This paper deals with the problem of scaling complex scenario measured experimental facilities and replicated by the use of Cathare2 code. ‘Kv-scaled’ calculation an important role in the frame of the “on-transient qualification” of the nodalization owing the procedure envisaged at Pisa University) and to evaluate the importance oe scale-distortions in boundary and initial conditions, which are foreseeable for tht in comparison with the transients, performed in the facilities. This is the way in orddemonstrate that the “nominal” calculation can be considered the "best estimateiction of the plant performance in the case of the transient considered. These steps a of the methodology developed with the purpose to set up a tool suitable for application BE codes to DBA and BDBA conditions (including AM scenarios) as needed for the licensing process. The reference data base for the activity is the Small Break Loss Of Coolant AccideLOCA) transient, counterpart of the LOBI facility experiment, that has been performed Integral Test Facility (ITF) PSB-VVER, installed at EREC (Electrogorsk, Russia), in framework of the OECD PSB-VVER Project. he calculation (PSB and Nuclear Power Plant) has been performed using Cathare 2 computer code and its accuracy has been demonstrated by the qualitative evaluation reported in the present document.