A Framework for handling Sodium Pool Fires for Fire Risk Assessment in Small Modular Reactors.

Internal fires remain a major contributor to overall plant risk in nuclear power plants (NPPs), reinforcing the importance of fire probabilistic risk assessment (PRA/PSA) for informed design and regulatory decisions. Originally developed under the Light Water Reactor Sustainability (LWRS) Program, the Fire Risk Investigation in 3D (FRI3D) framework provides a unified 3D environment for modelling and assessing internal fire scenarios using Fire Dynamics Simulator (FDS) and CFAST coupled with codes for cable failure analysis based on Nuclear Regulatory Commission Reports (NUREG-2178, NUREG-6931 along with a database of validated Heat Release Rates for the most sources. This paper presents a methodology for extending FRI3D to evaluate sodium pool-fire scenarios in liquid-metalcooled Small Modular Reactors (SMRs). The approach does not model sodium combustion through physics directly but employs heat-release-rate (HRR) curves and sodium burning rates derived from experiments and software such as that found in the SOFIRE-II simulations. The resulting HRR profiles represent the effective thermal power of sodium pool fires and serve as source terms for CFAST (to capture enclosure and ventilation effects) and FDS (to resolve convective and radiative heat transfer). The workflow automates mapping of sodium spill geometries from CAD/BIM models, configuration of HRR boundary conditions, and visualization of resulting temperature and heatflux distributions within FRI3D's 3D interface.

Keywords: Sodium pool fire; Fire PRA; Small Modular Reactors; FRI3D; CFAST; FDS..