Effects of Helium Mixing and Heat Transfer on Containment Design Pressure in a High-Temperature Gas-Cooled Reactor

Containment design pressure for a high-temperature gas-cooled reactor is determined by its response to a design basis depressurization accident. The effects of heat transfer to internal structures and of helium mixing significantly affect the response. In the mathematical model, the containment is divided into two regions; a lower region that contains only air, and an upper region that contains all the helium and whatever air is assumed to mix. Heat sinks are distributed vertically. At each instant, a given heat sink is calculated to be in either the unmixed region or the mixed region. In this way, both the mixing fraction and the heat transfer data can be changed. The peak pressure can be reduced by (a) placing heat sinks higher in the containment, (b) increasing the mixing fraction, and (c) accounting for heat transfer as the helium rises through the lower region.