IAEA SPE-4: Pre-test calculations jointly performed by the University of Pisa and the University of Zagreb

The document deals with the description of results obtained by Relap5/mod2 code in the pre-test blind simulation of an experiment performed in the VVER (water cooled- Water Moderated Energy Reactor) experimental simulator PMK-NVH installed at the Budapest Atomic Energy Research Institute in Hungary. The Relap is the well-known computer code developed at Idaho National Laboratory in US: the code is in use at UNIPI since more than a decade. The PMK-NVH loop is an Integral Test Facility (ITF) simulating with reduced height, full pressure, modulated linear power a Russian (Gidropress) type VVER-440. The concerned test was selected by International Atomic Energy Agency (IAEA) as Standard Problem Exercise 4 (SPE 4). The document describes the results of the pre-test calculation submitted (by UNIPI) to Hungary before the execution of the test. The activity is part of the SPE documentation (issued as IAEA report) and allows an objective evaluation of the capabilities of the computer code and of the code user team in predicting the scenario of an accident. This is relevant for demonstrating the capabilities in evaluating safety margins of existing NPP, with main reference to VVER (present case)