Methodology for accident analyses of fusion breeder blankets and its application to helium-cooled pebble bed blanket

•Test Blanket Systems (TBS) DEMO breeding blankets (BB) safety demonstration.•Comprehensive methodology for fusion breeding blanket accident analysis that addresses the specificity of the breeding blanket designs, materials, and phenomena.•Development of accident analysis specifications (AAS) via the use of phenomena identification and ranking tables (PIRT).•PIRT application to identify required physical models for BB accidents analysis, code assessment and selection.•Development of MELCOR and RELAP5 codes TBS models.•Qualification of the models via comparison with finite element calculations, code-tocode comparisons, and sensitivity studies.