A correlation of rewetting data

Abstract

Following a loss-of-coolant accident in a water reactor the fuel pins dry out and overheat and it becomes necessary to rewet them to restore normal temperatures. A thermal conduction analysis of rewetting is presented in which it is shown that the heat transfer coefficient associated with rewetting may be taken as an arbitrary function of surface temperature, rather than a constant, without changing the dependency of rewetting velocity on the other variables. An effective heat transfer coefficient then replaces the constant value used in previous expressions for the rewetting velocity. Experiments at atmospheric pressure show that the rewetting rate increases with inlet water subcooling. The available rewetting data at both atmospheric and elevated pressure have been analysed using an existing theoretical model. Taking the effective heat transfer coefficient as proportional to the product of mass flow rate and inlet subcooling a data fit has been achieved to within a factor of two. Expressions are given which predict rewetting rates for a wide range of pressures, wall temperatures, subcoolings, clad materials and geometries.