The Effects of Depressurizing into a Cavity for Small and Medium Sized Break Air Ingress Accident Scenarios

High resolution experiments of the Air Ingress accident scenario have been performed with the Helium Air Ingress gas Reactor Experimental (HAIRE) facility. The reactor vessel and reactor cavity of an HTGR are modeled in the experiments to study their effects on both the depressurization and air ingress phase of the Air Ingress accident scenario and provide an experimental database for the validation of computational models. While most of the studies present in the literature are focused on large breaks, the present work focuses on medium and small breaks instead, which might lead to scenarios more challenging to predict with HTGR safety analyses codes. In the present paper, the effects of helium/air mixing in a confined space are examined during the depressurization phase of an Air Ingress accident. Of particular note is the quick mixing of helium and air during the depressurization phase. Near instantaneously the helium and air form a uniform mixture in the reactor containment. This initial condition is useful to know for simulation purposes.