Post-test analysis performed by Relap5/mod3.2 code of the Bethsy test 6.9c (OECD/CSNI ISP 38)

The document deals with the description of results obtained by the Relap5 code in the post-test simulation of the shutdown-simulation experiment performed in the Pressurized Water Reactor (PWR) experimental simulator BETHSY installed at the CEA-CENG Research Center in France. 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 BETHSY is a medium-large scale Integral Test Facility (ITF) simulating with full height, full pressure, full linear power a French type PWR. The concerned test was selected as International Standard Problem 38 (ISP 38) 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 CEA (French Atomic Energy Commission) after the execution of the test; however the calculation results submitted before the execution of the test are discussed. This is part of post-test analysis: the comparison of about 60 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 PWR accident management situation (in this case)