Fire safety of nuclear power plants
Our work in fire risks assessment of nuclear power plants is based on the combination of advanced numerical simulations with statistical and empirical data.
Fires represent a significant portion of the accident risk of nuclear power plants. We provide tools for assessing the fire risks by combining the advanced numerical simulation technologies with empirical knowledge in a probabilistic framework.
By combining large fire spread simulations to Monte Carlo technique, we can evaluate the probabilities of the consequences of the fire. These results have been used as a part of the Probabilistic Risk Assessment of Finnish nuclear power plants.
We have assessed the performance of modern, flame-retardant electrical cables for the construction of new power plants and upgrade of the existing ones. Smoke spreading analyses have been carried out to understand the effects of transformer and pump fires.
A specific class of applications are the aircraft impact fires. VTT has created experimental techniques to characterize the aircraft fuel spray and can apply the gathered information in full-scale analysis of aircraft impact fire analyses for thermal impact, smoke penetration and liquid pooling.
We can evaluate the efficiency of different defense-in-depth levels from the ignition prevention, early detection and suppression to the manual suppression, consequence mitigation and fire spread control. Fire simulations can be coupled with structural analyses to evaluate the fire barrier performance.
Developing tools for fire safety research
We develop several tools for the quantitative fire hazard assessment. Internationally most significant work is related with Fire Dynamics Simulator (FDS), where we develop the pyrolysis, liquid pool fire and suppression models. Input parameter uncertainty can be taken into account with a self-developed Monte Carlo engine, Probabilistic Fire Simulator (PFS), which also has an interface with deterministic fire models.
Pyrolysis modelling requires many input parameters that can be estimated from small and bench scale experiments using a tool called Pyroplot. Stochastic Operation Time Model (SOTM) evaluates computationally the efficiency of fire service and other personnel operations.
Tool development takes place in Finnish national programmes for NPP safety and international co-operation.