An application of an automated procedure called GRESS for adding derivative-taking capability to FORTRAN computer codes is presented. The efficiency and usefulness of GRESS for enhancing the point depletion and radioactive decay code ORIGEN2 are discussed. A new version of ORIGEN2 is now available that has the capability of calculating first derivatives and sensitivities of any variable in the code with respect to any other variable. The capabilities of the enhanced version, ORIGEN2G, are exemplified by its use in a sensitivity study of a high-level nuclear waste disposal problem. By using GRESS, the enhanced version ORIGEN2G was produced, tested, and verified in 2 man-months compared to an estimated 1 to 2 man-yr of effort to program a code with comparable capabilities.