University of Maryland 2 x 4 loop experimental findings on the effects of inertial and buoyancy forces on annular flow mixing for rapid boron dilution transients

One of the main pieces of information required to resolve the consequences of a rapid boron dilution transient event is the determination of the temporal and spatial boron concentration at the entrance to the core. To that purpose, there are 4 distinct test series within the current test program. Test series A approaches a special effect type test. In this series, a front is injected which provides for a “clean” boundary condition. In addition, all cold legs except for one are isolated from the downcomer, thus limiting the path of the fluid through the downcomer and core. In series B, a slug is injected instead of the front injected in series A. In series C, only two cold legs are isolated allowing for limited bypass flow. In series D, all four cold legs participate in the test and the facility approaches an integral configuration.; The thermal tracking methods used to track the dilute front/slug as it moves through the downcomer are analyzed and determined to be valid for the range of the current test program. Heat transfer into and out of the downcomer can skew the temperature in the downcomer and must be minimized.; This experimental study offers a quantification of the flow regime that dominates the mixing in the downcomer during the subject rapid boron dilution transient. The dominant flow regimes in the downcomer are identified as turbulent beyond a transition Re of 15,000 and laminar below that. This knowledge is applied to their effect on the mixing figures of merit. It is observed that the flow regime has a significant effect on the mixing figures of merit.; The effects of buoyancy force on the dilute front/slug mixing are also explored. Buoyancy is determined to have significant effects on the mixing figures of merit, especially in the upper downcomer. Buoyancy also is shown to play a role in the flow path taken by the slug as it travels the downcomer for Froude numbers less than 9–10. Above this range, the buoyancy force no longer has any effect on the slug flow pattern. Methods of predicting flow patterns from initial conditions are explored.