Best-estimate codes have been developed in the nuclear industry to design and license nuclear power plants to a greater degree of accuracy and safety assurance. Such codes necessitate efforts to qualify their validity, particularly with modeling the complex thermal-hydraulics phenomena associated with Loss-of-Coolant Accident (LOCA) scenarios. Emergency spray cooling injection is a safety feature implemented in many Boiling Water Reactor (BWR) designs to re-flood a reactor during an accident. Significant experimental work has qualified the efficacy of spray cooling, and ongoing computational modeling efforts strive to more accurately portray the phenomena involved. This thesis examines the physical phenomena pertaining to emergency spray cooling injection over SVEA-type fuel assemblies. The US NRC thermal-hydraulics code TRACE version 5.0 Patch 4 has been chosen to simulate the separate-effect tests performed by ASEA-ATOM. The computational model was evaluated by performing forward uncertainty quantification using Dakota as the analysis tool and code driver. 31 parameters were identified in the TRACE model input, 24 of which pertain to the developed input model and 7 of which pertain to the physical constitutive models used in TRACE. The developed model was able to provide a reasonable prediction of the trend of the transient peak cladding temperature. The most influential parameters from the uncertainty quantification model were the countercurrent flow limiting (CCFL) model constant and rod/wall emissivity, emphasizing that detailed understanding of CCFL and an accurately determined radiation model is essential for accurate simulation of emergency BWR spray cooling systems. For the physical model sensitivity coefficients, the TRACE model was particularly sensitive to the dispersed film flow boiling (DFFB) wall-liquid and single-phase wall-vapor heat transfer coefficients which correspond to the flow regime expected at the occurrence of peak cladding temperature in a BWR LOCA reflood scenario with spray cooling present
