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.
Design of advanced micro-magnetic sensors for various applications
The state of the microstructures determines both the mechanical properties (hardness, yield strength, elongation, etc.) and micro-magnetic properties (magnetic Barkhausen noise (MBN), incremental permeability (IP), etc.). The non-destructive nature of the micro-magnetic testing technology facilitate it be a valuable tool for quality control in the manufacturing of ferromagnetic components. In the implementation of micro-magnetic testing, the functions and the geometry of the sensors need be customized for specific target properties and components. In this paper, four types of advanced or multifunctional sensors are presented and applied for micro-magnetic testing. First, a multifunctional sensor is developed for flat surface. Unique intermittent magnetizing method using superimposed magnetic fields of high and low frequencies enable the sensor to measure the magnetic Barkhausen noise, incremental permeability, eddy currents, tangential magnetic field and main flux. Second, to conduct magnetic Barkhausen noise testing at the inner corner of V-shape bending plate, a miniaturized sensor with U-shape roller magnetizer is designed to perfect contact with the corner region. Third, read head of a magnetic tape player is revised to act as high-lateral-resolution (up to 500μm) sensor for magnetic Barkhausen noise measurement in ferromagnetic film. Fourth, a slender probe is developed and embedded into an anti-bulking fixture that is clamped onto the flat specimen. With the slender probe together with the special fixture, the dependency of the magnetic Barkhausen noise on the compressive and tensile stress is first experimentally observed in a single flat specimen under continuous load.
A New Method for Coupled Elastic-Atomistic Modelling
Molecular Dynamics and Molecular Statics have become important tools for model investigations of crystal defects. In spite of the ever increasing computer power the size of the models which can be treated by these methods is very limited. Therefore, in order to avoid surface effects it is common practice to employ one of the following techniques: 
 
 
periodic boundary conditions or 
 
 
semidiscrete methods.