A single-pin coolant sub-channel model was implemented in BISON, the pin-scale simulation code. This enables BISON to compute the heat transfer coefficient and coolant temperature as a function of axial position along the fuel pin (rather than requiring this information to be supplied by the user). At present, the model is only applicable to pressurized water reactor coolant conditions, but modifications to include boiling water reactor (BWR) coolant conditions are in progress. A preliminary UO2 thermal and irradiation creep model has been implemented in BISON and is undergoing testing and comparison with independent calculations; the model appears to be working as expected. Implementation of VPSC into BISON was initiated, which will allow for a more fundamental prediction of cladding creep.
A preliminary UO2 fuel smeared-cracking model has been implemented in BISON. An initial test of the cracking model, integrated with the other fuel performance models already in BISON, included a simulation of the RISO GE7 bump test on rod ZX115. BISON results agreed well with experimental measurements of fuel centerline temperature, final fuel pin profile, and end-of-life fission gas release values. The results of this benchmarking were presented at the FUMEX III Benchmarking Meeting (Vienna, Austria) in December 2011, where results from other fuel performance codes performing the same calculation on the same pin were also presented; BISON results were extremely close to predictions made from other proven codes (e.g., TRANSURANUS, ENIGMA) for this experiment. [INL]