Development and validation of a CATHENA fuel channel model for a post-blowdown analysis of the high temperature thermal–chemical experiment CS28-1

To form a licensing basis for a new methodology for a fuel channel safety analysis code for CANDU-6 nuclear reactor, a CATHENA model for a post-blowdown fuel channel analysis has been developed, and tested for a high temperature thermal–chemical experiment CS28-1 [Lei, Q.M., 1993. Post-test analysis of the 28-element high-temperature thermal–chemical experiment CS28-1. In: 4th International Conference on Simulation Methods in Nuclear Engineering, Montreal, PQ, 1993]. Pursuant to the objective of this investigation, the current study has focused on understanding the involved phenomena, their interrelations, and how to maintain a good accuracy of the temperature and H 2 generation rate prediction without losing the important physics of the involved phenomena. The transient simulation results for the fuel element simulators (FESs) for the three fuel rings and the pressure tube were reasonably good as proven by the simulation results. This is thought to be due to success in reproducing the initial steady state condition well, and due to the detailed modeling features of CATHENA code for the coupled conduction, convection, and radiation heat transfer in a complex fuel bundle geometry. However, one problem still remained unresolved, i.e. the inability to accurately predict the pressure tube temperature at the initial steady state condition, and an adjustment of the CO 2 gap conductivity necessary to match the measured pressure tube temperatures. However, this raises a question as to how the transient FES and the pressure tube temperature can be predicted so well in spite of an insufficient justification for using the “non-participating medium assumption” for the CO 2 gas gap. Through this study and the affiliated previous study for the steady state, it was found that the radiation heat transfer model of CATHENA among the FESs of the three rings and the pressure tube as well as the exothermic metal–water reaction model based on the Urbanic–Heidrick correlation are reasonably accurate and sound. Also it was found that an accurate prediction of the initial condition of the experiment is very important for an accurate prediction of the whole transient as it serves as the starting point for the transient.