The MELTSPREAD-1 computer code for the analysis of transient spreading in containments

Transient spreading of molten core materials is important in the assessment of severe-accident sequences for Mk-I boiling water reactors (BWRs). Of interest is whether core materials are able to spread over the pedestal and drywell floors to contact the containment shell and cause thermally induced shell failure, or whether heat transfer to underlying concrete and overlying water will freeze the melt short of the shell. The development of a computational capability for the assessment of this problem was initiated by Sienicki et al. in the form of MELTSPREAD-O code. Development is continuing in the form of the MELTSPREAD-1 code, which contains new models for phenomena that were ignored in the earlier code. This paper summarizes these new models, provides benchmarking calculations of the relocation model against an analytical solution as well as simulant spreading data, and summarizes the results of a scoping calculation for the full Mk-I system