Recently, the fire protection programs at nuclear power plants (NPP) have been under a gradual transition from a deterministic, prescriptive approach to a Risk-Informed, Performance-Based (RIPB) approach based on NFPA 805. In the NFPA 805 transition, as a basis for Fire Risk Evaluation (FRE), a plant-specific Fire Probabilistic Risk Assessment (Fire PRA) is utilized by each NPP. In this research, an Integrated PRA (I-PRA) methodological framework for Fire PRA is developed to provide a unified multi-level probabilistic integration, beginning with spatio-temporal simulation models of underlying failure mechanisms (i.e., physical phenomena and human actions), connecting to component-level failures, and then linking to system-level risk scenarios in classical PRA. The simulation-based module, called the Fire Simulation Module (FSM), includes state-of-the-art models of fire initiation, fire progression, post-fire failure damage, fire brigade response, and scenario-based damage. Fire progression is simulated using a Computational Fluid Dynamics (CFD) fire model, i.e., Fire Dynamics Simulator (FDS) developed by National Institute of Standards and Technology (NIST), which numerically solves Navier-Stokes equations governing the turbulent flow field. Uncertainty propagation is performed to propagate parameter uncertainties and to characterize the uncertainty associated with the risk outputs. The I-PRA paves the way for reducing excessive conservatisms existing in the current Fire PRA, derived from (i) the modeling of fire progression and damage and (ii) the interactions between fire progression and manual fire suppression. The ongoing research focuses on several key elements in the Fire I-PRA framework: (a) developing a computational platform for modeling and quantifying dependent failure using simulation outputs; (b) advancing theory, methodology, and computational platform of uncertainty quantification; (c) creating an explicit interface between fire progression and manual fire suppression; and (d) connecting the FSM to a realistic plant PRA model.