Fundamental Derivation of the Equations Used in ASSERT-4 Subchannel Code

Abstract

The objective of this paper is to present the derivation of the basic equations used in the ASSERT-4 subchannel code. The first part of this paper deals with the basic mathematical tools required for the derivation and defines the averaging process to be used. Next the averaging of properties and certain important velocity fields in two phase Row are examined. Starting from the general local instant conservation equation these mathematical tools and averaging theorems are used to develop the formal derivation of the general space-time averaged conservation equation. From this general equation, the set of space-time averaged conservation equations for mass, momentum and energy are established. Using the set of space-time averaged conservation equations that have been developed as a starting point, the equations used in the ASSERT-4 subchannel code are derived. The necessary assumptions, that must be made to ass from the full three dimensional model, to the equations used in ASSERT-4 are detailed. The implications these assumptions have on the model are also discussed. Finally, the constitutive relations used to close the set of equations that has been developed are examined. The effects that the particular choices of constitutive relations have on the code predictions are then assessed by comparing the code predict ions against experimental data on two interconnected subchannels obtained at the Institut de Genie Energetique.