Analyses of corium spreading in Mark 1 containment geometry

Under Nuclear Regulatory Commission (NRC) sponsorship, analyses have been performed of melt spreading and containment shell heatup following postulated reactor vessel failure in the Mark 1 system. The overall objectives of this work are to lend support to confirmation of the conservative assumptions made in the probabilistic assessment of Theofanous et.al. in NUREG/CR-5423 (1989), extend the results from that study, and thereby assist in resolution of the Mark 1 shell vulnerability issue. The approach consists mainly of calculations using the MELTSPREAD-1 computer code developed at Argonne National Laboratory under Electric Power Research Institute (EPRI) sponsorship as well as other supporting analyses. MELTSPREAD-1 models fluid dynamic and heat transfer processes involved in the transient spreading of core and structural materials over concrete or steel and submerged beneath water as well as the heatup of a structural boundary such as the containment steel shell. The mechanistic MELTSPREAD-1 calculations thus complement the simpler treatment of melt spreading incorporated in NUREG/CR-5423