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Nondestructive characterization of neutron induced embrittlement in nuclear pressure vessel steel microstructure by using electromagnetic

: Altpeter, I.; Dobmann, G.; Hübschen, G.; Kopp, M.; Tschuncky, R.

Chady, Tomasz (Ed.):
Electromagnetic nondestructive evaluation XIV : Selected papers from the Fifteenth International Workshop on Electromagnetic Nondestructive Evaluation, which was held in Szczecin, Poland, from June 13 - 16, 2010
Amsterdam: IOS Press, 2011 (Studies in Applied Electromagnetics and Mechanics 35)
ISBN: 978-1-60750-749-9
ISBN: 978-1-60750-750-5
International Workshop on Electromagnetic Nondestructive Evaluation (ENDE) <15, 2010, Szczecin>
Fraunhofer IZFP ()
EMAT; 3MA; neutron embrittlement; pressure vessel

Using nuclear power for energy generation, pressure vessel walls are exposed to neutron fluences of different levels depending on the distance to the core. Hence materials undergo a change of microstructure in terms of embrittlement, to be measured as toughness reduction and shift of the Ductile-to-Brittle Transition Temperature (DBTT) to higher temperatures. Normally plant safety concerning this change in microstructure is ensured by destructive testing of surveillance samples. These are standard tensile and Charpy specimens which consist of exactly the same material as the pressure vessel and its weldments, being exposed to accelerated irradiation rates within special irradiation channels allowing a pronounced ageing. During revision downtime of the plant these samples are tested destructively in standard tensile tests at 423 K and 548 K respectively or by measuring the impact energy as a function of temperature in Charpy tests to determine the shift of DBTT. It is demonstrated that electromagnetic parameters allow characterizing the changes in the microstructure generated through neutron irradiation. After a defined calibration process a quantitative characterization of the embrittlement especially in terms of DBTT is possible. This has been demonstrated for reactor pressure vessel steels according to western design as well as to eastern specifications. As testing methods 3MA (Micromagnetic, Multiparameter, Microstructure and stress Analysis) and dynamic magnetostriction using EMATs (ElectroMagnetic Acoustic Transducers) have been applied.