Experimental Verification of the Behavior of Underclad Cracks Using Semi-Large Scale Specimens

During years 2005–2006 a series of semi-large scale experiments of specimens containing underclad (embedded) crack were performed in NRI Rez. The experiments were performed within EU PHARE project 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 fracture failure process of the specimens, and to exploit the obtained knowledge in the procedure for evaluation of integrity of WWER reactor pressure vessels. The specimens were manufactured from an artificially aged material of decommissioned (not operated) RPV of WWER-440 type. Each of specimens contained through-thickness crack embedded in the base material and was loaded by four-point-bending (4PB) loading. During loading, majority of specimens exhibited pop-ins followed by ductile tearing of cladding and final failure. 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 described in detail. New proposal for procedure of assessment of RPV integrity, based on the PHARE project, was prepared and will be presented in a separate paper.