Geometry Measurement of Core Baffle of VVER-1000 Type Reactors of NPP Temelín

Abstract

The degradation mechanism of radiation swelling causes increase of failures in the crystal lattice of the metal, which in consequence leads to an increase in the volume of the material and can and does result in a change in the geometry of the mentioned component. The macroscopic change in geometry can affect the component's ability to provide the required safety function. Therefore, a measuring device was designed and manufactured in the laboratories of the UJV Rez, a. s. which would enable accurate measurement of selected dimensions of the core baffle in the specific conditions of the reactor. The dimensions that are most affected by the development of radiation swelling according to the computational evaluation are measured. The measuring device was designed to allow measurement of the absolute distance of the opposite surfaces of the inner surface of the core baffle. The device consists of four measuring arms connected by a frame. Dimensional measurements are carried out using inductive sensors and optical sensors. The measuring device is equipped with cameras to determine the position. High accuracy, resistance of the device to ionizing radiation and hydrostatic pressure are essential for successful measurement. The first geometry measurement of core baffle was carried out of the Temelin NPP in 2022 and 2023 for unit two and one respectively. The geometry measurement on first unit was realized in this year and was successful too.