The evaluation of proposed plant modifications combines deterministic safety analysis focusing on design basis accidents and Probabilistic Safety Analysis (PSA) for beyond-design basis scenarios. While deterministic acceptance criteria must be met before and after plant modifications, modifications do affect safety. This paper discusses a study performed to quantify this impact, within the frame of the Safety Margin Analysis and Application (SM2A) task. For a hypothetical 10% power uprate for a Pressurized Water Reactor, the study focuses on the Small and Medium Loss of Coolant Accident (SLOCA and MLOCA) scenarios. A reduction of bounding assumptions and the explicit treatment of uncertainties in the accident sequence thermal-hydraulic analyses are key aspects of the SM2A analyses, which use elements of "best estimate plus uncertainty" deterministic safety analysis. An explicit treatment of the distribution of the time to switch to recirculation mode is one of the main features of the MLOCA analysis. The results demonstrate that the SM2A methodology is capable of quantifying small changes in the core damage frequency (CDF), which the bounding approach in PSA might mask. In addition, they underscore a need to address aleatory uncertainties explicitly in some PSA accident sequence calculations.