Experimental and Theoretical Investigation of Pressure Tube Circumferential Temperature Gradients During Slow Coolant Boil-Off

Abstract

A pressure-tube circumferential temperature distribution experiment under coolant boil-off conditions has been simulated using CATHENA (MOD-3.4a). The objectives of these simulations were to aid in the design of the experiment through pre-test simulations and to help in the analysis of the test results through post-test simulations. The predicted results from the post-test simulations of the boil-off test generally agreed well with the experimental data. Predicted pressure-tube temperatures near the stagnant end of the test section compared well with the measured temperatures, typically being within 45 degrees C or 6% of measured values prior to pressure-tube/calandria-tube ballooning contact. Measured and predicted pressure-tube temperatures at axial locations towards the steam exit end were good, however, not as good as near the stagnant end. This trend appeared to be related to the different local boil-off rates and the effect of the steam flowing towards the exit end. The general shape of the circumferential temperature distribution on the pressure tube during the boil-off transient, and the pressure-tube straining behaviour were well predicted. The predicted timing for the initial pressure-tube/calandria-tube contact was accurate to within 4 s near the stagnant end. The pressure tube was not predicted to fail in the post-test simulation, agreeing with experimental observations. Comparative studies through numerical and experimental data plots are reported in this paper.