The guidance for human factors validation of non-safety upgrades is limited. The NUREG-0711 review guide provides comprehensive guidance suitable for new builds or large-scale safety upgrades. Consequently, modernization projects must tackle several challenging questions regarding independence of evaluators, sufficiency and realism of test scenarios, performance measures and the identification of Human Engineering Discrepancies (HEDs). This paper presents a graded approach to human factors integrated system validation applied in turbine control system upgrade and control room modernization at four nuclear units at three Duke Energy sites. Targeted test scenarios with expert assessment, expert observations, simple rating scales and crew scenario interviews provided an approach that adequately could identify human performance aspects of the upgrade. Consistent results between performance measures and expert observations supported confidence in the approach. The upgrade project and operations management found the HEDs identified relevant and dispositioned the identified HEDs satisfactorily suggesting that the approach provided meaningful and useful results. The approach presented can be adapted and applied to other upgrade projects. The technical aspects of Duke’s Fleet Digital Upgrade Program and Control Room Modernization, and the fleet-level HFE Program developed by the Idaho National Laboratory, are the subject of separate, related papers.