Two test series were successfully carried out at MOTEL and HWAT facilities. Different technical problems (leakage in the steam generator, corrosion, etc.) during pre-tests at COSMOS-H and the material supply shortages during COVID made the generation of data for code validation impossible. The MOTEL cross-flow tests were done and data was measured for code validation. Figure 1 shows the coolant temperature measured along the core height for 3 different core regions. The first test series of HWAT consisted of 44 tests devoted to forced and natural circulation, and the transition from forced to natural circulation. Figure 2 exhibits the Wall temperature of the HWAT test section to investigate the transition from forced to natural circulation (Test 43). The second test series was carried out recently (see D2.10) too. Nine tests were done for different transient conditions e.g. LOCA induced boiling crisis (TG02.01) power transient (TG02.02 and .04), etc. Important parameters measured during the test TG02.01 are shown in Figure 3. The validation of TH-codes using McSAFER data was done by different institutions. Figure 4 shows the very good agreement of the coolant temperature along the MOTEL core predicted by ANSYS CFX compared to the data measured at location 14. Figure 5 exhibits the comparison of the void fraction and wall temperature measured along the radius of HWAT-test section (test Run 32) and the CFD-predictions having a good agreement. Figure 6 shows the comparison of the axial primary side temperature of the helical coil steam generator measured at different elevations in MOTEL with the ones predicted by TRACE and APROS.
Two transients for four core designs were analyzed successfully with different approaches. Low-order transport codes coupled with subchannel codes were used to investigate the REA of KSMR, and NuScale. High-fidelity coupled tools (MC and subchannel) were applied to the analysis of a long CWI (50 s) and of a short REA. For the first time, the CAREM CWI was analyzed with Serpent2/Subchanflow obtaining results at pin/subchannel level. Figure 7 shows the 2D fuel temperature distribution of the core at transient begin (axial level 14 (left)), where the hottest and coldest pin can be identified while on the right side, the DNBR predicted by the coupled code is exhibited. First-of-the-kind results were obtained for a NuScale REA loaded with ATF and non-ATF fuel by VTT, JRC KA and LUT. Figure 8 shows the evolution of the total power as predicted by the three institutions. As you can see there, the power increase is lower for ATF-cores; the maximal fuel temperature is lower for ATF than for non-ATF core loadings. These high fidelity tools are able to directly predict the safety parameters such as DNBR, Figure 9.
Multiscale methods based on system TH coupled with either subchannel or CFD codes are applied to analyze the 3D-TH phenomena within the RPV of SMART/NuScale and to test the models. The ATWS and boron dilution transients were analyzed using 1D/3D system TH-codes with Point kinetics. Figure 10 shows the evolution of the PZR-pressure and mass flow rate as predicted by TRACE and TRACE/SCF for ATWS. The NuScale boron dilution was also analyzed by different simulation tools. Figure 11 shows the evolution of the boron concentration (left) and of the coolant temperature of the eight sectors of the RPV at the core entrance predicted by ATHLET/FLUENT and ATHLET.
The SLB-transient of SMART and NuScale were analyzed with different coupled approaches based on multi-scale/-physics, where system TH codes are coupled with subchannel and CFD-codes. Three novel coupled codes were partly developed and applied for the analysis of SLB of both SMR-designs. The ICoCo-based coupling of TRACE/PARCS/OpenFOAM (KIT) and ATHLET/DYN3D/TrioCFD (HZDR), the Python/socket-based coupling in the Kraken Framework named TRACE/ANTS/OpenFOAM (VTT) and the user-defined coupling of ATHLET/DYN3D/FLUENT (UJV). Figure 12 exhibits the evolution of the total power and core mass flow rate (top) during the SLB-transient of SMART and the 3D detailed coolant temperature distribution at the core entrance predicted by OpenFOAM/TRACE in the coupled run at 50 s. Figure 13 gives the evolution of the steam line break flow and of the total power predicted with the coupled codes by HZDR, VTT, and UJV. The trends of these parameters are similar, quantitatively some differences exist among the provided solutions.
