Mechanical and Numerical Simulation Analysis for the Insertion Section Sampling of Irradiation Charpy Specimen Reconstitution

Abstract

The reactor pressure vessel (RPV) is one of the most critical equipment in the pressurized water reactor, and its structural integrity is the key factor that determines the operational safety and service life of the reactor. In practical applications, the aging degree of RPV can be evaluated through the ductile-brittle transition temperature (DBTT) curve of the Charpy impact specimen pre-placed in RPV. However, due to the space limitation inside the reactor core, the available irradiation surveillance specimens are limited for mechanical testing. Especially, most reactors have faced the problem of life extension in recent years, and the impact data of the irradiation surveillance specimen is an important basis for the life extension of the reactor. One of the solutions is to reconstitute new Charpy specimens from the impacted ones to obtain more impact data. In this paper, the basic methods for the reconstitution of RPV material Ni-Cr-Mo-V steel are studied. By testing the hardness change of the Charpy impact broken specimen along the length direction, the maximum value of the plastic deformation zone of the impact fracture is obtained. Besides, based on the Gurson-Tvergaard-Needleman (GTN) model, the impact process of the material in the upper shelf temperature region is calculated by ABAQUS numerical simulation. Compared with the tested microhardness results of the material, the maximum length of the insert section of Charpy impact specimen reconstitution is confirmed. It shows that for Ni-Cr-Mo-V steel, the maximum length of the plastic deformation zone at the upper shelf temperature region is about 7 mm, and the insert length of the reconstituted specimens can be selected to 20 mm. The results can be used as an important reference for establishing the fabrication standard of the reconstituted Charpy specimen of the reactor pressure vessel.