"OECD/CSNI ISP 20: post-test calculations and sensitivity analyses by RELAP5/MOD2 performed with reference to the SGTR accident occurred at DOEL-2 NPP"

The document deals with the description of results obtained by two Relap5/mod2 code version in the post test open simulation of a transient actually occurred in an existing Nuclear Power Plant (NPP), i.e. the Dole NPP in Belgium. 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 Doel NPP is a two-loop Westinghouse Pressurized Water Reactor (PWR) The concerned accident, following the availability of information of the Belgian owner of the NPP was selected by Organization for Economic Cooperation / Nuclear Energy Agency / Committee on the Safety of Nuclear Installations (OECD/NEA/CSNI) as International Standard Problem 20 (ISP 20). The document describes the results of the post-test calculation submitted (by UNIPI) to OECD after the occurrence of the accident and knowing the measured data. The accident was originated by the rupture of one tube in one of the two Steam Generators and is classified as a Steam Generator Tube Rupture (SGTR). The accident occurred during the heat-up period for the NPP following a scram: the core power was at ‘decay’ level and the initial pressure was close to the nominal pressure (15 MPa). The activity is relevant because addresses the scaling capability of the adopted computational tools: in this case there is no scale parameter in-between the measured data and the data expected in the reference prototype (i.e. the accident occurred in the prototype)