A study on the evolution of flame height and air entrainment volume rate for typical electrical cabinet fires in nuclear power plants

Electrical cabinet fires represent a significant threat to the operational safety of nuclear reactors. Despite numerous experimental and numerical studies that have explored the evolution of cabinet fires, the modeling of flame height has not received adequate attention which is crucial for fire risk assessment and the design of fire systems in nuclear power plants (NPPs). This pioneering work investigates the flame height and air entrainment volume rate for typical electrical cabinet fires in NPPs based on the Fire Dynamics Simulator (FDS) by considering different heat release rate (HRR) and top vent sizes (d). The results show that the bottom flame morphology inside the cabinet will change from square to rectangular, along with a consistent reduction in flame height. An increase in d correlates with a decrease in flame height. By introducing an equivalent rectangular fire source with dimensions of A × B, it is found that dimensionless flame height (Lf / B) has a power correlation with dimensionless air inflow volume rate (V̇a/Sṁf/ρa) of −2/3. Moreover, the analysis reveals that the air entrainment volume rate, namely the air inflow volume rate (V̇a), is positively correlated with both HRR and d. The dimensionless analysis indicates that V̇a/Sṁf/ρa is proportional to the dimensionless HRR (Q̇B∗) to the power of −2 and the vent area (A2/A1) to the power of 0.36, respectively. Consequently, a flame height model dependent solely on HRR and d is established. The proposed model for electrical cabinet fires will enhance the fire risk evaluation methodologies in the nuclear industry.