Development and Use of the CAFE-3D Code for Analysis of Radioactive Material Packages in Fire Environments

A computational fluid dynamics (CFD) based fire model has been successfully coupled to standard finite-element computer codes in order to permit design and risk analysis of radioactive material packages. The fire model, called Container Analysis Fire Environment (CAFE), is based on a three-dimensional finite volume formulation of basic fire chemistry and fluid dynamics. The fire model includes a variable-density primitive-variable formulation of mass, momentum, energy and species equations. Multiple chemical species and soot formation are included in the combustion model. Thermal radiation is modeled as diffusive radiation transport inside the flame zone and as view-factor radiation outside the flame zone. Turbulence is modeled with an eddy diffusivity model. The soot model can be optionally coupled to the diffusive radiation formulation with the use of the Rosseland approximation and the optical properties of soot. Currently the CAFE-3D code is coupled to the MSC P/Thermal computer code and the coupling to the ANSYS/Mechanical finite-element code is expected to be completed in the near future. The model is normally used to represent a fully engulfing pool fire typical of regulatory qualification conditions. Other fire positions and configurations, including fires with packages that have internal passages like those in some storage casks, can also be simulated. In order to permit analysis in a relatively short time on a standard engineering computer work station, the fire model runs periodically during a package thermal calculation to update local fire conditions. The frequency and duration of the fire update calculation is user controlled with preset time and/or temperature increase criteria. This paper outlines the key features of the CAFE-3D code and presents examples of its use. Typical fire finite volume grids are described and the methods of surface coupling to the finite element codes are also discussed