Effect of Axially Non-Uniform Pressure Tube Diametral Creep on Mass and Enthalpy Imbalance for a 37-Element Bundle

Abstract

The subchannel analysis code COBRA-IV has been used to predict the thermohydraulic parameters in an axially non-uniform, radially uniform, crept pressure tube, containing 37-element fuel bundles. The axial creep profile was assumed to be similar to the axial flux distribution. Geometrical variations with diametral creep were evaluated with the code GEODATA at all axial nodes. Variations of subchannel loss factors at spacer planes and endplates with creep were also modelled. A conservative prediction of the reduction in pressure drop with creep was obtained using the FIREBIRD-III code. Finally, a map was developed for the expected reduction in critical channel power with creep.