Post-Test Numerical Analysis of a Helium-Cooled Breeding Blanket First Wall under LOFA Conditions with the MELCOR Fusion Code

Abstract

The validation of numerical tools employed in the analysis of incidental transients in a fusion reactor is a topic of main concern. KIT is taking part in this task providing both experimental data and by performing numerical analysis in support of the main codes used for the safety analyses of the Helium Cooled Pebble Bed (HCPB) blanket concept. In recent years, an experimental campaign has been performed in the KIT-HELOKA facility to investigate the behavior of a First Wall Mock-Up (FWMU) under Loss Of Flow Accident (LOFA) conditions. The aim of the experimental campaign was twofold: to check the expected DEMO thermal-hydraulics conditions during normal and off-normal conditions and to provide robust data for code validation. The present work is part of these validation efforts, and it deals with the analysis of the LOFA experimental campaign with the system code MELCOR 1.8.6 for fusion. A best-estimate methodology has been used in support of this analysis to ease the distinction between user’s assumptions and code limitations. The numerical analyses are here described together with their goals, achievements, and lesson learnt.

Best-Estimate for System Codes (BeSYC): A New Software to Perform Best-Estimate Plus Uncertainty Analyses with Thermal-Hydraulic and Safety System Codes for Both Fusion and Fission Scenarios

“…Figure 5 shows the results achieved from the application of the best-estimate methodology against the tests performed for two channels of the first wall mock-up (MELCOR 1.8.6 code, see [9] for further details). The analysis was mostly performed to demonstrate that the best-estimate input deck (blue curve) was capable to better reproduce the experimental trends compared to the default input deck (red curve) considered as starting point of the analysis.…”

“…Then, the BeSYC software was used for the post-test analysis with RELAP5-3D and MELCOR 1.8.6 of a experimental campaign performed in the KIT HELOKA-HP facility [8,9]. For this analysis, 10 responses and about 100 parameters were selected to reproduce the different experimental scenarios (11 tests).…”

“…Moreover, in these scenarios (not discussed here for sake of brevity), the software demonstrated its capabilities when dealing with the different aspects of the analysis. Further information on the LOFA experimental campaign and the post-test analysis performed with BeSYC and the RELAP5-3D code can be found in [8], while the post-test analysis with BeSYC and the MELCOR 1.8.6 code are described in [9]. the 11 tests), apply the best-estimate methodology, write the best-estimate input deck, and execute it.…”

“…The present paper describes the structure, the mathematical framework, and the validation of this software. This paper is published in conjunction with two other papers showing the application of BeSYC with both RELAP5-3D and MELCOR 1.8.6 codes against the data gathered from an experimental campaign on a helium-cooled first wall mock-up (FWMU) under Loss Of Flow Accident (LOFA) conditions [8,9]. Even if not yet used for any real-case scenario, the BeSYC software supports also MELCOR 2.2.…”

“…The tool has been extensively validated against both examples provided in literature and hand-made test cases. Then, BeSYC was used for the analysis of several pressure drop characterization tests and a LOFA experimental campaign performed on a helium-cooled first wall mock-up in the KIT HELOKA-HP facility [8,9]. These two works do not only represent the validation of the RELAP5-3D and MELCOR 1.8.6 codes in DEMO relevant conditions but also the last validation step of the BeSYC software.…”