The design of PSB-VVER experiments carried-out inside the TACIS contract N. 30303

Integral Test Facility (ITF) experimental programs are relevant for validating the Best Estimate (BE) Thermal Hydraulic codes (TH) used for transient and accident analyses, design of Accident Management (AM) procedures, licensing of Nuclear Power Plants (NPP), etc. The validation process is based on well designed experiments. It consists in the comparison of the measured and calculated parameters and the determination whether a computer code has an adequate capability in predicting the major phenomena expected to occur for transient and/or accidents. University of Pisa (UNIPI) was responsible of the numerical design of the 12 experiments executed in PSB-VVER facility, operated at Electrogorsk Research and Engineering Center (EREC), in the framework of the TACIS Contract 3.03.03 Part A. This paper describes the methodology adopted at UNIPI, starting form the scenarios foreseen in the final Test Matrix (TM) until the execution of the experiments. This process considers three key topics: a) the scaling issue and the simulation, with unavoidable distortions, of the expected performance of the reference NPP, b) the code assessment process involving the identification of phenomena challenging the code models, c) the features of the concerned ITF (scaling limitations, control logics, data acquisition system, instrumentation, etc.). An overview of all the activities performed in this respect is provided focusing the discussion on the relevance of the heat losses. This issue is particularly relevant for addressing the scaling approach related to the power and volume of the facility. (author)