Nondestructive Characterization of Neutron Induced Embrittlement in Nuclear Pressure Vessel Steel Microstructure by Using Electromagnetic Testing
By using nuclear power for energy generation the pr essure vessel wall is exposed to neutron fluences of different levels depending on the distance to th e core. Hence materials undergo a change in their microstructure in terms of embrittlement, to be mea sured as toughness reduction and shift of the Ductile-to-Brittle Transition Temperature (DBTT) to higher temperatures. Normally plant safety concerning this change in mic rostructure is assured by destructively testing surveillance samples. These are standard te nsile and ISO V-specimen which consist of exactly the same material as the pressure vessel and its we ld metal, being exposed to accelerated irradiation rates within special irradiation channels allowing a pronounced ageing. It is demonstrated that electromagnetic parameters allow to characterize the changes in the microstructure generated through neutron irradiatio n. After a defined calibration process a quantitative characterization of the embrittlement specially in terms of the shift of the DBTT is possible. This has been demonstrated for reactor pr essu e vessel steels used in nuclear power plants o f eastern and western designs. As testing methods 3MA ( icromagnetic, Multiparameter, Microstructure and stress A nalysis) [1] and the dynamic magnetostriction using EMAT (Electromagnetic Acoustic Transducers) have been applied in a nondestructive c ombination measurement system. Further experiments show the possibility to measure 3MA and dynamic magnetostriction quantities through an 8 mm thick austenitic stainle ss steel cladding.
Micromagnetic Microstructure- and Stress-Independent Materials Characterization in Reactor Safety Research
Reactor safety research aims at the safe operation of nuclear power plants during their service life. In this respect, Fraunhofer IZFP’s micromagnetic multiparameter, microstructure, and stress analysis (3MA) has already made a significant contribution to the understanding of different aging mechanisms of component materials and their characterization. The basis of 3MA is the fact that microstructure and mechanical stress determine both the mechanical and magnetic material behavior. The correlation between features of magnetic and mechanical material behavior enables the micromagnetic prediction of mechanical properties and stress, both of which can decisively influence the service life. The Federal Ministry for Economic Affairs and Energy (BMWi) funded this research, handling the mutually superimposed microstructural and stress-dependent influences, a substantial challenge, especially under practical conditions. This superposition leads to ambiguities in the micromagnetic features. The 3MA testing system has been extended by more sophisticated evaluation methods being able to cope with more complex datasets. Investigations dealing with the expansion of the feature extraction and machine learning methods have led to a more precise distinction between microstructural and stress-dependent influences. This approach provides the basis for future applications in reactor safety.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.