FAXMOD and its application on the prediction of high temperature creep and sheath ballooning behaviour

FAXMOD, like its sister code FULMOD [1] for normal reactor operating conditions, is a two-dimensional finite-element code, three-dimensional when used in its axisymmetric mode. It can examine specifically multi-dimensional effects such as circumferential temperature variations due to non-uniform pellet-sheath gaps, longitudinal variations due to fuel pin end conditions, variations due to sheath appendages, etc. The code currently contains a transient thermal analysis, an elastoplastic analysis and a crepp analysis. This paper focuses on the verification of the high temperature sheath creep analysis of the code. Comparisons between FAXMOD predictions using a specific creep law and out-reactor transient tube burst data demonstrate the code's capability to model high temperature creep behaviour within experimental accuracy. The treatment of sheath ballooning is discussed. The code's capability to represent both the fuel and sheath during an assumed fast transient is also demonstrated. (orig.)