Internal fires remain a significant contributor to overall plant risk in nuclear power plants (NPPs), underscoring the importance of fire probabilistic risk assessment (PRA/PSA) in supporting design and regulatory decisions. The Fire Risk Investigation in 3D (FRI3D) framework, originally developed under the Light Water Reactor Sustainability (LWRS) Program, provides an integrated 3D environment for modeling and analyzing internal fire scenarios. FRI3D couples fire modeling tools such as Fire Dynamics Simulator (FDS) and CFAST with cable failure models based on NRC guidance (NUREG-2178 and NUREG-6931), along with a validated database of heat release rate (HRR) profiles for common fire sources.

This work presents a methodology for evaluating smoke effects from sodium pool fires in a liquid-metal-cooled Small Modular Reactor (SMR) compartment using FRI3D. Rather than explicitly modeling sodium combustion physics, the approach utilizes experimentally derived sodium burning rates and HRR curves informed by tools such as SOFIRE-II. These HRR profiles are used as source terms in FDS simulations to represent the thermal behavior of sodium pool fires.

The resulting simulations provide spatial and temporal distributions of smoke optical density, which are used to assess operator visibility and habitability. These results are further visualized within FRI3D’s 3D interface, enabling enhanced interpretation of smoke propagation and its impact.