*Article* **Micromagnetic Characterization of Operation-Induced Damage in Charpy Specimens of RPV Steels**

**Madalina Rabung 1,\*, Melanie Kopp 1, Antal Gasparics 2, Gábor Vértesy 2, Ildikó Szenthe 2, Inge Uytdenhouwen <sup>3</sup> and Klaus Szielasko <sup>1</sup>**


**Featured Application: In this study, the influence of neutron irradiation on the mechanical properties of nuclear pressure vessel materials is investigated using two independent methods of nondestructive magnetic testing. A correlation was found between magnetic characteristics and neutron irradiation-induced damage, regardless of the applied measurement technique. Additionally, by merging the outcome of both testing methods and applying a calibration/training procedure, the damage to reactor steel was successfully predicted. The results are helpful for the potential future practical application of these techniques to the regular inspection of nuclear reactors.**

**Abstract:** The embrittlement of two types of nuclear pressure vessel steel, 15Kh2NMFA and A508 Cl.2, was studied using two different methods of magnetic nondestructive testing: micromagnetic multiparameter microstructure and stress analysis (3MA-X8) and magnetic adaptive testing (MAT). The microstructure and mechanical properties of reactor pressure vessel (RPV) materials are modified due to neutron irradiation; this material degradation can be characterized using magnetic methods. For the first time, the progressive change in material properties due to neutron irradiation was investigated on the same specimens, before and after neutron irradiation. A correlation was found between magnetic characteristics and neutron-irradiation-induced damage, regardless of the type of material or the applied measurement technique. The results of the individual micromagnetic measurements proved their suitability for characterizing the degradation of RPV steel caused by simulated operating conditions. A calibration/training procedure was applied on the merged outcome of both testing methods, producing excellent results in predicting transition temperature, yield strength, and mechanical hardness for both materials.

**Keywords:** neutron irradiation embrittlement; reactor pressure vessel; magnetic nondestructive evaluation; micromagnetic multiparameter microstructure and stress analysis 3MA; magnetic adaptive testing
