The main degradation mechanism of NPP’s components is radiation damage, but these processes are situated only in the core region of the reactor pressure vessel (RPV). The main mechanical loading of all individual parts of NPP’s primary circuit are the influence of high pressure at elevated temperature till 300°C. These processes lead to the fatigue damage of structural materials, which is characterized as the thermal fatigue or thermal ageing. The decommissioning of two V1 units in Slovakia provides a great opportunity to preserve materials from equipment that was in conditions of real operation for decades (app. 28–29 campaigns). VUJE, in cooperation with other partners, prepared necessary steps to create a material archive and related database including all relevant information from the decommissioned units of WWER-440 reactors. The main goal is to evaluate the real influence of long-term operation (LTO) on the degradation of NPP parts, such as steam-generators (SGs).
The Small Punch Test (SPT) methods are mainly used for evaluation of materials actual state. By the SPT technique it is possible to evaluate the basic tensile properties as the ultimate tensile strength and the yield stress of the tested materials from a very small amount of obtained material. The paper deals with description of special sampling from steam generators of operating units in Slovakia and subsequent testing of samples taken by the SPT method. All these results were compared with reference testing on materials taken from decommissioned V1 NPP.
The article deals with the real defect, a crack that occurred on a part of the steam pipeline of the separator and the steam superheater of the turbo-generator in the V2 nuclear power plant (NPP) in Jaslovské Bohunice. The damage was caused by the mechanism of erosion-corrosion, which led to a reduction of the pipe wall with the critical thickness. The main cause of the failure was identified to be the usage of unsuitable steel, instead of the required steel EN 10028-2, during the reconstruction of the pipeline.
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