Icone15-10326 Experimental Evaluation of Ability of Relap5 and Drako[○!r] to Calculate Water Hammer With Phase Changes

Abstract

A proper calculations of loadings caused by water hammer (hydraulic transients) occurring in pipeline systems in nuclear power plants are very important issue according to systems viability, safety and reliability. Calculating the water hammer loadings on pipe sections according to the classical one-dimensional (1D) theory of liquid transient flow in a pipeline, and then transferring the results to strength analyses of pipeline structure (walls), is nowadays the most common calculation procedure used in Sweden. This procedure assumes that the respond of the pipeline structure to the pressure surges is quasi-steady -dynamic interaction between the fluid and the pipeline construction is set aside. For calculating the hydraulic loadings in the 1D domain so-called network programs are used -Relap5 and Drako are the representatives of this kind of programs which are the most commonly used in Sweden nowadays. As a third party accredited inspection body INSPECTA NUCLEAR AB reviews all calculations of water hammer loadings. A question of vital importance for the reviewer is the knowledge about the ability of the programs to calculate the loadings under different conditions. While Relap5 and Drako calculations of the loadings without phase changes have been investigated quite well, the ability of the programs to calculate the loadings when phase changes occur cannot be considered to be sufficient. The presented work shall be seen as an attempt to illustrate the ability of Relap5 and Drako programs to calculate the water hammer with phase changes. Some parametric analyses have been performed in order to investigate the influence of digitizing of time and space. All differences between the results obtained with Relap5 and Drako are discussed. The calculations are compared with experimental results. The experiments have been conducted at a test rig designed and constructed at the Szewalski Institute of Fluid-Flow Machinery of the Polish Academy of Sciences (IMP PAN) in Gdansk, Poland. The comparisons of calculated and measured pressure surges show significant differences between them. The discrepancies are discussed and conclusions are presented.