Two-Phase Flow Interfacial Structure in CANDU Reactor Fuel Channel and Feeder Pipe Under Postulated Accident Conditions

Abstract

Experiments were conducted to study the two-phase flow structure relevant to the flow behaviour of the header, feeder, and fuel channel systems in CANDU reactors during postulated accidents. The test loop consisted of a series of instrumented vertical and horizontal pipes with an inner diameter of 32 mm. The test section of the loop simulated a horizontal fuel channel connected with a vertical inlet feeder and a vertical outlet feeder in the primary heat transport system of a CANDU reactor. Wire- mesh sensors were used to measure two-phase flow interfacial parameters such as void fraction distribution, interfacial area concentration, bubble interfacial velocity, and bubble diameter distribution. The experiments were conducted for a series of flow conditions corresponding to various postulated loss-of-coolant accidents, covering various flow regimes for vertical and horizontal flows. The results of the experiments were used to study and model the effect of flow channel orientation (vertical vs. horizontal) on the flow regime and interfacial structure. Furthermore, a drift-flux analysis was carried out based on this new database, and several drift-flux correlations were evaluated. The high-resolution two-phase flow data obtained in this work is appropriate for benchmarking and developing three-dimensional thermal-hydraulic system codes and computational fluid dynamics codes for CANDU-type reactors.