An Alternative Method for Thermal Plume–Induced Aerosol Release and Deposition Calculations in Large Geometries Using fireFoam

Abstract

Being a particle physics laboratory, the European Organization for Nuclear Research (CERN) plans, constructs, and maintains installations emitting ionizing radiation during operation. Activation of present material is a consequence. Hence, fire scenarios for certain CERN installations must take into account the presence of radioactive material. Releases of gaseous, liquid, or solid combustion products, e.g., attached to aerosols, are taken so far into account by a worst case approach. Scenarios taking place in underground installations assume hence a smoke transport coefficient of 100% of release toward the surface level, independent of the local geometry. For a radioactive inventory identified in a certain fire load, this results in a conservative release.

To overcome this conservative worst case approach, a computational fluid dynamics model based on FM Global’s fireFoam 2.2.x is proposed. Its Lagrangian library was modified in order to provide aerosol release and deposition information based on more detailed interaction data between Lagrangian particles and their surrounding geometry. Results are shown for a CERN-typical large-scale experimental cavern placed 100 m below surface level. A simple diffusion burner is modeled inside the cavern to create a thermal plume emerging from a 1.5-MW fire over 14 min. Lagrangian particles are used to model aerosols with an aerodynamic diameter of 1, 10, and 100 μm, injected into the emerging thermal plume. Results for particle release and deposition vary according to aerodynamic diameter. In the present case, maximums of ~32% and 39% are found for 1- and 10-μm particles, respectively, being released to the surface level.

Keywords:

• Fire
• computational fluid dynamics
• aerosol transport

Acknowledgments

This work was mainly funded by the German Federal Ministry of Education and Research, providing a 3-year scholarship within the Wolfgang-Gentner-Programme at CERN. Further contribution in terms of funding and computational resources has been made possible by the Institute of Process Equipment and Environmental Engineering, Department of Process Design and Safety, Otto-von-Guericke-University Magdeburg, the CMS collaboration at CERN, and the CERN radiation protection group.

Special thanks are due to the FM Global fireFoam team, in particular P. Chatterjee and K. Meredith; the CERN CFD team past and present members; and D. Christ and H. Jasak, Wikki Ltd., for their patient help in understanding OpenFOAM code and providing the interaction submodel.

A great help was also Openclipart.org, making available the small flame used in Fig. 1 (Ref. 29).

Notes

^a The original nRebound interaction submodel for the Lagrangian particle library has been written by D. Christ, Wikki Ltd., London, United Kingdom, commissioned by the authors.