UNB CANDU-6 Primary Heat Transport System Code: Development and Validation of a Thermal-Hydraulic Expansion

Abstract

Reduced capacity for heat transfer in the CANDU steam generator has safety consequences such as risk of fuel dryout due to higher reactor inlet header temperature (RIHT). To identify methods to maintain the RIHT within operational margins, it is necessary to model boiler thermal degradation mechanisms (deposition and fouling) and their effects on heat transfer.In the recent add-on to UNB’s CANDU-6 primary heat transport system code, steam generator behaviour is modelled numerically via heat transfer mechanisms and updated thermodynamic equations for the properties D₂O and H₂O available from IAPWS. Station data is used for benchmarking of oxide growth kinetic constants and for events such as chemical and mechanical cleaning, pressure changes, bypass flow, and purification. A set of boiler tubes, grouped into bundles based on U-bend arc lengths, is simulated. Model output includes a detailed deposit distribution and temperature profile for each bundle along with accurate RIHT predictions.