[en] The sensitivities of a mixed oxide (2Wt%PuO₂ - 8% ²⁴⁰Pu) fueled, light water moderated critical lattice experiment carried out at Battelle Northwest Laboratories under EPRI sponsorship have been determined. A two-dimensional diffusion theory analysis was performed and the sensitivity of the eigenvalue (k) and four reaction rate ratios to changes in nuclear data have been determined. The sensitivity analysis capability was extended to include upscattering and multi-dimension ability. A covariance matrix has been developed for ²³⁹Pu, and the uncertainty associated with calculated performance parameters due to uncertainties in nuclear data has been obtained