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 measurements of ferromagnetic materials: Validation of a 3D numerical model
Abstract This work if focused on (nondestructive) micromagnetic measurements for ferromagnetic materials in view of Material Characterization (MC). The interest in micromagnetic measurements arises from their correlation to mechanical properties. It is well known that the microstructure of a material affects both mechanical and magnetic properties, therefore it is possible to infer mechanical properties from micromagnetic measurements. This is very convenient because micromagnetic measurements can be carried out in a fast, cheap and nondestructive manner, if compared to mechanical measurements. To date, a lot of experimental work has been carried in the past years but there is still some lack of proper numerical models capable of modelling micromagnetic measurements, especially when considering 3D models. In this paper we present an experimental validation of an ad-hoc 3D numerical model capable of modelling the response in micromagnetic characterization of ferromagnetic materials.
The fragmentation of small asteroids in the atmosphere
The fragmentation of a small asteroid in the atmosphere greatly increases its cross-sections for aerodynamic braking and energy dissipation. The differential pressure across a meteoroid disperses its fragments at a velocity that increases with atmospheric density and impact velocity and decreases with meteoroid density. At a typical impact velocity of 22 km/s, the atmosphere absorbs more than half the kinetic energy of stony meteoroids with diameters, D M < 220 M AND IRON METEOROIDS WITH D M < 80 m. The corresponding diameter for comets with impact velocity 50 km/s is D M < 1600 m. Most of this energy dissipation occurs in a fraction of a scale height, which causes large meteoroids to appear to »explode« or »flare« at the end of their visible paths