OECD/CSNI ISP 33: Post-test analysis of the PACTEL natural circulation experiment performed by CATHARE 2 v1.3E Code", OECD CSNI Final Workshop on ISP 33 - Lappeenranta (SF), May 17-20, 1993

The document deals with the description of results obtained by the Relap5 code in the post-test simulation of the Natural Circulation (NC) scenario / experiment performed in the Russian Pressurized Water Reactor (WWER = Water cooled, Water Moderated Energy Reactor) experimental simulator PACTEL installed at the Lappenranta University Research Center in Finland. The Relap5 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 PACTEL I a scaled down Integral Test Facility (ITF) simulating with full height, full pressure, full linear power a Russian type 6-loops WWER-440. The concerned test was selected as International Standard Problem 33 (ISP 33) by OECD/NEA/CSNI (Organization for Economic Cooperation and Development / Nuclear Energy Agency / Committee on the Safety of Nuclear Installations). The document describes the results of the post-test calculation submitted (by UNIPI) to Lappeenranta University after the execution of the test. This is called open post-test analysis: the comparison of about 40 calculated time trends with measured data allows an 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 WWER-440 (in this case).