Qualification of MELCOR and RELAP5 models for EU HCLL TBS accident analyses

Highlights: • Test Blanket Systems (TBS) safety demonstration. • DEMO breeding blankets (BB) safety demonstration. • Development of MELCOR and RELAP5 codes TBS models. • Qualification of the models via comparison with finite element calculations, code-to-code comparisons, and sensitivity studies. • 32 h loss-of-offsite power (LOOP) accident analyses by MELCOR and RELAP5 codes. - Abstract: The F4E, Amec Foster Wheeler and INL comprehensive methodology for fusion breeding blanket accident analysis starts with the selection of reference accident scenarios, the development of detailed accident analysis specifications and the assessment of analysis codes. Models of each TBS are then constructed using the selected codes (MELCOR and RELAP5-3D) and modelling approaches. The models are qualified according to a test matrix including comparison with TBM finite element design analyses, code-to-code comparisons for both TBS normal operation and transient cases, and sensitivity studies for accident scenarios. The qualification test cases that are executed gradually move from models of separate systems to complete TBS models, and from the simulation of steady-state and normal plasma pulse operation to consideration of power excursions, operational transients and accident events. Finally, both of the qualified models are used to analyse a selected accident scenario (a 32 h loss-of-offsite power) together with sensitivity studies dedicated to the evaluation of uncertainties. This step completes the qualification process. The results obtained in the qualification of the EU HCLL TBS models are reported in the paper.