Publication
The OpenFOAM Fuel Behaviour Analysis Tool (OFFBEAT), developed jointly by EPFL and PSI in Switzerland, is rapidly gaining recognition as a comprehensive code for multi-dimensional thermo-mechanical fuel behaviour analysis. Like for any novel code, verification and validation (V&V) studies are crucial to test the capabilities of the code as new developments are made. The verification and validation of OFFBEAT is an ongoing effort and new verification studies are done as new models or methodology is implemented in the code. At the same time validation against experimental data are carried out to test the capabilities of the code to simulate fuel behaviour in normal and accidental conditions. In this paper, validation studies of OFFBEAT have been done for the REBEKA tests, which are separate effects tests to obtain data on cladding ballooning and burst under typical loss-of-coolant accident (LOCA) conditions. For the verification study, a code-to-code comparison of OFFBEAT is made with more validated codes such as Falcon and BISON. The results are compared with those obtained using Falcon, which is the reference fuel performance code at PSI, and with the results available in open literature using the BISON fuel performance code. A 2D axisymmetric analysis has been done to predict the burst temperature as a function of the rod internal pressure at different heating rates. The obtained results are compared with experimental data and are found to be in good agreement. The code-to-code comparison with BISON and Falcon shows that OFFBEAT results are in close agreement to BISON results, whereas Falcon underpredicts the burst temperatures. Further 3D analysis has been done using OFFBEAT and the 3D results are in good agreement with the 2D results, showcasing OFFBEAT's capabilities to model multi-dimensional phenomena. An azimuthal temperature gradient in the cladding leads to non-uniformity in the ballooning of the cladding, bowing of the cladding and higher burst temperatures, which was also predicted in the experiments and in the study done using the BISON code. This V&V study provides great insights into the cladding ballooning and burst behaviour in separate-effects tests during LOCA conditions and proves OFFBEAT's capability to simulate multi-dimensional, macroscopic fuel behaviour during accident scenarios.