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Enhancing Nuclear Safety

SYLVIA computer code system[Computer Code system to study fire ventilation and airborne Contamination]

The SYLVIA software system simulates the consequences of a fire in an industrial facility equipped with a ventilation network. It calculates the progression of the fire, the transport of hot gases and soot, the resuspension and transport of radioactive aerosols, the plugging of filters, and any damage to fire compartmentalisation equipment such as fire doors and dampers.SYLVIA is the reference calculation tool at IRSN that is used in support of nuclear faci-lity safety assessments. It is especially used to conduct hundreds of simulations that are required as part of probabilistic safety assessments.

Implementation and portabilitySYLVIA is implemented via the PELICANS platform of software components developed by IRSN and available under a free software licence (https://gforge.irsn.fr/gf/project/pelicans).LINUX, SOLARIS and Windows 2000/XP ensure the portability of SYLVIA.

Flexible and user-friendly SYLVIA simulates the various different phenomena involved (fire, ventilation and airborne contamination) either coupled or separately and on various different modelling levels. A Man-Machine Interface (MMI) simpli-fies user data input, is used to control data consistency and relevance, and generates graphics of the calculation results. When SYLVIA is coupled with SUNSET, an IRSN uncertainty propagation tool, parametric and sensitivity studies can be performed taking into account the usually very small computation time.

Physical modelsA two zone model is used to simulate a fire : the volume of each room is divided into two zones of variable height in which the thermodynamic proper-ties (pressure, temperature and concentration of gaseous and particle species) are uniform, with the upper zone containing hot gases and smoke. The ventilation system is modelled according to a series of components, pipes, filters, valves, fans, etc. Mass and heat exchange correlations (between zones, flame and walls) supplement the mass and energy balance equations for each zone. The aerosol resus-pension and deposition rates on room walls and in the ventilation system are also estimated. IRSN constantly works to validate the software, parti-cularly through the numerous large-scale tests it conducts.

Future prospectsOne of the key medium-term phases involves coupling SYLVIA to the 3D ISIS software which is designed to precisely simulate a fire. This software developed by IRSN is available under an open-source licence (https://gforge.irsn.fr/gf/project/isis). IRSN will thus benefit from the precision of a 3D simula-tion of a fire developing in a room covered by ISIS, together with the capacities of SYLVIA to describe an entire ventilation network. The combustion models used to simulate fires of complex equipment (glove boxes, electrical cabinets, electrical cableways, waste drums, etc.) are also improved on a constant basis.

SYLVIA software licenceSYLVIA is distributed under an open-source licence to industrial players and is made available to univer-sities free of charge within the scope of specific agreements.

Contactsylvia@irsn.fr.