NUMERICAL ANALYSIS OF HELIUM-AIR CONCENTRATION OF A SCALED-DOWN HTGR SYSTEM

A potential accident scenario for a High-Temperature Gas-cooled Reactor (HTGR) is a catastrophic break of the primary boundary system. It can lead to air ingress into the reactor vessel which can result in oxidation of the reactor fuel elements, and therefore lead to a radioactive release. A scaled-down HTGR facility was designed and built by the
University of Idaho (UI), where experiments will be conducted to examine the mixing of air and helium, and venting of air from the cavity section during a break in the primary coolant boundary. In order to have a better understanding of the gas dynamics that take place inside of the facility, a computational fluid dynamics (CFD) model of the system is needed. A CFD model of the scaled-down HTGR facility is desired in order to have a better visualization of the
helium and air flow patterns for instrumentation placing, and to compute the air concentration in the cavity of the containment building of the reactor pressure vessel as a function of time. This study provides a description of the scaled-down HTGR, details about the CFD model setup, and discusses the numerical results obtained in regards to the air concentration.