[2I15-17] Thermal Hydaulics at Accident

[2I16] Study on Air Ingress Phenomena during a Depressurization Accident of VHTR

(4) Air ingress process during a double coaxial pipe rupture

*Tetsuaki Takeda¹, Naoki Saito¹ (1. University of Yamanashi)

Keywords:High temperature gas cooled reactor, Natural circulation, Molecular diffusion

A depressurization accident is one of the design-basis accidents of a Very High Temperature Reactor (VHTR) such as Gas Turbine High Temperature Reactor 300 for Cogeneration (GTHTR300C). The experimental apparatus consists of a double coaxial cylinder and a horizontal double coaxial pipe. First, the experimental apparatus is filled with helium gas. After the heater temperature is reached at steady state, the valves attached to the horizontal double coaxial pipe are opened at the same time to simulate the primary pipe rupture accident. Experimental results are as follows. Immediately after opening the valves, the flow velocity at a horizontal double coaxial pipe increased rapidly because air entered into the apparatus by the counter-current flow. After that, the flow velocity decreased. It is considered that the stable density stratified fluid layer was formed and the flow velocity decreased. Afterwards, the flow velocity increased again.