Sodium boiling experiments in an annular test section under flow rundown conditions

Experiments have been carried out using sodium in an annular test section geometry to simulate boiling development in a fast reactor core under the somewhat improbable conditions of primary circulator pump run-down with coincidental failure of the reactor trip system. Induction heating of the outer tube was used, the axial heat flux distribution being linear. Boiling was achieved by means of a steady reduction of the coolant flow from normal steady state values, heat fluxes being appropriate to reactor conditions. Boiling was allowed to continue until indications of permanent dryout of the heated tube were received, at which stage power was terminated to prevent damage to the test section. The results obtained provide useful information on the transient development of boiling, the axial distribution of void within the channel, initial superheat, liquid film thickness, dryout and rewetting. The experiments thus proviede a source of data against which computer codes such as BLOW3, based on theoretical models of boiling may be validated. (orig.)