Models and calculation hypotheses for hydraulics analysis of the fire extinguishing water system in Cernavoda NPP

Fire extinguishing system utilizing hydrants from Reactor Building is interfaced with the fire extinguishing system from the Service Building. The installation is permanently under 93 MPa pressure while the temperature is that of the environment. The installation consists of carbon-steel pipes with various diameters, insulations, fittings and interior fire hydrants. Regardless of the calculation scheme of fire in the turbine zone or fire in nuclear zone, the most unfavorable situations concerning the location of hydrants and rings distance to the water pumping station was considered. Calculation formulas for the hydraulic resistance are given as a function of equipment pressure loss, density and fluid speed through the equipment. PIPENET code was used for calculations in case of 90 angle bends and 45 angle bends and separate calculations were done for bends of other different angles in the system, Therefore, the total bend resistance coefficient was determined as a sum of the local resistance coefficients, and the distributed resistance coefficients. A description of PIPENET code for flow of single phased fluids, both gases and liquids is given. Its features are: - Large number of input and output values; - Nets comprising any ramification and loop arrangement; - Systems in closed loop or open loop; - Incompressible and compressible fluids; - Fixed and variable temperature fluids; - Fittings and pipe dimensions according to catalogs, or specially defined by the user. The section 4 describes creation of a PIPENET network consisting of pipes, tubing, pumps, vents, filters, etc. and the links between them. Finally, a description of the calculation model for the reactor building is given