Theses and Dissertations Collection

The Very High Temperature Reactor (VHTR) is a promising Gen-IV reactor design. It is a helium cooled reactor capable of heating its coolant to 1000◦ C before it exits the reactor core. Such exit temperatures make it feasible to achieve a power output of 800 MWth. Its design is currently being researched by the United States Department of Energy (DOE).One element of its design currently under investigation is the possibility of a failure at a fuel rod drive housing, or any other instrumental housing located on the reactor pressure vessel (RPV). A structural failure of the RPV would lead to a rapid depressurization of the reactor’s pressurized loop and a loss of cooling accident (LOCA). If oxygen enters the reactor core following the LOCA, it could chemically react with the high temperature graphite in the reactor core, jeopardizing the reactor core’s structural integrity, and risking a release of radioactive contamination to the surrounding environment. One way of preventing air ingress into the reactor core is by understanding the mixing phenomena of helium and air in the containment structure surrounding the RPV. This thesis discusses the experimental and computational efforts performed at the University of Idaho to understand the helium/air mixing patterns inside the VHTR’s containment structure following a LOCA.