VALIDATION OF THE ASSERT SUBCHANNEL CODE - PREDICTION OF CRITICAL HEAT-FLUX IN STANDARD AND NONSTANDARD CANDU BUNDLE GEOMETRIES

The ASSERT code has been developed to address the three-dimensional co mputation of flow and phase distribution and fuel element surface temp eratures within the horizontal subchannels of Canada uranium deuterium (CANDU) pressurized heavy water reactor fuel channels and to provide a detailed prediction of critical heat flux (CHF) distribution through out the bundle. The ASSERT subchannel code has been validated extensiv ely against a wide repertoire of experiments; its combination of three -dimensional prediction of local flow conditions with a comprehensive method of predicting CHF at these local conditions makes it a unique t ool for predicting CHF for situations outside the existing experimenta l database. In particular, ASSERT is an appropriate tool to systematic ally investigate CHF under conditions of local geometric variations, s uch as pressure tube creep and fuel element strain. The numerical meth odology used in ASSERT, the constitutive relationships incorporated, a nd the CHF assessment methodology are discussed. The evolutionary vali dation plan is also discussed, and early validation exercises are summ arized. More recent validation exercises in standard and nonstandard g eometries are emphasized.