Analysis and evaluation of Groeneveld-Stewart correlation uncertainty in calculation of minimum wall wetting temperature
Based on comparison with results of reported experiments, the author has performed an uncertainty evaluation of the Groeneveld-Stewart correlation that is used as a closure relation in computer programs designed for thermal-hydraulic calculations - computer codes - for estimation of minimum wall-wetting temperature. The evaluation has shown that this correlation gives a conservative estimate of the mentioned parameter for the saturated water line and vapor-water flow. The paper analyzes the influence that the correlation development methods and assumptions (indirect sources of uncertainty) have on quantified discrepancy of calculation and experiment (RMS deviation). Results of mathematical analysis are used to develop a modified Groeneveld-Stewart correlation that would reduce the discrepancy for the subcooled water region. The paper addresses the problem of what software and technology should be used to account for indirect sources of uncertainty of multi-factor closure relations in calculations by the GRS statistical method. A specific proposal of how to include this correlation uncertainty calculation in the KORSAR functional software is made. The KORSAR code and PANDA programs and GRS method have been used to analyze numerically the effect of the Groeneveld-Stewart correlation uncertainty on calculation of the peak-clad temperature for the VVER-1000 LB LOCA scenario. It is found that consideration of the correlation uncertainty in this scenario leads to about 1000С deviation in the calculated parameter value.