Semi-Large Scale Experiments Performed on Specimens With Underclad Cracks

Abstract

During years 2005–2006, a series of semi-large scale experiments on specimens containing underclad (embedded) crack were performed in NRI Rez. The experiments were performed within EU PHARE project EUROPAID/116529/D/SV/CZ, in cooperation with VTT, FNS, TVONS (Finland) and Tecnatom (Spain). The aim of the project was to investigate fracture mechanics properties of cladding, in particular, to establish the role of cladding in the fracture/failure process of the specimen, and based on obtained results to improve the current procedure for evaluation of integrity of WWER reactor pressure vessels. The specimens were manufactured from artificially aged material of decommissioned (not operated) reactor pressure vessel of WWER 440 Type NPP. Each of the specimens contained through-thickness crack embedded in the base material (with approx. 3 mm ligament separating the upper crack front from cladding), and was loaded by four-point-bending loading at room temperature. During loading, majority of specimens exhibited pop-ins followed by ductile tearing of cladding and final failure; only 3 specimens fractured through suddenly, without preceding pop-ins. Evaluation of the experiments concentrated on both process of cleavage fracture in base material and process of ductile tearing in cladding. In the presented paper, the results of experiments are in detail described, including photos from the experiments and photos taken with using high-speed video camera during some of experiments.