## 5 Results and Discussions  
In this section, the numerical results obtained by using the nodalization described in Section 3 and applying the boundary conditions of the experimental test reported in Section 2 are presented. According to the boundary conditions of the experimental test, a transient of 3600 s was simulated by imposing the PLOFA starting time at 1800 s. The FPS power was imposed according to Figure 2.  
Similarly to the experiment, the required LBE mass flow rate is obtained by imposing the Argon mass flow rate (TDPV3 and J004 in Figure 5), as explained in Section 2. In Figure 6 the experimental LBE mass flow rate is reported with black diamonds, while the numerical value obtained by applying the nominal conditions is reported with a dotted light blue line. Due to the approximation introduced by the simplified numerical geometry and the assumptions adopted in terms of concentrated pressure drops, the obtained LBE mass flow rate overestimates the experimental value. Therefore, in order to assure the same initial conditions of the experiments, the LBE mass flow was reduced by following two different approaches. As a first approach, the pressure drops inside the riser (PIPE 130) were increased, the resulting LBE mass flow is reported with the dash-dotted orange line. As a second approach, the LBE mass flow was directly imposed as an input parameter according to the dashed purple line shown in Figure 6. In these simulations, mass flow rates are applied by using the component TMDPJUN, which joins a TMDPVOL to the corresponding hydrodynamic volume. The TMDPJUN imposes the desired temperature, pressure and static quality of the injected fluid, while the TMDPJUN applies the chosen mass flow rate (liquid and/or gas phase) as a function of the time. Thus, under both forced circulation during normal operation and natural circulation after the PLOFA, the thermal behavior of the system is simulated. The initial temperature of both the whole HERO-loop and the bottom part of the pool (PIPE 253-BRANCH 260) was set to 420 \({}^{\circ}\)C. According to the experiment, a temperature equal to 475 \({}^{\circ}\)C was initially applied in the rest of the pool [7,8]. For the secondary side of the SGBT the inlet temperature of the water was set equal to 336 \({}^{\circ}\)C and the related mass flow rate was implemented according to Figure 4.  
In this work results in terms of the temperatures reached inside the FPS and in the outlet region of HERO-SGBT are also reported and analyzed. In Figure 7 the temperature trends measured during the experiment at the inlet and outlet of the FPS are reported and compared to the related numerical values obtained by implementing the different trends of LBE mass flow rate reported in Figure 6. In the same way, Figure 8 shows the comparison between experimental and numerical results of the HERO-SGBT outlet temperature. In the legends of both Figures 7 and 8 the experimental data are nominated with \"Exp.\", the numerical analysis carried out under nominal condition with \"Nom.\", while numerical cases with increased pressure drops and LBE mass flow rate imposed as input are reported with \"PressDrop\" and \"ImpImp\", respectively. According to the obtained numerical results, by approaching the experimental LBE mass flow rate the FPS temperatures evaluated numerically become closer to the related experimental results. Before the PLOFA starting time, the inlet and outlet temperature slightly increase in the experiments while both decrease in the numerical analyses. Furthermore, compared to the nominal case, when a lower LBE mass flow rate is applied a more effective cooling is performed by the water mass flow rate, which is kept constant. As a result, a lower LBE temperature is evaluated. After the transient, the experimental and numerical analyses behave similarly from a qualitative point of view for: both the nominal case and the numerical analysis with increased pressure drops in the riser.