Methodology for coupling thermal-hydraulic codes for primary system and containment analysis

The present report describes a coupling methodology adopted to link a nuclear reactor thermal-hydraulic primary system code to a containment system code, set up in the frame of task LP2- E.1 of the AdP PAR2008-09 assigned to CIRTEN. The codes to be coupled were chosen to be the RELAP5 Mod3.3 patch 3 and the Gothic version 7.2b(QA). The RELAP5 code was provided to the University of Pisa by ISPRA together with the FORTRAN source program, while the executable version of the Gothic code and limited rights to use it for the purposes of the present work were acquired from Numerical Applications, Inc. (NAI). A procedure for exchanging information between the two running codes was also acquired from NAI. The procedure included a limited coupling between primary system and containment, allowing only for the exchange of information required to simulate a water blowdown from primary system to the containment at a single location in the plant. Starting from this example, a procedure customised for more general applications was set up, in order to make possible the first validation calculations, to be described in a further report. The procedure is aimed at allowing bi-directional exchanges of mass and energy at multiple junctions, also including the exchange of noncondensable gases.