## 3 Results
### LOFA Tests with a Sensitivity Matrix Coming from the Pre-Calibrations  
The MELCOR 1.8.6 complete model was employed to simulate 11 LOFA scenarios (the same ones investigated with RELAP5-3D [4]):  
* Six cases for the heat load of 300 kW/m\({}^{2}\): 0% valve open (full LOFA), 5%, 10%, 20%, 40%, and 60%;
* Five cases for the heat load of 330 kW/m\({}^{2}\): 0% valve open, 5%, 10%, 20%, and 40%. Each MELCOR input deck was created starting from the parameters obtained from the preliminary calibrations and employing the initial conditions related to each individual scenario. Then, the sensitivities coming from the preliminary calibrations were considered as a good starting point for the subsequent analysis with the best-estimate methodology. The different scenarios can be divided into three categories:  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Resposes** & **Experimental Results** & **Best-Estimated Results** \\ \hline \multicolumn{3}{c}{330 kW/m\({}^{2}\)—No heat load} \\ \hline \(\Delta\)p—Ch. 2 (MPa) & 7.70 \(\pm\) 0.015 & 7.67 \(\pm\) 7.6 \(\times\) 10\({}^{3}\) \\ \hline \(\Delta\)p—Ch. 3 (MPa) & 7.69 \(\pm\) 0.015 & 7.67 \(\pm\) 7.5 \(\times\) 10\({}^{-3}\) \\ \hline \(\Delta\)p—Ch. 4 (MPa) & 7.7 \(\pm\) 0.015 & 7.67 \(\pm\) 7.7 \(\times\) 10\({}^{-3}\) \\ \hline \(\Delta\)p—Ch. 7 (MPa) & 7.72 \(\pm\) 0.015 & 7.71 \(\pm\) 8.2 \(\times\) 10\({}^{-3}\) \\ \hline \(\Delta\)p—Ch. 8 (MPa) & 7.71 \(\pm\) 0.015 & 7.71 \(\pm\) 8.2 \(\times\) 10\({}^{-3}\) \\ \hline \multicolumn{3}{c}{330 kW/m\({}^{2}\)—No heat load} \\ \hline Outlet T.—Ch. 2 (\({}^{\circ}\)C) & 302.5 \(\pm\) 1.5 & 300.2 \(\pm\) 0.2 \\ \hline Outlet T.—Ch. 3 (\({}^{\circ}\)C) & 324.2 \(\pm\) 1.6 & 320.6 \(\pm\) 0.4 \\ \hline Outlet T.—Ch. 4 (\({}^{\circ}\)C) & 321.1 \(\pm\) 1.6 & 315.6 \(\pm\) 0.3 \\ \hline Outlet T.—Ch. 7 (\({}^{\circ}\)C) & 323.5 \(\pm\) 1.6 & 319.6 \(\pm\) 0.3 \\* LOFAs not approaching the 550 \({}^{\circ}\)C limit (40% and 60% valve open). Damages on the surface under heat load may arise if this temperature is exceeded, so 550 \({}^{\circ}\)C is used as a safety limit;
* LOFAs approaching the 550 \({}^{\circ}\)C limit, but without showing symptoms of back-flows (5%, 10%, and 20% valve open);
* LOFAs approaching the 550 \({}^{\circ}\)C limit and showing signs of back-flows (0% valve open). In contrast to those performed in [4], the \"average\" tests investigated in the present paper are not created taking into account all the repetitions performed during the different days, but only those performed on a specific day. This reduced set of experiments was chosen being sufficiently representative of the whole experimental campaign. The comparison between the experimental data and the best-estimate results obtained from the best-estimate methodology for the 40% valve opening scenario at 300 kW/m\({}^{2}\)--representative for category C1--are shown in Figure 6 (outlet pressure) and Figure 7 (outlet temperature). As it can be observed, the code is able to correctly simulate both the pressure and the temperature trends, but quantitative differences exist in the latter because of the impossibility to reproduce the friction heating. These results show also a small range of uncertainty for the temperatures due to use of a sensitivity matrix obtained in steady-state conditions instead of transient conditions. Figure 6: Outlet coolant pressure—300 kW/m\({}^{2}\), 40% valve opening scenario. The results for the 10% valve opening scenario at 300 kW/m\({}^{2}\) are reported in Figures 8 and 9 (scenario representative of the C2 category). In this scenario, the residual coolant flow rate is not sufficient to control the temperature increase, and the tests terminated after a few seconds to comply with the 550 \({}^{\circ}\)C safety limit. This scenario is again well-reproduced, but the temperature trends shown by the MELCOR code differ from the experimental ones.