ABSTRACT
This chapter shows important issues concerning the transport and deposition of radionuclides in the reactor coolant system (RCS) under accident conditions and examines how such issues are being treated or should be treated by the various available computer codes. The RAFT code was the first reactor cooling system fission product transport code to attempt to model the nucleation of fission product vapors as they escape the fuel. TRAPMELT3 models the complex reactor cooling system in an idealized way but, within this idealism, treats the major phenomena in an interactive fashion. A phenomenon which has received attention in the MCT2 code is fluid recirculation within the RCS, especially within the core and steam separators and dryers. Various reviewers have identified as major uncertainties the modeling of flow patterns in the RCS, re-evolution/re-entrainment of deposits, and the nucleation and condensation of vapors both from the core region directly and that from re-evolved deposits.
