Composition and magnetic character of nanometre-size Cu precipitates in reactor pressure vessel steels: implications for nuclear power plant lifetime extension

The sensitivity of positrons to nanometre-size Cu precipitates in Fe alloys has enabled us to apply a novel spin-polarized element-specific method to probe the composition and magnetic character of the precipitates responsible for reactor pressure vessel (RPV) steel embrittlement. The results clearly show that the precipitates are non-magnetic and place an upper limit of about 10 at% on their Fe content. The practical implication of this result is that the Cu precipitate contribution to RPV steel embrittlement saturates, is, not expected to contribute further during lifetime extension. Our study demonstrates that polarized positrons can be used as a powerful probe of the magnetic character of nanoscale materials, even those embedded in a strongly magnetic host.