Evaluation of sensitivity coefficients of effective multiplication factor with respect to prompt fission neutron spectrum

Nagaya, Yasunobu  ; Kodeli, I.*; Chiba, Go; Ishikawa, Makoto

This paper unveils that two types of sensitivity coefficients with respect to the fission spectrum exist: unconstrained and constrained sensitivity coefficients. The impact due to the difference of the coefficients has been investigated for the change in the effective multiplication factor and the uncertainty of the factor with respect to the fission spectrum. It is analytically shown that whichever of the sensitivity coefficients is used, the same result can be obtained. However, if the unconstrained sensitivity coefficient is used, the zero-sum constraint for the absolute covariance matrix must be satisfied with high accuracy in numerical applications.