Characteristics of heat transfer inside a tube during sodium‐water reaction in a FBR steam generator

Sodium reacts chemically with water in the case of an unexpected tube failure of a steam generator (SG) in a fast breeder reactor (FBR). In order to predict the event with high accuracy, it is very important to understand the characteristics of heat transfer inside the tube in detail during the tube failure due to the sodium–water reaction. Experiments were performed by using purified water under the following conditions: initial pressure of 11.2–13.4 MPa, initial water temperature of 200 °C, and water mass flux of 45.7 to 3630 kg/(m²s). The test tube was heated rapidly by high‐frequency induction current. The time averaged heat flux was estimated by using an inverse solution from the measured temperatures at two points on three different locations along the tube. It was confirmed that the derived values agreed with the measured heat fluxes on the outer surface within 20% accuracy. It was found that the characteristics of the heat transfer strongly depend on the flow rate. The heat transfer on the wall changed from nucleate boiling to transient‐film boiling during increasing the heat flux and returned to the nucleate boiling during decreasing the heat flux. A counterclockwise cycle always appeared in the transition boiling region, where the nucleate and film boiling coexisted and the area ratio of these varied with time. The adequacy of heat transfer correlations to evaluate tube overheating was confirmed. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20320