For our senior design project, our group designed a new facility to be built at Oregon State University to supplement the existing High Temperature Test Facility (HTTF). The HTTF was designed to be a small scale model of the Modular High Temperature Gas Reactor (MHTGR) and collect data on steady state operations and certain transients for research purposes. The HTTF can fully conduct tests on Depressurized Conduction Cooldowns, but is limited in its capacity to explore Pressurized Conduction Cooldown (PCC) transients due to the reduced pressure of the design compared to a full scale MHTGR. A PCC transient is a casualty where system pressure remains unchanged, but forced convection through the core is lost, usually due to loss of pump power. In such a situation, the reactor is shut down, but continues to produce significant decay heat for several days. A combination of natural circulation and thermal radiation are needed to cool the core in order to prevent fuel melting and core damage. This is the phenomenon our group’s project was designed to investigate. Specifically, our design needs to model the progression of a PCC transient, analyze the coolant flow characteristics, and simulate how natural circulation develops in this event. In order to accomplish these goals, three major design challenges had to be overcome. First, our experiment had to be sized properly such that the data collected is similar to and representative of a full sized MHTGR core, despite the reduced size. Second, a flow instrumentation scheme had to be devised to accurately measure the low density, low speed coolant flow. Finally, electrical connections had to be designed that accommodate not only the extreme temperatures and pressures of operation, but also the thermal stresses and expansion of the core structural components that result. If constructed at OSU, our project’s design could be used to verify computer simulations of PCC events and help guarantee the safe design and operation of high temperature gas reactors in the future.
