TRAC-PF1/MOD2 analysis of downflow in a ribbed vertical annulus

As part of an effort to upgrade the calculation of the emergency cooling system assembly power limits at the Savannah River plant (SRP), a number of heat transfer experiments were designed and conducted to measure the local effective heat transfer coefficients for a two-phase downflow in a ribbed annulus. In the present study, the unpowered portion of these experiments is analyzed using the new version of their transient reactor analysis code, TRAC-PF1/MOD2. Only the results of base study are reported in this paper. The Los Alamos National Laboratory (LANL) TRAC series of computer codes was developed to analyze transients in pressurized light water reactors (PWRs). The design and flow configuration in PWRs are considerably different from those encountered in the fuel assemblies at SRP. What we refer to as a base study is the application of the TRAC code without modifications in the constitutive packages to account for the characteristics of a downflow in a ribbed annulus, which is typical of the SRP fuel assembly flow configuration. As outlined in this paper, TRAC performed very well in modeling the qualitative behavior of all existing data. Quantitatively, the discrepancies ranged from 0 to 100%. The details of these results are documentedmore » in this paper. Section II provides a brief description of the experimental setup and the resulting data for the three experiments mentioned above.« less