Results of TEMPA-SC Code Calculations of the IAEA Benchmark Exercise on Defining Stable Water Flow Boundaries at Supercritical Pressure in a Heated Pipe

One of the problems of innovative reactor plant (RP) with supercritical water SCWR is providing its operation stability. Mechanisms that cause instability are similar to those that occur in boiling-water reactors BWR. However, they may have some specific features concerning, for example, deteriorated heat transfer conditions and appreciably greater thermodynamic liquid nonequilibrium in the flow. Therefore the tasks of development and verification of computational methods and programs that would allow to define SCWR stability boundaries are urgent. Within IAEA Coordinated Research Project (CRP) «Heat Transfer Behaviour and Thermo-hydraulics Codes Testing for SCWRs» it was proposed to take the first step and to propose thermal-hydraulic codes testing on the basis of available data or data that are developed by CRP participants. The testing was realized comparing the results of different codes and computational methods, with the purpose to reveal possible mistakes and shortcomings, and to estimate possible range of computational results. Specifications of two benchmarks were prepared: - Benchmark Exercise No.1 «Steady state flow in a heated pipe» (hosted by OKB «GIDROPRESS»); - Benchmark Exercise No.2 «Stability» (hosted by University of Pisa, Italia). A circular pipe 4.27 m in length, inside diameter 8.4 mm and uniform heating was considered in Benchmark Exercise No.2. It was necessary to plot flow instability boundary of water and other liquids in the plane of dimensionless groups NSPC and NTPC that define, correspondingly, liquid underheating to pseudo critical temperature at heated channel inlet (sub-pseudocritical number) and liquid heating in the channel (trans-pseudocritical number). At the same time it was necessary to perform the analysis for various values of local coefficient of hydraulic resistance at pipe inlet, for vertical and horizontal flows. Calculations of Benchmark Exercise No.2 for vertical water flow were performed in OKB «GIDROPRESS» by thermal-hydraulic code TEMPA-SC. There was some difference between calculated boundaries of stable water flow and those obtained by methods based on linear stability analysis. This difference was increasing as local coefficient of hydraulic resistance at inlet was decreasing. Sensitivity analysis of TEMPA-SC calculation results to different parameters of the computational model was performed. Benchmark Exercise No.2 is described in the report. The calculation results of OKB «GIDROPRESS» and the results of linear stability analysis of the University of Pisa are presented.