Evaluation of experiments on semi-large scale specimens with underclad cracks with focus on constraint and RPV integrity evaluation

摘要

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 specimens, and to exploit the obtained knowledge in the procedure for evaluation of integrity of WWER reactor pressure vessels. Experimental results of the project were described in details e.g. in paper [1]. In the present paper, brief summary of experimental results is provided, and FE evaluation of the experiments is described, with focus on (1) constraint evaluation, and (2) application of the experimental results to the reactor pressure vessel (RPV) integrity evaluation. FE evaluation within point (1) covers, among others, evaluation of J-integral in the moment of cleavage fracture initiation for both upper and lower crack fronts, and evaluation of some type of constraint parameter. Three types of constraint parameter were calculated: T-stress based on elastic calculation, T-stress based on elastic-plastic calculation and Q-stress parameter. In the paper, detailed development of elastic-plastic T-stress as well as Q-stress parameter with loading is presented for one specimen that sustained the highest load. Within point (2), an evaluation of the experiments with respect to the pressurized thermal shocks (PTS) procedure currently being used in the RPV integrity evaluation is performed, and the idea how the results of experiments were used for development of a modified PTS procedure to be used in RPV integrity evaluation in very short future, is briefly described.