Study of the magnetic properties of steels for reactor pressure vessels embrittled by neutron irradiation

RODOLFO KEMPF; JOAQUIN SACANELL; CINTHIA RAMOS; JULIÁN MILANO; ELIN WINKLER; A. BUTERA; A. M. FORTIS

Buenos Aires

Conferencia; X Latin American Workshop on Magnetism, Magnetic Materials and Their Applications; 2013

We present a study of the magnetic properties of ferritic iron to analyze their behavior when they are subjected to irradiation in a nuclear reactor. The purpose of this work is to the study of the embrittlement that happens in reactor pressure vessels (RPV) steels during neutron irradiation. We tested SA-508 class III iron, which will be used in the construction of several nuclear reactors under development in Argentina. We show the characterization by Magnetization measurements,Ferromagnetic resonance and Mossbauer spectroscopy in samples irradiated with fast neutrons (E > 1 MeV) at a  uence of 6.6 x 1021 nm􀀀2. Irradiations were performed in controlled atmosphere at 275oC (i.e. reactor operation temperature) with 3.715 x 1015 and 1.857 x 1015 nm􀀀2s􀀀1 neutron  uxes in order to study the in uence of diusion of alloying elements.Through our measurements we obtained the saturation of the magnetization, the coercive eld, theferromagnetic resonance eld and its linewidth. We observed a reduction of the saturation of the magnetization an increase of the coercive eld and a reduction of the resonant eld while increasing the neutron flux of the irradiation. Those results are consistent with the formation of Mn rich precipitates induced by an enhanced diusion due to irradiation. This is also consistent with the increase of the relative paramagnetic fraction obtained by Mossbauer spectroscopy, which is related with this kind of precipitates. Our results suggest that samples with small neutron  fluxes,in which irradiation took place for longer time, precipitates are larger than those corresponding to large neutron  fluxes. Those precipitates constitute a barrier for the magnetic domain walls, thus increasing the measured coercive eld. Consequently, the mentioned techniques could be used to estimate the material degradation of the reactor vessel steel.