Studying End Plate Deformation Effects In 37-Element CANDU® Fuel Bundles Using Finite Element Analysis

Abstract

The CANDU® industry has supported the energy transition away from fossil fuels for over 50 years whilst continuing to invest in design and safety improvements. As part of this investment, they have pursued development of fuel bundle deformation models. The Royal Military College of Canada (RMC) has supported model development since 2015; demonstrating feasibility to replicate thermal bowing of fuel elements and begin work on a 3D bundle model using Finite Element Analysis (FEA). This study adds to that model by refining boundary conditions and applied loads, with a specific focus on end plate deformation. End plates have seldom been the focus of modeling studies and are in need of further investigation. A model with several reactor based loads and frictional contact between the bundle and pressure tube was developed. In doing so, the effects of end plate constraints from both fuel latch and Fuel String Supporting Shield Plug (F3SP) modified fuel channels were compared. Deformation characteristics of the final models were in close agreement with measurements of an irradiated bundle from the Bruce generating station. Within the end plate, stresses were observed to concentrate in corners of the lower webs while deformation was greatest in the center ring. The bundle’s end plate orientation was observed to affect end plate deformation, with increases of up to 54% in some instances. Thicker end plates reduced fuel element deformation by an average of 15% and decreased maximum end plate deformation by up to 21%. Controlling bundle orientation and increasing end plate thickness were assessed as promising factors for mitigating bundle deformation.