MAGNETIC CHARACTERIZATION OF NEUTRON IRRADIATED REACTOR STEEL MATERIAL

Gábor Vértesy - Ivan Tomáš - Ferenc Gillemot - Richárd Székely

   Inspection of neutron-irradiation-generated degradation is a very important task. In ferromagnetic materials, such as nuclear reactor pressure vessel steel, the structural degradation is connected with a change of their magnetic properties. In this work the applicabil-ity of a novel magnetic nondestructive method (Magnetic Adaptive Testing, MAT), which is based on systematic measurement and evaluation of minor magnetic hysteresis loops, is shown for inspection of neutron irradiation embrittlement in nuclear reactor pres-sure vessel steel. Three series of samples, made of JRQ, 15H2MFA and 10ChMFT type steels were measured by MAT. The sam-ples were irradiated by E>1 MeV energy neutrons with neutron fluence of 1.58x10¹⁹ – 1.19x10²⁰ n/cm². Regular, monotonously in-creasing correlation was found between the optimally chosen MAT degradation functions and the neutron fluence, in all three types of the materials. Shift of the ductile-brittle transition temperature, Δ DBTT, independently determined as a function of neutron fluence for the 15H2MFA material, was also employed. A sensitive, linear correlation was found between the Δ DBTT and values of the MAT degradation functions. Based on these results, MAT is considered to be a promising complimentary tool. It can serve in future, perhaps, even for replacement of the destructive tests within the surveillance programs, which are presently used for in-spection of neutron irradiation generated embrittlement of nuclear reactor pressure vessel steel.

Keywords: neutron irradiation, steel degradation, nuclear reactor pressure vessel, magnetic NDT, magnetic adaptive testing

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