Development and Validation of Fuel Performance Codes (POKEVA):POKEVA summary report

Assessment, validation, and further development of the fuel behaviour codes in use at VTT have been continued topically, with attention to the most timely requirements. The main achievements include: (1) Development of a probabilistic procedure applicable for general transient conditions, or for evaluation of the number of failed rods in an accident, particularly, was completed by a suggested two-stage approach one of which features an innovative use of neural networks methodology. (2) Use of the coupled thermal-hydraulic fuel code FRAPTRAN-GENFLO was established as a versatile tool to simulate integral loss-of-coolant test arrangements and as the core tool in the probabilistic transient analyses. (3) An extensive study on the VTT-amended ENIGMA steady-state code and its several sub-models was compiled. (4) A comprehensive interpretation of the outcome of the in-pile measurements from the OECD Halden Project rod overpressure tests was issued. (5) A coupling to the ENIGMA code input from a lattice physics code was created to realistically account for the effect of gadolinium or other additives on power distribution in the pellet. (6) Recent versions of the IRSN SCANAIR code for reactivity accident analyses have been installed and applied in power reactor applications. (7) Two new versions of the USNRC FRAPCON and FRAPTRAN codes were assembled. A version of FRAPCON 3.4 consolidating previous practical amendments and cleared of intractable parts of obsolete coding was issued. (8) Part was taken in three systematic international benchmark exercises that effectively support the code validation