Modelling Methodology for Obstructions in the sub-channel Code ASSERT IV

Abstract

In general, pressure drop in a CANDU fuel string is important because of its impact on equipment size and on its impact on thermalhydraulic behaviour for both normal and abnormal operating conditions. In sub-channel codes, such as ASSERT, characterising the frictional and form losses of the individual sub-channels is also important when modelling local flow void distribution in the fuel string. This in turn will impact on the prediction of phenomena such as critical heat flux. A model has been previously developed, based on form loss equations found in Idelchik, to predict subchannel form losses using the local geometry as input to the model. This model has exhibited good results. Recently, detailed pressure drop experiments have been carried out that help to better quantify the components of the overall pressure drop in a fuel string. These experimental results have been used to improve the existing model, and to develop a more comprehensive modelling methodology for use in ASSERT. The result is an integrated friction and form loss model that can reproduce the total fuel string pressure drop, and provide insight into the bundle overage losses associated with each of the components for use in bundle average fuel string models. This paper discusses the methodology used to integrate local form losses due to end plates into the new model and how the modelling envelope is defined.