Validation of the FINIX fuel behavior code version 0.13.9

The FINIX fuel performance code has been developed at VTT to be coupled to existing thermal-hydraulics, reactor dynamics or neutronics codes used at VTT. In this report, the FINIX model is validated against experimental data from the OECD/NEA International Fuel Performance Experiments database. Transient scenarios used in the FRAPTRAN-1.4 integral assessment are used to compare transient performance of FINIX against the results calculated by FRAPTRAN. FRAPTRAN is a computer code for transient analysis of fuel rods developed at the Pacific Northwest National Laboratory in the US.

The comparisons to experimental data offer the best insight into how the FINIX model reflects real-world situations. When comparing the results calculated by FINIX to those calculated by another code, the assumptions and simplifications in the other code must be taken into account. Therefore during the validation process some investigation is done into FRAPTRAN as to clarify the manner in which FRAPTRAN calculates its results.

According to the validation results, FINIX calculates very similar results compared to FRAPTRAN. Some differences arise due to, for example, FINIX’s lack of plastic clad deformation models and rod failure criteria. However, despite these differences, the temperature distributions match very closely. When compared to experimental steady state irradiation data, the error between computed and experimental centreline temperature increases with burnup. This can be explained by the lack of models for some burnup-dependent phenomena. Some open questions remain concerning the mechanical model in FINIX.