Finite element analyses were performed to investigate the leakage and structural integrity of the bolted flange joint assembly (BFJA) and Grayloc ® clamp connector (GCC), when each assembly was subjected to the external loads of bolt preload, internal pressure and thermal loadings. The thermal loadings were of both spatially-uniform and spatiallynonuniform temperatures on the assemblies. The initial bolt preload applied on the BFJA and the GCC was 60,000 N and 6,000 N, respectively. The internal pressure for both assemblies was 27 MPa. The BFJA was found to have satisfactory leakage and structural performance for the thermal loadings expected on the low-temperature (260°C) side of the Carleton Supercritical Water (CSCW) loop. The GCC was found to have satisfactory leakage and structural performance for the thermal loadings expected on the hightemperature (600°C) side of the CSCW loop. The leakage integrity of the GCC was found to remain intact for a temperature difference of 15°C between the inner and outer surfaces of the flange. This was not the case for a temperature difference of 100°C.iii AcknowledgementsThe effort in putting together this research work has been shared by many people.Foremost, I am grateful of Allah for blessing me with the intellect and knowledge to pursue this research work. I would like to thank Carleton University for providing me with the platform for undertaking this research work and providing me with the latest facilities to assist me in my research work.