Risk assessment of thermal striping in MYRRHA research reactor

The thermal striping is one of the problems encountered in nuclear facilities. It may affect the reactor main components structural integrity and, sometimes, it can cause their rapid failure. The thermal striping problem touches, in general, mixing zones of industrial facilities. While it affects several areas as the core of liquid metal reactors that is due to the larger difference between core inlet and core outlet temperature, these reactors are more vulnerable to striping compared to water reactors. It is true that a better understanding of the induced thermal loads and associated damage mechanisms are obtained nowadays, thanks to recent developments in different domains such as CFD calculation and fatigue modelling. However, in the MYRRHA reactor project, the coolant used will be the Lead Bismuth Eutectic (LBE), i.e. a liquid-metal with a high thermal conductivity. Such conditions are broadly different compared to the most conventional coolant that is water. The present paper presents an assessment of the consequences of thermal striping under the severe conditions of the MYRRHA reactor. The results of the study can be considered as satisfactory since the risk to structural integrity appears to be globally low. A number of aspects will however require further investigation as the reactor design progresses.