MODELING OF REFLOODING

The state of the art in modeling reflooding situations, mainly with th e two-fluid system analysis codes, is reviewed; certain related genera l code development issues are included. Our current modeling of refloo ding is reasonable and can be made sufficiently conservative for safet y assessments, but it is not outstanding. Fundamental understanding of the detailed two-phase flow and heat transfer mechanisms has not prog ressed significantly over the state already available several years ag o. The better understanding of system behavior achieved by the coordin ated program of large-scale experiments is summarized and its impact o n the modeling work discussed. In the future, factors such as the addi tional accident scenaria now considered, the new and advanced reactor types being analyzed, and the geometric growth of computing capacity a re likely to drive our efforts. The new requirements and challenges ca n be met best by building into the codes pieces of understanding of th e actual physical processes at the most fundamental level practicable. The discussion focuses on the existing codes and their successes and shortcomings; both certain specialized and the more complex general-pu rpose system codes are considered. The aim is not to conduct an exhaus tive review of all aspects of the problem, but rather to reach consens us on certain issues.