Changes in magnetic properties of neutron irradiated RPV steel

Conventional magnetic parameters and Barkhausen noise have been measured in pressure vessel steel samples both as-received and irradiated with doses of up to 10¹⁸ n/cm². The conventional magnetic parameters, i.e. coercive force, remanence and maximum induction did not change significantly with irradiation, whereas the Barkhausen noise amplitude and energy during a magnetization cycle decreased markedly with irradiation dose. A three stage variation of Barkhausen noise with neutron dose was observed in the present work, namely an initial decrease, a near plateau and rapid decrease. The three stage variation with neutron dose is in qualitative agreement with computer simulations of the radiation damage process performed by Beeler (1965). The hardness also varied in three stages in a reverse manner with transition at the same doses