LOCAL PARAMETERS SUSCEPTIBILITY CHECKUP USING FRACTURE TOUGHNESS DATA V. Kozák and A. Novák ,QVWLWXWH RI 3K\VLFV RI 0DWHULDOV $FDGHP\ RI 6FLHQFHV RI WKH &]HFK 5HSXEOLF äLåNRYD Brno, Czech Republic ABSTRACT Fracture toughness transition behavior of C-Mn cast steel intended for fabrication of large transport and storage container for spent nuclear fuel (ŠKODA 440/84) has been carried out. The fracture resistance has been assessed using data from static tests of the bend CVN and pre-cracked (PCVN) specimens and from the axisymmetric notched tensile specimens. Local material parameters have been calculated arising from Beremin approach. Transferability of the crack resistance data received on the small pre-cracked CVN specimens has been tested using toughness scaling models for correction. The small PCVN specimens have been thus used for the prediction of the fracture toughness. As the reference data the fracture toughness values from the 1T specimens with various crack lengths have been used. INTRODUCTION Transport and storage containers have to ensure the storage of radioactive material safely for the environment for the supposed container lifetime, in case of most severe accident loading and earthquake. For the safe enclosure of radioactive material during transportation there has to be shown that crack initiation will not occur at the tip of this postulated crack like reference flaw. For an acceptable design the applied stress intensity factor even in case of most severe accident loading (earth quake etc.) has to be smaller than the material fracture toughness at the design temperature (divided by a safety factor). For the safe storage of spent nuclear fuel an additional embrittling effects (age hardening due to service temperatures and irradiation) should be taken into account. Irradiation of steel (although comparably smaller than that in nuclear pressure vessels) decreases the fracture toughness and increases the risk of brittle fracture. The container lifetime (supposed at minimum about 60 years) is controlled by shift of transition region and due to this by lower shelf region occurrence at service temperature Several approaches might be applied or developed in order to solve the problem of the container integrity from the point of view of material fracture resistance and its prediction. Its capability to predict the fracture behavior for any configuration of defect and component could be accepted as a very hard criterion of the assessment procedure. The statistical local approach (Beremin conception) using procedure recently suggested by TC 1 within ESIS. As the local material parameters (Weibull stress and location parameter) are transferable to any component including test specimen, the shift of brittle to ductile transition curve for pre-cracked specimen (due to any embrittlement) could be directly predicted from notched ones. The methodology of master curve (MC) is currently widely used for transition behavior evaluation of fracture toughness. The verification of this concept has been performed for steel of pressure vessel and
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