Assessments of long term mechanical behavior of CANDU fuel channel by means of PFEM analysis

Structural analysis with finite elements method is today a usual way to evaluate and predict the behavior of structural assemblies exposed to severe conditions, in order to ensure their safety end reliability. CANDU 600 fuel channel is an example in which long time irradiation with implicit consequences on material properties evolution interfere with the corrosion and thermal aggression. A high degree of uncertainty in the evolution of the material's properties must be considered. These are the reasons for developing, in association with deterministic evaluations with computer codes, the probabilistic and statistical methods, in order to predict the structural components response. In INR (Institute of Nuclear Research) in the past years, a code for thermo-mechanical analysis of the fuel channel from CANDU 600 nuclear power plant of Cernavoda was developed using finite element methods (FEM). The CANTUP code evaluate the stress and strain state of the mechanical assembly of fuel channel, considered to be divided into pressure tube, calandria tube and four spacers, supposed to be equidistantly distributed along the pressure tube. The main achievement obtained with this code was the prediction of the long-term behavior of the sag of the pressure tube, by analysis in which the creep phenomenon and the contact between the spacers and calandria tube were considered. This reason has sustained the attempt to estimate the possibility to use this code in order to perform probabilistic evaluations. (authors)