IRSN, Institut de radioprotection et de sûreté nucléaire

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Calculation software system SYLVIA

Software System for Analysing the Ventilation of a fire
and Aerocontamination

The SYLVIA software system, developped by IRSN, simulates the consequences of a fire in an industrial facility featuring a ventilation network. It calculates the development of the fire, the transportation of hot gases and soot, the resuspension and the transportation of aerosols, whether radioactive or not, the clogging of filters and the damage of isolating equipment such as firebreak doors and fire dampers.

The SYLVIA software system simultaneously processes all of the different phenomena brought into play (fire, ventilation, airborne contamination). 

The SYLVIA software system is the reference fire calculation tool used at the IRSN for evaluating the safety of nuclear facilities; it more particularly allows the hundreds of simulations associated with probabilistic safety studies to be performed.

Physicals models  
Modelling of the fire is a zone-based approach: the volume of each room is divided into two zones of variable height in which the thermodynamic properties (pressure, temperature and concentration of the gaseous and particulate species) are uniform, the upper zone containing the hot gases and soots.

The ventilation network is modelled using a set of elements, conduits, filters, valves, fans, etc. Mass and heat exchange correlations (between zones, flames and walls) supplement the mass and energy balance equations for the zones. The rates of putting into suspension and deposition of the aerosols on the walls of the rooms and in the ventilation network are also estimated. 

Constant attention is paid to system validation, particularly on the basis of the numerous full-scale tests performed by the IRSN.
Sylvia uses simplified models to reduce the computing time, but these models are robust enough for reliable safety support studies. For more complex computations, it can be coupled with the ISIS software.

A flexible and user-friendly system

A HMI (human machine interface) facilitates data entry by the user, checks data consistency and relevance and allows graphic post-processing of the calculation results.

When coupled with the Sunset software, the IRSN's uncertainties propagation tool, the SYLVIA system enables parametric and sensitivity studies to be carried out thanks to the usually very short calculation time of applications.

When coupled with the Isis software, a CFD (Computer Fluid Dynamics) tool for fire simulations developed by IRSN and available under an open-source license, Sylvia not only benefits from the accuracy provided by the 3D simulation of the fire progression (in the room analyzed with ISIS), but also from its own capacity to describe a complete ventilation network.
Implementation et portability

Implementation of the SYLVIA system is based on the PELICANS software components platform developed at the IRSN and available under an open-source license (

The Sylvia system is portable under Linux (64 bits) and Windows 7/10 (64bits).



New developments in progress on the Sylvia software include the improvement of the radiation model to take obstacles into account and interact with neighboring facilities, the development of a phenomenological clogging model and the creation of an application specifically for engineers in charge of fire prevention.
Constant efforts are made to improve the combustion models of complex solid fire sources (glove boxes, electrical cabinets, cables trays, waste packages, etc.).

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Access to SYLVIA

SYLVIA is distributed to industrial companies under a paying license, and can be made available free of charge to university organizations in the framework of specific contracts.

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