An advanced lower and upper bound shakedown analysis method to enhance the R5 high temperature assessment procedure

• Main Author: Ure, James Michael
• Published: University of Strathclyde 2013
• Subjects: 629.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.588978

A nuclear power station contains some of the most extreme environments and operating conditions seen by metallic components. In order to ensure the continued safe operation of these plant components rigorous structural integrity assessments are performed. Part of this structural assessment involves demonstrating that the component in question will not fail by ratcheting. In the UK the R5 procedure forms the cornerstone of these integrity assessments. The R5 rules for shakedown, whilst easily implemented, can give an overly pessimistic estimate of the shakedown status. This means that a computationally expensive nonlinear finite element analysis must be conducted. The Linear Matching Method (LMM) is one of the recently developed Direct Methods for shakedown analysis. This upper bound method has the ability to give more accurate shakedown limits than the simplified R5 route and with less computational expense than nonlinear finite element analysis. This thesis details the steps taken to take the LMM from being a research based method into a tool which can be used for regular integrity analyses within EDF. Firstly a conservative lower bound to the shakedown limit is derived and added to the LMM. The theoretical development and numerical implementation of this calculation is detailed. Convergence improvements are also investigated to improve the numerical difficulties often suffered by lower bound shakedown calculations. The LMM is implemented in Abaqus through user subroutines. To make the LMM suitable for regular use a user interface has been created via a plug-in for Abaqus. This plug-in automatically configures the model for the analysis, meaning that the user now has access to LMM analyses without having to carry out the code changes which were required with the research version of the method. The resulting analysis tool has been delivered to EDF so their engineers can now access accurate shakedown analyses through a convenient user-interface.