Scaling analyses of a SB-LOCA counterpart test between BETHSY and LSTF facilities and a three loops PWR

The use of System Codes for Scaling Analysis and the use of Scaling Tools for the Analysis of Code Predictions

“…This simple use of a "scaling equation" evaluated by a system code illustrates how it can help capturing the physics of the transient phase, identifying quickly the dominant processes and quantifying the impact of distorted phenomena, but also suggesting some weaknesses of the code nodalization. Another distortion was observed in the BETHSY calculation [9] due to an accumulator discharge, which is much faster than in the reactor. This is due to the full height design of the BETHSY accumulator.…”

“…Then the fluid mass repartition in the various components is controlled by some force balance equations, which may be specific to the component and to the physical situations. Table I gives an example for a 6% cold leg break SBLOCA as investigated in [9]. For each PoI, the effects are given, as well as the impact on the PCT and the scaling equation that may be used in a scaling analysis.…”

“…One main benefit of using system codes for scaling analyses is that the terms of the scaling equations can be estimated as function of time and may provide more information than a estimation of terms for a transient phase. Figure 3 shows the CATHARE code simulations (from Ciechocki et al, [9]) of a 6% cold leg SBLOCA transient of a PWR and the corresponding 6.2-TC transient in the BETHSY ITF , which was scaled using the power-to-volume scaling method and the height conservation [12]. A very important bifurcating event is the crossing of primary and secondary pressures since it initiates a second depressurization and has an impact on the timing of the accumulator discharge.…”

“…This heat release depends on the history of the transient and no coarse evaluation for a transient phase can predict its relative weight better than a code transient simulation. During the first blowdown phase of the 6% cold leg SBLOCA (Ciechocki et al, [9]) , the pressurizers empty and their pressures are mainly governed by the exiting liquid volume flow rate 𝑄 𝑙,𝑝𝑟𝑧 and the flashing 𝑄 𝑖,𝑝𝑟𝑧 (Figure 4). During the first one or two seconds 𝑄 𝑙,𝑝𝑟𝑧 is partly compensated by vapour heating at the interface 𝑄 𝑖𝑣,𝑝𝑟𝑧 .…”

“…Several authors have reported such analyses (Munoz-Cobo et al, [5], Reventos et al [6] Martinez-Quiroga & Reventos [7]). Examples commented here are based on recent work performed at CEA by Ciechocki et al [8,9]. Some guidelines and recommendations are drawn on the selection of the "scaling equations" to be used in the scaling analyses, on the various methods for estimating terms of the selected equations, and on the acceptability limits for the distortions.…”