Evaluation of possible leakage causes in a natural circulation helium loop

Abstract

With the development of IVth. Generation nuclear reactors, the safety systems have to be adjusted to comply with the specific requirements of these new reactor designs and handle any nuclear accident in the best possible way. The Fukushima accident showed that the decay heat present after the reactor shutdown can still be a threat, and robust and reliable safety systems must be introduced. The natural circulation loop represents such a system since the main driving force is partially supplied by the decay heat itself. To investigate the possibilities of using a natural circulation system, we built an experimental helium loop, where the thermodynamic and hydraulic properties of the system were studied. During the measurements, coolant leakages were observed. The scale of the experimental device is close to the scale of a real application; therefore, any unexpected behavior should be properly investigated and reported, especially if the phenomena involve concerns about possible coolant leakage. This paper reports and analyzes measured leakage rates during several measurements on a large-scale, high-temperature, high-pressure natural circulation loop.