Reduced scope modelling of nuclear power plants’ ventilation system and its interaction with fire.

A fire in a confined but mechanically ventilated environment
(CMVE) behaves differently from an open environment which has
unlimited air supply. CMVEs are typical of nuclear power plants,
where complex ventilation networks enable pressure cascades to
ensure the confinement of gaseous and particulate releases during accidents or fires. When a fire happens in a CMVE, pressure
increases due to hot gas expansion, which can alter the ventilation conditions. Altered ventilation changes the dynamics of the availability of fresh air or exhaust of smoke to fire, leading to a change in the fire’s heat release rate. To correctly estimate the heat release
rate of a fire through simulations, it becomes of the utmost importance that one has a reliable ventilation system model so that
it correctly interacts with a fire. At times, the lack of data on ventilation system specifics hinders building a reliable ventilation system model for simulations. In such cases, one has to rely on the
test data to extract values and parameters for a simplified ventilation system model. This work presents a systematic approach to finding required values and parameters for reduced scope modelling of a ventilation system such that the interaction of a ventilation system with a fire can be reliably studied. CFD-based Fire Dynamics Simulator software has been used, and a test case has been taken from the OECD NEA FAIR project. The test case has a fire in a compartment, leading to pressure variation and consequent change in volumetric flow rates in ducts. From the test data, a ventilation system with a reduced scope has been built, which led to satisfactory pressure development and volumetric flow rates in ducts in simulation compared to actual test results.