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(NSRF, BIGR, etc.) show tendencies that increased burn-up reduces the mechanical damage threshold. The evaluation of the CABRI tests shows that at very high power densities in the fuel the strain behavior of the fuel is not only determined by the fuel temperature. Analyses with TESPA-ROD clearly confirm that the power density predominantly determines the strain behavior of the fuel. A strain model approach has been developed that consistently models the experimental data from the CABRI tests on UO2 fuel. The application of this approach to experimental data of the Russian test facility BIGR (Kurchatov Institute) confirms that the strain model developed is fully valid.

FRAPCON is a computer code for the transient analysis of oxide fuel rod. It was created by Pacific Northwest National Laboratory (PNL), USA. FRAPCON-3 calculates the steady-state response of light water reactor fuel rods during long-term burnup. The code calculates the cladding temperature, internal pressure, and cladding deformation of a fuel rod as functions of time dependent rod power and coolant boundary conditions.

The phenomena modeled by the code include
• heat conduction through the fuel and cladding
• cladding elastic and plastic deformation,
• fuel-cladding mechanical interaction,
• fission gas release,
• fuel rod internal gas pressure,
• gap heat transfer between fuel cladding,
• cladding oxidation,
• heat transfer from cladding to coolant.

The code contains the necessary material properties, water properties, and heat-transfer correlations. The FRAPCON-3 code is designed to generate initial conditions for transient fuel rod analyses. Therefore, the code FRAPCON-3 provides the fuel rod initial condition for the GRS transient fuel rod code TESPA-ROD.