Estimate of the Local Cladding Overheating Caused by Pin Bundle Distortion in an LMFBR Assembly

摘要

This paper presents a conservative estimate of the cladding temperature increase (over nominal temperature) caused by a bundle-duct interference of 100 mils (0 to 1 in.) in a typical LMFBR pin bundle. Parameters affecting global and local heating that is caused by bundle-duct interaction (BDI) are described. The highlights and shortcomings of previous work on the subject are discussed. The geometry of the distorted bundle is conservatively obtained by linearly superimposing calculated local distortions onto global distortions obtained from a bundle compression test. Significant local reduction in the area of hot the channel is predicted. The edge pins are expected to contact the duct wall, but no pin-to-pin contact is predicted. The thermal-hydraulic analysis is done in two steps. First, the COBRA-WC Code is used to determine the subchannel temperature distribution. Second, based on coolant flow velocity measurements in a scaled (6X) model of a distorted pin bundle, the cladding temperature at the contact is predicted as a function of the contact width. (ERA citation 08:051152)