Active control to avoid surge development in the case of a pipe rupture in a direct cycle HTGR

This work concerns the design and safety analysis of a direct cycle gas cooled reactor and is concentrated on surge occurrence, development, consequences, and control in case of a pipe rupture. To describe these phenomena, a specific turbomachine model is used. The dynamic behaviour of the compressor and different anti-surge configurations are tested. The tendancies (role of actuators, sensors, gain, bandwith, plenum size) are in a good agreement with bibliographical data. The application to transient simulations of gas cooled nuclear reactors (hypothetical 10 inch break accident) shows that deep surge has to be avoided to protect compressor, heat exchangers and other pipes, whenever possible. The effect of using active control with the bypass line are pointed out. Different strategies for active control deployment are studied and different levels of efficiency are obtained. The complete avoidance of any surge oscillation requires the use of multiple very fast valves with a dedicated control command. (author)