Material used in nuclear power plants, e.g. reactor pressure vessels and other primary components, are subjected to ageing processes which resulting can be degradation of their properties. Long-term temperature, neutron and gamma irradiation exposure are the mainly factors to such degradations. Changing in internal structure of the materials and thus changes in mechanical and physical properties is going to be the result of that environmental exposure. When those properties decrease or increase below or above certain threshold values the lifetime of the component can be reduced. Therefore the component performance is changed in a jeopardising way. Degradation process occurring in critical steel components like the reactor pressure vessel needs to be understood and quantified for a correct structural analysis evaluation and plant life management in view of a safe and economical operation of nuclear power plants. The measurements and studies of changes of material properties by destructive and non-destructive tests are key tools for such an important issue. Special techniques and innovative methodologies are in constant progress for a better in-service inspection and monitoring of samples and components. Within the frame of the AMES (Ageing Materials European Strategies) programme of JRC, experimental studies on demonstrating which ND methods have potentials for ageing assessment and monitoring are carried out; among these the micromagnetic measurements are included. An experimental study comprising material testing, measurements and signal analysis has been carried out on different model alloys, at fresh and irradiated conditions. Alloys have been modelled by different element composition in order to study the effect of alloying elements (P, Cu and Ni) on the material properties when they are exposed to radiation. Irradiation effects were studied through transition temperature curves in sub-size Charpy-V specimens with dimensions 3x 4 x 27 mm. The irradiated samples received a dose of 10mdpa at 270°C in the LYRA rig at the High Flux Reactor (HFR) in Petten of the Joint Research Centre. Destructive and non-destructive techniques have been combined in order to characterise the degree of property changes. Specimens were prepared for different tests; material analysis and micromagnetic property measurements were performed. Among the measurements, the Barkhausen signal and micromagnetic response associated to it, were selected to perform a complex analysis The results of the different tests and measurements, both destructive and non-destructive, are analysed and presented in this paper mainly in view to demonstrate capability to follow the degradation process by the Barkhausen method.
Publication Source: 3nd International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, November 14-16, 2001, Seville Spain. Publisher: Tecnatom s.a. - [Homepage]
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