ABSTRACT
This chapter presents overview on: severe accident phenomena, the nature of the interaction between thermalhydraulics and activity transport, reactor cooling system transport codes, and containment transport codes. The combination of in-reactor tests, out-reactor tests, TMI-2 analyses, thermodynamic calculations and reaction kinetics are greatly improving the people understanding of the complex nature of fission product release from UO2 fuel. In a related vein, it has become obvious that the current suite of thermalhydraulics and mass transport computer codes, which had been developed almost exclusively for purposes of analysing accidents in pressurized water reactors, is inadequate for use in the analysis of boiling water reactor accidents. In the discussion of Dr. Beahm's paper it was suggested that a valuable use of TRENDS would be to examine the sensitivity of the iodine release to the environment in severe accidents to the form in which the iodine enters the containment.
