Uncertainties identification and initial evaluation in the accident analyses of fusion breeder blankets

The F4E, Amec Foster Wheeler and INL comprehensive methodology for fusion breeding blanket accident analysis has been applied thus far to three accident scenarios: 32 h Loss-Of-Offsite Power, Loss Of Flow Accident (LOFA) and LOFA followed by failure of breeder unit cooling plate (i.e. in-box LOCA) as aggravating failure. The impact of uncertainties associated with the accident analyses is addressed to provide sufficient confidence in the level of conservatism in the results. The approach adopted reflects the maturity of the design and takes the form of an uncertainty Phenomena Identification and Ranking Table assessment and associated sensitivity calculations. Thus the significant areas of uncertainty effects on the analysis results are identified. The paper reports the performed expert reviews of areas of uncertainty. Our approach has a number of significant advantages of flexibility, practicality, and improved understanding. Similar sources of uncertainty exist in the application of codes models to represent complex physical phenomena: code models, validation and verification; system model representation; operating parameters; and effect of scale. The identified helium-cooled lead-lithium and pebble-bed breeder blankets accidents analyses uncertainties and results obtained in their assessment both in models qualifications and applications to three selected accident scenarios are reported. Finally the contribution of performed uncertainty evaluations to the assessment, verification and improvement of fusion adapted MELCOR code is discussed.