Monte Carlo calculations of eigenvalue sensitivities to system dimensions - 5-13

A Monte Carlo method is developed that computes sensitivities or derivatives of the k-eigenvalue with respect to interface boundary locations for uniform expansions or contractions. The method is implemented in a research version of MCNP6 and its results are compared with reference solutions obtained from equivalent multigroup calculations with PARTISN (discrete ordinates) and direct Monte Carlo perturbations. The test problems involve finding the sensitivity of the radius of a bare uranium sphere, the interface location of a reflected uranium sphere, and the radii of plates in the Zeus benchmark. The results match within 5% except for the radii of the thin uranium plates, which agree to within about 10%. (authors)