Influence of heat losses and accumulated heat upon the accident process evolution

Studies of accident processes in the primary circuit of nuclear power plants are limited to experiments at scaled mockups-test facilities. Presently, it is the common understanding that only the qualitative reproduction of the phenomena being studied is possible when simulating the accident processes at these test facilities. More or less, correct modeling of the reference nuclear power plant is possible only through use of the computer codes based on the mathematical models of the two-phase flows using numerous empirical correlations. Test facilities are being used for validation of these computer codes. In the case of an accident process, it is crucial that simulations at the test facilities correctly account for ambient heat losses and accumulated heat because both under- and over-estimation of these factors might lead to the significant distortion of the whole accident process being simulated. The EREC operates two integral test facilities simulating the primary circuit of the Russian designed pressurized water reactor WWER-1000. This paper deals with two experiments performed at the ISB-WWER Integral Test Facility which is the ERE's pilot test facility. The ISB- WWER simulates the reference reactor WWER-1000 with a volumetric power scale of 1:3000. All the elevations are kept to a 1 : 1 scale. The primary circuit of the ISB- WWER consists of intact and broken loops that are connected to the reactor model. These two loops are simulating four loops of the reference NPP with WWER-1000 reactor. The loops' mass flow rates ratio is 1:3. The reactor model consists of the downcomer, the core simulator, the by-pass section and the upper plenum. The facility is designed for operations at a maximum pressure of 25 MPa and a core simulator power of 1.8 MW. (authors)