Abstract:
In a Modular High Temperature Gas Reactor (MHTGR), the Depressurized Conduction Cooldown (DCC) event can be separated into three distinct stages: 1) depressurization, 2) air ingress and, 3) natural circulation. During normal operations, the HTGR utilizes forced convection to move the helium coolant through the reactor core. Thus, during normal operations the helium is pressurized to about 7 MPa. As a result of the high pressure system, when a DCC event is initialized, there exists a pressure difference between the helium coolant inside the vessel and the ambient air outside the vessel. After depressurization there exist an air-helium mixture of higher density than the helium in the reactor vessel. This results in the air-helium mixture ingressing into the reactor vessel through stratified flow.
The High Temperature Test Facility (HTTF), under construction at Oregon State University, is a scaled model of the MHTGR. The HTTF is being built for code validation purposes. This study is to utilize CFD methods to simulate a DCC event in the HTTF. With this CFD simulation the effects of the depressurization stage on the rest of the model will be quantified.
