Regulatory Approaches, Current Practices and Experience in Reactor Internals Swelling Evaluation in the Framework of the DELISA-LTO Project

The project “DEscription of the extended LIfetime and its influence on the SAfety operation and construction materials performance – Long Term Operation with no compromises in the safety” (DELISA-LTO) funded by the European Union started in June 2022. The project aims to determine the most affected and endangered reactor pressure vessel components from the viewpoint of long-term operation, to describe the effect of the long-term operation on material properties, and to develop a simulation tool capable of predicting an unacceptable state of the material. The project is focused explicitly on the water-cooled water-moderated power reactor (VVER). Nevertheless, the approach also allows easy transferability to other light-water reactor technologies. The DELISA-LTO project focuses explicitly on the thermal aging and swelling of the loaded structural materials. This article pays attention on the irradiation swelling phenomenon and describes approaches to swelling evaluation in some EU countries and in Ukraine. The most affected components from the swelling point of view are reactor pressure vessel internals. For a better understanding of the swelling effect on the reactor internals, a separate work package (WP3) was organized within the DELISA-LTO project, which includes the following steps: (1) definition and comparison of regulatory requirements, current practices, approaches for swelling calculation/ analysis, and specific aspects of swelling analysis; (2) developing and testing models of reactor internals for swelling evaluation (2D model and simplified approach); (3) benchmark of swelling evaluation (3D model and sophisticated approach). The results of the first part of WP3, i.e. comparison of regulatory requirements, current practices and experience, are presented in this paper.