Recent Extensions to the Capabilities of the Fuel and Wall Models in the ASSERT Subchannel Code

Abstract

The ASSERT subchannel code has been developed to address the computation of flow and phase distribution within the subchannels of CANDU fuel bundles which are horizontal. Unlike conventional subchannel codes, designed primarily to model flow in vertical fuel bundles and use a homogeneous-mixture model of two-phase flow, ASSERT uses a drift-flux model which permits the phases to have unequal velocities, and includes gravity terms which make it possible to analyze separation tendencies that may occur in horizontal flow. ASSERT has options to salve the resulting equations using either the drift-flux or the homogeneous-mixture model with various options for thermal disequilibrium. Parallel phenomenological investigation is required to ensure that the computer code incorporates the mechanisms necessary to simulate experimentally observed trends, The ASSERT development program, therefore, contains a number of coordinated experimental and analytical projects, each providing information essential for the central project. This permits constructive validation of the computer code accompanied by progressive improvement . This paper discusses recent extensions to the capabilities of fuel and wall models in ASSERT, permitting the calculation of multidimensional temperature distributions in the fuel rods and channel structure.