Magnetic measurements to evaluate irradiation effects on Reactor Pressure Vessel high nickel steel

摘要

With the aim to characterise material changes due to irradiation exposure, the possibility of using magnetic measurements have been continuously studied. In this work, a further study is described dealing with a reactor pressure vessel (RPV) shell of a Russian WWER-1000 nuclear power plant type. The shell has been cut into blocks and finally several sets of Charpy specimens were manufactured and a large fraction of them exposed to neutron irradiation in the High Flux Reactor (HFR), Petten, of the JRC-IE, in order to assess irradiation effects on the given 15Kh2MNFAA low alloy steel. The irradiation was carried out at 290°C and a t a fluence of 1.8 1023 n.m-2 (E>1 MeV). The scope of this paper is to present the evaluation of the effect of irradiation on magnetic properties and its possible relation to mechanical properties changes, as a consequence of embrittlement on irradiated Charpy specimens. In this case the Charpy specimens were standard full size CV-n type with very well known cutting orientation with reference to the original pressure vessel shell. This is very important since the cutting orientation of specimen often have such strong effect on the magnetic Barkhausen signal to mask the irradiation effects on specimens The magnetic measurements carried out included Barkhausen signal and the so called RXI value; which is the relative induction values to changing on intensity of magnetic flux within the specimen. The results highlight the necessity to treat magnetic measurements on Charpy specimens in a statistical way.