems compared to those calculated by the CLUTCH method.