Enhancement of Heat Transfer in Fuel Assemblies of High Performance Light Water Reactors

Abstract

Heat transfer in fuel assemblies for a High Performance Light Water Reactor can be achieved either with artificial surface roughness of the fuel claddings or by a spiral cross flow between the fuel pins, for which purpose a staircase type grid spacer has been designed. An application of earlier test results with rough claddings for gas cooled reactors to supercritical water conditions, together with new heat transfer estimates for a spiral flow, indicates that the heat transfer coefficient of the coolant at the cladding surface can be increased by more than a factor of two, which will reduce the peak cladding temperature by at least 50 C. This improvement shall allow either to increase the core outlet temperature at a given cladding temperature or to reduce the peak temperature at the envisaged core outlet temperature. The paper includes analyses and design details for realization of such enhancement of heat transfer.