Incipient Boiling of Sodium in an Annular Channel Heated by a Single-Pin with Blockage

Abstract

In simulation of partial failure affecting a fast breeder core, experiments on sodium boiling were performed in a single vertical channel of annular cross section (15 mm I.D.), indirectly heated by high flux heater pin (6.5 mm O.D., 60 em heating length) and provided with a blockage disk (11 mm O.D., 1 mm thick, obstructing 42% of the channel area). The experimental conditions were; Pressure of cover gas: 1.0 kgjcm 2 abs., Heat flux: 0-80 W ;cm 2 , Flow rate of sodium: 1-4 1/min.The results revealed that the degree of incipient boiling superheat is reduced to a fraction of the value obtained previously for direct joule heating under similar conditions, and that, consequently, the intensity of pressure pulses is correspondingly reduced. On the other hand, the incipient boiling superheat increases, together with the extent of its scattering, with rising intensity of the heat flux.Local boiling was observed to precede the onset of bulk boiling, causing small pressure spikes to be detected by all three pressure sensors installed along the test channel. The pressures evaluated from the measured velocities of the liquid sodium column based on single-bubble model were compared with the measured pressure signals, and a fairly good agreement was obtained.