Experimental investigation on boiling heat transfer characteristics of the spent fuel bundle under flooded condition

Abstract

Heat removal of the spent fuel in the spent fuel pool normally depends on the forced-circulation system in the pool. Once the forced-circulation cooling system fails, decay heat of the spent fuel can only be removed by the natural convection of the coolant. If this situation lasts for a long time, temperature of the water in the pool may continue increasing till the pool-type boiling occurs. It is important to research the boiling heat transfer characteristics for the design and safety assessment of the spent fuel pool. Researches on the pool boiling have already been extensively performed, but few is on the spent fuel assemblies which are vertical, long-span and tight bundles. This paper presents the pool boiling behavior of the heated vertical bundles flooded in the water which models the spent fuel stored in the pool. A series of experiments were carried out with different heated powers. Temperatures of the bundles were measured and heat transfer coefficients were obtained. High-speed camera was used to capture the two-phase flow patterns in the experiments. The highest temperature of the spent fuel cladding is about 115 °C during the saturate boiling state. This datum confirms the safety of the spent fuel under flooded condition.