Pre- and post-test calculations to natural circulation experiments at the integral test facility ISB-VVER using the thermalhydraulic code ATHLET

In 1995 at the integral test facility ISB-VVER in Elektrogorsk near Moscow natural circulation experiments were performed, which were scientifically a ccompanied by the Forschungszentrum Rossendorf. These experiments were the first of this kind at a test facility, which models VVER-1000 thermalhydrau lics. Using the code ATHLET which is being developed by 'Gesellschaft fur A nlagen und Reaktorsicherheit', pre- and post-test calculations were done to determine the thermalhydraulic events to be expected and to define and tun e the boundary conditions of the test. The conditions found for natural cir culation instabilities and cold leg loop seal clearing could be confirmed b y the tests. Besides the thermalhydraulic standard measuring system, the fa cility was equipped with needle shaped conductivity probes for measuring th e local void fractions. (C) 1999 Elsevier Science S.A. All rights reserved.