The Leakage of Water into Sodium in Steam Generators and Test Rigs

When water and sodium react, hydrogen is released to enter cover gas spaces and become absorbed into the sodium. Changes in hydrogen concentration are measured with suitable instruments to monitor steam generator vessels for water leakage. Interpreting the amplitude and rate of change of signals as potential damage to the unit requires two correlations:

1. prediction of the quantity or rate of water injection from changes in hydrogen concentrations
2. prediction of heat transfer tube wastage from quantity of water injected or rate of injection of water.

Experimental data were used to develop two restricted application correlations covering the worst possible wastage case. The maximum wastage is given by

and the quantity of hydrogen released by a given quantity of water is shown to be given by a model based on the equilibrium pressure of hydrogen above sodium. These correlations were developed for wastage damage and hydrogen release for a given quantity of water. Based on these correlations, system shutdown criteria were written to guide the operator of a steam generator test rig should a small water-to-sodium leak occur. Predictions from the correlations were used to specify a leak detection system for both a test facility and a plant steam generator. To meet these specifications, it is essential that the in-sodium detection of hydrogen by hydrogen diffusion tube meters become a stable and reliable technique. Operating experience with the leak detection system on the steam generator test rig test facility (which monitored naturally occurring leaks) showed that the shutdown criteria were practical and realistic in guiding system operators.