Evaluation of Internal Fire Hazards in Indian Nuclear Power Plants

In Nuclear Power Plants (NPPs), Structures, Systems and Components (SSCs) are grouped/ ranked on the basis of their function and their significance for safety. However, failure due to common cause such as fire may simultaneously affect the redundant SSCs and their support systems such as air supply, power supply or cooling water supply. All foreseeable internal hazards and external hazards, which may affect the safety of the nuclear power plant directly or indirectly due to common cause failure, are identified and their effects are evaluated. The NPP design takes into account effects of various internal hazards such as internal fire, internal flood, missiles due to rotating equipment, jet impact, pipe whip, structure collapse and falling objects, etc. Defence in Depth (DiD) Philosophy is being followed for fire protection of NPPs. Safety related SSCs are designed and are installed in such a way that it reduces the risk of fires. Emphasis is on providing passive and active fire protection. Fire Hazard Analysis (FHA) of the NPPs is carried out by using Fire Containment approach and Fire Influence Approach. Wherever, redundant items important to safety are placed in different fire compartments, analysis is carried out using containment approach and required rating for passive fire barriers is estimated in FHA. In situations where separate fire compartments cannot be provided to segregate safety related SSCs, analysis for influence of fire on other redundant equipment is carried out using quantitative FHA methods or multi-compartment two zone models or Computational Fluid Dynamics (CFD) techniques. The time to damage estimated in FHA is used as an input for fire probabilistic safety analysis studies. This paper is about fire hazards in NPPs, fire protection philosophy and the methodology for evaluation of internal fire hazards. Further two case studies are also presented.