Validation of the CATHENA Fuel Channel Model for the Post Blowdown Analysis for the CS28-1 Experiment, I - Steady State

Abstract

To form a licensing basis for the new methodology of the fuel channel safety analysis code system for CANDU-6, a CATHENA model for the post-blowdown fuel channel analysis has been developed, and tested for a high temperature thermal-chemical experiment CS28-1. As the major concerns of the post-blowdown fuel channel analysis are with the current CANDU-6 design characteristics how much of the decay heat can be discharged to the moderator via a radiation and a convective heat transfer at the expected accident conditions, and how much zirconium sheath would be oxidized to generate H₂ gas at what fuel temperatures, this study has focused on understanding these phenomena, their interrelations, and a way to maintain good accuracy in the fuel temperature prediction throughout the post blowdown phase of a LBLOCA. Considering that an accurate prediction of the initial steady state of the experiment is important to better prediction, it was attempted to find what factors significantly contributes the prediction accuracy. As a result, the use of the constant emissivity of 0.80 for the entire transient for FES, and the non-participating medium treatment of the CO₂ gas annuls in CATHENA radiation model and the inability of CATHENA modeling of the possible natural convective heat transfer between the hot PT outer wall and the cold CT inner wall are identified as these factors. However the radiation model of CATHENA between FESs and PT is found to be accurate in the order of TC measurement accuracy reported Based on the prediction comparison of the current CATHENA model and the experiment data, the steady state model seems adequate as a starting point of the following high temperature thermal-chemical experiment of a metal water reaction.