Experimental study on the blowdown load during the steam generator feedwater line break accident in the evolutionary pressurized water reactor

Integral effect tests using the ATLAS facility were performed to obtain the thermal-hydraulic parameters such as dynamic and static pressures, local temperatures, and flow rates during a feedwater line break of a steam generator. The break of a feedwater line was simulated using a double rupture disc assembly in order to satisfy the requirements for the break opening time of around a few milliseconds. In the present study, estimated break opening time was less than 1.5 ms and broken areas were 48.1% and 93.4% of the feedwater line, respectively. The maximum dynamic pressures of about 1.57 bar were obtained inside of feedwater box that was closest to the break location of the feedwater line. After the break of the feedwater line, propagation of the pressure wave along the distance from the break location inside the steam generator was clearly and pertinently observed in all the tests. From a structural integrity point of view, however, the risk induced by this maximum dynamic load could be treated to be insignificant. Based on the present experimental data, an analysis was performed using the best-estimate thermal-hydraulic system code, MARS 3.1 with an aim of qualitatively validating the test results and also evaluating the blowdown load prediction capability of the best-estimate system code in the simulation of steam generator feedwater line break. Calculation results on overall trends of the dynamic pressure behavior are comparable with the test results which indicate the feasibility of dynamic load prediction using the MARS code. As the break opening time became shorter and the broken area became larger, the dynamic pressures were calculated to be significant values in the sensitivity analyzes. (C) 2011 Elsevier Ltd. All rights reserved.